SEMTECH SC4502

SC4502/SC4502H 1.4Amp, 2MHz Step-Up Switching Regulator with Soft-Start POWER MANAGEMENT Features Description The SC4502/SC4502H is a high-frequency current-mode ‹ Low saturation voltage switch: 210mV step-up switching regulator with an integrated 1.4A (250mV for the SC4502H) power transistor. Its high switching frequency (program- ‹ Constant switching frequency current-mode control mable up to 2MHz) allows the use of tiny surface-mount ‹ Programmable switching frequency up to 2MHz external passive components. Programmable soft-start ‹ Soft-Start function eliminates high inrush current during start-up. The inter- ‹ Input voltage ranges from 1.4V to 16V nal switch is rated at 32V (40V for the SC4502H) mak- ‹ Output voltage up to 32V (40V for the SC4502H) ing the converter suitable for high voltage applications ‹ Low shutdown current such as Boost, SEPIC and Flyback. ‹ Adjustable undervoltage lockout threshold ‹ Small low-profile thermally enhanced lead free The operating frequency of the SC4502/SC4502H can package. This product is fully WEEE and RoHS be set with an external resistor. The ability to set the compliant. operating frequency gives the SC4502/SC4502H design Applications flexibilities. A dedicated COMP pin allows optimization of ‹ Flat screen LCD bias supplies the loop response. The SC4502/SC4502H is available in thermally enhanced 10-pin MLPD package. ‹ TFT bias supplies ‹ XDSL power supplies ‹ Medical equipment ‹ Digital video cameras ‹ Portables devices ‹ White LED power supplies Typical Application Circuit D1 L1 VIN VOUT 5V 12V 10BQ015 R1 Efficiency 8 6,7 866K 95 IN SW 10.5 H, 700KHz H, 1.4MHz 3 2 µ 5.3µ OFF ON SHDN FB 90 C2 C1 SC4502 10µF 2.2µF 10 1 85 SS COMP R2 GND ROSC R3 80 100K C3 4,5 9 C6 47nF 75 R4 3.3µH, 2MHz C4 70 65 All Capacitors are Ceramic. 60 V = 5V IN 55 V = 12V OUT 50 f(R MHz) (KΩ) R (KΩ) C(C pF)(L pF) (µH) 0.0 0.1 0.2 0.3 0.4 0.5 3 4 4 6 1 02 .737 3. 20 3. 1- 50 10.5 (Falco D08019) Load Current (A) 10 .453 9. 90 .5 5- 6 5.3 (Sumida CDRH5D28) 2276 3. 50 .3 32 32) 3.3 (Coilcraft DO1813P Figure 1(b). Efficiencies of 5V to 12V Boost Converters at 700KHz, 1.4MHz and 2MHz. Figure 1(a). 5V to 12V Boost Converter. Revision: July 25, 2005 1 www.semtech.com Efficiency (%) SC4502/SC4502H POWER MANAGEMENT Absolute Maximum Rating Exceeding the specifications below may result in permanent damage to the device, or device malfunction. Operation outside of the parameters specified in the Electrical Characteristics section is not implied. Pl arameter Sp ymbo Ts y Unit SV upply Voltage -V 0.3 to 16 IN SV W Voltage -V 0.3 to 32 SW SV W Voltage (SC4502H) -V 0.3 to 40 SW FV B Voltages -V 0.3 to 2.5 FB SV HDN Voltage -0.3 to V+V 1 SHDN IN OT perating Temperature Range -C 40 to +85 ° A Thermal Resistance Junction to Ambient (MLPD-10) 4W 0 °C/ θ JA MT aximum Junction Temperature 1C 60 ° J ST torage Temperature Range -C 65 to +150 ° STG LT ead Temperature (Soldering)10 sec 2C 60 ° LEAD ED SD Rating (Human Body Model) E0 S 2V 00 Electrical Characteristics Electrical Characteristics Unless other specified: V = 2V, SHDN = 1.5V, R = 7.68kΩ, -40°C < T = T < 85°C OSC IN A J Ps arameter Tn est Condition Mp i Tx y Mt a Uni Minimum Operating Voltage 14 .3 1V . Maximum Operating Voltage 1V 6 T=4 25°C 12 .2210 .24 1V .26 A Feedback Voltage -40°C < T<7 85°C 17 .21 1V .26 A FV eedback Voltage Line Regulation 1.5V <<1 16V 0% .0 IN FB Pin Bias Current 40 0 8A n −1 Error Amplifier Transconductance 60 µΩ Error Amplifier Open-Loop Gain 4B 9 d CV OMP Source Current =5 1.1V µA FB CV OMP Sink Current =5 1.4V µA FB VQV uiescent Supply Current = 1.5V, V=1 0 ( Not Switching ) 16 . 1A . m IN SHDN COMP VSV upply Current in Shutdown =0 0 18 1 µA IN SHDN Switching Frequency 15 .3 17 . 1z . MH Maximum Duty Cycle 80 5 9 % Minimum Duty Cycle 0% Switch Current Limit 12 .4 A SI witch Saturation Voltage =0 1.3A 20 1 3V 4 m SW Switch Saturation Voltage (SC4502H) I=0 1.3A 20 5 3V 9 m SW  2005 Semtech Corp. www.semtech.com 2 SC4502/SC4502H POWER MANAGEMENT Electrical Characteristics (Cont.) Unless other specified: V = 2V, SHDN = 1.5V, R = 7.68kΩ, -40°C < T = T < 85°C OSC IN A J Ps arameter Tn est Condition Mp i Tx y Mt a Uni SV witch Leakage Current =1 5V 01 .0 mA SW Shutdown Threshold Voltage 11 .02 18 . 