DATA SHEET SKY87203: 3.5 A Constant On-Time, Step-Down DC-DC Converter Applications Description Portable devices The SKY87203 is a variable switching frequency, 3.5 A constant on-time, synchronous step-down converter. The device provides an output voltage from 0.9 V to 4.0 V from input voltage ranging from 2.7 V to 6.0 V, while keeping excellent line and load regulation and maximizing efficiency. Access points Set-top boxes Input voltage range: 2.7 V to 6.0 V The constant on-time control allows easy loop stabilization with minimal external components while providing fast transient response. Output voltage range: 0.9 V to 4.0 V Power sequencing is controlled by the EN and PG pins. Variable switching frequency: 600 kHz to 1.5 MHz The SKY87203 has cycle-by-cycle current limits and thermal shutdown to protect against fault conditions. Features Up to 3.5 A continuous output current 95% peak efficiency Typical switch on resistance: 50 m PMOS, 40 m NMOS 80% light load efficiency Power sequencing The SKY87203 is available in a 12-pin, 2 mm 2 mm Quad Flat No-Lead (QFN) package. A typical application circuit is shown in Figure 1. The pin configuration and packages are shown in Figure 2. Signal pin assignments and functional pin descriptions are provided in Table 1. Cycle-by-cycle over-current protection Auto-discharge at power-off Over-temperature protection Control loop stabilization with low ESR ceramic capacitors Soft start Low profile, QFN (12-pin, 2 mm 2 mm) package (MSL1, 260 C per JEDEC J-STD-020) Skyworks Green™ products are compliant with all applicable legislation and are halogen-free. For additional information, refer to Skyworks Definition of Green™, document number SQ04-0074. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202456C • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • October 27, 2014 1 DATA SHEET • SKY87203: STEP-DOWN DC-DC CONVERTER SKY87203 Input Voltage 2.7 V to 6 V 1 C1 22 μF 10 8 Power Good 9 VIN OUT FB EN PG FSET 4 L1 2, 11 1 μH 6 C2 22 μF Output Voltage 3.6 V R1 294 kΩ 7 R2 57.6 kΩ 5 R3 300 kΩ PGND AGND Enable LX PVIN 3, 12 t0282 VIN Figure 1. Typical Application Circuit PVIN 1 10 9 PG 8 EN LX LX 2 11 PGND 12 7 FB AGND 4 5 6 OUT FSET PGND 3 S3203 Figure 2. SKY87203-11 Pinout – 12-Pin QFN Package (Top View) Table 1. SKY87203 Signal Descriptions Pin Name Description Pin Name Description 1 PVIN Power supply. 7 FB Feedback voltage pin. Used to control the converter output voltage according to the ratio of the feedback resistor. 2 LX Switch node, connected to inductor. 8 EN Enable pin, active high. 3 PGND Power ground. 9 PG Power good pin. Open drain with internal pull-up resistor. 4 AGND Analog ground. 10 VIN Analog supply pin. 5 FSET Switching frequency adjust pin. Connect with a resistor to ground. If this pin is left floating, the switching frequency is 1.2 MHz for an input voltage equal to 5 V and an output voltage equal to 1.2 V. 11 LX Switch node, connected to inductor. 6 OUT Output voltage sensing pin. 12 PGND Power ground. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 2 October 27, 2014 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • 202456C DATA SHEET • SKY87203: STEP-DOWN DC-DC CONVERTER Electrical and Mechanical Specifications The absolute maximum ratings of the SKY87203 are provided in Table 2. Recommended operating conditions are specified in Table 3. Electrical specifications are provided in Table 4. Table 2. SKY87203 Absolute Maximum Ratings (Note 1) Parameter Symbol Minimum Maximum Units VIN 0.3 +6.5 V Switching voltage (LX to ground) VLX 0.3 VIN + 0.3 V Signal pins (FB, OUT, EN, PG to ground) VFB, VOUT, VEN, VPG 0.3 +6.5 V Maximum continuous current for load switch IMAX Junction temperature TJ Storage