SEMTECH SC4503

SC4503 1.3MHz Step-Up Switching Regulator with 1.4A Switch POWER MANAGEMENT Features Description Features The SC4503 is a 1.3MHz current-mode step-up switch- ‹ Low Saturation Voltage Switch: 260mV at 1.4A ing regulator with an integrated 1.4A power transistor. ‹ 1.3MHz Constant Switching Frequency Its high switching frequency allows the use of tiny sur- ‹ Peak Current-mode Control face-mount external passive components. The SC4503 ‹ Internal Compensation features a combined shutdown and soft-start pin. The ‹ Programmable Soft-Start optional soft-start function eliminates high input current ‹ Input Voltage Range From 2.5V to 20V and output overshoot during start-up. The internal com- ‹ Output Voltage up to 27V pensation network accommodates a wide range of volt- ‹ Uses Small Inductors and Ceramic Capacitors age conversion ratios. The internal switch is rated at 34V ‹ Low Shutdown Current (< 1μA) making the device suitable for high voltage applications ‹ Low ProŢ le 5-Lead TSOT-23 and 8-Lead 2X2mm such as Boost and SEPIC. MLPD-W packages ‹ Fully WEEE and RohS compliant The SC4503 is available in low-proŢ le 5-lead TSOT-23 and 8-lead 2X2mm MLPD-W packages. The SC4503’s low shutdown current (< 1μA), high frequency operation and Applications small size make it suitable for portable applications. ‹ Local DC-DC Converters ‹ TFT Bias Supplies ‹ XDSL Power Supplies ‹ Medical Equipment ‹ Digital Cameras ‹ Portable Devices ‹ White LED Drivers Typical Application Circuit Typical Application Circuit D1 L1 Efficiency vs Load Current VIN VOUT 95 12V, 0.5A 5V 4.7µH 1.3MHz 10BQ015 90 5 1 C4 R1 85 IN SW 15pF 432k 80 SC4503 C1 C2 1µF 3 75 4 4.7µF ON OFF SHDN/SS FB 70 GND R2 65 2 49.9k 60 V = 12V OUT 55 50 C1: Murata GRM188R61A105K 0.001 0.010 0.100 1.000 C2: Murata GRM21BR61C475K Load Current (A) L1: Sumida CDC5D23B-4R7 Figure 1(b). EfŢ ciency of the 5V to 12V Boost Converter Figure 1(a). 5V to 12V Boost Converter May 4, 2007 www.semtech.com 1 Efficiency (%) SC4503 POWER MANAGEMENT Absolute Maximum Ratings Absolute Maximum Ratings Exceeding the speciŢ cations below may result in permanent damage to the device or device malfunction. Operation outside of the parameters speciŢ ed in the Electrical Characteristics section is not recommended. Parameter Symbol Maximum Units Supply Voltage V -0.3 to 20 IN SW Voltage V -0.3 to 34 SW V FB Voltages V -0.3 to V +0.3 FB IN SHDN/SS Voltage V -0.3 to V +1 SHDN IN Thermal Resistance Junction to Ambient (TSOT - 23) θ 191* °C/W JA Thermal Resistance Junction to Ambient (2X2 mm MLPD-W) θ 78* °C/W JA Maximum Junction Temperature T 150 J Storage Temperature Range T -65 to +150 STG °C Lead Temperature (Soldering)10 sec (TSOT - 23) T 260 LEAD Peak IR Reţ ow Temperature (2X2mm MLPD-W) T 260 IR ESD Rating (Human Body Model) ESD 2000 V *Calculated from package in still air, mounted to 3” x 4.5”, 4 layer FR4 PCB with thermal vias under the exposed pad as per JESD51 standards. Electrical Characteristics Unless speciŢ ed: V = V = 3V, -40°C < T = T < 85°C IN SHDN/SS A J Parameter Conditions Min Typ Max Units Under-Voltage Lockout Threshold 2.2 2.5 Maximum Operating Voltage 20 V Feedback Voltage 1.225 1.250 1.275 Feedback Line Voltage Regulation 2.5V < V < 20V 0.02 %/V IN FB Pin Bias Current -25 -50 nA Switching Frequency 1.15 1.30 1.55 MHz Minimum Duty Cycle 0 % Maximum Duty Cycle 86 90 Switch Current Limit 1.4 1.9 2.5 A Switch Saturation Voltage I = 1.4A 260 430 mV SW Switch Leakage Current V = 5V 0.01 1 µA SW V Quiescent Supply Current V = 2V, V = 1.5V (not switching) 0.8 1.1 mA IN SHDN/SS FB V Supply Current in Shutdown V = 0 0.01 1 µA IN SHDN/SS  2007 Semtech Corp. 2 www.semtech.com SC4503 POWER MANAGEMENT Electrical Characteristics (Cont.) Unless speciŢ ed: V = V = 3V, -40°C < T = T < 85°C IN SHDN/SS A J Parameter Conditions Min Typ Max Units SHDN/SS Switching Threshold V = 0V 1.4 V FB Shutdown Input High Voltage 2 V Shutdown Input Low Voltage 0.4 V = 2V 22 50 SHDN/SS SHDN/SS Pin Bias Current V = 1.8V 20 45 µA SHDN/SS V = 0V 0.1 SHDN/SS Thermal Shutdown Temperature 155 °C Thermal Shutdown Hysteresis 10 Pin ConŢ guration - TSOT - 23 Ordering Information (1,2) Device Top Mark Package Top View SC4503TSKTRT BH00 TSOT-23 SW 1 5 IN SC4503EVB Evaluation Board GND 2 Notes: FB 3 4 SHDN/SS (1) Available in tape and reel only. A reel contains 3,000 devices. (2) Available in lead-free package only. Device is WEEE and RoHS compliant. 