1V .1 V=6 1.2V -4. µA SHDN Shutdown Pin Current V=0 0 0.1 µA SHDN SV oft-Start Charging Current =5 0.3V 1. µA SS Thermal Shutdown Temperature 1C 60 ° Thermal Shutdown Hysteresis 1C 0 ° Pin Configurations Ordering Information (1)(2) DevicePT ackage Temp. Range( ) A TOP VIEW S0 C4502MLTRTMC LPD-1 -40 to 85° S0 C4502HMLTRTMC LPD-1 -40 to 85° Sd C4502EVB Evaluation Boar Sd C4502HEVB Evaluation Boar Notes: (1) Only available in tape and reel packaging. A reel contains 3000 devices for MLP package. (2) Lead free product. This product is fully WEEE and (10 Pin - MLPD, 3 x 3mm) RoHS compliant.  2005 Semtech Corp. 3 www.semtech.com SC4502/SC4502H POWER MANAGEMENT Pin Descriptions Pe inPn in Nam Pin Functio 1P COM The output of the internal transconductance error amplifier. This pin is used for loop compensation. 2B F The inverting input of the error amplifier. Tie to an external resistive divider to set the output voltage. Shutdown Pin. The accurate 1.1V shutdown threshold and the 4.6uA shutdown pin current hysteresis allow the user to set the undervoltage lockout threshold and hysteresis for the switching 3N SHD regulator. Pulling this pin below 0.1V causes the converter to shut down to low quiescent current. Tie this pin to IN if the UVLO and the shutdown features are not used. This pin should not be left floating. 4D ,5 GN Ground. Tie both pins to the ground plane. Pins 4 and 5 are not internally connected. 6W ,7 S Collector of the internal power transistor. Connect to the boost inductor and the rectifying diode. 8NI. Power Supply Pin. Bypassed with capacitors close to the pin 9C ROS A resistor from this pin to the ground sets the switching frequency. Soft-Start Pin. A capacitor from this pin to the ground lengthens the start-up time and reduces start- 1S 0 S up current. Exposed Pad The exposed pad must be soldered to the ground plane on the PCB for good thermal conduction. Block Diagram IN SW SW 8 6 7 4.6µA SHDN 3 + CMP INTERNAL REG - SUPPLY 1.1V ENABLE VOLTAGE THERMAL REFERENCE SHUTDOWN CLK 1.242V + R FB EA - 2 Q - PWM REG S + COMP 1 1.5µA SS + 10 I-LIMIT ILIM - REG_GOOD R SENSE ENABLE + + ISEN Σ - + CLK SLOPE COMP 4 5 ROSC OSCILLATOR GND GND 9 Figure 2. SC4502/SC4502H Block Diagram.  2005 Semtech Corp. www.semtech.com 4 SC4502/SC4502H POWER MANAGEMENT Typical Characteristics Switching Frequency Feedback Voltage vs Temperature R vs Switching Frequency vs Temperature OSC 1.3 1.7 100 R = 7.68KΩ OSC 1.6 V = 2V IN V = 12V 1.25 IN 25ºC 1.5 10 V = 2V IN 1.2 1.4 1.3 1.15 1 -50 -25 0 25 50 75 100 125 -50 -25 0 25 50 75 100 125 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Temperature (ºC) Temperature (ºC) Frequency (MHz) Switch Saturation Voltage Switch Saturation Voltage Minimum V vs Temperature IN vs Switch Current vs Switch Current 500 500 1.5 SC4502H SC4502 400 400 1.4 300 300 1.3 85ºC 85ºC 200 200 1.2 25ºC 25ºC 100 100 1.1 0 0 1 00.511.5 2 00.5 11.5 2 -50 -25 0 25 50 75 100 125 Switch Current (A) Switch Current (A) Temperature (ºC) V Current in Shutdown IN Shutdown Threshold V Quiescent Current vs Temperature vs Input Voltage IN vs Temperature 1.3 50 1.20 Not Switching V = 2V IN 1.2 40 1.15 VIN = 16V -40ºC 1.1 30 125ºC 1.10 1 20 V = 2V IN 1.05 0.9 10 VSHDN = 0 0.8 0 1.00 -50 -25 0 25 50 75 100 125 0 5 10 15 20 -50 -25 0 25 50 75 100 125 Temperature (ºC) Input Voltage (V) Temperature (ºC)  2005 Semtech Corp. 5 www.semtech.com Feedback Voltage (V) CESAT VIN Current (mA) V (mV) V (mV) CESAT ROSC (K ) Ω VIN Current ( A) µ Shutdown Threshold (V) Input Voltage (V) Frequency (MHz) SC4502/SC4502H POWER MANAGEMENT Typical Characteristics Shutdown Pin Current V Current vs SHDN Pin Voltage vs Temperature IN V Current vs SHDN Pin Voltage IN 1.2 -3 0.1 V = 2V V = 2V IN IN V = 1.25V SHDN 1 0.08 125ºC 25ºC 0.8 -4 0.06 VIN = 2V 0.6 0.04 0.4 -5 V = 12V IN 125ºC -40ºC 0.02 0.2 -40ºC 0 0 -6 0 0.5 1 1.5 0 0.2 0.4 0.6 0.8 1 1.2 -50 -25 0 25 50 75 100 125 SHDN Voltage (V) SHDN Voltage (V) Temperature (ºC) Switch Current Limit Soft-Start Charging Current Transconductance vs Temperature vs Temperature vs Temperature 2.4 2 80 V = 0.3V SS VIN = 2V 1.8 70 2.2 1.6 60 2 1.4 50 1.8 1.2 40 1 1.6 30 -50 -25 0 25 50 75 100 125 -50 -25 0 25 50 75 100 -50 -25 0 255075 100 125 Temperature (ºC) Temperature (ºC) Temperature (ºC)  2005 Semtech Corp. www.semtech.com 6 VIN Current (mA) Current (µA) -1 VIN Current (mA) Transconductance ( ) µΩ Current Limit (A) Current ( A) µ SC4502/SC4502H POWER MANAGEMENT Operation Applications Information The SC4502/SC4502H is a programmable constant- Setting the Output Voltage frequency