SEMTECH SC4501

SC4501 2Amp, 2MHz Step-Up Switching Regulator with Soft-Start POWER MANAGEMENT Features Description The SC4501 is a high-frequency current-mode step-up � Low saturation voltage switch: 220mV at 2A switching regulator with an integrated 2A power transis- � Constant switching frequency current-mode control tor. Its high switching frequency (programmable up to � Programmable switching frequency up to 2MHz 2MHz) allows the use of tiny surface-mount external pas- � Soft-Start function sive components. Programmable soft-start eliminates high � Input voltage range from 1.4V to 16V inrush current during start-up. The internal switch is rated � Output voltage up to 32V at 32V making the converter suitable for high voltage ap- � Low shutdown current plications such as Boost, SEPIC and Flyback. � Adjustable undervoltage lockout threshold � Small low-profile thermally enhanced packages The operating frequency of the SC4501 can be set with an external resistor. The ability to set the operating frequency Applications gives the SC4501 design flexibilities. A dedicated COMP pin allows optimization of the loop response. The SC4501 � Flat screen LCD bias supplies is available in thermally enhanced 8-Pin MSOP and 10-pin � TFT bias supplies MLPD packages. � XDSL power supplies � Medical equipment � Digital video cameras � Portables devices � White LED power supplies Typical Application Circuit D1 L1 VIN VOUT 12V, 0.7A 5V 10BQ015 R1 6 5 174K Efficiency IN SW 3 95 OFF ON 2 SHDN FB 10.5μH, 700KHz 4.7μH, 1.4MHz C2 C1 SC4501 90 10μF 2.2μF 8 1 SS COMP 85 R2 GND ROSC R3 20K C3 4 7 C6 80 47nF R4 3.3μH, 2MHz C4 75 70 All Capacitors are Ceramic. 65 MSOP-8 Pinout 60 f / MHz R / KΩ R / KΩ C / pF C / pF L / μH 3 4 4 6 1 55 V = 5V IN V = 12V OUT 0.7 22.1 22.1 2200 - 10.5 (Falco D08019) 50 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 1.35 30.9 9.31 820 - 4.7 (Falco D08017) Load Current (A) 2 63.4 4.75 470 22 3.3 (Coilcraft DO1813P) Figure 1(a). 5V to 12V Boost Converter. Figure 1(b). Efficiencies of 5V to 12V Boost Converters at 700KHz, 1.4MHz and 2MHz. Revision: October 25, 2005 1 www.semtech.com Rev.1 March 24, 2011 Efficiency (%) SC4501 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. Parameter Symbol Typ Units Supply Voltage V -0.3 to 18 V IN SW Voltage V -0.3 to 32 V SW FB Voltages V -0.3 to 2.5 V FB SHDN Voltage V -0.3 to V + 1 V SHDN IN Operating Temperature Range T -40 to +85 °C A Thermal Resistance Junction to Ambient (MSOP-8) 40 θ JA °C/W Thermal Resistance Junction to Ambient (MLPD-10) 40 θ JA Maximum Junction Temperature T 160 °C J Storage Temperature Range T -65 to +150 °C STG Lead Temperature (Soldering)10 sec T 260 °C LEAD ESD Rating (Human Body Model) ESD 2000 V Electrical Characteristics Unless specified: V = 2V, SHDN = 1.5V, R = 7.68kΩ, -40°C < T = T < 85°C OSC IN A J Parameter Test Conditions Min Typ Max Unit Undervoltage Lockout Threshold 1.3 1.4 V Maximum Operating Voltage 16 V T = 25°C 1.224 1.242 1.260 V A Feedback Voltage -40°C < T < 85°C 1.217 1.267 V A Feedback Voltage Line 1.5V < V < 16V 0.01 % IN Regulation FB Pin Bias Current 40 80 nA −1 Error Amplifier Transconductance 60 μΩ Error Amplifier Open-Loop Gain 49 dB COMP Source Current V = 1.1V 5 μA FB COMP Sink Current V = 1.4V 5 μA FB V Quiescent Supply Current V = 1.5V, V = 0 ( Not Switching ) 1.1 1.6 mA IN SHDN COMP V Supply Current in Shutdown V = 0 10 18 μA IN SHDN Switching Frequency 1.27 1.5 1.77 MHz Maximum Duty Cycle 85 90 % Minimum Duty Cycle 0% Switch Current Limit 2 2.8 A Switch Saturation Voltage I = 2A 220 350 mV SW www.semtech.com © 2005 Semtech Corp. 2011 2 SC4501 POWER MANAGEMENT Electrical Characteristics (Cont.) Unless specified: V = 2V, SHDN = 1.5V, R = 7.68kΩ, -40°C < T = T < 85°C OSC IN A J Parameter Test Conditions Min Typ Max Unit Switch Leakage Current V = 5V 0.01 1 μA SW Shutdown Threshold Voltage 1.02 1.1 1.18 V V = 1.2V -4.6 μA SHDN Shutdown Pin Current V = 0 0 0.1 μA SHDN Soft-Start Charging Current V = 0.3V 1.5 μA SS Thermal Shutdown Temperature 160 °C Thermal Shutdown Hysteresis 10 °C Pin Configurations Ordering Information (1)(2) Device Package Temp. Range( T ) A TOP VIEW SC4501MLTRT MLPD-10 -40 to 85°C (3) SC4501MSETRT MSOP-8-EDP SC4501EVB Evaluation Board Notes: (1) Only available in tape and reel packaging. A reel contains 3000 devices for MLP package and 2500 devices for MSOP. (2) Lead free product. This product is fully WEEE and (10 Pin - MLPD, 3 x 3mm) RoHS compliant and halogen-free. (3) Contact factory for availability. TOP VIEW 1 COMP 8 SS FB 2 7 ROSC 6 3 IN SHDN 5 SW GND 4 (8 Pin MSOP-EDP) www.semtech.com © 2005 Semtech Corp. 2011 3 SC4501 POWER MANAGEMENT Pin Descriptions (MSOP-8) Block Diagram Pin Pin Name Pin Function 1 COMP The output of the internal transconductance error amplifier. This pin is used for loop compensation. 