temperature TSTG Power pins (PVIN, VIN to ground) 65 3.5 A +150 C +150 C Soldering temperature (at leads, 10 sec) TLEAD +260 C Thermal resistance, junction-to-ambient θJA 80 C/W Thermal resistance, junction-to-case θJC 16 C/W Power dissipation @ 25 C PD 1.6 W Note 1: Exposure to maximum rating conditions for extended periods may reduce device reliability. There is no damage to device with only one parameter set at the limit and all other parameters set at or below their nominal value. Exceeding any of the limits listed here may result in permanent damage to the device. CAUTION: Although this device is designed to be as robust as possible, electrostatic discharge (ESD) can damage this device. This device must be protected at all times from ESD. Static charges may easily produce potentials of several kilovolts on the human body or equipment, which can discharge without detection. Industry-standard ESD precautions should be used at all times. Table 3. SKY87203 Recommended Operating Conditions Parameter Symbol Minimum Typical Maximum Units Input voltage range VIN 2.7 6.0 V Output voltage range VOUT 0.9 4.0 V Table 4. SKY87203 Electrical Specifications (1 of 2) (Note 1) (VIN = 5.0 V, TA = –40 C to +85 C [Typical Values are TA = +25 C], Unless Otherwise Noted) Parameter Symbol Test Condition Min Typical Max Units Input shutdown current ISHDN VEN = 0 V 0 A Quiescent supply current IQ VEN = 2 V, VFB = 0.63 V, VIN = 3.6 V 40 A Feedback voltage VFB 2.7 V ≤ VIN ≤ 6.0 V Feedback input bias current IFB VFB = 0.6 V 0.591 0.600 0.609 V 10 nA High side switch on resistance (Note 2) RDS(ON)_P 50 m Low side switch on resistance (Note 2) RDS(ON)_N 40 m Switch leakage VEN = 0 V, VIN = 6.0 V, VLX = 0 V and 6.0 V PFET current limit 3.6 Dampening resistor RDAMP 0 2 A 4.5 6.0 A 200 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202456C • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • October 27, 2014 3 DATA SHEET • SKY87203: STEP-DOWN DC-DC CONVERTER Table 4. SKY87203 Electrical Specifications (2 of 2) (Note 1) (VIN = 5.0 V, TA = –40 C to +85 C [Typical Values are TA = +25 C], Unless Otherwise Noted) Parameter On time Symbol tON Test Condition Min Typical Max VIN = 5.0 V, VOUT = 1.2 V RFSET = 600 k, PWM Mode (0.6 MHz) 430 ns VIN = 5.0 V, VOUT = 1.2 V RFSET = 300 k, PWM Mode (1.2 MHz) 220 ns VIN = 3.6 V, VOUT = 1.2 V RFSET = 300 k, PWM Mode (1.2 MHz) 277 ns VIN = 5.0 V, VOUT = 1.2 V FSET = floating, PWM Mode (1.2 MHz) 210 ns VIN = 5.0 V, VOUT = 1.2 V RFSET = 240 k, PWM Mode (1.5 MHz) 170 ns Minimum off time tOFF 30 ns Soft-start time tSS_ON 1 ms VIN discharge N-MOSFET switch on resistance (Note 2) RDSON_DSCHg 10 VIN discharge time VIN_DSCHG VIN (falling) = UVLO UVLO VIN (falling) 1 V 90 PG pin upper trip threshold VFB 0.66 V +10 % PG pin lower trip threshold VFB 0.54 V 10 % PG pin delay 200 ms s 90 PG pin sink current capability VPG_LO 0.4 PG pin logic high voltage VPG_HI PG pin internal pull-up resistor RPG 500 k Output voltage discharge resistor RDSCHG 100 Under-Voltage Lock Out UVLO 4.9 VIN rising 2.35 UVLO hysteresis 2.50 2.65 V mV 0.4 VEN_L VEN_H V V 400 EN pin input voltage: Logic low Logic high 1.2 V V 2 0 A A Thermal shutdown 150 °C Thermal hysteresis (Note 2) 30 °C EN pin input current VEN = 2 V VEN = 0 V Note 1: Performance is guaranteed only under the conditions listed in this table. Note 2: Specification guaranteed by design. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 4 Units October 27, 2014 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • 202456C DATA SHEET • SKY87203: STEP-DOWN DC-DC CONVERTER Typical Performance Characteristics Typical performance characteristics of the SKY87203 are illustrated in Figures 3 through 21. The output voltage is 3.6 V. 80 60 85 ºC 25 ºC 40 –40 ºC 70 60 VIN = 4.2 V 50 VIN = 5.0 V t0252 Quiescent Current (μA) 80 t0251 Quiescent Current (μA) 100 40 20 2.7 3.0 3.3 3.6 3.9 4.2 4.5 4.8 5.1 5.4 5.7 −40 6.0 −15 35 60 85 Temperature (ºC) Supply Voltage (V) Figure 3. Quiescent Current (Close Loop) vs Supply Voltage Figure 4. Quiescent Current (Close Loop) vs Temperature 2 1.5 1.5 1 0.5 1 0.5 t0254 EN Off Threshold (V) 2 t0253 EN On Threshold (V) 10 0 0 −40 −15 10 35 60 −40 85 −15 35 60 85 Temperature (ºC) Temperature (ºC) Figure 6. EN Off Threshold vs Temperature (VIN = 5 V, Load = 0 mA) Figure 5. EN On Threshold vs Temperature (VIN = 5 V, Load = 0 mA) 0.610 Feedback Voltage (V) 2 1.5 1 0.600 0.595 t0255 0.5 0.605 t0256 2.5 Frequency (MHz) 10 0.590 0 −40 −15 10 35 60 Temperature (ºC) Figure 7. Frequency vs Temperature (VIN = 5 V, Load = 500 mA) 85 −40 −15 10 35 60 85 Temperature (ºC) Figure 8. Feedback Voltage vs Temperature (VIN = 5 V, Load = 0 mA) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202456C • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • October 27, 2014 5 70 70 65 65 NMOS RDS(ON) (mΩ) PMOS RDS(ON) (mΩ) DATA SHEET • SKY87203: STEP-DOWN DC-DC CONVERTER 60 55 50 55 50 45 40 t0238 t0237 45 60 40 –40 –15 10 35 60 85 –40 –15 10 Temperature (ºC) 35 60 85 Temperature (ºC) Figure 9. PMOS RDS(ON) vs Temperature (VIN = 5 V) Figure 10. NMOS RDS(ON) vs Temperature (VIN = 5 V) 3.80 98 3.75 96 VOUT (V) 92 3.65 3.60 VIN = 4.2 V VIN = 4.2 V 90 3.55 VIN = 5.0 V VIN = 6.0 V t0239 88 86 10 100 1000 3.50 VIN = 5.0 V VIN = 6.0 V t0240 Efficiency (%) 3.70 94 3.45 10 100 IOUT (mA) IOUT (mA) Figure 11. Efficiency vs IOUT Figure 12. VOUT vs IOUT VOUT (AC) 200 mV/div ILOAD 1 A/div 0.7 A t0241 0.2 A t0242 VOUT (AC) 100 mV/div ILOAD 1 A/div 1000 50 μs/div Figure 13. Load Transient (Load = 0.2 A to 2 A) 50 μs/div Figure 14. Load Transient (Load = 0.7 A to 3.5 A) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 6 October 27, 2014 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • 202456C DATA SHEET • SKY87203: STEP-DOWN DC-DC CONVERTER VOUT 2 V/div 0V VEN 2 V/div 0V PG 2 V/div t0243 0V 200 μs/div Figure 15. Power Good Delay VOUT 2 V/div VOUT 2 V/div 0V VEN 2 V/div VEN 2 V/div 0V 0A ILX 2 A/div VLX 5 V/div 0A t0244 0V VLX 5 V/div 0V t0245 ILX 1 A/div 0V 0V 400 μs/div 1 ms/div Figure 17. Shutdown Waveform (Load = 2 A) Figure 16. Shutdown Waveform (Load = 0 A) VEN 2 V/div VEN 2 V/div 0V 0V 0A ILX 1 A/div 0V 400 μs/div Figure 18. Soft Start Waveform (Load = 0 A) VLX 5 V/div 0V 0A t0247 VLX 5 V/div VOUT 2 V/div 0V t0246 VOUT 2 V/div ILX 1 A/div 0V 400 μs/div Figure 19. Soft Start Waveform (Load = 2 A) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202456C • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • October 27, 2014 7 DATA SHEET • SKY87203: STEP-DOWN DC-DC CONVERTER VOUT (AC) 50 mV/div VOUT (AC) 50 mV/div ILX (AC) 1 A/div VLX 2 V/div 0V 1 μs/div Figure 20. Typical Switching Waveform (0 A Load) VLX 2 V/div t0249 0A t0248 ILX 1 A/div 0V 1 μs/div Figure 21. Typical Switching Waveform (2 A Load) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 8 October 27, 2014 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • 202456C DATA SHEET • SKY87203: STEP-DOWN DC-DC CONVERTER VIN Auto Discharge VIN PVIN + EN Voltage References and UVLO – VREF COMP + FB + – PWM Control and Logic Driver Ramp Circuit LX OUT 0.66 V RDAMP VOUT Discharge FSET + – – + 0.54 V + PGND – PG t0283 Figure 22. SKY87203 Functional Block Diagram Functional Description The SKY87203 is an adaptive constant on-time, adjustable voltage step-down DC-DC converter. A constant on-time control architecture offers a simpler control loop and faster transient response than a fixed-frequency Pulse Width