SC4626 2.5MHz, 1A Synchronous Step Down Regulator in SOT23-5 POWER MANAGEMENT Features Description VIN Range: 2.9 – 5.5V VOUT Options: 1.0 - 3.3V Up to 1A Output Current 2.5MHz Switching Frequency Efficiency Up to 93% Low Output Noise Across Load Range Excellent Transient Response Start Up into Pre-Bias Output 100% Duty-Cycle Low Dropout Operation <1µA Shutdown Current Internal Soft Start Input Under-Voltage Lockout Output Over-Voltage, Current Limit Protection Over-Temperature Protection Adjustable Output Voltage SOT23-5 Package Fully WEEE and RoHS Compliant The SC4626 is a high efficiency, synchronous step-down regulator providing up to 1A output current in a SOT235 package. The device requires only three external filter components for a complete step-down regulator solution. The input voltage range is 2.9 to 5.5V with either factory programmed outputs from 1.0 to 3.3V or adjustable output via an external resistor divider. The converter operates at fixed 2.5MHz switching frequency allowing small L/C filtering components. The voltage mode architecture is compatible with chip inductors and capacitors for minimum PCB footprint and lowest overall system cost. Up to 93% efficiency is achieved with low RDS(ON) internal switches. PWM constant frequency operation ensures low output ripple across the load range. 100% duty-cycle provides 300mV dropout voltage at 1A which extends the minimum input voltage for 2.5V and 3.3V outputs. Excellent transient response is achieved with no external compensation components. The SC4626 provides input under-voltage, output overvoltage, output short circuit and over-temperature protection to safeguard the device and system under fault conditions. The regulator provides integrated soft-start to minimize inrush currents. Standby quiescient current is less than 1µA. Applications Bluetooth Radios DSC and PMPs GPS Devices xDSL Systems POL Regulators Portable HDD Wireless LAN The SC4626 is available in a SOT23-5 package. Typical Application Circuit VIN 2.9V to 5.5V Enable LX VIN CIN 10µF VOUT 1.20V/1A COUT 10µF GND EN L 2.2µH VOUT SC4626C August 27, 2010 www.semtech.com SC4626 Pin Configuration Ordering Information (TOP VIEW) VIN 1 GND 2 EN 3 5 4 LX Device Package & Description SC4626xSKTRT(2)(3)(4) SOT23-5 SC4626xEVB(5) Evaluation Board - Standard Size (i.e., Wire Wound Inductor) SC4626xEVB-1(5) Evaluation Board - Small Size (i.e., Chip Inductor) Notes: (1) Measured in free convection, mounted on 10mm x 10mm, 2 layer FR4 PCB shown in figure 4 with copper of 1oz for each layer. (2) Available in tape and reel only. A reel contains 3,000 devices. (3) Device is Pb-free, Halogen free, and RoHS/WEEE compliant. (4) “x” is the code of the output voltage. See Table 1 for the code. For example, the device number for VOUT= 1.20V is SC4626CSKTRT. (5) “x” is the code of the output voltage. See Table 1 for the code. For example, the EVB for VOUT= 1.20V is SC4626CEVB (Standard Size) or SC4626CEVB-1 (Small Size). VOUT SOT23-5 θJA = 90°C/W(1) Marking Information Table 1: Available Output Voltages x Code VOUT(1) A 1.00 C 1.20 E 1.28 F 1.30 H 1.50 L 1.80 Y 2.50 Z 3.30 Notes: (1) Contact factory for unavaliable output voltage options. Marking for SOT23, 5 Lead Package: x = Code of the output voltage (Example: C for VOUT=1.20V) yyww = Datecode (Example: 0852) © 2009 Semtech Corp. www.semtech.com SC4626 Recommended Operating Conditions Absolute Maximum Ratings VIN Supply Voltage ……………………………… -0.3 to 6.0V VIN Supply Voltage ……………………………… 2.9 to 5.5V LX Voltage ………….. Maximum Output Current VOUT Voltage -1 to VIN+1V, -3V (20ns Max), 6V Max …………………………… 1.0A ……………………………… -0.3 to VIN+0.3V EN Voltage …………………………………. -0.3 to VIN+0.3V Thermal Information Peak IR Reflow temperature …………………………. 