2 FB 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 3 SHDN 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. 4 GND Ground. Tie to the ground plane. 5 SW Collector of the internal power transistor. Connect to the boost inductor and the rectifying diode. 6 IN Power Supply Pin. Bypassed with capacitors close to the pin. 7 ROSC 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- 8SS 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 6 5 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 + 8 I-LIMIT ILIM - REG_GOOD R SENSE ENABLE + + ISEN Σ - + CLK SLOPE COMP 4 ROSC OSCILLATOR GND 7 Figure 2. SC4501 (MSOP-8) Block Diagram. www.semtech.com © 2005 Semtech Corp. 2011 4 SC4501 POWER MANAGEMENT Pin Descriptions (MLPD - 10) Pin Pin Name Pin Function 1 COMP The output of the internal transconductance error amplifier. This pin is used for loop compensation. 2 FB 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 3 SHDN 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. 4,5 GND Ground. Tie both pins to the ground plane. Pins 4 and 5 are not internally connected. 6,7 SW Collector of the internal power transistor. Connect to the boost inductor and the rectifying diode. 8 IN Power Supply Pin. Bypassed with capacitors close to the pin. 9 ROSC 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- 10 SS 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 ENABL E 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 + + Σ ISEN - + CLK SLOPE COMP 4 5 ROSC OSCILLATOR GND GND 9 Figure 3. SC4501 (MLPD-10) Block Diagram. www.semtech.com © 2005 Semtech Corp. 2011 5 SC4501 POWER MANAGEMENT Typical Characteristics Switching Frequency Feedback Voltage vs Temperature R vs Switching Frequency OSC vs Temperature 100 1.7 1.3 ROSC = 7.68KΩ 1.6 VIN = 2V 1.25 VIN = 12V 25ºC 10 1.5 VIN = 2V 1.2 1.4 1.15 1 1.3 -50 -25 0 25 50 75 100 125 0.0 0.5 1.0 1.5 2.0 2.5 3.0 -50 -25 0 25 50 75 100 125 Temperature (ºC) Frequency (MHz) Temperature (ºC) Switch Current Limit Switch Saturation Voltage vs Temperature Minimum V vs Temperature vs Switch Current IN 400 3 1.5 2.8 25ºC 1.4 300 85ºC 2.6 1.3 200 2.4 1.2 -40ºC 100 2.2 1.1 2 0 1 0 0.5 1 1.5 2 2.5 3 -50 -25 0 25 50 75 100 -50 -25 0 25 50 75 100 125 Switch Current (A) Temperature (ºC) 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 VIN = 2V 1.05 0.9 10 V = 0 SHDN 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) www.semtech.com © 2005 Semtech Corp. 2011 6 Feedback Voltage (V) VCESAT (mV) VIN Current (mA) OSC R (KΩ) Current Limit (A) IN V Current (μA) Shutdown Threshold (V) Input Voltage (V) Frequency (MHz) SC4501 POWER MANAGEMENT Typical Characteristics Shutdown Pin Current V Current vs SHDN Pin Voltage V Current vs SHDN Pin Voltage vs Temperature IN 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 V = 2V IN 0.6 0.04 0.4 -5 V = 12V IN 125ºC -40ºC 0.02 0.2 -40ºC 0 0 -6 0 0.2 0.4 0.6 0.8 1 1.2 0 0.5 1 1.5 -50 -25 0 25 50 75 100 125 SHDN Voltage (V) SHDN Voltage (V) Temperature (ºC) Soft-Start Charging Current Transconductance vs Temperature vs Temperature 2 80 V = 0.3V VIN = 2V SS 1.8 70 1.6 60 1.4 50 40 1.2 30 1 -50 -25 0 255075 100 125 -50 -25 0 255075 100 125 Temperature (ºC) Temperature (ºC) www.semtech.com © 2005 Semtech Corp. 7 2011 VIN Current (mA) Current (μA) VIN Current (mA) -1 Transconductance (μΩ ) Current ( A) μ SC4501 POWER MANAGEMENT Operation Application Information The SC4501 is a programmable constant-frequency peak Setting the Output Voltage current-mode step-up switching regulator with an integrated 2A power transistor. Referring to the block An external resistive divider R and R with its center tap 1 2 diagrams in Figures 2 and 3, the power transistor is tied to the FB pin (Figure 4) sets the output voltage. switched on at the trailing edge of the clock. Switch V ⎛ ⎞ OUT current is sensed with an integrated sense resistor. The R = R −1 ⎜ ⎟ (1) 1 2 1.242V ⎝ ⎠ sensed current is summed with the slope-compensating ramp before compared to the output of the error VOUT amplifier EA. The PWM comparator trip point determines the switch turn-on pulse width. The current-limit SC4501 comparator ILIM turns off the power switch when the R1 40nA switch current exceeds the 2.8A current-limit threshold. 