5-LEAD TSOT-23 Pin Descriptions - TSOT -23 Pin Pin Name Pin Functions Collector of the internal power transistor. Connect to the boost inductor and the freewheeling 1SW diode. The maximum switching voltage spike at this pin should be limited to 34V. 2 GND Ground. Tie to ground plane. The inverting input of the error ampliŢ er. Tie to an external resistive divider to set the output volt- 3FB age. Shutdown and Soft-start Pin. Pulling this pin below 0.4 shuts down the converter. Applying more than 2V at this pin enables the SC4503. An external resistor and an external capacitor con- nected to this pin soft-start the switching regulator. The SC4503 will try to pull the SHDN/SS pin 4 SHDN/SS below its 1.4V switching threshold regardless of the external circuit attached to the pin if VIN is below the under-voltage lockout threshold. Tie this pin through an optional resistor to IN or to the output of a controlling logic gate if soft-start is not used. See Applications Information for more details. Power Supply Pin. Bypassed with capacitor close to the pin. 5IN  2007 Semtech Corp. 3 www.semtech.com SC4503 POWER MANAGEMENT Pin ConŢ guration - 2mm X 2mm MLPD Ordering Information Top View (1,2) Device Top Mark Package 2mmX2mm 8 8 SW SW 1 1 NC NC SC4503WLTRT E00 MLPD-W 7 7 SW SW 2 2 GND GND SC4503_MLPD EVB Evaluation Board 6 6 GND GND IN IN 3 3 Notes: (1) Available in tape and reel only. A reel contains 3,000 devices. (2) Available in lead-free package only. Device is WEEE and 5 5 SHDN/ SHDN/SS SS 4 4 FB FB RoHS compliant. 8-LEAD 2X2mm MLPD-W Pin Descriptions - 2X2mm MLPD-W Pin Pin Name Pin Functions Collector of the internal power transistor. Connect to the boost inductor and the free- 1,2 SW wheeling diode. The maximum switching voltage spike at this pin should be limited to 34V. 3 IN Power Supply Pin. Bypassed with capacitor close to the pin. Shutdown and Soft-start Pin. Pulling this pin below 0.4 shuts down the converter. Apply- ing more than 2V at this pin enables the SC4503. An external resistor and an external capacitor connected to this pin soft-start the switching regulator. The SC4503 will try 4 SHDN/SS to pull the SHDN/SS pin below its 1.4V switching threshold regardless of the external circuit attached to the pin if VIN is below the under-voltage lockout threshold. Tie this pin through an optional resistor to IN or to the output of a controlling logic gate if soft-start is not used. See Applications Information for more details. The inverting input of the error ampliŢ er. Tie to an external resistive divider to set the 5FB output voltage. 6,7 GND Ground. Tie to ground plane. 8 N.C. No Connection. EDP Solder to the ground plane of the PCB.  2007 Semtech Corp. 4 www.semtech.com SC4503 POWER MANAGEMENT Block Diagram IN SW 5 1 + Z1 1V REF NOT READY - Q2 SHDN/SS T > 155° ° ° °C VOLTAGE THERMAL J 4 REFERENCE SHUTDOWN CLK 1.25V + R FB EA - Q3 2 Q - PWM S + + D1 I-LIMIT ILIM - Q1 R SENSE + + ISEN Σ Σ Σ Σ - + OSCILLATOR SLOPE COMP 2 GND Figure 2. SC4503 Block Diagram  2007 Semtech Corp. 5 www.semtech.com SC4503 POWER MANAGEMENT Typical Characteristics Switching Frequency FB Voltage vs Temperature vs Temperature 1.30 1.5 1.4 1.25 1.3 1.20 1.2 1.15 1.1 1.10 1.0 -50 -25 0 255075 100 125 -50 -25 0 255075 100 125 Temperature (°C) Temperature (°C) Switch Current Limit V Under-voltage Lockout IN vs Temperature Threshold vs Temperature 2.0 2.6 1.8 2.4 2.2 1.6 2.0 1.4 1.8 1.2 V = 3V SHDN/SS 1.6 1.0 -50 -25 0 255075 100 125 -50 -25 0 255075 100 125 Temperature (°C) Temperature (°C) Switch Saturation Voltage V Quiescent Current IN vs Temperature vs Switch Current 400 0.80 125°C 300 0.75 25°C 0.70 200 0.65 100 -40°C V = 1.5V FB 0.60 0 -50 -25 0 255075 100 125 0.0 0.5 1.0 1.5 2.0 Temperature (°C) Switch Current (A)  2007 Semtech Corp. 6 www.semtech.com FB Voltage (V) V (mV) CESAT UVLO Threshold (V) V Current (mA) IN Current Limit (A) Frequency (MHz) SC4503 POWER MANAGEMENT Typical Characteristics (Cont.) Shutdown Pin Current Shutdown Pin Current vs Shutdown Pin Voltage vs Shutdown Pin Voltage 50 70 -40°C 60 40 50 -40°C 25°C 25°C 30 40 30 20 20 10 85°C 10 85°C 0 0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 0 5 10 15 20 Shutdown Pin Voltage (V) Shutdown Pin Voltage (V) V Quiescent Current IN Shutdown Pin vs Shutdown Pin Voltage Thresholds vs Temperature 1000 1.5 V = 3V V = 1.5V IN FB 800 Switching 1.0 600 125°C 25°C 400 0.5 Shutting Down To I < 1µA IN 200 -40°C 0.0 0 -50 -25 0 255075 100 125 0.0 0.5 1.0 1.5 2.0 Temperature (°C) Shutdown Pin Voltage (V) Switch Current Limit Switch Current Limit vs Shutdown Pin Voltage vs Shutdown Pin Voltage 2.5 2.5 D = 50% D = 80% 2.0 2.0 -40°C 1.5 1.5 -40°C 85°C 25°C 1.0 1.0 25°C 85°C 0.5 0.5 0.0 0.0 1.2 1.4 1.6 1.8 2.0 1.2 1.4 1.6 1.8 2.0 Shutdown Pin Voltage (V) Shutdown Pin Voltage (V)  2007 Semtech Corp. 7 www.semtech.com V Current ( A) IN µ µ µ µ Current limit (A) Shutdown Pin Current ( µ µ µ µA) SHDN Thresholds (V) Current limit (A) Shutdown Pin Current ( A) µ µ µ µ SC4503 POWER MANAGEMENT Applications Information clamped by D1 and Q1, follows the voltage at the SHDN SS Operation pin. The input inductor current, which is in