peak current-mode step-up switching regulator with an integrated power transistor. As shown in the block An external resistive divider R and R with its center tap 1 2 diagram in Figure 2, the power transistor is turned on at tied to the FB pin (Figure 3) sets the output voltage. the trailing edge of the clock. Switch current is sensed  V  OUT with an integrated sense resistor. The sensed current R = R −1   1 2 (1) 1.242V   signal is summed with the slope-compensating ramp before compared to the output of the error amplifier EA. VOUT The PWM comparator trip point determines the switch turn-on pulse width. The current-limit comparator ILIM SC4502/SC4502H R1 turns off the power switch when the switch current 40nA exceeds the 2A current-limit threshold. ILIM therefore 2 FB provides cycle-by-cycle current limit. Current-limit is not R2 affected by slope compensation because the current limit comparator ILIM is not in the PWM signal path. Figure 3. The Output Voltage is set with a Resistive Divider Current-mode switching regulators utiilize a dual-loop feedback control system. In the SC4502/SC4502H the amplifier output COMP controls the peak inductor current. The input bias current of the error amplifier will introduce This is the inner current loop. The double reactive poles an error of: of the output LC filter are reduced to a single real pole by the inner current loop, easing loop compensation. Fast ΔV 40nA ⋅() R //R ⋅100 OUT 1 2 = % transient response can be obtained with a simple Type-2 (2) V 1.242V OUT compensation network. In the outer loop, the error amplifier regulates the output voltage. The percentage error of a V = 5V converter with R = OUT 1 100KΩ and R = 301KΩ is The switching frequency of the SC4502/SC4502H can 2 be programmed up to 2MHz with an external resistor ΔV 40nA ⋅() 100KΩ // 301KΩ ⋅100 from the ROSC pin to the ground. For converters requiring OUT = = 0.24% V 1.242V extremely low or high duty cycles, the operating frequency OUT can be lowered to maintain the necessary minimum on Operating Frequency and Efficiency time or the minimum off time. Switching frequency of SC4502/SC4502H is set with The SC4502/SC4502H requires a minimum input of 1.4V an external resistor from the ROSC pin to the ground. A to operate. A voltage higher than 1.1V at the shutdown graph showing the relationship between R and pin enables the internal linear regulator REG in the OSC switching frequency is given in the “Typical SC4502/SC4502H. After V becomes valid, the soft- REG Characteristics”. start capacitor is charged with a 1.5µA current source. A PNP transistor clamps the output of the error amplifier High frequency operation reduces the size of passive as the soft-start capacitor voltage rises. Since the COMP components but switching losses are higher. The efficiencies voltage controls the peak inductor current, the inductor of 5V to 12V converters operating at 700KHz, 1.4MHz current is ramped gradually during soft-start, preventing and 2MHz are plotted in Figure 1(b) for SC4502. high input start-up current. Under fault conditions (V <1.4V or over temperature) or when the shutdown IN Duty Cycle pin is pulled below 1.1V, the soft-start capacitor is discharged to ground. Pulling the shutdown pin below 0.1V The duty cycle D of a boost converter in continuous reduces the total supply current to 10µA. conduction mode is:  2005 Semtech Corp. 7 www.semtech.com SC4502/SC4502H POWER MANAGEMENT Applications Information V It is worth noting that I is directly proportional to the IN OUTMAX 1− V + V OUT D V IN D = ratio of . Equation (4) over-estimates the maximum V (3) CESAT V 1− OUT V + V OUT D output current at high frequencies (>1MHz) since switching losses are neglected in its derivation. where V is the switch saturation voltage and V is the CESAT D Nevertheless it is a useful first-order approximation. voltage drop across the rectifying diode. Using V = 0.3V, V = 0.5V and I = 1.4A in (3) and Maximum Output Current CESAT D LIM (4), the maximum output currents for three V and V IN OUT combinations are shown in Table 1. In a boost switching regulator the inductor is connected to the input. The DC inductor current is the input current. When the power switch is turned on, the inductor current D V(V V ) ( V ) I ( A ) IN OUT OUTMAX flows through the switch. When the power switch is off, 22 .5 1005 .82 0.2 the inductor current flows through the rectifying