2 FB ILIM therefore provides cycle-by-cycle current limit. Current-limit is not affected by slope compensation R2 because the current comparator ILIM is not in the PWM signal path. Current-mode switching regulators utilize a dual-loop Figure 4. The Output Voltage is set with a Resistive Divider feedback control system. In the SC4501 the amplifier output COMP controls the peak inductor current. This is The input bias current of the error amplifier will introduce the inner current loop. The double reactive poles of the an error of: 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 The switching frequency of the SC4501 can be programmed 100KΩ and R = 301KΩ is 2 up to 2MHz with an external resistor from the ROSC pin to the ground. For converters requiring extreme duty ΔV 40nA() 100K //301K 100 OUT = = 0.24% cycles, the operating frequency can be lowered to V 1.242V OUT maintain the necessary minimum on time or the minimum off time. Operating Frequency and Efficiency The SC4501 requires a minimum input of 1.4V to operate. Switching frequency of SC4501 is set with an external A voltage higher than 1.1V at the shutdown pin enables resistor from the ROSC pin to the ground. A graph showing the internal linear regulator REG in the SC4501. After V REG the relationship between R and switching frequency is becomes valid, the soft-start capacitor is charged with a OSC given in the “Typical Characteristics”. 1.5μA current source. A PNP transistor clamps the output of the error amplifier as the soft-start capacitor voltage High frequency operation reduces the size of passive rises. Since the COMP voltage controls the peak inductor components but switching losses are higher. The efficiencies current, the inductor current is ramped gradually during of 5V to 12V converters operating at 700KHz, 1.35MHz soft-start, preventing high input start-up current. Under and 2MHz are shown in Figure 1(b). The peak efficiency fault conditions (V <1.4V or over temperature) or when IN of the SC4501 appears to decrease 0.5% for every the shutdown pin is pulled below 1.1V, the soft-start 100KHz increase in frequency. capacitor is discharged to ground. Pulling the shutdown pin below 0.1V reduces the total supply current to 10μA. www.semtech.com © 2005 Semtech Corp. 2011 8 SC4501 POWER MANAGEMENT Application Information It is worth noting that I is directly proportional to the OUTMAX Duty Cycle V IN ratio . Equation (4) over-estimates the maximum V OUT The duty cycle D of a boost converter is: output current at high frequencies (>1MHz) since V IN switching losses are neglected in its derivation. 1 − V + V Nevertheless it is a useful first-order approximation. OUT D D = V (3) CESAT 1 − V + V Using V = 0.3V, V = 0.5V and I = 2A in (3) and (4), OUT D CESAT D LIM the maximum output currents for three V and V IN OUT where V is the switch saturation voltage and V is CESAT D combinations are shown in Table 1. voltage drop across the rectifying diode. Maximum Output Current V ( V ) V ( V ) D I ( A ) IN OUT OUTMAX In a boost switching regulator the inductor is connected 2.5 12 0.820 0.35 to the input. The DC inductor current is the input current. When the power switch is turned on, the inductor current 3.3 5 0.423 1.14 flows into the switch. When the power switch is off, the 5 12 0.615 0.76 inductor current flows through the rectifying diode to the output. The output current is the average diode current. The diode current waveform is trapezoidal with pulse width Table 1. Calculated Maximum Output Current [ Equation (4)] (1 – D)T (Figure 5). The output current available from a boost converter therefore depends on