turn controlled The SC4503 is a 1.3MHz peak current-mode step-up by the error ampliŢ er output, also ramps up gradually. switching regulator with an integrated 1.4A (minimum) Soft-starting the SC4503 in this manner eliminates high power transistor. Referring to the block diagram, Figure input current and output overshoot. Under fault condition 2, the clock CLK resets the latch and blanks the power (V < 2.2V or over-temperature), the soft-start capacitor is IN transistor Q conduction. Q is switched on at the trailing discharged to 1V. When the fault condition disappears, the 3 3 edge of the clock. converter again undergoes soft-start. Switch current is sensed with an integrated sense resistor. Setting the Output Voltage The sensed current is summed with the slope-compensat- ing ramp and fed into the modulating ramp input of the An external resistive divider R and R with its center tap 1 2 PWM comparator. The latch is set and Q conduction is tied to the FB pin (Figure 3) sets the output voltage. 3 terminated when the modulating ramp intersects the error ampliŢ er (EA) output. If the switch current exceeds 1.9A (the 9 § · 287 5 =5 − (1) ¨ ¸   typical current-limit), then the current-limit comparator ILIM ©9 ¹ will set the latch and turn off Q . Due to separate pulse- 3 width modulating and current limiting paths, cycle-by-cycle VOU VOU VOU VOUT T T T current limiting is not affected by slope compensation. SC SC SC SC450 450 450 4503 3 3 3 R1 R1 R1 R1 The current-mode switching regulator is a dual-loop feed- 25nA 25nA 25nA 25nA back control system. In the inner current loop the EA output 3 3 3 3 FB FB FB FB controls the peak inductor current. In the outer loop, the error ampliŢ er regulates the output voltage. The double R2 R2 R2 R2 reactive poles of the output LC Ţ lter are reduced to a single real pole by the inner current loop, allowing the internal loop compensation network to accommodate a wide range of Figure 3. R - R Divider Sets the Output Voltage 1 2 input and output voltages. The input bias current of the error ampliŢ er will introduce SHDN SS Applying 0.9V at the pin enables the voltage refer- an error of: ence. The signal “REF NOT READY” does not go low until V exceeds its under-voltage lockout threshold (typically IN Q$ • (5°«5 )• 2.2V). Assume that an external resistor is placed between ∆9   287 = −  (2) 9 9 287 the IN and the SHDN SS pins during startup. The voltage reference is enabled when the SHDN SS voltage rises to The percentage error of a V = 5V converter with R = OUT 1 0.9V. Before V reaches 2.2V, “REF NOT READY” is high. IN 100kΩ and R = 301kΩ is 2 Q turns on and the Zener diode Z loosely regulates the 2 1 SHDN SS voltage to 1V (above the reference enabling volt- ∆9 Q$ • (N°«N)• 287 = − = − age). The optional external resistor limits the current drawn 9 9 287 during under-voltage lockout. This error is much less than the ratio tolerance resulting When V exceeds 2.2V, “REF NOT READY” goes low. Q turns IN 2 from the use of 1% resistors in the divider string. off, releasing SHDN SS. If an external capacitor is connected from the SHDN SS pin to the ground, the SHDN SS voltage will ramp up slowly. The error ampliŢ er output, which is  2007 Semtech Corp. 8 www.semtech.com SC4503 POWER MANAGEMENT Applications Information (Cont.) where I is the switch current limit. LIM Duty Cycle It is worth noting that I is directly proportional to the OUTMAX 9 The duty cycle D of a boost converter in continuous-conduc- ,1 ratio and that switching losses are neglected in its tion mode (CCM) is: 9 287 derivation. Equation (4) therefore over-estimates the 9 ,1 maximum output current, however it is a useful Ţ rst-order  − 9 +9 287 ' approximation. ' = (3) 9 &(6$7  − 9 +9 Using V = 0.3V, V = 0.5V and I =1.4A in (3) and (4), 287 ' CESAT D LIM the maximum output current for three V and V combi- IN OUT where V is the switch saturation voltage and V is volt- CESAT D nations are tabulated (Table 1). age drop across the rectifying diode. Maximum Output Current V V V V (V) (V) (V) (V) V V V V (V) (V) (V) (V) D D D D IIII (A) (A) (A) (A) IN IN IN IN OUT OUT OUT OUT OUT OUT OUT OUT 3.3 3.3 3.3 3.3 12 12 12 12 0.754 0.754 0.754 0.754 0.34 0.34 0.34 0.34 In a boost switching regulator the inductor is connected 3.3 3.3 3.3 3.3 5 5 5 5 0.423 0.423 0.423 0.423 0.80 0.80 0.80 0.80 to the input. The inductor DC current is the input current. When the power switch is turned on, the inductor current 5 5 5 5 1 1 1 12 2 2 2 0.615 0.615 0.615 0.615 0.53 0.53 0.53 0.53 ţ ows into the switch. When the power switch is off, the T Table 1 able 1.. Calculat Calculated Maximum Output Currents ed Maximum Output Currents inductor current ţ ows through the rectifying diode to the output. The output current is the average diode current. The