Modulation (PWM) control architecture. The constant on-time converter maintains a constant output frequency because the “on” time is inversely proportional to the supply voltage. As the input voltage decreases, the “on” time is increased, maintaining a relatively constant period. The device is enabled using the EN input. When the EN pin is pulled high, the converter starts up under the control of a 1 ms soft start routine. Under light load conditions, the switch enters pulse-skipping mode to ensure regulation is maintained. This effectively changes the switching frequency. To maintain a wide input voltage range, the switching period is extended when either the minimum “off” or “on” time is reached. The frequency is also affected when switching operates in discontinuous mode. The “on” time of the switching pulses can be estimated using the following equation: t ON VOUT The minimum off time is fixed at 30 ns to prevent runaway inductor current during load transients. A functional block diagram of the SKY87203 is shown in Figure 22. Constant On-Time (COT) Operation In normal continuous conduction mode, where the inductor current (IL) never reaches zero, the high-side MOSFET is turned on for a fixed interval (tON) determined by the COT sub-circuit (a one-shot timer) within the PWM Control and Logic functional block. During that fixed interval, the inductor current starts to ramp up. At the end of the tON period, the high-side MOSFET is turned off and the low-side MOSFET is turned on causing the inductor current to ramp down. Until this point, the voltage on the FB pin (VFB) goes below the reference voltage (VREF) on the comparator, which restarts the one-shot timer and initiates the next cycle. The ideal tON time in continuous conduction mode is determined by the following relationships: Duty cycle (D) = VOUT V IN 0.833 s V IN Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202456C • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • October 27, 2014 9 DATA SHEET • SKY87203: STEP-DOWN DC-DC CONVERTER On time (tON) = D Light Load Operation 1 f SW In discontinuous conduction mode, the SKY87203 uses a passive damping scheme to reduce the amplitude and duration of ringing that occurs at the switching node (LX). If switching frequency (fSW) = 1.2 MHz, the on-time equation can be rewritten as: tON VOUT 0.833 s V IN Enable and Soft Start When the input voltage is greater than the Under-Voltage Lockout (UVLO) threshold, the SKY87203 is enabled by pulling the EN pin higher than 1.2 V. If the EN pin is left floating or pulled down to ground, the regulator is disabled. There is an internal 1 M resistor from the EN pin to ground. The COT circuit generates an “on” time proportional to the ideal duty cycle and holds the switching frequency constant. However, due to nonlinearities in the COT circuit, propagation delays, and non-ideal switch voltage drops due to output current loads, the actual operating frequency can vary slightly. When DC current loads are less than half of the peak-to-peak current ripple in the inductor, the inductor current can drop to zero or even become negative. When this happens, the SKY87203 operates in discontinuous conduction mode. The SKY87203 step-down regulator soft-start control prevents output voltage overshoot and limits inrush current when either the input power or the enable input is applied. After the regulator is enabled, the SKY87203 ramps up the internal target voltage with a controlled slew rate of 1 ms. During the “off” time, the low-side MOSFET is on and the discontinuous conduction mode comparator monitors the current. When the current is zero, the low-side MOSFET is turned off, which prevents the current from going negative. When the