the converter Considerations for High Frequency Operation operating duty cycle. The power switch current in the SC4501 is internally limited to 2A. This is also the maximum The operating duty cycle of a boost converter decreases as inductor or the input current. By estimating the conduction V approaches V . The PWM modulating ramp in a losses in both the switch and the diode, an expression of IN OUT current-mode switching regulator is the sensed current ramp the maximum available output current of a boost converter of the control switch. This current ramp is absent unless can be derived: the switch is turned on. The intersection of this ramp with the output of the voltage feedback error amplifier I V ⎡ D V −D() V − V ⎤ LIM IN D D CESAT determines the switch pulse width. The propagation delay I = 1 − − OUTMAX ⎢ ⎥ (4) V 45 V OUT IN time required to immediately turn off the switch after it ⎣ ⎦ is turned on is the minimum switch on time. Regulator where I is the switch current limit. closed-loop measurement shows that the SC4501 has LIM a minimum on time of about 150ns at room temperature. The power switch in the SC4501 is either not turned on I IN at all or for at least 150ns. If the required switch on time is shorter than the minimum on time, the regulator will Inductor Current either skip cycles or it will start to jitter. Switch Current ON OFF ON Example: Determine the maximum operating frequency Diode Current of a Li-ion cell to 5V converter using the SC4501. Assuming that V =0.5V, V =0.3V and V =2.6 - 4.2V, D CESAT IN the minimum duty ratio can be found using (3). DT (1-D)T I OUT 4.2 ON OFF ON OFF ON 1 − 5 + 0.5 D = = 0.25 MIN 0.3 1 − Figure 5. Current Waveforms in a Boost Regulator 5 + 0.5 www.semtech.com © 2005 Semtech Corp. 9 2011 SC4501 POWER MANAGEMENT Application Information D() V − V The absolute maximum operating frequency of the IN CESAT ΔI = (5) L fL D 0.25 MIN = = 1.67MHz converter is therefore . The where f is the switching frequency and L is the inductance. 150ns 150ns actual operating frequency needs to be lower to allow for Substituting (3) into (5) and neglecting V , CESAT modulating headroom. ⎛ ⎞ V V IN IN ⎜ ⎟ ΔI = 1 − The power transistor in the SC4501 is turned off every L (6) ⎜ ⎟ + fL V V ⎝ OUT D ⎠ switching period for an interval determined by the In current-mode control, the slope of the modulating discharge time of the oscillator ramp and the propagation (sensed switch current) ramp should be steep enough to delay of the power switch. This minimum off time limits lessen jittery tendency but not so steep that large flux swing the maximum duty cycle of the regulator at a given decreases efficiency. Inductor ripple current ΔI between L V OUT 25-40% of the peak inductor current limit is a good switching frequency. A boost converter with high ratio V In compromise. Inductors so chosen are optimized in size and DCR. Setting ΔI = 0.3 (2) = 0.6A, V =0.5V in (6), requires long switch on time and high duty cycle. If the L D required duty cycle is higher than the attainable maximum, ⎛ ⎞ ⎛ ⎞ V V V V IN IN IN IN then the converter will operate in dropout. (Dropout is a ⎜ ⎟ L = ⎜1 − ⎟ = 1 − ⎜ ⎟ (7) ⎜ ⎟ fΔI V + V 0.6f V + 0.5 condition in which the regulator cannot attain its set L ⎝ OUT D ⎠ OUT ⎝ ⎠ output voltage below current limit.) where L is in μH and f is in MHz. The minimum off times of closed-loop boost converters set Equation (6) shows that for a given V , ΔI is the highest to various output voltages were measured by lowering their OUT L input voltages until dropout occurs. It was found that the () V + V OUT D V = when . If V varies over a wide range, then IN minimum off time of the SC4501 ranged from 80 to 110ns IN 2 at room temperature. choose L based on the nominal input voltage. Beware of dropout when operating at very low input voltages The saturation current of the inductor should be 20-30% (1.5-2V) and with off times approaching 110ns. Shorten higher than the peak current limit (2.8A). Low-cost powder the PCB trace between the power source and the device iron cores are not suitable for high-frequency switching input pin, as line drop may be a significant percentage of power supplies due to their high core losses. Inductors the