260°C ESD Protection Level …………………………………. (2) Thermal Resistance, Junction to Ambient(1) ………… 90°C/W 3kV Maximum Junction Temperature …………………… +150°C Operating Junction Temperature …………… -40 to +125˚C Storage Temperature Range ………………… -65 to +150 °C Exceeding the absolute maximum ratings may result in permanent damage to the device and/or device malfunction. Operation outside of the parameters specified in the Electrical Characteristics section is not recommended. Notes: (1) Measured in free convection, mounted on 10mm x 10mm, 2 layer FR4 PCB shown in figure 4 with copper of 1oz for each layer. (2) Tested according to JEDEC standard JESD22-A114-B. Electrical Characteristics Unless specified: VIN = 5.0V; -40°C<TA<+85 °C; TJ(MAX)=125°C; Unless otherwise noted typical values are TA=+25 °C. Parameter Symbol Under-Voltage Lockout UVLO Output Voltage Tolerance Conditions Min Typ Max Units Rising VIN 2.60 2.70 2.80 V Hysteresis 250 ΔVOUT VIN=3.6V to 5.0V; No Load -2.5 ILIMIT Peak inductor current 1.5 IQ EN= VIN, No Load 7.5 ISHDN EN= GND 1 High Side Switch Resistance RDSON_P ILX= 100mA 0.15 Low Side Switch Resistance RDSON_N ILX= -100mA 0.125 VIN=5.5V; LX=0V; EN=GND 1 (1) Current Limit VIN Supply Current VIN Shutdown Current LX Leakage Current ILK(LX) VIN=5.5V; LX=5.0V; EN=GND -10 mV +2.5 % A mA 10 µA Ω 10 -1 µA Line Regulation ΔVLINE-REG VIN= 3.6 – 5.0V; IOUT=0A ±1.0 % Load Regulation(2) ΔVLOAD-REG VIN= 5.0V; IOUT=10mA – 1.0A ±1.0 % Oscillator Frequency FOSC Soft-Start Time(2) TSS 2.0 2.5 3.0 100 MHz µs EN Input High Current IEN_HI EN=VIN -2.0 2.0 µA EN Input Low Current IEN_LO EN=GND -2.0 2.0 µA EN Input High Threshold VEN_HI EN Input Low Threshold VEN_LO © 2009 Semtech Corp. 1.2 V 0.4 V www.semtech.com SC4626 Electrical Characteristics (continued) Unless specified: VIN = 5.0V; -40°C<TA<+85 °C; TJ(MAX)=125°C; Unless otherwise noted typical values are TA=+25 °C. Parameter Symbol VOUT Over Voltage Protection(2) VOVP Thermal Shutdown Temperature (2) TSD TSD_HYS Thermal Shutdown Hysteresis (2) Conditions Min Typ Max Units 115 % Junction Temperature +160 °C Junction Temperature 10 °C Notes: (1) The “Output Voltage Tolerance” includes output voltage accuracy, voltage drift over temperature and the line regulation. (2) Guaranteed by design. © 2009 Semtech Corp. www.semtech.com SC4626 Typical Characteristics Circuit Conditions: VOUT=1.0V (SC4626A), 1.5V (SC4626H) & 3.3V (SC4626Z);CIN= 10uF/6.3V;COUT= 10uF/6.3V for L=2.2uH;COUT= 22uF/6.3V for L=1uH. Unless otherwise noted, L= 2.2uH (TOKO: 1071AS-2R2M). Efficiency Efficiency vs. Load Current (VOUT=3.3V) Efficiency Efficiency vs. Load Current (VOUT=1.5V) 100% 100% VIN= 4.0V 95% VIN= 5.0V 90% 90% 85% 85% Efficiency (%) Efficiency (%) 95% 80% 75% VIN= 3.3V 75% 70% 70% VOUT= 1.50V TA=25°C 65% VIN= 5.0V 80% VOUT= 3.30V TA=25°C 65% 60% 60% 0.0 0.2 0.4 0.6 0.8 0.0 1.0 0.2 0.8 Efficiency Efficiency vs. Load Current (VIN=5.0V, VOUT=3.3V) 100% 100% 95% 90% Efficiency (%) L=1071AS-1R0N (33m_typ) 85% 80% 75% L=MDT2520-CR1R0M (60m_typ) 70% 65% 85% L=1071AS-1R0N (33m_typ) 80% L=MDT2520-CR1R0M (60m_typ) 75% 70% VIN= 5.0V VOUT= 1.0V TA=25°C 1.0 L=1071AS-2R2N (50m_typ) L=1071AS-2R2N (50m_typ) 90% Efficiency (%) 0.6 Efficiency Efficiency vs. Load Current (VIN=5.0V, VOUT=1.0V) 95% VIN= 5.0V VOUT= 3.3V TA=25°C 65% L=LQM2HPN1R0MG0 L=LQM2HP1R0MG0 (55m_typ) 60% 60% 0.0 0.2 0.4 0.6 0.8 0.0 1.0 0.2 Output Current (A) Total Loss vs. LoadLosses Current (VOUT=1.5V) 0.4 0.6 Output Current (A) 0.8 1.0 Total Loss vs. LoadLosses Current (VOUT=3.3V) 500 500 VOUT= 1.50V TA=25°C VOUT= 3.30V TA=25°C 400 400 VIN= 3.3V 300 Loss (mW) Loss (mW) 0.4 Output Current (A) Output Current (A) 200 VIN= 5.0V 100 300 VIN= 5.0V 200 100 VIN= 4.0V 0 0 0.0 0.2 0.4 0.6 0.8 1.0 0.0 Output Current (A) © 2009 Semtech Corp. 0.2 0.4 0.6 0.8 1.0 Output Current (A) www.semtech.com SC4626 Typical Characteristics (continued) Circuit Conditions: VOUT=1.0V (SC4626A), 1.5V (SC4626H) & 3.3V (SC4626Z);CIN= 10uF/6.3V;COUT= 10uF/6.3V for L=2.2uH;COUT= 22uF/6.3V for L=1uH. Unless otherwise noted, L= 2.2uH (TOKO: 1071AS-2R2M). (P &Temperature N) Over Temperature RRDSON vs. DS(ON) RDSON (P& N) over Line RDS(ON) vs. Input Voltage 190 210 VIN= 5.0V ILX= ±100mA 170 190 P-Channel RDS(ON) (m) RDS(ON) (m) P-Channel 170 150 N-Channel 130 150 130 110 TA= 25°C ILX= ±100mA N-Channel 110 90 2.5 3.0 3.5 4.0 4.5 5.0 5.5 -40 -15 Input Voltage (V) 5% 60 85 1.0% 4% 0.8% VOUT= 3.3V 3% 0.6% 2% 0.4% 1% 0.2% Variation Variation 35 Frequency Variation SwitchingSwitching Frequency vs. Temperature Switching Frequency vs. Variation over Line Switching Frequency Input Voltage 0% -1% -2% -0.2% -0.6% IOUT= 0A TA= 25°C -4% 0.0% -0.4% VOUT= 1.5V -3% VIN= 5.0V IOUT= 0A -0.8% -5% -1.0% 2.5 3.0 3.5 4.0 4.5 5.0 5.5 -40 -15 Input Voltage (V) 10 35 60 85 Ambient Temperature (°C) Line Regulationvs. over Temperature Line Regulation Temperature Line Regulation ove Line Line Regulation 1.0% 1.0% 0.8% 0.8% 0.6% 0.6% VOUT= 1.5V 0.4% 0.4% 0.2% Regulation Regulation 10 Ambient Temperature (°C) 0.0% -0.2% 0.2% 0.0% -0.2% -0.4% -0.4% VOUT= 