diode to the output. The maximum output current is the average 35 .3 00 .423 0.8 diode current. The diode current waveform is trapezoidal with pulse width (1 – D)T (Figure 4). The output current 521503 .61 0.5 available from a boost converter therefore depends on the converter operating duty cycle. The power switch Table 1. Calculated Maximum Output Current [ Equation (4)] current in the SC4502/SC4502H is internally limited to 2A. This is also the maximum inductor or the input current. Considerations for High Frequency Operation By estimating the conduction losses in both the switch and the rectifying diode, an expression of the maximum The operating duty cycle of a boost converter decreases available output current of a boost converter can be as V approaches V . The PWM modulating ramp in a IN OUT derived as follows: current-mode switching regulator is the sensed current signal. This current ramp is absent unless the switch is turned on. The intersection of this ramp with the output I V  D V − D() V − V  LIM IN D D CESAT I = 1− − of the voltage feedback error amplifier determines the OUTMAX   (4) V 45 V OUT  IN  switch pulse width. The propagation delay time required to immediately turn off the switch after it is turned on is where I is the switch current limit. LIM the minimum switch on time. Regulator closed-loop measurement shows that the SC4502/SC4502H has a minimum on time of about 150ns at room temperature. The power switch in the SC4502/SC4502H is either not I IN turned on at all or on for at least 150ns. If the required Inductor Current switch on time is shorter than the minimum on time, the Switch Current regulator will either skip cycles or it will start to jitter. ON OFF ON Diode Current Example: Determine the maximum operating frequency of a Li-ion cell to 5V converter using the SC4502. Assuming that V =0.5V, V =0.3V and V =2.6V - 4.2V, D CESAT IN DT (1-D)T the minimum duty ratio can be found using (3). I OUT ON OFF ON OFF ON 4.2 1− 5 + 0.5 D = = 0.25 MIN 0.3 Figure 4. Current Waveforms in a Boost Regulator 1− 5 + 0.5  2005 Semtech Corp. www.semtech.com 8 SC4502/SC4502H POWER MANAGEMENT Applications Information operating in continuous-conduction mode is The absolute maximum operating frequency of the D⋅() V −V D 0.25 IN CESAT MIN ΔI = (5) = = 1.67MHz converter is therefore . The L f⋅L 150ns 150ns where f is the switching frequency and L is the inductance. actual operating frequency needs to be lower to allow for modulating headroom. Substituting (3) into (5) and neglecting V , CESAT The power transistor inside the SC4502/SC4502H is   V V turned off every switching cycle for an interval determined IN IN   ΔI = 1− L   (6) by the discharge time of the oscillator ramp plus the f ⋅L V + V OUT D   propagation delay of the power switch. This minimum off In peak current-mode control, the slope of the modulating time limits the maximum duty cycle of the regulator at a (sensed switch current) ramp should be steep enough to given switching frequency. A boost converter with high lessen jittery tendency but not so steep that large flux V OUT swing decreases efficiency. Inductor ripple current DI ratio requires long switch on time and high duty cycle. L V In between 25%-40% of the peak inductor current limit is a If the required duty cycle is higher than the attainable good compromise. Inductors so chosen are optimized in maximum, the converter will operate in dropout. (Dropout size and DCR. Setting ΔI = 0.3•(1.4A) = 0.42A, V =0.5V L D is the condition in which the regulator cannot attain its in (6), set output voltage below current limit.)     V V V V IN IN IN IN     L = 1 − = 1 − (7)     The minimum off times of closed-loop boost converters set f ⋅ ΔI V + V 0.42A ⋅ f V + 0.5V L  OUT D   OUT  to various output voltages were measured by lowering their where L is in µH and f is in MHz. input voltages until dropout occurs. It was found that the minimum off time of the SC4502/SC4502H ranged from Equation (6) shows that for a given V , ΔI is the highest 80ns to 110ns at room temperature. OUT L () V + V OUT D V = when . If V varies over a wide range, then Beware of dropout while operating at very low input IN IN 2 voltages (1.5V-2V) with off time approaching 110ns. choose L based on the nominal input voltage. Shorten the PCB trace between the power source and the device input pin, as line drop may be a significant The saturation current of