input voltage. A regulator in dropout may appear as if with ferrite cores should be used. it is in current limit. The cycle-by-cycle current limit of the SC4501 is duty-cycle and input voltage invariant and is Input Capacitor typically 2.8A. If the switch current limit is not at least 2A, then the converter is likely in dropout. The switching The input current in a boost converter is the inductor frequency should then be lowered to improve controllability. current, which is continuous with low RMS current ripples. A 2.2-4.7µF ceramic input capacitor is adequate for most Both the minimum on time and the minimum off time applications. reduce control range of the PWM regulator. Bench measurement showed that reduced modulating range Output Capacitor started to be a problem at frequencies over 2MHz. Although the oscillator is capable of running well above 2MHz, Both ceramic and low ESR tantalum capacitors can be controllability limits the maximum operating frequency. used as output filtering capacitors. Multi-layer ceramic capacitors, due to their extremely low ESR (<5mΩ), are Inductor Selection the best choice. Use ceramic capacitors with stable temperature and voltage characteristics. One may be The inductor ripple current ΔI of a boost converter L tempted to use Z5U and Y5V ceramic capacitors for operating in continuous-conduction mode is output filtering because of their high capacitance and 2011 www.semtech.com © 2005 Semtech Corp. 10 SC4501 POWER MANAGEMENT Application Information forward voltages). This is because the diode conduction small sizes. However these types of capacitors have high interval is much longer than that of the transistor. temperature and high voltage coefficients. For example, Converter efficiency will be improved if the voltage drop the capacitance of a Z5U capacitor can drop below 60% across the diode is lower. of its room temperature value at –25°C and 90°C. X5R ceramic capacitors, which have stable temperature and The rectifying diodes should be placed close to the SW voltage coefficients, are the preferred type. pins of the SC4501 to minimize ringing due to trace inductance. Surface-mount equivalents of 1N5817, The diode current waveform in Figure 5 is discontinuous 1N5818, MBRM120 (ON Semi) and 10BQ015 (IRF) are with high ripple-content. In a buck converter the inductor all suitable. ripple current ΔI determines the output ripple voltage. L The output ripple voltage of a boost regulator is however Soft-Start much higher and is determined by the absolute inductor current. Decreasing the inductor ripple current does not Soft-start prevents a DC-DC converter from drawing appreciably reduce the output ripple voltage. The current excessive current (equal to the switch current limit) from flowing in the output filter capacitor is the difference the power source during start up. If the soft-start time is between the diode current and the output current. This made sufficiently long, then the output will enter regulation capacitor current has a RMS value of: without overshoot. An external capacitor from the SS pin to the ground and an internal 1.5µA charging current V OUT source set the soft-start time. The soft-start voltage ramp I −1 OUT (8) V at the SS pin clamps the error amplifier output. During 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 fault is When the switch is turned on, the output capacitor supplies detected, then the soft-start capacitor will be discharged the load current I (Figure 5). The output ripple voltage OUT 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. I DT OUT Shutdown 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 SC4501. For most applications, a 10-22µF ceramic capacitor is Forcing the shutdown pin below 1.1V stops switching. sufficient for output filtering. It is worth noting that the Pulling this pin below 0.1V completely shuts off the SC4501. output ripple voltage due to discharging of a 10µF ceramic The total V current decreases to 10µA at 2V. Figure 6 capacitor (9) is higher than that due to its ESR. IN shows several ways of interfacing the control logic to the shutdown pin. Beware that the shutdown pin is a high Rectifying Diode impedance pin. It should always be driven from a