3.3V -0.6% -0.6% IOUT= 0A TA= 25°C -0.8% VOUT= 1.5V IOUT= 0A -0.8% -1.0% -1.0% 2.5 3.0 3.5 4.0 4.5 5.0 5.5 -40 Input Voltage (V) © 2009 Semtech Corp. -15 10 35 60 85 Ambient Temperature (°C) www.semtech.com SC4626 Typical Characteristics (continued) Circuit Conditions: VOUT=1.0V (SC4626A), 1.5V (SC4626H) & 3.3V (SC4626Z);CIN= 10uF/6.3V;COUT= 10uF/6.3V for L=2.2uH;COUT= 22uF/6.3V for L=1uH. Unless otherwise noted, L= 2.2uH (TOKO: 1071AS-2R2M). Load Regulation Load Regulation (VOUT=3.3V) Load Regulation Load Regulation (VOUT=1.5V) 1.0% 1.0% VOUT= 1.50V TA=25°C 0.6% 0.6% 0.4% 0.4% 0.2% VOUT= 3.30V TA=25°C 0.8% Load Regulation Load Regulation 0.8% VIN= 3.3V 0.0% -0.2% -0.4% VIN= 4.0V 0.2% 0.0% -0.2% -0.4% VIN= 5.0V -0.6% VIN= 5.0V -0.6% -0.8% -0.8% -1.0% -1.0% 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 Output Current (A) 1.0% 5% 0.8% 4% 0.6% 3% 0.4% 2% 0.2% 1% Variation Variation 0.6 0.8 1.0 60 85 Hysteresis Variation UVLOUVLO Hysteresis Variation Rising Threshold Variation UVLOUVLO Rising Threshold Variation 0.0% -0.2% 0% -1% -0.4% -2% -0.6% -3% -0.8% 0.4 Output Current (A) -4% IOUT= 0A -1.0% IOUT= 0A -5% -40 -15 10 35 60 85 -40 Ambient Temperature (°C) -15 10 35 Ambient Temperature (°C) Voltage of 100%Duty Duty Cycle Operation DropoutDropout Voltage in 100% Cycle Operation 400 TA= 25°C Dropout Voltage (mV) 350 L= MDT2520-CR1R0M (DCR= 60m_typ) 300 250 200 150 100 L= 1071AS-2R2N (DCR=50m_typ) 50 0 0.0 0.2 0.4 0.6 0.8 1.0 Output Current (A) © 2009 Semtech Corp. www.semtech.com SC4626 Typical Waveforms Circuit Conditions: VOUT=1.5V (SC4626H); L= 2.2uH (TOKO: 1071AS-2R2M); CIN= COUT= 10uF/6.3V (Murata: GRM21BR60J106K). Output Voltage Ripple (V=1.5V) OUT=1.5V) Output Voltage Ripple (VOUT Output Voltage Ripple (V=1.5V) OUT=1.5V) Output Voltage Ripple (VOUT VOUT 10mV/div VOUT 10mV/div ILX ILX 500mA/div 500mA/div VLX VLX 2V/div 2V/div VIN=5.0V IOUT=0A 500ns/div VIN=5.0V IOUT=1.0A 4626-w1 Output Voltage Ripple (V=1.5V) OUT=1.5V) Output Voltage Ripple (VOUT 500ns/div 4626-w2 Output Voltage Ripple (V=1.5V) OUT=1.5V) Output Voltage Ripple (VOUT VOUT 10mV/div VOUT 10mV/div ILX ILX 500mA/div 500mA/div VLX VLX 2V/div 2V/div VIN=3.3V IOUT=0A 500ns/div VIN=3.3V IOUT=1.0A 4626-w3 (VOUT TransientTransient ResponseResponse (VOUT=1.5V; 0A=1.5V) to 0.5A) 500ns/div 4626-w4 Transient Response OUT=1.5V) Transient Response (VOUT=1.5V;(V0.5A to 1.0A) VOUT VOUT 100mV/div 100mV/div IOUT IOUT 500mA/div 500mA/div VIN=5.0V IOUT=0A to 0.5A © 2009 Semtech Corp. 50µs/div 4626-w5 VIN=5.0V IOUT=0.5A to 1A 50µs/div 4626-w6 www.semtech.com SC4626 Typical Waveforms (continued) Circuit Conditions: VOUT=1.5V (SC4626H); L= 2.2uH (TOKO: 1071AS-2R2M); CIN= COUT= 10uF/6.3V (Murata: GRM21BR60J106K). Up (VOUT=1.5V) Start UpStart (Enable)(V =1.5V) OUT Up (VOUT=1.5V) Start UpStart (Enable)(V =1.5V) OUT VIN VIN 2V/div 2V/div VEN VEN 2V/div 2V/div VOUT VOUT 1V/div 1V/div VIN=5.0V ROUT=1k VIN=5.0V ROUT=1.5 100µs/div Start Up (Vup =1.5V), OUTV Start Up (Power ) (VOUTEN=VIN =1.5V) IN 100µs/div Start Up (Vup =1.5V), OUTV Start Up (Power ) (VOUTEN=VIN =1.5V) IN VIN VIN 2V/div 2V/div VOUT VOUT 500mV/div 500mV/div VIN=5.0V ROUT=1k VIN=5.0V ROUT=1.5 200µs/div Start UpUp intointo Pre-Biased OUT=1.5V) Enable Start Pre-Bias Output Output(V(Enable) 200µs/div ShutdownShutdown-Disable (Disable) (VOUT=1.5V) VIN 2V/div VIN 2V/div VEN 2V/div VEN 2V/div VOUT VOUT 500mV/div 500mV/div VIN=5.0V ROUT=1k © 2009 Semtech Corp. VIN=5.0V ROUT=1.5 200µs/div 50µs/div www.semtech.com SC4626 Typical Waveforms (continued) Circuit Conditions: VOUT=3.3V (SC4626Z); L= 2.2uH (TOKO: 1071AS-2R2M); CIN= COUT= 10uF/6.3V (Murata: GRM21BR60J106K). Output Voltage Ripple (V=3.3V) OUT=3.3V) Output Voltage Ripple (VOUT Output Voltage Ripple (V=3.3V) OUT=3.3V) Output Voltage Ripple (VOUT VOUT 10mV/div VOUT ILX 10mV/div 500mA/div ILX 500mA/div VLX VLX 2V/div 2V/div VIN=5.0V IOUT=0A 500ns/div VIN=5.0V IOUT=1.0A 4626-w13 (VOUT TransientTransient ResponseResponse (VOUT=3.3V; 0A=3.3V) to 0.5A) 500ns/div 4626-w14 Transient Response OUT=3.3V) Transient Response (VOUT=3.3V;(V0.5A to 1.0A) VOUT VOUT 100mV/div 100mV/div IOUT IOUT 500mA/div 500mA/div VIN=5.0V IOUT=0A to 0.5A 50µs/div VIN=5.0V IOUT=0.5A to 1A 4626-w15 Up (VOUT=3.3V) Start UpStart (Enable)(V =3.3V) OUT 50µs/div 4626-w16 Up (VOUT=3.3V) Start UpStart (Enable)(V =3.3V) OUT VIN VIN 5V/div 5V/div VEN VEN 2V/div 2V/div VOUT VOUT 1V/div 1V/div