the inductor should be 20%- percentage of the input voltage. A regulator in dropout 30% higher than the peak current limit (2A). Low-cost may appear as if it is in current limit. The cycle-by-cycle powder iron cores are not suitable for high-frequency current limit of the SC4502/SC4502H is duty-cycle and switching power supplies due to their high core losses. input voltage invariant and is typically 2A. If the switch Inductors with ferrite cores should be used. current limit is not at least 1.4A, then the converter is likely in dropout. The switching frequency should then be Input Capacitor lowered to improve controllability. The input current in a boost converter is the inductor Both the minimum on time and the minimum off time current, which is continuous with low RMS current ripples. reduce control range of the PWM regulator. Bench A 2.2µF-4.7µF ceramic input capacitor is adequate for measurement showed that reduced modulating range most applications. started to be a problem at frequencies over 2MHz. Although the oscillator is capable of running well above 2MHz, Output Capacitor controllability limits the maximum operating frequency. Both ceramic and low ESR tantalum capacitors can be Inductor Selection used as output filtering capacitors. Multi-layer ceramic capacitors, due to their extremely low ESR (<5mΩ), are The inductor ripple current ΔI of a boost converter L the best choice. Use ceramic capacitors with stable  2005 Semtech Corp. 9 www.semtech.com SC4502/SC4502H POWER MANAGEMENT Applications Information temperature and voltage characteristics. One may be Volts higher than the output voltage. For switching tempted to use Z5U and Y5V ceramic capacitors for regulators operating at low duty cycles (i.e. low output output filtering because of their high capacitance and voltage to input voltage conversion ratios), it is beneficial small sizes. However these types of capacitors have high to use rectifying diodes with somewhat higher RMS temperature and high voltage coefficients. For example, current ratings (thus lower forward voltages). This is the capacitance of a Z5U capacitor can drop below 60% because the diode conduction interval is much longer of its room temperature value at –25°C and 90°C. X5R than that of the transistor. Converter efficiency will be improved if the voltage drop across the diode is lower. ceramic capacitors, which have stable temperature and voltage coefficients, are the preferred type. The rectifying diodes should be placed close to the SW pins of the SC4502/SC4502H to minimize ringing due The diode current waveform in Figure 4 is discontinuous to trace inductance. Surface-mount equivalents of with high ripple-content. In a buck converter, the inductor 1N5817, 1N5819, MBRM120, MBR0520 (ON Semi) and ripple current ΔI determines the output ripple voltage. L 10BQ015, 10BQ040 (IRF) are all suitable. The output ripple voltage of a boost regulator is however much higher and is determined by the absolute value of Soft-Start the inductor current. Decreasing the inductor ripple current does not appreciably reduce the output ripple Soft-start prevents a DC-DC converter from drawing voltage. The current flowing in the output filter capacitor excessive current (equal to the switch current limit) from is the difference between the diode current and the the power source during start up. If the soft-start time is output current. This capacitor current has a RMS value made sufficiently long, then the output will enter regulation of: without overshoot. An external capacitor from the SS pin to the ground and an internal 1.5µA charging current source set the soft-start time. The soft-start voltage ramp V OUT I −1 OUT (8) at the SS pin clamps the error amplifier output. During V IN regulator start-up, COMP voltage follows the SS voltage. The converter starts to switch when its COMP voltage If a tantalum capacitor is used, then its ripple current rating exceeds 0.7V. The peak inductor current is gradually in addition to its ESR will need to be considered. increased until the converter output comes into regulation. If the shutdown pin is forced below 1.1V or if a fault When the switch is turned on, the output capacitor supplies situation is detected, then the soft-start capacitor will the load current I (Figure 4). The output ripple voltage OUT be discharged to ground immediately. due to charging and discharging of the output