low- impedance source or tied to a resistive divider. Floating For high efficiency, Schottky barrier diodes should be used the shutdown pin will result in undefined voltage. In Figure as rectifying diodes for the SC4501. These diodes should 6(c) the shutdown pin is driven from a logic gate whose have a RMS current rating of at least 1A and a reverse V is higher than the supply voltage of the SC4501. The blocking voltage of at least a few Volts higher than the OH diode clamps the maximum shutdown pin voltage to one output voltage. For switching regulators operating at low diode voltage above the input power supply. duty cycles (i.e. low output voltage to input voltage conversion ratios), it is beneficial to use rectifying diodes with somewhat higher RMS current ratings (thus lower 2011 www.semtech.com © 2005 Semtech Corp. 11 SC4501 POWER MANAGEMENT Application Information IN IN SC4501 SC4501 SHDN SHDN (a) (b) V IN IN IN SC4501 SC4501 1N4148 SHDN SHDN (c) (d) Figure 6. 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). Programming Undervoltage Lockout V and V are therefore: H L The SC4501 has an internal V undervoltage lockout IN ⎛ R ⎞ 3 (UVLO) threshold of 1.4V. The transition from idle to V = ⎜1 + ⎟() 1.1V H ⎜ ⎟ R ⎝ 4 ⎠ switching is abrupt but there is no hysteresis. If the input (10) voltage ramp rate is slow and the input bypass is limited, V = V − V = V −I R L H HYS H HYS 3 then sudden turn on of the power transistor will cause a dip in the line voltage. Switching will stop if V falls below IN Re-arranging, the internal UVLO threshold. The resulting output voltage rise may be non-monotonic. The 1.1V disable threshold of V HYS R = the SC4501 can be used in conjunction with a resistive 3 (11) I HYS voltage divider to raise the UVLO threshold and to add an UVLO hysteresis. Figure 7 shows the scheme. Both V and H R 3 R = V (the desired upper and the lower UVLO threshold 4 V L H (12) −1 voltages) are determined by the 1.1V threshold crossings, 1.1 www.semtech.com © 2005 Semtech Corp. 12 2011 SC4501 POWER MANAGEMENT Application Information The turn off voltage is: V = V − V = 2.75 − 0.69 = 2.06V > 1.4V . L H HYS IN 6/8 Frequency Compensation I HYS Figure 8 shows the equivalent circuit of a boost converter 4.6μA using the SC4501. The output filter capacitor and the load R3 SWITCH CLOSED form an output pole at frequency: WHEN Y = “1” SHDN 2I 2 OUT 3 + ω = − = − p2 (13) V C R C Y OUT 2 OUT 2 - 1.1V R4 COMPARATOR V OUT R = where C is the output capacitor and is the OUT 2 I OUT SC4501 equivalent load resistance. The zero formed by C and its equivalent series resistance 2 Figure 7. Programmable Hysteretic UVLO Circuit (ESR) is neglected due to low ESR of the ceramic output capacitor. with V > 1.4V . There is also a right half plane (RHP) zero at angular L frequency: Example: Increase the turn on voltage of a V = 3.3V boost IN converter from 1.4V to 2.75V. 2 R () 1 −D OUT ω = (14) Z2 L Using V = 2.75V and R = 100KΩ in (12), H 4 ω decreases with increasing duty cycle D and increasing z2 R = 150KΩ . 3 I . Using the 5V to 12V boost regulator (1.35MHz) in OUT Figure 1(a) as an example, The resulting UVLO hysteresis is: 5V R ≥ = 6.8Ω V = I R = 4.6μA •150KΩ = 0.69V . OUT HYS HYS 3 0.74A I OUT V IN POWER V STAGE OUT ESR R R1 C5 OUT C2 FB - COMP Gm + R3 1.242V C6 RO R2 C4 VOLTAGE REFERENCE Figure 8. Simplified Block Diagram of a Boost Converter www.semtech.com © 2005 Semtech Corp. 13 2011 SC4501 POWER MANAGEMENT Application Information 1 1 ω = − = − p1 5 R C 4.7MΩ • 820pF O 4 1 − 12 + 0.5 D = = 0.62 −1 0.3 = −260 rads = −41Hz 1 − 12 + 0.5 C and R also forms a zero with angular frequency: 4 3 Therefore 1 1 ω = − = − Z1 2 R C 30.9KΩ • 820pF −1 3 4 ω ≤ = 29.4Krads = 4.68KHz p2 −1 () 6.8Ω •() 10μF = −39.5 Krads = −6.3KHz and 2 6.8Ω •() 1 − 0.62 The poles p , p and the RHP zero z all increase phase −1 1 2 2 ω ≥ = 209Krads = 33.3KHz Z2 shift in the loop response. For stable operation, the overall 4.7μH loop gain should cross 0dB with -20dB/decade slope. Due to the presence of the RHP zero, the 0dB crossover frequency The spacing between p and z is the closest when the 2 2 z converter is delivering the maximum output current from 2 should not be higher than . Placing z near p nulls its 1 2 the lowest V . This represents the worst-case compensation 3 IN condition. Ignoring C and C for the moment, C forms a effect and maximizes loop bandwidth. Thus 5 6 4 low frequency pole with the equivalent output resistance R of the error amplifier: O V C OUT 2 R C ≈ 3 4 (15) 2I OUT(MAX) AmplifierOpenLoop Gain 49dB R = = = 4.7MΩ O −1 Transconduc tance 60μΩ R determines the mid-band loop gain of the converter. 