VIN=5.0V ROUT=1k © 2009 Semtech Corp. VIN=5.0V ROUT=3.3 200µs/div 10 200µs/div www.semtech.com SC4626 Typical Waveforms (continued) Circuit Conditions: VOUT=3.3V (SC4626Z); L= 2.2uH (TOKO: 1071AS-2R2M); CIN= COUT= 10uF/6.3V (Murata: GRM21BR60J106K). Start Up (Vup =3.3V), OUTV Start Up (Power ) (VOUTEN=VIN =3.3V) IN Start Up (Vup =3.3V), OUTV Start Up (Power ) (VOUTEN=VIN =3.3V) IN VIN VIN 2V/div 2V/div VOUT VOUT 1V/div 1V/div VIN=5.0V ROUT=1k VIN=5.0V ROUT=3.3 200µs/div Start Up Up intointo Pre-Biased OUT=3.3V)(Enable) Start Pre-BiasOutput Output(V(Enable) VIN 200µs/div Start Pre-Biased Output (Power (VOUT=3.3V)(Power Up) StartUp Upinto into Pre-Bias Output Up V ) IN VIN 2V/div 2V/div VEN 2V/div VOUT VOUT 1V/div 1V/div VIN=5.0V ROUT=1k VIN=5.0V ROUT=1k 200µs/div Shutdown-Disable (VOUT =3.3V) Shutdown (Disable) (VOUT =3.3V) 200µs/div Shutdown-Disable (VOUT =3.3V) Shutdown (Disable) (VOUT =3.3V) VIN VIN 5V/div 5V/div VEN VEN 2V/div 2V/div VOUT VOUT 2V/div 2V/div VIN=5.0V ROUT=33 © 2009 Semtech Corp. VIN=5.0V ROUT=3.3 500µs/div 11 100µs/div www.semtech.com SC4626 Typical Waveforms (continued) Circuit Conditions: VOUT=1.0V (SC4626A); L= 1.0uH (Murata: LQM2HPN1R0NG0L); CIN= 10uF/6.3V; COUT= 22uF/6.3V (Murata: GRM21BR60J226M). Output Voltage Ripple (V=1.0V) OUT=1.0V) Output Voltage Ripple (VOUT Output Voltage Ripple (V=1.0V) OUT=1.0V) Output Voltage Ripple (VOUT VOUT VOUT 10mV/div 10mV/div ILX ILX 500mA/div Offset: 0A 500mA/div VLX VLX 2V/div 2V/div VIN=3.3V IOUT=0A 500ns/div VIN=3.3V IOUT=1.0A 4626-w25 Output Voltage Ripple (V=1.0V) OUT=1.0V) Output Voltage Ripple (VOUT 500ns/div 4626-w26 Output Voltage Ripple (V=1.0V) OUT=1.0V) Output Voltage Ripple (VOUT VOUT VOUT 10mV/div 10mV/div ILX ILX 500mA/div 1A/div VLX VLX 2V/div 2V/div VIN=5.0V IOUT=0A 500ns/div VIN=5.0V IOUT=1.0A 4626-w27 Transient Response (V=1.0V) OUT=1.0V) Transient Response (VOUT 500ns/div 4626-w28 Transient Response (V=1.0V) OUT=1.0V) Transient Response (VOUT VOUT VOUT 20mV/div 20mV/div IOUT IOUT 500mA/div 500mA/div VIN=5.0V IOUT=0A to 0.5A © 2009 Semtech Corp. 50µs/div 4626-w29 12 VIN=5.0V IOUT=0.5A to 1A 50µs/div 4626-w30 www.semtech.com SC4626 Pin Descriptions Pin # Pin Name 1 VIN Input power supplies. Powers the internal circuitry and is connected to the source of high-side P channel MOSFET. 2 GND Ground connection. 3 EN 4 VOUT 5 LX © 2009 Semtech Corp. Pin Function Enable pin. When connected to logic high or tied to VIN pin, the SC4626 is on. When connected to logic low, the device enters shutdown and consumes less than 1µA of current. The enable pin has a 1 MΩ internal pulldown resistor. This resistor is switched in circuit whenever the EN pin is below the enable input high threshold, or when the part is in undervoltage lockout. Output voltage sense pin. Switching node - connect an inductor between this pin and the output capacitor. 13 www.semtech.com SC4626 Block Diagram VIN + Current Amp Internal Oscillator VOVP VOUT Voltage Select Plimit Comp Plimit Amp Ramp Generator + + + - Control Logic OVP Error Amp LX + PWM Comp 500mV Ref GND EN © 2009 Semtech Corp. 14 www.semtech.com SC4626 Applications Information adjusted to meet the equation shown above. Detailed Description The SC4626 is a synchronous step-down pulse width modulated (PWM) voltage mode DC-DC regulator operating at 2.5MHz fixed-frequency. The switching frequency is chosen to minimize the size of the external inductor and capacitors while maintaining high efficiency. Protection Features The SC4626 provides the following protection features: Thermal Shutdown Current Limit Over-Voltage Protection Soft-Start Operation • • • • Operation During normal operation, the internal highside PMOS device is activated on each rising edge of the internal oscillator. The voltage feedback loop uses an internal feedback resistor divider. The period is set by the on board oscillator when in PWM mode at average to high loads. The device has an internal low-side synchronous NMOS device and does not require a Schottky diode on the LX pin. The device operates as a buck converter in PWM mode with a fixed frequency of 2.5MHz. Thermal Shutdown The device has a thermal shutdown feature to protect the SC4626 if the junction temperature exceeds 160°C. During thermal shutdown, the on-chip power devices are disabled with the LX output floating. When the die temperature drops by 10°C, the part will initiate a soft start