EN signal is pulled low, the regulator forces the converter into a low-power, non-switching state, and forces the switching node into a high-impedance shutdown state. Both the high-side MOSFET and the low-side MOSFET remain off with the output capacitor supplying the load current until the FB pin voltage goes below the reference voltage, triggering a new switching cycle. The switching frequency decreases in light load conditions. PG (Power Good) Pin The SKY87203 has an open drain with a 500 k pull-up resistor pin indicator (PG). When the FB pin is within ±10 percent of regulation voltage, the PG pin is pulled up to VIN by the internal resistor. If the FB pin voltage is not within ±10 percent of regulation voltage, the PG pin is pulled down to ground by an internal MOSFET. The MOSFET has a maximum RDS(ON) of less than 100 . Waveforms for both continuous conduction mode and discontinuous conduction mode are shown in Figure 23. VHSG GND VLSG GND IL VSW VOUT tON tOFF VFB GND IOUT ΔIL VFB tON VFB(DC) tOFF2 VHYS VREF tOFF1 Continuous Discontinuous Figure 23. Continuous and Discontinuous Mode Wave Forms Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 10 October 27, 2014 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • 202456C DATA SHEET • SKY87203: STEP-DOWN DC-DC CONVERTER Current Limit and Short Circuit Protection Table 5. Adjustable Resistor Values The SKY87203 includes protection for overload condition and short-circuit conditions by current-limiting the high-side MOSFETs. The SKY87203 enters over-load protection mode or short-circuit protection mode when the inductor current hits the current limit (4.5 A). The device will try to recover from the short circuit by entering a “hiccup” mode, in which the regulator disables the output power stage, discharges the soft-start capacitor, and automatically tries a soft start again. If the overload or the shortcircuit condition still holds after a soft start ends, the SKY87203 repeats this protection operation cycle until the short circuit disappears and the output rises back to the regulation level. Flexible Switching Frequency Select Function The SKY87203 has a flexible switching frequency select function to satisfy the variable application requirement. If this pin is left floating, the switching frequency is 1.2 MHz. A resistor (R3) is connected between the FSET pin and ground to adjust the switching frequency according to the following relationship: Frequency = 1.2 MHz (300 k/R3) Output Voltage (V) RFB2 (k 1%) (RFB1 = 200 k 1%) 1.0 300 1.2 200 1.8 100 2.5 63.2 3.3 44.2 VIN Auto Discharge The SKY87203 has a VIN auto-discharge function for USB applications in which a large inrush current supplied by a large VIN capacitor during a hot plugging operation exceeds the allowed USB current limit. When VIN voltage falls below the UVLO threshold, an N-MOSFET switch discharges the VIN to ground until VIN is less than 1 V. The discharge time is typically 90 ms for the condition UVLO VIN 1 V. For example, a 500 F bulk input capacitor needs about 80 ms to discharge an input voltage from 2.1 V to 1.0 V as illustrated in Figure 25. Application Information RFB1 VOUT 0.6 V 1 As shown in Table 5, the values for both RFB1 and RFB2 are rounded to the nearest 1 percent resistor value, and typically selected to be between 10 k and 200 k. The lower resistance value improves the noise immunity, but results in higher feedback current (which reduces the efficiency). VOUT RFB1 FB RFB2 Figure 24. Feedback Resistive Divider Circuit VOUT 2 V/div 0V ILX 20 mA/div 0 mA t0250 The SKY87203 output voltage is adjustable from 0.9 V up to 4.0 V by connecting the FB pin to the center tap of a resistor-divider between the output and ground (see