diode current waveform is trapezoidal with pulse width Maximum Duty-Cycle Limitation (1 – D)T (see Figure 4). The output current available from The power transistor in the SC4503 is turned off every IIII switching period for 80ns. This minimum off time limits the IN IN IN IN maximum duty cycle of the regulator. A boost converter with Inductor Inductor Inductor Inductor 9 C C C Cu u u ur r r rr r r rent ent ent ent 287 S S S Sw w w wiiiittttch C ch C ch C ch Cu u u ur r r rr r r rent ent ent ent high ratio requires long switch on time and high duty ON ON ON ON OF OF OF OFF F F F ON ON ON ON 9 ,1 0 0 0 0 Di Di Di Diod od od ode C e C e C e Cu u u urr rr rr rrent ent ent ent cycle. If the required duty cycle is higher than the attain- able maximum, then the converter will operate in dropout. (Dropout is a condition in which the regulator cannot attain DT DT DT DT (1 (1 (1 (1- - - -D D D D)T )T )T )T its set output voltage below current limit.) IIII OU OU OU OUT T T T ON ON ON ON OF OF OF OFF F F F ON ON ON ON OF OF OF OFF F F F ON ON ON ON 0 0 0 0 Note: dropout can occur when operating at low input volt- ages (<3V) and with off times approaching 100ns. Shorten Figure 4. Current W Figure 4. Current W Figure 4. Current W Figure 4. Current Wa a a av v v ve e e ef f f forms in a Boost Con orms in a Boost Con orms in a Boost Con orms in a Boost Conv v v ve e e er r r rt t t ter er er er the PCB trace between the power source and the device input pin, as line drop may be a signiŢ cant percentage of a boost converter therefore depends on the converter oper- the input voltage. A regulator in dropout may appear as ating duty cycle. The power switch current in the SC4503 is if it is in current limit. The cycle-by-cycle current limit of internally limited to at least 1.4A. This is also the maximum the SC4503 is duty-cycle and input voltage invariant and peak inductor or the peak input current. By estimating the should be at least 1.4A. If the converter output is below conduction losses in both the switch and the diode, an its set value and switch current limit is not reached (1.4A), expression of the maximum available output current of a then the converter is likely in dropout. boost converter can be derived: Example: Determine the highest attainable output voltage ª º , 9 ' 9 −'() 9 −9 /,0 ,1 ' ' &(6$7 when boosting from a single Li-ion cell. , =  − − (4) 2870$; « » 9  9 287 ¬ ,1 ¼ Equation (3) can be re-arranged as:  2007 Semtech Corp. 9 www.semtech.com SC4503 POWER MANAGEMENT Applications Information (Cont.) lessen jittery tendency but not so steep that large ţ ux swing decreases efŢ ciency. For continuous-conduction mode 9 −'9 ,1 &(6$7 9 = −9 (5) 287 ' operation, inductor ripple current ΔI between 0.35A and L  −' 0.6A is a good compromise. Setting ΔI = 0.43A, V = 0.5V L D and f = 1.3MHz in (7), Assuming that the voltage of a nearly discharged Li-ion cell is 2.6V. Using V =0.5V, V =0.3V and D=0.86 in (5), D CESAT § · § · 9 9 9 9 ,1 ,1 ,1 ,1 ¨ ¸ ¨ ¸ / =  − =  − (8) ¨ ¸ ¨ ¸ I∆, 9 +9  9 +  − • /© 287 '¹ © 287 ¹ 9 < − =9 287  − where L is in μH. Transient headroom requirement further reduces the maxi- mum achievable output voltage to below 16V. Equation (7) shows that for a given V , ΔI is the highest OUT L (9 +9 ) 287 ' when 9 = . If V varies over a wide range, then Minimum Controllable On-Time ,1 IN  choose L based on the nominal input voltage. The operating duty cycle of a boost converter decreases as V approaches V . Sensed switch current ramp modulates IN OUT The saturation current of the inductor should be 20-30% the pulse width in a current-mode switching regulator. This higher than the peak current limit (1.9 A). Low-cost powder current ramp is absent unless the switch is turned on. The iron cores are not suitable for high-frequency switching intersection of this ramp with the error ampliŢ er output power supplies due to their high core losses. Inductors determines the switch on-time. The propagation delay with ferrite cores should be used. time required to immediately turn off the switch after it is turned on is the minimum controllable on time. Measured Discontinuous-Conduction Mode minimum on time of the SC4503 is load-dependent and 9 287 ranges from 180ns to 220ns at room temperature. The The output-to-input voltage conversion ratio 0 = in 9 switch in the SC4503 is either not turned on, or, for at least ,1 continuous-conduction mode is limited by the maximum this minimum. If the regulator requires a switch on-time duty cycle D : less than this controllable minimum, then it will either skip MAX cycles or start to jitter.   