recovery to normal operation. Current Limit The internal PMOS power device in the switching stage is protected by current limit feature. If the output is loaded above the PMOS current limit for 32 consecutive cycles, the SC4626 enters foldback current limit mode and the output current is limited to the current limit holding current (ICL_HOLD) of a few hundred milliampere. Under these conditions the output voltage will be the product of I CL_HOLD and the load resistance. The current limit holding current (ICL_HOLD) will be decreased when output voltage is increased. The load presented must fall below the current limit holding current for the SC4626 to exit foldback current limit mode. Figure 2 shows the typical current limit holding current decreasing rate over different output voltage. The SC4626 is capable of sustaining a indefinite short circuit without damage and will resume normal operation when the fault is removed. The foldback current limit mode will be disabled during the Current Limit Holding Current over Vout soft-start. C FF [nF ] = 10 × (VOUT − 0.5)2 VOSTD ×( ) RFB1[kΩ] ⋅ (VOUT − VOSTD ) VOSTD − 0.5 ,where the VOSTD is the standard voltage shown in Table 1. To simplify the design, it is recommended to program the desired output voltage from standard 1.0V as shown in Figure 1 with a proper CFF calculated from the equation Schematic of Adjustable VOUT from SC4626A (Std VOUT=1.0V) shown above. For programming the output voltage from other standard voltage, the RFB1, RFB2 and CFF need to be L VIN VIN VOUT LX CIN REN COUT GND RFB1 Enable EN CFF 150 TA= 25°C Current Limit holding Current (mA) Output Voltage Selection The SC4626 is designed for fixed output voltage. There are some options for preset output voltage shown in Table 1. If the voltage desired is not shown in the Table 1, it can be programmed via an external resistor divider. There will be typical 1uA current flowing into the VOUT pin. The typical schematic of adjustable output voltage option from the part with standard 1.0V, the SC4626A, is shown in Figure 1. The CFF is needed for maintain the performance of the transient response. The proper value of CFF can be calculated by the equation 120 VIN= 5.0V 90 60 30 VIN= 3.6V VOUT SC4626A RFB2 10k 0 RFB1 = (VOUT − 1) × RFB 2 1.0 1.5 2.0 2.5 3.0 3.5 Output Voltage (V) Figure 1 — Typical schematic for adjustable output voltage option from standard 1.0V of SC4626A Note: (1) REN is optional. © 2009 Semtech Corp. and C (2) R =10k FB2 =10nF for standard design. FF Figure 2 — Current limit holding current decreasing rate vs. output voltage 15 www.semtech.com SC4626 Applications Information (continued) Over-Voltage Protection In the event of a 15% over-voltage on the output, the PWM drive is disabled with LX pin floating. of output filter can be defined by the equation fC Soft-Start The soft-start mode is activated after VIN reaches its UVLO and EN signal is set high to enable the part. An over temperature shutdown event will also activate the soft start sequence. Soft-start mode controls the maximum current during startup thus limiting in-rush current. The PMOS current limit is stepped through four soft start levels of approximately 20%, 25%, 40%, & 100%. Each step is maintained for 20μs following internal reference start up of 20μs giving the total nominal startup period of 100μs. During startup, the chip operates in controlling the inductor current swings between 0A and current limit. If VOUT reaches 90% of the target within the first 2 current levels, the chip continues in hysteretic mode till the end of the soft-start time period before switching to PWM mode. If VOUT does not reach 90% by the end of the second current limit level, soft start will continue to level 3 or level 4 till the output voltage reaches 96% and will then transition into PWM mode. After the full soft start time period, the SC4626 will switch into PWM mode operation regardless of the VOUT level. 