capacitor is therefore: The SS pin can be left open if soft-start is not required. Shutdown I ⋅D ⋅ T OUT ΔV = OUT (9) C OUT The input voltage and shutdown pin voltage must be greater than 1.4V and 1.1V respectively to enable the SC4502/ For most applications, a 10µF - 22µF ceramic capacitor SC4502H. Forcing the shutdown pin below 1.1V stops is sufficient for output filtering. It is worth noting that the the SC4502/SC4502H from switching. Pulling this pin output ripple voltage due to discharging of a 10µF ceramic below 0.1V completely shuts off the SC4502/SC4502H. capacitor (9) is higher than that due to its ESR. The total V shutdown current decreases to 10µA at 2V. IN Figure 5 shows several ways of interfacing the control Rectifying Diode logic to the shutdown pin. Beware that the shutdown pin is a high impedance pin. It should always be driven from For high efficiency, Schottky barrier diodes should be used a low-impedance source or tied to a resistive divider. as rectifying diodes for the SC4502/SC4502H. These Floating the shutdown pin will result in undefined voltage. diodes should have a RMS current rating between 0.5A In Figure 5(c) the shutdown pin is driven from a logic and 1A with a reverse blocking voltage of at least a few  2005 Semtech Corp. www.semtech.com 10 SC4502/SC4502H POWER MANAGEMENT Applications Information IN IN SC4502 SC4502 SC4502H SC4502H SHDN SHDN (a) (b) V IN IN IN SC4502 SC4502 1N4148 SC4502H SC4502H SHDN SHDN (c) (d) Figure 5. Methods of Driving the Shutdown Pin (a) Directly Driven from a Logic Gate (b) Driven from an Open-drain N-channel MOSFET or an Open-Collector NPN Transistor (V < 0.1V) OL (c) Driven from a Logic Gate with V > V OH IN (d) Combining Shutdown with Programmed UVLO (See Section Below). gate whose V is higher than the supply voltage of the in conjunction with a resistive voltage divider to raise the OH SC4502/SC4502H. The diode clamps the maximum UVLO threshold and to add an UVLO hysteresis. Figure 6 shutdown pin voltage to one diode voltage above the shows the scheme. Both V and V (the desired upper H L input power supply. and the lower UVLO threshold voltages) are determined by the 1.1V threshold crossings, V and V are therefore: H L Programming Undervoltage Lockout   R 3   V = 1+ ⋅() 1.1V H   R  4  The SC4502/SC4502H has an internal V undervoltage IN (10) lockout (UVLO) threshold of 1.4V. The transition from idle V = V − V = V − I R L H HYS H HYS 3 to switching is abrupt but there is no hysteresis. If the Re-arranging, input voltage ramp rate is slow and the input bypass is V limited, then sudden turn on of the power transistor will HYS R = (11) 3 cause a dip in the line voltage. Switching will stop if V I HYS IN falls below the internal UVLO threshold. The resulting R 3 output voltage rise may be non-monotonic. The 1.1V R = 4 V H disable threshold of the SC4502/SC4502H can be used − 1 (12) 1.1V  2005 Semtech Corp. 11 www.semtech.com SC4502/SC4502H POWER MANAGEMENT Applications Information V = V − V = 2.75V − 0.69V = 2.06V > 1.4V . L H HYS IN Frequency Compensation 6/8 Figure 7 shows the equivalent circuit of a boost converter I HYS using the SC4502/SC4502H. The output filter capacitor 4.6µA and the load form an output pole at frequency: R3 SWITCH CLOSED WHEN Y = “1” 2 ⋅I 2 OUT ω = = p2 (13) V ⋅ C R ⋅C SHDN OUT 2 OUT 2 3 + V OUT Y R = where C is the output capacitance and is OUT 2 I - OUT 1.1V R4 COMPARATOR the equivalent load resistance. SC4502/SC4502H The zero formed by C and its equivalent series resistance 2 (ESR) is neglected due to low ESR of the ceramic output capacitor. Figure 6. Programmable Hysteretic UVLO Circuit There is also a right half plane (RHP) zero with angular frequency: with V > 1.4V . L 2 R ⋅() 1− D = 3.3V boost Example: Increase the turn on voltage of a V OUT IN ω = (14) Z2 converter from 1.4V to 2.75V. L Using V = 2.75V and R = 100KΩ in (12), ω decreases with increasing duty cycle D and increasing H 4 z2 I . Using the 5V to 12V boost regulator (1.4MHz) in OUT Figure 1(a) as an example, R = 150KΩ . 