00 < < = = = = Inductor Selection  − −''  − −  0$; 0$; The inductor ripple current ΔI of a boost converter in con- Higher voltage conversion ratios can be achieved by oper- L tinuous-conduction mode is ating the boost converter in full-time discontinuous-con- V OUT '(9 −9 ) ,1 &(6$7 duction mode (DCM). DeŢ ne R = as the equivalent ∆, = (6) / I OUT I/ output load resistance. The following inequalities must be where f is the switching frequency and L is the induc- tance. satisŢ ed for DCM operation: Substituting (3) into (6) and neglecting V , CESAT /I 0 − (9) <  5 0 § · 9 9 ,1 ,1 ¨ ¸ ∆, =  − (7) / ¨ ¸ I/ 9 +9 and, © 287 '¹ 9 $ 287 In current-mode control, the slope of the modulating , = < (10) 287 5 0 (sensed switch current) ramp should be steep enough to  2007 Semtech Corp. 10 www.semtech.com SC4503 POWER MANAGEMENT Applications Information (Cont.) Switch on duty ratio in DCM is given by, When the switch is turned on, the output capacitor supplies the load current I (Figure 4). The output ripple voltage OUT due to charging and discharging of the output capacitor /I ' = 00 − (11) is therefore: 5 Higher input current ripples and lower output current are , '7 287 ∆9 = 287 (13) the drawbacks of DCM operation. & 287 Input Capacitor For most applications, a 10-22µF ceramic capacitor is suf- The input current in a boost converter is the inductor cur- Ţ cient for output Ţ ltering. It is worth noting that the output rent, which is continuous with low RMS current ripples. A ripple voltage due to discharging of a 10µF ceramic capaci- 2.2-4.7µF ceramic input capacitor is adequate for most tor (13) is higher than that due to its ESR. applications. Rectifying Diode Output Capacitor For high efŢ ciency, Schottky barrier diodes should be used Both ceramic and low ESR tantalum capacitors can be as rectifying diodes for the SC4503. These diodes should used as output Ţ ltering capacitors. Multi-layer ceramic have an average forward current rating at least equal to the capacitors, due to their extremely low ESR (<5mΩ), are output current and a reverse blocking voltage of at least the best choice. Use ceramic capacitors with stable a few volts higher than the output voltage. For switching temperature and voltage characteristics. One may be regulators operating at low duty cycles (i.e. low output tempted to use Z5U and Y5V ceramic capacitors for output voltage to input voltage conversion ratios), it is beneŢ cial Ţ ltering because of their high capacitance density and to use rectifying diodes with somewhat higher average cur- small sizes. However these types of capacitors have high rent ratings (thus lower forward voltages). This is because temperature and high voltage coefŢ cients. For example, the diode conduction interval is much longer than that of the capacitance of a Z5U capacitor can drop below 60% the transistor. Converter efŢ ciency will be improved if the of its room temperature value at –25°C and 90°C. X5R voltage drop across the diode is lower. ceramic capacitors, which have stable temperature and voltage coefŢ cients, are the preferred type. The rectifying diodes should be placed close to the SW pin of the SC4503 to minimize ringing due to trace induc- The diode current waveform in Figure 4 is discontinuous tance. Surface-mount equivalents of 1N5817 and 1N5818, with high ripple-content. Unlike a buck converter in which MBRM120, MBR0520L, ZHCS400, 10BQ015 and equiva- lent are suitable. the inductor ripple current ∆I determines the output ripple L voltage. The output ripple voltage of a boost regulator is Shutdown and Soft-Start much higher and is determined by the absolute inductor current. Decreasing the inductor ripple current does not reduce the output ripple voltage appreciably. The current The shutdown (SH SHD DN N SS SS ) pin is a dual function pin. When SH SHD DN N SS SS flowing in the output filter capacitor is the difference driven from a logic gate with V >2V, the pin OH between the diode current and the output current. This functions as an on/off input to the SC4503. When the capacitor current has a RMS value of: shutdown pin is below 2V, it clamps the error ampliŢ er output to 99 and reduces the switch current limit. 6+'1 6+'166 66 Connecting R and C to the SH SHD DN N SS SS pin (Figure 5) slows 9 287 SS SS , − (12) 287 the voltage rise at the pin during start-up. This forces the 9 ,1 peak inductor current (hence the input current) to follow a slow ramp, thus achieving soft-start. If a tantalum capacitor is used, then its ripple current rating in addition to its ESR will need to be considered.  