1 2S L COUT Values outside this range may lead to instability, malfunction, or out-of-specification performance. When choosing an inductor, it is important to consider the change in inductance with DC bias current. The inductor saturation current is specified as the current at which the inductance drops a specific percentage from the nominal value. This is approximately 30%. Except for short-circuit or other fault conditions, the peak current must always be less than the saturation current specified by the manufacturer. The peak current is the maximum load current plus one half of the inductor ripple current at the maximum input voltage. Load and/or line transients can cause the peak current to exceed his level for short durations. Maintaining the peak current below the inductor saturation specification keeps the inductor ripple current and the output voltage ripple at acceptable levels. Manufacturers often provide graphs of actual inductance and saturation characteristics versus applied inductor current. The saturation characteristics of the inductor can vary significantly with core temperature. Core and ambient temperatures should be considered when examining the core saturation characteristics. The SC4626 is capable of starting up into a pre-biased output. When the output is precharged by another supply rail, the SC4626 will not discharge the output during the soft start interval. Shut Down When the EN pin voltage goes low, the SC4626 will run in shutdown mode, drawing less than 1μA from the input power supply. The internal switches and bandgap voltage will be immediately turned off. When the inductance has been determined, the DC resistance (DCR) must be examined. The efficiency that can be achieved is dependent on the DCR of the inductor. The lower values give higher efficiency. The RMS DC current rating of the inductor is associated with losses in the copper windings and the resulting temperature rise of the inductor. This is usually specified as the current which produces a 40˚C temperature rise. Most copper windings are rated to accommodate this temperature rise above maximum ambient. Inductor Selection The SC4626 converter has internal loop compensation. The compensation is designed to work with a output filter corner frequency is less than 100kHz over any operating condition, tolerance and bias effect. The corner frequency Magnetic fields associated with the output inductor can interfere with nearby circuitry. This can be minimized by the use of low noise shielded inductors which use the minimum gap possible to limit the distance that magnetic fields can radiate from the inductor. However shielded inductors typically have a higher DCR and are thus less efficient than a similar sized non-shielded inductor. © 2009 Semtech Corp. 16 www.semtech.com SC4626 Applications Information (continued) Vout Code (Vout) A(1.0V),C(1.2V),E(1.28V),F(1.3V),H(1.5V) Inductor Output Capacitor Description Vender Part Number Description Vender Part Number Qty. 2.2uH, 60m(max) Wire Wound 2.8x3.0x1.5(mm) TOKO 1071AS-2R2M 10uF,6.3V X5R,0805 Murata GRM21BR60J106K 1 1.0uH, 40m(max) Wire Wound 2.8x3.0x1.5(mm) TOKO 1071AS-1R0N 22uF,6.3V X5R,0805 Murata GRM21BR60J226M 1 2.2uH, 120m(max) Wire Wound 2.5x2.0x1.2(mm) TOKO 1222AS-H-2R2M 10uF,6.3V X5R,0805 Murata GRM21BR60J106K 1 22uF,6.3V X5R,0805 Murata GRM21BR60J226M 1 10uF,6.3V X5R,0805 Murata GRM219R60J106K 1 22uF,6.3V X5R,0805 Murata GRM21BR60J226M 1 10uF,4.0V X5R,0603 Murata GRM188R60G106M 2 1.0uH, 80m(max) Multilayer Chip 2.5x2.0x1.0(mm) 1.0uH, 69m(max) Multilayer Chip 2.5x2.0x1.0(mm) TOKO Murata MDT2520-CR1R0M LQM2HPN1R0MG0 Table 2a – Recommended L and output capacitors for Vout=1.0V to 1.5V Vout Code (Vout) L(1.8V),Y(2.5V),Z(3.3V) Inductor Output Capacitor Description Vender Part Number Description Vender Part Number Qty. 2.2uH, 60m(max) Wire Wound 2.8x3.0x1.5(mm) TOKO 1071AS-2R2M 10uF,6.3V X5R,0805 Murata GRM21BR60J106K 1 1.0uH, 40m(max) Wire Wound 2.8x3.0x1.5(mm) TOKO 1071AS-1R0N 22uF,6.3V X5R,0805 Murata GRM21BR60J226M 1 2.2uH, 120m(max) Wire Wound 2.5x2.0x1.2(mm) TOKO 1222AS-H-2R2M 10uF,6.3V X5R,0805 Murata GRM21BR60J106K 1 22uF,6.3V X5R,0805 Murata GRM21BR60J226M 1 10uF,4.0V X5R,0603 Murata GRM188R60G106M 2 1.0uH, 80m(max) Multilayer Chip 2.5x2.0x1.0(mm) TOKO MDT2520-CR1R0M Table 2b – Recommended L and output capacitors for Vout=1.8V to 3.3V © 2009 Semtech Corp. 17 www.semtech.com SC4626 Applications Information (continued) Capacitors with X7R or X5R ceramic dielectric are recommended for their low ESR and superior temperature and voltage characteristics. Y5V capacitors should not be used as their temperature coefficients make them unsuitable for this application. The SC4626 is compatible with small shielded chip inductors for low cost, low profile applications. The inductance roll off characteristic of chip inductor is worse