3 The resulting UVLO hysteresis is: 5V R ≥ = 10Ω OUT 0.5A V = I R = 4.6µA •150KΩ = 0.69V HYS HYS 3 The turn off voltage is: I OUT V IN POWER V STAGE OUT ESR R R1 C5 OUT C2 FB - COMP Gm + R3 1.242V C6 RO R2 VOLTAGE C4 REFERENCE Figure 7. Simplified Block Diagram of a Boost Converter  2005 Semtech Corp. www.semtech.com 12 SC4502/SC4502H POWER MANAGEMENT Applications Information 1 1 ω = = p1 R C 4.7MΩ • 560pF 5 O 4 1− −1 12 + 0.5 = 380 rads ⇒ 60Hz D = = 0.62 0.3 1− C and R also forms a zero with angular frequency: 4 3 12 + 0.5 1 1 Therefore ω = = z1 R C 59KΩ • 560pF 3 4 −1 2 = 30.3 Krads ⇒ 4.8KHz −1 ω ≤ = 20Krads ⇒ 3.18KHz p2 () 10Ω ⋅(10µF) and The poles p , p and the RHP zero z all increase phase 1 2 2 shift in the loop response. For stable operation, the overall 2 10Ω ⋅() 1− 0.62 −1 loop gain should cross 0dB with -20dB/decade slope. Due ω ≥ = 272Krads ⇒ 43.4KHz z2 5.3µH to the presence of the RHP zero, the crossover frequency z 2 The spacing between p and z is the closest when the should not be higher than . Placing z near p nulls its 2 2 1 2 3 converter is delivering the maximum output current from effect and maximizes loop bandwidth. Thus the lowest V . This represents the worst-case IN compensation condition. Ignoring C and C for the 5 6 moment, C forms a low frequency pole with the V ⋅C 4 OUT 2 R C ≈ 3 4 (15) equivalent output resistance R of the error amplifier: O 2 ⋅I OUT(MAX) AmplifierOpen Loop Gain 49dB R determines the mid-band loop gain of the converter. 3 R = = = 4.7MΩ O −1 Transconductance Increasing R increases the mid-band gain and the 60µΩ 3 crossover frequency. However it reduces the phase margin. The values of R and C can be determined 3 4 GN GN GN GND D D D R3 R3 R3 R3 C3 C3 C3 C3 R4 R4 R4 R4 C4 C4 C4 C4 C6 C6 C6 C6 R2 R2 R2 R2 U1 U1 U1 U1 C1 C1 C1 C1 SH SH SH SHD D D DN N N N L1 L1 L1 L1 R1 R1 R1 R1 C5 C5 C5 C5 C2 C2 C2 C2 D1 D1 D1 D1 VO VO VO VOU U U UT T T T VI VI VI VIN N N N Figure 8. Suggested PCB Layout for the SC4502/SC4502H. Notice that there is no via directly under the device. All vias are 12mil in diameter.  2005 Semtech Corp. 13 www.semtech.com SC4502/SC4502H POWER MANAGEMENT Applications Information empirically by observing the inductor current and the The input bypass capacitors should also be placed close output voltage during load transient. Compensation is to the input pins. Shortening the trace at the SW node optimized when the largest R and the smallest C without reduces the parasitic trace inductance. This not only 3 4 producing ringing or excessive overshoot in its inductor reduces the EMI but also decreases the sizes of the current and output voltage are found. Figures 9(b), 10(c), switching voltage spikes and glitches. 11(b) and 11(c) show load transient responses of empirically optimized DC-DC converters. In a battery- Figure 8 shows how various external components are and operated system, compensating for the minimum V placed around the SC4502/SC4502H. The frequency- IN the maximum load step will ensure stable operation over setting resistor should be placed near the ROSC pin with the entire input voltage range. a short ground trace on the PC board. These precautions reduce switching noise pickup at the ROSC pin. C adds a feedforward zero to the loop response. In some 5 cases, it improves the transient speed of the converter. To achieve a junction to ambient thermal resistance (θ ) JA C rolls off the gain at high frequency. This helps to of 40°C/W, the exposed pad of the SC4502/SC4502H 6 should be properly soldered to a large ground plane. Use stabilize the loop. C and C are often not needed. 5 6 only 12mil diameter vias in the ground plane if necessary. Avoid using larger vias under the device. Molten solder Board Layout Considerations may seep through large vias during reflow, resulting in poor adhesion, poor thermal conductivity and low In a step-up switching regulator, the output filter reliability. capacitor, the main power switch and the rectifying diode carry switched 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 SC4502/SC4502H, grounding the output filter capacitor next to the SC4502/SC4502H ground pin minimizes size of the high di/dt current loop. Typical Application Circuits D1 L1 VIN VOUT 5.6µH 3.3V 12V, 0.3A 10BQ015 R1 8 6,7 174K IN SW 3 2 OFF ON SHDN FB C2 SC4502 10µF C1 10 1 SS COMP 2.2µF R2 ROSC R3 GND 20K 40.2K C3 4,5 9 47nF R4 C4 9.31K 1.8nF 40µs/div Upper Trace : Output Voltage, AC Coupled, 1V/div L1: Sumida CR43 Lower Trace : Inductor Current, 0.5A/div Figure 9(a). 1.35 MHz All Ceramic Capacitor 3.3V to 12V Boost Figure 9(b). Load Transient Response of the Circuit in Figure Converter. 