2007 Semtech Corp. 11 www.semtech.com SC4503 POWER MANAGEMENT Applications Information (Cont.) SH SHD DN N SS SS The minimum voltage for switching is 1.4V. The Pulling the SH SHD DN N SS SS pin below 0.4V shuts down the SC4503, graph “Switch Current Limit vs. Shutdown Pin Voltage” in drawing less than 1µA from the input power supply. For voltages above 2V and below 0.4V, the SH SHD DN N SS SS pin can be the “Typical Characteristics” shows that the SH SHD DN N SS SS pin regarded as a digital on/off input. Figure 5 shows several voltage needs to be at least 2V for the SC4503 to deliver ways of interfacing the control logic to the shutdown pin. In SH SHD DN N SS SS its rated power. The effect of the voltage on the Figure 5(a) soft-start is not used and the logic gate drives SC4503 is analog between 1.4V and 2V. Within this range the shutdown pin through a small ( ≈ 1kΩ ) optional resistor the switch current limit is determined not by ILIM but in- R . R limits the current drawn by the SC4503 internal stead by the PWM signal path (see Figure 2). Moreover it SS SS varies with duty cycle and the shutdown pin voltage. V IN IN IN End of Soft-start SC4503 SC4503 V > 2V OH R V > 2V SS SHDN/SS V < 0.4V OL R LIM SHDN/SS SHDN/SS C SS (a) (b) IN V IN End of Soft-start IN V > 2V SHDN/SS 1.7V < V < 2V OH R SC4503 SS SC4503 V < 0.4V V ≈ 0 OL OL R D SS SS SHDN/SS SHDN/SS I I SHDN/SS SHDN/SS CMDSH-3 C SS C SS (c) (d) V V IN IN IN IN End of Soft-start SC4503 SC4502 1N4148 R V > 2V SS V > V SHDN/SS OH IN SHDN/SS SHDN/SS R SS C SS C SS (e) (f) Figure 5. Methods of Driving the Shutdown Pin and Soft-starting the SC4503 (a) Directly Driven from a Logic Gate. R Limits the Gate Output Current during Fault, LIM (b) Soft-start Only, (c) Driven from a Logic Gate with Soft-start, (d) Driven from a Logic Gate with Soft-start (1.7V < V < 2V), OH (e) Driven from an Open-collector NPN Transistor with Soft-start and (f) Driven from a Logic Gate (whose V > V ) with Soft-start. OH IN  2007 Semtech Corp. 12 www.semtech.com SC4503 POWER MANAGEMENT Applications Information (Cont.) ,,  287 287 Output Ţ lter pole, ω ω = = − − = = − − , SS circuit from the driving logic gate during fault condition. 99 && 5& 5& 287 287   In Figure 5(f) the shutdown pin is driven from a logic gate whose V is higher than the supply voltage to the SC4503.  OH Compensating zero, ω ω = = − − and == The diode clamps the maximum shutdown pin voltage to 55&& && && one diode voltage above the input power supply.  55() ()  − −'' Right half plane (RHP) zero, ω ω = = . == During soft-start, C is charged by the difference between // SS the R current and the shutdown pin current, ,, . In SS 6+'1 6+'166 66 steady state, the voltage drop across R reduces the shut- SS IIII OUT OUT OUT OUT V V V V down pin voltage according to the following equation: IN IN IN IN PO PO PO POW W W WE E E ER R R R V V V V OUT OUT OUT OUT STA STA STA STAG G G GE E E E 99 = =99 − −55 ,, (14) (1 (1 66 66 ESR ESR ESR ESR 6+'1 6+'166 66 6+'1 6+'166 66 C4 C4 C4 C4 R R R R R1 R1 R1 R1 C2 C2 C2 C2 FB FB FB FB In order for the SC4503 to achieve its rated switch current, - - - - COMP COMP COMP COMP Gm Gm Gm Gm 99 must be greater than 2V in steady state. This 6+'1 6+'166 66 + + + + puts an upper limit on R for a given enable voltage V (= R R R RC C C C 1.252 1.252 1.252 1.252V V V V SS EN R R R R O O O O R2 R2 R2 R2 ,, voltage applied to R ). The maximum speciŢ ed is SS 6+'1 6+'166 66 C C C C VO VO VO VOL L L LT T T TAG AG AG AGE E E E C C C C 99 = =99 50µA with (see “Electrical Characteristics”). REFER REFER REFER REFERE E E ENCE NCE NCE NCE 6+'1 6+'166 66 The largest R can be found using (14): SS R R R RO O O O is is is is tttth h h he e e e equ equ equ equiiiiva va va valent lent lent lent outpu outpu outpu output t t t r r r re e e esist sist sist sistan an an ance ce ce ce of of of of the the the the e e e er r r rro ro ro ror r r r a a a am m m mp p p plif lif lif lifie ie ie ier r r r 99 − − (1 (10,1 0,1 55 < < 66 66 Figure 6. Figure 6. Figure 6. Figure 6. Sim Sim Sim Simpli pli pli pliŢŢŢŢ ed Eq ed Eq ed Eq ed Equiv uiv uiv uivalent Model of a Boost alent Model of a Boost alent Model of a Boost alent Model of a Boost  µ µ$$ Con Con Con Conv v v ve e e er r r rt t t ter er er er If the enable signal is less than 2V, then the interfacing The poles p , p and the RHP zero z all increase phase 1 2 2 options shown in Figures 5(d) and 5(e) will be preferred. The shift in the loop response. For stable operation, the over- methods shown in Figures 5(a) and 5(c) can still be used all loop gain should cross 0dB with -20dB/decade slope. however the switch current limit will be reduced. Variations Due to the presence of the RHP zero, the 0dB crossover of ,, and switch current limit with SH SHD DN N SS SS pin voltage ω ω ]] 6+'1 6+'166 66 frequency should not be more than . The internal  and temperature are shown in the “Typical Characteristics”. compensating zero z provides phase boost beyond p . In Shutdown pin current decreases as temperature increases. 