resulting in high ripple current and increased output voltage ripple at heavy load operation. SC4626 has OCP peak inductor current threshold of 1.5A minimum, to support 1A DC load current, the inductor ripple current at 1A DC load current needs to be less than 1A. The output voltage droop due to a load transient is determined by the capacitance of the ceramic output capacitor. The ceramic capacitor supplies the load current initially until the loop responds. Within a few switching cycles the loop will respond and the inductor current will increase to match the required load. The output voltage droop during the period prior to the loop responding can be related to the choice of output capacitor by the relationship Final inductor selection depends on various design considerations such as efficiency, EMI, size, and cost. Table 2a and 2b list the manufacturers of recommended inductor and output capacitors options. Chip inductors provide smaller footprint and height with lower efficiency and increased output voltage ripple. Transient load performance is equivalent to wire wound inductors. Figure 3 shows the typical efficiency curves for different inductors. COUT = 3 ⋅ ∆I LOAD VDROOP ⋅ f OSC Efficiency The output capacitor RMS current ripple may be calculated from the equation 100% L=1071AS-2R2N (50m_typ) 95% Efficiency (%) 90% I COUT ( RMS ) = 85% L=1071AS-1R0N (33m_typ) 1 VOUT ⋅ (VIN ( MAX ) − VOUT ) L ⋅ f OSC ⋅ VIN 2 3 80% L=MDT2520-CR1R0M (60m_typ) 75% 70% VIN= 5.0V VOUT= 3.3V TA=25°C 65% Table 3 lists the manufacturers of recommended output capacitor options. L=LQM2HP1R0MG0 (55m_typ) CIN Selection The SC4626 source input current is a DC supply current with a triangular ripple imposed on it. To prevent large input voltage ripple, a low ESR ceramic capacitor is required. A minimum value of 4.7μF should be used. It is important to consider the DC voltage coefficient characteristics when determining the actual required value. To estimate the required input capacitor, determine the acceptable input ripple voltage and calculate the minimum value required for CIN from the equation 60% 0.0 0.2 0.4 0.6 Output Current (A) 0.8 1.0 Figure 3 — Typical efficiency curves (VIN=5.0V, VOUT=3.3V) COUT Selection The internal voltage loop compensation in the SC4626 limits the minimum output capacitor value to 10µF if using the inductor of 2.2µH. This is due to its influence on the the loop crossover frequency, phase margin, and gain margin. Increasing the output capacitor above this minimum value will reduce the crossover frequency and provide greater phase margin. A total output capacintance should not exceed 30uF to avoid any start-up problems. For most typical applications, it is recommended to use output capacitance of 10uF to 22uF. When choosing output capacitor’s capacitance, verify the voltage derating effect from the capacitor vendors data sheet. © 2009 Semtech Corp. C IN VOUT 1 − VIN = ∆V − ESR ⋅ f OSC I OUT VOUT VIN The input capacitor RMS ripple current varies with the 18 www.semtech.com SC4626 Applications Information (continued) input and output voltage. The maximum input capacitor RMS current is found from the equation I CIN ( RMS ) = VOUT VIN VOUT 1 − VIN The input voltage ripple and RMS current ripple are at maximum when the input voltage is twice the output voltage or 50% duty cycle. The input capacitor provides a low impedance loop for the edges of pulsed current drawn by the PMOS switch. Low ESR/ESL X5R ceramic capacitors are recommended for this function. To minimise stray inductance ,the capacitor should be placed as closely as possible to the VIN and GND pins of the SC4626. Type Rated Voltage (VDC) Value at 3.3V (μF) Dimensions LxWxH (mm) 10±10% X5R 10 4.42 2.0x1.25x1.25 (EIA:0805) Murata GRM21BR71A106K 10±10% X7R 10 4.88 2.0x1.25x1.25 (EIA:0805) Murata GRM21BR60J106K 10±10% X5R 6.3 4.05 2.0x1.25x1.25 (EIA:0805) Murata GRM21BR70J106K 10±10% X7R 6.3 4.91 2.0x1.25x1.25 (EIA:0805) Murata GRM21BR60J226M 22±20% X5R 6.3 6.57 2.0x1.25x1.25 (EIA:0805) Manufacturer Part Nunber Value (μF) Murata GRM21BR61A106K Table 3 – Recommended Capacitors © 2009 Semtech Corp. 19 www.semtech.com SC4626 Applications Information (continued) PCB Layout Considerations The layout diagram in Figure 4 shows a recommended PCB top-layer and bottom layer for the SC4626 and supporting components. Fundamental layout rules must be followed since the