3 Increasing R increases the mid-band gain and the crossover 3 GND GND C3 C3 R R4 4 R3 R3 C4 C4 C6 C6 R2 R2 U1 U1 U1 U1 C1 C1 L1 L1 SHDN SHDN SHDN R1 R1 C C5 5 C2 C2 D1 D1 VOUT VOUT VI VIN N Figure 9. Suggested PCB Layout for the SC4501. Notice that there is no via directly under the device. All vias are 12mil in diameter. www.semtech.com © 2005 Semtech Corp. 2011 14 SC4501 POWER MANAGEMENT Application Information frequency. However it reduces the phase margin. The the size of the loop formed by these components should values of R and C can be determined empirically by be minimized. Since the power switch is integrated inside 3 4 observing the inductor current and the output voltage the SC4501, grounding the output filter capacitor next to during load transient. Compensation is optimized when the SC4501 ground pin minimizes size of the high di/dt the largest R and the smallest C without producing current loop. The input bypass capacitors should also be 3 4 ringing or excessive overshoot in its inductor current and placed close to the input pins. Shortening the trace at the output voltage are found. Figures 10(b), 11(c), 12(b) and SW node reduces the parasitic trace inductance. This not 12(c) show load transient responses of empirically only reduces EMI but also decreases the sizes of the optimized DC-DC converters. In a battery-operated switching voltage spikes and glitches. system, compensating for the minimum V and the IN maximum load step will ensure stable operation over the Figure 9 shows how various external components are placed entire input voltage range. around the SC4501. The frequency-setting resistor should be placed near the ROSC pin with a short ground trace C adds a feedforward zero to the loop response. In some on the PC board. These precautions reduce switching 5 cases it improves the transient speed of the converter. C noise pickup at the ROSC pin. 6 rolls off the gain at high frequency. This helps to stabilize To achieve a junction to ambient thermal resistance (θ ) the loop. C and C are often not needed. JA 5 6 of 40°C/W, the exposed pad of the SC4501 should be properly soldered to a large ground plane. Use only 12mil Board Layout Considerations diameter vias in the ground plane if necessary. Avoid using larger vias under the device. Molten solder may seep In a step-up switching regulator, the output filter capacitor, through large vias during reflow, resulting in poor adhesion, the main power switch and the rectifying diode carry poor thermal conductivity and low reliability. switched currents with high di/dt. For jitter-free operation, Typical Application Circuits D1 L1 VIN VOUT 3.3μH 3.3V 12V, 0.4A 10BQ015 R1 6 5 174K IN SW 3 OFF ON 2 SHDN FB C2 SC4501 10μF C1 8 1 SS COMP 2.2μF R2 GND ROSC R3 20K 22.1K C3 4 7 47nF R4 C4 9.31K 1.5nF 40μs/div Upper Trace : Output Voltage, AC Coupled, 1V/div L1: Cooper-Bussmann SD25-3R3 Lower Trace : Inductor Current, 0.5A/div Figure 10(b). Load Transient Response of the Circuit in Figure Figure 10(a). 1.35 MHz All Ceramic Capacitor 3.3V to 12V Boost 10(a). I is switched between 0.1A and 0.4A at Converter. Pinout Shown is for MSOP-8 LOAD 1A/μs. www.semtech.com © 2005 Semtech Corp. 2011 15 SC4501 POWER MANAGEMENT Typical Application Circuits Efficiency 95 V = 5V OUT D1 L1 90 VOUT 2.6 - 4.2V 1.2MHz 1.8μH 5V, 0.8A 85 10BQ015 V = 4.2V IN R1 80 6 5 301K IN SW 75 3 2 OFF ON SHDN FB 1-CELL 70 C1 C2 SC4501 LI-ION 10μF 2.2μF 8 1 SS COMP 65 R2 R3 GND ROSC 100K 60 17.4K C3 4 7 VIN = 3.6V VIN = 2.6V 47nF R4 55 C4 10.7K 1nF 50 0.001 0.010 0.100 1.000 Load Current (A) L1: Sumida CR43 Figure 11(a). 