1 2 general the converter is more stable with widely spaced 99 Switch current limit at a given also decreases as 6+'1 6+'166 66 Ţ lter pole p and the RHP zero z . The RHP zero moves to 2 2 temperature rises. Lower shutdown pin current ţ owing low frequency when either the duty-cycle D or the output through R at high temperature results in higher shutdown SS current I increases. It is beneŢ cial to use small inductors OUT pin voltage. However reduction in switch current limit (at and larger output capacitors especially when operating at a given 99 ) at high temperature is the dominant 99 6+'1 6+'166 66 287 287 high ratios. effect. 99 ,1,1 A feed-forward capacitor C is needed for stability. The value Feed-Forward Compensation 4 of C can be determined empirically by observing the induc- 4 Figure 6 shows the equivalent circuit of a boost converter. tor current and the output voltage during load transient. µ µVV µ µVV Important poles and zeros of the overall loop response Starting with a value between and , C is 4 are: 55 55   adjusted until there is no excessive ringing or overshoot in  ω = − Low frequency integrator pole, , S inductor current and output voltage during load transient. 5& 2 & Sizing the inductor such that its ripple current is about 0.5A also improves phase margin and transient response.  2007 Semtech Corp. 13 www.semtech.com SC4503 POWER MANAGEMENT Applications Information (Cont.) Figures 7(a)-7(c) show the effects of different values of Board Layout Considerations inductance and feed-forward capacitance on transient re- sponses. In a battery-operated system if C is optimized for In a step-up switching regulator, the output Ţ lter capacitor, 4 the minimum V and the maximum load step, the converter the main power switch and the rectifying diode carry pulse IN will be stable over the entire input voltage range. currents with high di/dt. For jitter-free operation, the size of the loop formed by these components should be minimized. Since the power switch is integrated inside the SC4503, V OUT grounding the output Ţ lter capacitor next to the SC4503 0.5V/div ground pin minimizes size of the high di/dt current loop. The input bypass capacitors should also be placed close to the input pins. Shortening the trace at the SW node reduces I L1 the parasitic trace inductance. This not only reduces EMI 0.5A/div but also decreases switching voltage spikes. Figure 8 shows how various external components are 40µs/div placed around the SC4503. (a) L = 5.6µH and C = 2.2pF 1 4 The large surrounding ground plane acts as a heat sink for the device. V OUT 0.5V/div VOUT VIN D1 L1 I L1 0.5A/div SW JP C2 C1 R1 C4 U1 40µs/div R3 FB R2 (b) L = 5.6µH and C = 3.3pF 1 4 C3 SHDN/SS GND V OUT 0.5V/div Figure 8. Suggested PCB Layout for the SC4503. I L1 0.5A/div 40µs/div (c) L = 3.3µH and C = 2.7pF 1 4 Figure 7. Different inductances and feed-forward capaci- tances affect the load transient responses of the 3.3V to 12V step-up converter in Figure 10(a). I is switched between 90mA and 280mA. OUT  2007 Semtech Corp. 14 www.semtech.com SC4503 POWER MANAGEMENT Typical Application Circuits L1 D1 5V 10µH ZHCS400 + R3 D2 24V 54.9k MM5Z24VT1 _ 5 1 C2 C1 C4 0.22µF 4.7µF IN SW SC4503 220pF 4 3 R4 SHDN/SS FB 301k GND C5 C3 2 22nF R1 R2 56nF 63.4 63.4 L1: Murata LQH32C C1: Murata GRM219R60J475K Figure 9. Driving Two 6 White LED Strings from 5V. Zener diode D protects the converter 2 from over-voltage damage when both LED strings become open.  2007 Semtech Corp. 15 www.semtech.com SC4503 POWER MANAGEMENT Typical Application Circuits D1 L1 VIN VOUT 3.3V 12V 2.7µH 10BQ015 5 1 C4 R3 R1 IN SW 15k 2.2pF 866k SC4503 C1 C2 2.2µF 3 4 4.7µF SHDN/SS FB GND C3 R2 56nF 2 100k L1: Coiltronics LD1 C1: Murata GRM188R61A225K C2: Murata GRM21BR61C475K Figure 10(a). 3.3V to 12V Boost Converter with Soft-start Efficiency vs Load Current 95 1.3MHz 90 85 80 75 70 65 60 V = 12V OUT 55 40µs/div 50 0.001 0.010 0.100 1.000 Upper Trace : Output Voltage, AC Coupled, 0.5V/div Load Current (A) Lower Trace : Input Inductor Current, 0.5A/div Figure 10(b). EfŢ ciency vs Load Current Figure 10(c). Load Transient Response of the Circuit in Figure 10(a). I is switched between OUT 90mA and 280mA  2007 Semtech Corp. 16 www.semtech.com Efficiency (%) SC4503 POWER MANAGEMENT Typical Application Circuits Efficiency vs Load Current D1 L1 VOUT 2.6 - 4.2V 95 5V 1.5µH 3.3V 10BQ015 90 OFF ON 5 1 C4 < 0.4V 85 R1 V = 4.2V IN IN SW 10pF 187k 80 R3 1-CELL SC4503 C1 15k C2 LI-ION 75 4.7µF 4 3 10µF V = 3.6V V = 2.6V IN IN SHDN/SS FB 70 GND C3 65 R2 2 56nF 60.4k 60 V = 5V OUT 55 1.3MHz 50 L1: TDK VLF4012AT 0.001 0.010 0.100 1.000 C1: Murata GRM188R60J475K Load Current (A) C2: Murata GRM21BR60J106K Figure 11(a). Single Li-ion Cell to 5V Boost Converter Figure 11(b). EfŢ ciency of the Li-ion Cell to 5V Boost Converter V = 2.6V V = 4.2V IN IN 40µs/div 40µs/div Upper Trace : Output Voltage, AC Coupled, 0.2V/div Upper Trace : Output Voltage, AC Coupled, 0.2V/div Lower Trace : Inductor Current, 0.5A/div Lower Trace : Inductor Current, 0.5A/div Figure 11(c). Load Transient Response. I is switched Figure 11(d). Load Transient Response. I is switched OUT OUT between 0.1A and 0.5A between 0.15A and 0.9A  2007 Semtech Corp. 17 www.semtech.com Efficiency (%) SC4503 POWER MANAGEMENT Typical Application Circuits VOUT C5 L1 D1 3.3V, 0.45A 2.6 - 4.2V 3.3µH 2.2µF 10BQ015 5 1 C4 R1 R3 L2 IN SW 15pF 412k 8.06k 3.3µH SC4503 1-CELL C1 C2 LI-ION 1µF 4 3 10µF SHDN/SS FB GND C3 R2 2 0.22µF 249k L1 and L2: Coiltronics DRQ73-3R3 C1: Murata GRM188R61A105K C2: Murata GRM21BR60J106K C5: Murata GRM188R61A225K Figure 12(a). Single Li-ion Cell to 3.3V SEPIC Converter. Efficiency vs Load Current 85 V = 3.3V OUT V = 3.6V 80 IN 75 70 65 60 55 50 V = 2.6V IN 45 V = 3.6V IN 40 35 V = 4.2V IN 40µs/div 30 0.001 0.010 0.100 1.000 Upper Trace : Output Voltage, AC Coupled, 0.2V/div Load Current (A) Lower Trace : Input Inductor Current, 0.2A/div Figure 12(b). EfŢ ciency vs Load Current Figure 12(c). Load Transient Response of the Circuit in Figure 12(a). I is switched between OUT 100mA and 500mA  2007 Semtech Corp. 18 www.semtech.com Efficiency (%) SC4503 POWER MANAGEMENT Typical Application Circuits D2 D3 D4 D5 OUT2 26V (10mA) C5 C6 C7 C8 0.1µF 0.1µF 0.1µF 1µF D1 L1 3.3V OUT1 4.7µH 9V (0.3A) 10BQ015 R1 5 1 309k C4 IN SW 12pF 3.3V OFF ON SC4503 C2 < 0.4V 3 R3 4 4.7µF X 2 SHDN/SS FB RUN 17.8k GND C1 R2 C9 C3 2 0.1µF 49.9k 4.7µF 56nF D7 OUT3 -8.5V (10mA) C10 D6 1µF D2 - D7 : BAT54S L1 : Sumida CDC5D23B-4R7M C2: Murata GRM21BR61C475K C1: Murata GRM188R61A105K Figure 13(a). Triple-Output TFT Power Supply with Soft-Start CH4 CH1 CH2 CH3 400µs/div 40µs/div CH1 : OUT1 Voltage, 5V/div Upper Trace : Output Voltage, AC Coupled, 0.5V/div CH2 : OUT2 Voltage, 20V/div Lower Trace : Inductor Current, 0.5A/div CH3 : OUT3 Voltage, 5V/div CH4 : RUN Voltage, 5V/div Figure 13(b). TFT Power Supply Start-up Transient as Figure 13(c). Load Transient Response. I OUT1 the RUN Voltage is Stepped from 0 to is switched between 50mA and 3.3V 350mA  2007 Semtech Corp. 19 www.semtech.com SC4503 POWER MANAGEMENT EVB Schematic D1 L1 SS13 4.7uH 12VOUT 5VIN U1 C1 R1 R2 C2 C3 8 1 10uF N.C. SW 0R 432K N.P. 10uF 7 2 GND SW 6 3 GND VIN C4 15pF R3 47K OFF/ON 5 4 FB SHDN/SS R4 R5 0R C5 JP1 SC4503_MLPD 49.9K 100nF L1 4.7uH D1 SS13 12VOUT 5VIN 1 5 SW VIN R1 C2 C3 R2 2 R3 C1 0R GND N.P. 10uF 432K 47K 10uF C4 15pF OFF/ON 34 FB SHDN R4 U1 0R SC4503 R5 C5 JP1 49.9K 100n  2007 Semtech Corp. 20 www.semtech.com SC4503 POWER MANAGEMENT Outline Drawing - TSOT-23 DIMENSIONS INCHES MILLIMETERS A DIM MIN NOM MAX MIN NOM MAX - - - - A .039 1.00 e1 D - - A1 .000 .004 0.00 0.10 - - A2 .028 .035 0.70 0.90 - - N b .012 .020 0.30 0.50 2X E/2 - - c .003 .008 0.08 0.20 E1 E D .110 .114 .118 2.80 2.90 3.00 E1 .060 .063 .067 1.50 1.60 1.70 12 E .110 BSC 2.80 BSC ccc C e .037 BSC 0.95 BSC e1 .075 BSC 1.90 BSC 2X N/2 TIPS .012 .018 .024 0.30 0.45 0.60 e L L1 (.024) (0.60) B N 5 5 - - 01 0° 8° 0° 8° aaa .004 0.10 D bbb .008 0.20 aaa C ccc .010 0.25 A2 A SEATING H PLANE A1 C c bxN GAGE bbb C A-B D PLANE 0.25 L 01 (L1) DETAIL A SEE DETAIL A SIDE VIEW NOTES: 1. CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES). 2. DATUMS AND TO BE -A- -B- DETERMINED AT DATUM PLANE -H- 3. DIMENSIONS "E1" AND "D" DO NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. 4. REFERENCE JEDEC STD MO-193, VARIATION AB. Land Pattern - TSOT-23 DI DIMENSIONS MENSIONS X DIM DIM INCHES INCHES MILL MILLIM IMET ETE ER RS S (.087) (2.20) C C G G .031 0.80 (C) G Z P P .037 0.95 Y X X .024 0.60 Y Y .055 1.40 Z Z .141 3.60 P NOTES: 1. THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY. CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR COMPANY'S MANUFACTURING GUIDELINES ARE MET.  2007 Semtech Corp. 21 www.semtech.com SC4503 POWER MANAGEMENT Outline Drawing - 8 Lead 2X2mm MLPD-W B A D DIMENSIONS INCHES MILLIMETERS DIM MIN NOM MAX MIN NOM MAX E A .028 .030 .031 0.70 0.75 0.80 PIN 1 A1 .000 .001 .002 0.00 0.02 0.05 INDICATOR (.008) (0.20) A2 (LASER MARK) b .007 .010 .012 0.18 0.25 0.30 D .075 .079 .083 1.90 2.00 2.10 D1 .059 .063 .067 1.50 1.60 1.70 E .075 .079 .083 1.90 2.00 2.10 E1 .031 .035 .039 0.80 0.90 1.00 A e .020 BSC 0.50 BSC SEATING L .008 .012 .016 0.20 0.30 0.40 PLANE aaa C N 8 8 aaa .003 0.08 A1 A2 C bbb .003 0.08 D1 1 2 LxN E/2 E1 N bxN e bbb C A B e/2 D/2 NOTES: 1. CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES). 2. COPLANARITY APPLIES TO THE EXPOSED PAD AS WELL AS THE TERMINALS. Land Pattern - 8 Lead 2X2mm MLPD-W Contact Information Semtech Corporation Power Management Products Division 200 Flynn Road, Camarillo, CA 93012 Phone: (805) 498-2111 Fax: (805) 498-3804 www.semtech.com  2007 Semtech Corp. 22 www.semtech.com