layout is critical for achieving the performance specified in the Electrical Characteristics table. Poor layout can degrade the performance of the DC-DC converter and can contribute to EMI problems, ground bounce, and resistive voltage losses. Poor regulation and instability can result. L CIN The following guidelines are recommended when developing a PCB layout: 1. The input capacitor, CIN should be placed as close to the VIN and GND pins as possible. This capacitor provides a low impedance loop for the pulsed currents present at the buck converter’s input. Use short wide traces to connect as closely to the IC as possible. This will minimize EMI and input voltage ripple by localizing the high frequency current pulses. 2. Keep the LX pin traces as short as possible to minimize pickup of high frequency switching edges to other parts of the circuit. COUT and L should be connected as close as possible between the LX and GND pins, with a direct return to the GND pin from COUT. 3. Route the output voltage feedback/sense path away from inductor and LX node to minimize noise and magnetic interference. 4. Use a ground plane referenced to the SC4626 GND pin. Use several vias to connect to the component side ground to further reduce noise and interference on sensitive circuit nodes. 5. If possible, minimize the resistance from the VOUT and GND pins to the load. This will reduce the voltage drop on the ground plane and improve the load regulation. And it will also improve the overall efficiency by reducing the copper losses on the output and ground planes. © 2009 Semtech Corp. VOUT COUT U1 GND VIN (a) Top layer GND EN (b) Bottom layer Figure 4 — Recommended PCB Top & Bottom Layer Layout 20 www.semtech.com SC4626 Outline Drawing – SOT23-5 A e1 2X E/2 ccc C DIM D A A1 A2 b c D E1 E e e1 L L1 N 01 aaa bbb ccc N EI 1 E 2 2X N/2 TIPS e B D aaa C A2 DIMENSIONS INCHES MILLIMETERS MIN NOM MAX MIN NOM MAX .035 .000 .035 .010 .003 .110 .060 - .045 - .057 .006 .051 .020 .009 .118 .069 .114 .063 .110 BSC .037 BSC .075 BSC .012 .018 .024 (.024) 5 0° 10° .004 .008 .008 0.90 0.00 .90 0.25 0.08 2.80 1.50 - 1.15 - 1.45 0.15 1.30 0.50 0.22 3.00 1.75 2.90 1.60 2.80 BSC 0.95 BSC 1.90 BSC 0.30 0.45 0.60 (0.60) 5 0° 10° 0.10 0.20 0.20 A SEATING PLANE A1 C H bxN bbb C A-B D c GAGE PLANE 0.25 L 01 (L1) SEE DETAIL DETAIL A A SIDE VIEW NOTES: 1. CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES). 2. DATUMS -A- AND -B- TO BE DETERMINED AT DATUM PLANE -H3. DIMENSIONS "E1" AND "D" DO NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. Land Pattern – SOT23-5 X DIM (C) G Z Y P C G P X Y Z DIMENSIONS INCHES MILLIMETERS (.098) .055 .037 .024 .043 .141 (2.50) 1.40 0.95 0.60 1.10 3.60 NOTES: 1. © 2009 Semtech Corp. THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY. CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR COMPANY'S MANUFACTURING GUIDELINES ARE MET. 21 www.semtech.com SC4626 © Semtech 2010 All rights reserved. Reproduction in whole or in part is prohibited without the prior written consent of the copyright owner. The information presented in this document does not form part of any quotation or contract, is believed to be accurate and reliable and may be changed without notice. No liability will be accepted by the publisher for any consequence of its use. Publication thereof does not convey nor imply any license under patent or other industrial or intellectual property rights. Semtech assumes no responsibility or liability whatsoever for any failure or unexpected operation resulting from misuse, neglect improper installation, repair or improper handling or unusual physical or electrical stress including, but not limited to, exposure to parameters beyond the specified maximum ratings or operation outside the specified range. SEMTECH PRODUCTS ARE NOT DESIGNED, INTENDED, AUTHORIZED OR WARRANTED TO BE SUITABLE FOR USE IN LIFE-SUPPORT APPLICATIONS, DEVICES OR SYSTEMS OR OTHER CRITICAL APPLICATIONS. INCLUSION OF SEMTECH PRODUCTS IN SUCH APPLICATIONS IS UNDERSTOOD TO BE UNDERTAKEN SOLELY AT THE CUSTOMER’S OWN RISK. Should a customer purchase or use Semtech products for any such unauthorized application, the customer shall indemnify and hold Semtech and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs damages and attorney fees which could arise. 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 © 2009 Semtech Corp. 22 www.semtech.com