Figure 24). The resistive feedback voltage divider sets the output voltage according to the following relationship: RFB 2 2.2 V VIN 1 V/div Setting the Output Voltage 20 ms/div Figure 25. VIN Auto Discharge Inductor Selection Inductor values ranging from 0.82 H to 4.7 H are recommended for most SKY87203 applications. Given the desired input and output voltages, the inductor value and switching frequency determine the ripple current: V V I L OUT 1 OUT VIN f SW L Lower ripple current reduces core losses in the inductor, Effective Series Resistance (ESR) losses in the output capacitors, and output voltage ripple. Highest efficiency operation is obtained at low frequency with a small ripple current. However, achieving this requires a large inductor. There is a trade-off between component size, efficiency, and operating frequency. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202456C • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • October 27, 2014 11 DATA SHEET • SKY87203: STEP-DOWN DC-DC CONVERTER to the capacitor’s ESL. Estimate the output voltage ripple due to the output capacitance, ESR, and ESL as follows: A reasonable starting point is to choose a ripple current that is about 30 percent of the maximum output current, IOUT(MAX). The largest ripple current occurs at the highest input voltage, Vin. To guarantee that ripple current does not exceed a specified maximum, the inductance should be chosen according to the following relationship: VOUT L f SW I L( MAX ) 1 VOUT VIN ( MAX ) VOUT ( RIPPLE ) VRIPPLE( C ) VRIPPLE( ESR ) VRIPPLE( ESL ) Where the output ripple due to output capacitance, ESR, and ESL is: V RIPPLE( C ) V RIPPLE( ESR ) I L ESR The maximum inductor peak current is calculated according to: I L( MAX ) I OUT I L 8 C OUT f SW I L( MAX ) VRIPPLE( ESL ) ( VIN VOUT ) 2 ESL ESL VIN L L The peak to peak inductor current, IL, is: Manufacturer specifications list both the inductor DC current rating, which is a thermal limitation, and the peak current rating, which is determined by the saturation characteristics. The inductor should not show any appreciable saturation under normal load conditions. I L VIN VOUT VOUT V IN L f SW The capacitive ripple and ESR ripple are phase shifted from each other. Depending on the type of output capacitor chemistry, one of them typically dominates. When ceramic capacitors are used that generally have low ESR, VRIPPLE(C) dominates. When electrolytic capacitors are used, VRIPPLE(ESR) dominates. The saturation current is a very important parameter for inductor selection. It must be more than the maximum peak current through the inductor – an adequate margin is important for a safe application. Use ceramic capacitors for low ESR and low ESL at the switching frequency of the converter. The ripple voltage due to ESL is negligible when using ceramic capacitors. Some inductors that meet the peak and average current rating requirements still result in excessive losses due to a high Direct Current Resistance (DCR). Always consider the losses associated with DCR and their effect on the total regulator efficiency when selecting an inductor. After a load step occurs, the output capacitor must support the difference between the load requirement and inductor current. Once the average inductor current increases to the DC load level, the output voltage recovers. Therefore, based on limitations in the ability to discharge the inductor, a minimum output voltage deviation may be determined by the following: Recommended inductors are listed in Table 6. Output Capacitor Selection The output capacitor limits the output ripple and provides current during large load transitions. A 22 F X5R or X7R ceramic capacitor typically provides