1.2 MHz All Ceramic Capacitor Single Li-ion Cell Figure 11(b). Efficiency of the Single Li-ion Cell to 5V Boost to 5V Boost Converter. Converter in Figure 11(a). V =2.6V IN 40μs/div Upper Trace : Output Voltage, AC Coupled, 0.5V/div Lower Trace : Inductor Current, 0.5A/div Figure 11(c). Load Transient Response of the Circuit in Figure 11(a). I is switched between 0.2A and 0.7A at LOAD 1A/μs. www.semtech.com © 2005 Semtech Corp. 2011 16 Efficiency (%) SC4501 POWER MANAGEMENT Typical Application Circuits 4-CELL VOUT C6 L1 D1 5V 3.6 - 6V 4.9μH 2.2μF 10BQ015 C5 R1 6 5 60.4K 47pF IN SW 3 2 OFF ON SHDN FB C2 C1 SC4501 10μF 2.2μF 8 1 SS COMP L2 R2 GND ROSC R3 4.9μH 20K 20K C3 4 7 47nF R4 C4 7.68K 560pF L1 and L2: Coiltronics CTX5-1 Figure 12(a). 1.5 MHz All Ceramic Capacitor 4-Cell to 5V SEPIC Converter. Pinout Shown is for MSOP-8. V =3.6V V =6V 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 : Input Inductor Current, 0.2A/div Lower Trace : Input Inductor Current, 0.2A/div Figure 12(b). Load Transient Response of the Circuit in Figure Figure 12(c). Load Transient Response of the Circuit in Figure 12(a). I is switched between 50mA and 350mA 12(a). I is switched between 80mA and 600mA LOAD LOAD at 1A/μs. at 1A/μs. 2011 www.semtech.com © 2005 Semtech Corp. 17 SC4501 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 2.2μH 8V (0.55A) 10BQ015 R5 R1 6 5 150K 274K IN SW 3 2 SHDN FB C2 C1 SC4501 10μF 2.2μF C9 8 1 SS COMP 0.1μF R6 R2 GND ROSC R3 100K 49.9K 40.2K C3 4 7 47nF R4 C4 7.68K 820pF D7 OUT3 -8V (10mA) C10 L1 : Cooper-Bussmann SD25-2R2 D6 1μF D2 - D7 : BAT54S Figure 13(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 13(c). TFT Power Supply Start-up Transient as the Figure 13(b). TFT Power Supply V Start-up Transient. IN SHDN Pin is stepped from 0 to 2V. www.semtech.com © 2005 Semtech Corp. 2011 18 SC4501 POWER MANAGEMENT Typical Application Circuits - 3.4V to 3.8V + 0.7A (FLASH) D2 0.2A (TORCH) R6 0.1Ω LXCL-PWF1 R1 698 D1 L1 2.6 - 4.2V 2.2μH 10BQ015 SUMIDA CR43 1/2 LM358 Q1 6 5 MMBT3904T 1-CELL IN SW LI-ION OFF ON 3 2 SHDN FB C2 C1 SC4501 2.2μF C5 R6 4.7μF 8 1 0.1μF 17.4K SS COMP R2 GND ROSC 43.2K C4 R5 M1 4 7 C3 10nF 10K MMBF2201NT1 R4 10nF 8.06K TORCH FLASH TM Figure 14(a). 1.4MHz Luxeon Flash White LED Driver for Camera Phones V = 2.6V V = 4.2V IN IN CH1 CH1 CH2 CH2 CH3 CH3 CH4 CH4 4ms/div 4ms/div (b) (c) CH1 : Torch/Flash Control Voltage, 5V/div CH2 : FB Pin Voltage, 1V/div CH3 : LED Current, 0.5A/div CH4 : Inductor Current, 1A/div Figure 14(b) and 14(c). Photo Flash LED Current is Switched Between Torch Mode (0.2A) and Flash Mode (0.7A). Higher LED Current (>0.7A) in Flash Mode is Possible with Fresh Battery. www.semtech.com © 2005 Semtech Corp. 2011 19 - + + SC4501 POWER MANAGEMENT Outline Drawing - MSOP-8L-EDP e/2 DIMENSIONS INCHES MILLIMETERS A D DIM MIN NOM MAX MIN NOM MAX N - - - - A .043 1.10 - - A1 .000 .006 0.00 0.15 - - 2X E/2 A2 .030 .037 0.75 0.95 - - b .009 .015 0.22 0.38 E1 E c - - .003 .009 0.08 0.23 PIN 1 D .114 .118 .122 2.90 3.00 3.10 INDICATOR E1 .114 .118 .122 2.90 3.00 3.10 E .193 BSC 4.90 BSC ccc C 12 e .026 BSC 0.65 BSC 2X N/2 TIPS e F .068 .076 .080 1.73 1.93 2.03 L .016 .024 .032 0.40 0.60 0.80 B (.037) (0.95) L1 N 8 8 - - 01 0° 8° 0° 8° D aaa C aaa .004 0.10 bbb .005 0.13 A2 A ccc SEATING .010 0.25 PLANE A1 C bxN H bbb C A-B D c GAGE F PLANE EXPOSED PAD L 01 0.25 (L1) F DETAIL A BOTTOM VIEW SEE DETAIL A SIDE VIEW NOTES: 1. CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES). 2. DATUMS AND TO BE DETERMINED AT DATUM PLANE -A- -B- -H- 3. DIMENSIONS "E1" AND "D" DO NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. 4. REFERENCE JEDEC STD MO-187, VARIATION AA-T. Land Pattern - MSOP-8L-EDP F DIMENSIONS DIM INCHES MILLIMETERS (.161) (4.10) C F .081 2.08 F Z (C) G G .098 2.50 P .026 0.65 X .016 0.40 Y .063 1.60 Z .224 5.70 P X NOTES: 1. THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY. CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR COMPANY'S MANUFACTURING GUIDELINES ARE MET. www.semtech.com © 2005 Semtech Corp. 20 2011 SC4501 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 - - - - A2 (.008) (0.20) 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 bxN e 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 C (.112) (2.85) G .075 1.90 H H .055 1.40 (C) G Z K .087 2.20 P .020 0.50 Y X .012 0.30 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 2011 www.semtech.com © 2005 Semtech Corp. 21