9(a). I is switched between 0.1A and 0.3A LOAD at 1A/µs.  2005 Semtech Corp. www.semtech.com 14 SC4502/SC4502H POWER MANAGEMENT Typical Application Circuits Efficiency vs Load Current 95 D1 L1 VOUT 90 2.6 - 4.2V 1.5MHz 2.5µH 5V, 0.5A 85 10BQ015 R1 80 8 6,7 301K V = 4.2V IN IN SW 75 3 2 OFF ON SHDN FB 1-CELL 70 C1 C2 SC4502 LI-ION 10µF 2.2µF 10 1 65 SS COMP V = 3.6V IN VIN = 2.6V R2 R3 GND ROSC 100K 60 34.8K C3 V = 5V OUT 4,5 9 47nF R4 55 C4 7.68K 1nF 50 0.001 0.010 0.100 1.000 L1: Sumida CDRH5D28 Load Current (A) Figure 10(a). 1.5 MHz All Ceramic Capacitor Single Li-ion Cell Figure 10(b). Efficiency of the Single Li-ion Cell to 5V Boost to 5V Boost Converter. Converter in Figure 10(a). V =2.6V IN 40µs/div Upper Trace : Output Voltage, AC Coupled, 0.5V/div Lower Trace : Inductor Current, 0.5A/div Figure 10(c). Load Transient Response of the Circuit in Figure . 10(a). I is switched between 90mA and 0.5A LOAD at 1A/µs.  2005 Semtech Corp. 15 www.semtech.com Efficiency (%) SC4502/SC4502H POWER MANAGEMENT Typical Application Circuits 4-CELL VOUT C6 L1 D1 3.6 - 6V 5V, 0.5A 3.3µH 2.2µF 10BQ015 R1 8 6,7 60.4K IN SW 3 2 OFF ON SHDN FB C2 C1 SC4502 2.2µF 10µF 10 1 SS COMP L2 R2 R3 GND ROSC 3.3µH 20K 35.7K C6 C3 4,5 9 22pF 47nF R4 C4 7.68K 1.5nF L1 and L2: Coiltronics DRQ73-3R3 Figure 11(a). 1.5 MHz All Ceramic Capacitor 4-Cell to 5V SEPIC Converter. V =3.6V IN V =6V IN 40µs/div 40µs/div Upper Trace : Output Voltage, AC Coupled, 0.5V/div Upper Trace : Output Voltage, AC Coupled, 0.5V/div Lower Trace : Input Inductor Current, 0.2A/div Lower Trace : Input Inductor Current, 0.2A/div Figure 11(b). Load Transient Response of the Circuit in Figure Figure 11(c). Load Transient Response of the Circuit in Figure 11(a). I is switched between 150mA and 11(a). I is switched between 250mA and LOAD LOAD 450mA at 1A/µs. 700mA at 1A/µs.  2005 Semtech Corp. www.semtech.com 16 SC4502/SC4502H POWER MANAGEMENT Typical Application Circuits D2 D3 D4 D5 OUT2 23V (10mA) C5 C6 C7 C8 0.1µF 0.1µF 0.1µF 1µF L1 D1 3.3V OUT1 8V (0.4A) 3.3µH 10BQ015 R5 R1 8 6,7 150K 274K IN SW 3 2 SHDN FB C2 C1 SC4502 2.2µF C9 10µF 10 1 SS COMP 0.1µF R6 R2 GND ROSC R3 100K 49.9K 33.2K C3 4,5 9 47nF R4 C4 7.68K 1.5nF D7 OUT3 -8V (10mA) C10 L1 : Coiltronics SD18-3R3 D6 1µF D2 - D7 : BAT54S Figure 12(a). 1.5MHz Triple-Output TFT Power Supply. CH4 CH4 CH1 CH1 CH2 CH2 CH3 CH3 2ms/div 4ms/div CH1 : OUT1 Voltage, 5V/div CH1 : OUT1 Voltage, 5V/div CH2 : OUT2 Voltage, 10V/div CH2 : OUT2 Voltage, 10V/div CH3 : OUT3 Voltage, 5V/div CH3 : OUT3 Voltage, 5V/div CH4 : SHDN Voltage, 2V/div CH4 : Input Voltage, 2V/div Figure 12(c). TFT Power Supply Start-up Transient as the Figure 12(b). TFT Power Supply V Start-up Transient. IN SHDN Pin is stepped from 0 to 2V.  2005 Semtech Corp. 17 www.semtech.com SC4502/SC4502H POWER MANAGEMENT Typical Application Circuits Efficiency at 14V input D1 L1 VIN VOUT 90 14V 35V 1.4MHz 6.8µH 85 SS14 R1 8 6,7 80 17.4K IN SW 75 3 2 OFF ON SHDN FB C2 70 C1 1.0MHz 10µH SC4502H 10µF 2.2µF 10 1 SS COMP 65 R3 R2 GND ROSC 5.11K 649 60 C3 4,5 9 47nF 55 R4 C4 1.5nF 50 0 0.05 0.1 0.15 0.2 Load (A) Figure 13(a). All Ceramic Capacitor High Voltage Application Figure 13(b). Efficiency of the All Ceramic Capacitor High Voltage Application L R (KΩ Ω Ω Ω Ω) f (MHz) 1 4 18 .011 5. 10uH IHLP-2525BD_0 10 .411 6.8uH IHLP-2525BD_0  2005 Semtech Corp. www.semtech.com 18 Efficiency (%) SC4502/SC4502H POWER MANAGEMENT Outline Drawing - MLPD-10, 3 x 3mm A E DIMENSIONS B INCHES MILLIMETERS DIM MIN NOM MAX MIN NOM MAX A .031 - .039 0.80 - 1.00 - - A1 .000 .002 0.00 0.05 - (.008) - - (0.20) - A2 b .007 .009 .011 0.18 0.23 0.30 E C .074 .079 .083 1.87 2.02 2.12 D .042 .048 .052 1.06 1.21 1.31 PIN 1 E .114 .118 .122 2.90 3.00 3.10 INDICATOR e .020 BSC 0.50 BSC (LASER MARK) L .012 .016 .020 0.30 0.40 0.50 N 10 10 aaa .003 0.08 bbb .004 0.10 A SEATING PLANE aaa C A1 C A2 C 1 2 LxN D N e bxN bbb C A B NOTES: 1. CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES). 2. COPLANARITY APPLIES TO THE EXPOSED PAD AS WELL AS TERMINALS. Land Pattern - MLPD-10, 3 x 3mm K DIMENSIONS DIM INCHES MILLIMETERS (.112) (2.85) C G .075 1.90 H H .055 1.40 (C) G Z K .087 2.20 P .020 0.50 X .012 0.30 Y Y .037 0.95 X Z .150 3.80 P NOTES: 1. THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY. CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR COMPANY'S MANUFACTURING GUIDELINES ARE MET. Contact Information Semtech Corporation Power Management Products Division 200 Flynn Road, Camarillo, CA 93012 Phone: (805)498-2111 FAX (805)498-3804  2005 Semtech Corp. 19 www.semtech.com