sufficient bulk capacitance to stabilize the output during large load transitions and has the ESR and Equivalent Series Inductance (ESL) characteristics necessary for low output ripple. V SOAR( C ) I 2 OUT L 2 C OUT VOUT V SOAR( ESR ) I OUT ESR Where VSOAR is the output voltage overshoot and undershoot deviation. The key parameters for selecting the output capacitors are capacitance, ESR, ESL, and voltage ratings. Output ripple occurs due to variations in the charge stored in the output capacitor, the voltage drop due to the capacitor’s ESR, and the voltage drop due Table 6. Recommended Inductor Selection Manufacturer Part Number Inductance (H) Saturation Current (A) Temperature Current (A) Typical DCR (m) Size W L H (mm) Sumida 0520CDMCDS-1ROMC 1 8 5.9 17 5.75 5.45 2 Sumida 0420CDMCBDS-1R0MC 1 6.8 5.5 17 4.75 4.35 2 Wurth 74404063010 1 7.5 5.2 10 6 6 2.6 Toko FDSD0515-H-1R0M 1 8.7 6.1 25 5.2 4.9 1.5 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 12 October 27, 2014 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • 202456C DATA SHEET • SKY87203: STEP-DOWN DC-DC CONVERTER The ceramic output capacitor provides low ESR and low ESL, which results in low output ripple dominated by capacitive ripple voltage (VOUT(C)). However, due to the lower capacitance value, the load transient response is significantly worse. Therefore, ceramic output capacitors are generally recommended only for designs with soft load transients (slow di/dt and/or small load steps). Tantalum and electrolytic capacitors can provide a high capacitance, low-cost solution. The bulk capacitance provides minimal output voltage drop/soar after load transients occur. Input Capacitor Selection Typically, the input impedance is so low (or has other input capacitance distributed throughout the system) that a single 22 F (X7R or X5R) ceramic capacitor located near the SKY87203 is sufficient. However, additional input capacitance may be necessary depending on the impedance of the input supply. Always examine the ceramic capacitor DC voltage coefficient characteristics when evaluating ceramic bypass capacitors. Besides the capacitance requirement, the RMS current rating of the input capacitor must be able to support the pulsed current drawn by the step-down regulator. The input RMS current requirement may be determined by: VOUT V 1 OUT VIN VIN I RMS ( MAX ) I OUT 2 The input capacitor provides a low impedance loop for the pulsed current drawn by the SKY87203. Low ESR/ESL (X7R and X5R) ceramic capacitors are ideal for this function. To minimize stray inductance, the capacitor should be placed as close as possible to the high-side MOSFET. This keeps the high frequency content of the input current localized, minimizing EMI and input voltage ripple. The proper placement of the input capacitor can be seen in the Evaluation Board layout. Recommended input capacitors are listed in Table 7. Layout Recommendations Make the power trace as short and wide as possible, including the input/output power lines and switching node, etc. VOUT V 1 OUT VIN V D 1 D IN VPP VPP ESR f SW ESR f SW I I OUT OUT I RMS I OUT 1 V 4 PP ESR f SW I OUT For best performance of the SKY87203, the following guidelines should be followed when designing the PCB layout: To estimate the required input capacitance, determine the acceptable input ripple level (VPP) and solve the following equation: C IN C IN I OUT D 1 D The terms D and “1 – D” appear in both input ripple voltage and input capacitor RMS current equations. The maximum value for D occurs when VOUT = 0.5 × VIN (50 percent duty cycle). This results in a set of “worst case” capacitance and RMS current design requirements: While the two-layer PCB is enough for most applications, large and integral multilayer ground planes are ideal for high-power applications. Large areas of copper have lower resistance and help to dissipate heat. Put the input and output capacitor as close as possible to the IC to get the best filter result. Feedback and shutdown circuits should not be close to large AC signals involving the power inductor and switching node. Place the feedback resistors close to the output terminals. Connect the analog and power grounds together with a single short line. Connect all low-current loop grounds to analog ground to decrease the power ground noise on the analog ground and to achieve better load regulation. Table 7. Recommended Input/Output Capacitor Selection Manufacturer Part Number Capacitance (F) Voltage (V) Temperature Coefficient Case Murata GRM188R71H104KA93D 0.1 50.0 X7R 0603 Murate GRM21BR70J106ME76 10.0 6.3 X7R 0805 Murata GRM219R61A226MEA0 22.0 10.0 X5R 0805 Murate GRM1885C1H220JA01 22.0 50.0 C0G 0603 KEMET T520D477M006ATE025 470.0 6.3 ±20% Tol, –55 °C to +105 °C 7343 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202456C • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • October 27, 2014 13 DATA SHEET • SKY87203: STEP-DOWN DC-DC CONVERTER Evaluation Board Description Package and Handling Information The SKY87203 Evaluation Board is used to test the performance of the SKY87203 step-down DC-DC converter. An Evaluation Board schematic diagram is provided in Figure 26. Layer details for the SKY87203 Evaluation Board are shown in Figure 27. Component values for the SKY87203 Evaluation Board are listed in Table 8. Instructions on the shipping container label regarding exposure to moisture after the container seal is broken must be followed. Otherwise, problems related to moisture absorption may occur when the part is subjected to high temperature during solder assembly. Package Dimensions The PCB layout footprint for the SKY87203 is provided in Figure 28. Typical case markings for the SKY87203 are shown in Figure 29. Package dimensions for the 12-pin, 2 mm 2 mm QFN package are shown in Figure 30. Tape and reel dimensions are shown in Figure 31. The SKY87203 is rated to Moisture Sensitivity Level 1 (MSL1) at 260 C. It can be used for lead or lead-free soldering. For additional information, refer to the Skyworks Application Note, Solder Reflow Information, and document number 200164. Care must be taken when attaching this product, whether it is done manually or in a production solder reflow environment. Production quantities of this product are shipped in a standard tape and reel format. Switch Node SKY87203 10 Supply Voltage C1_1 Bulk Cap (optional) C1 22 μF R4 274 kΩ 8 C4 (optional) 1 μF Power Good VIN EN PG AGND 9 PVIN 4 LX OUT FB FSET PGND 1 2, 11 L1 1 μH C2 22 μF 6 R1 294 kΩ 7 Output Voltage 3.6 V C3 (optional) R2 57.6 kΩ 5 R3 (optional) 3, 12 t0284 Figure 26. SKY87203 Evaluation Board Schematic Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 14 October 27, 2014 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • 202456C DATA SHEET • SKY87203: STEP-DOWN DC-DC CONVERTER Top Layer Detailed View Bottom Layer t0593 Figure 27. SKY87203 Evaluation Board Assembly Drawing Table 8. Evaluation Board Bill of Materials (BOM) Component Value Part Number Manufacturer Description C1, C2 22 F GRM219R61A226MEA0 Murata Ceramic, 0805, X5R, 10 V, 20% R1 294 k RC0603FR-07294KL Yageo 1/10 W, 1%, 0603, SMD R2 57.6 k RC0603FR-07457K6L Yageo 1/10 W, 1%, 0603, SMD R4 274 k RC0603FR-07274KL Yageo 1/10 W, 1%, 0603, SMD L1 1 H 0520CDMCDS-1R0MC Sumida 8 A, 17 m, SMD Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202456C • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • October 27, 2014 15 DATA SHEET • SKY87203: STEP-DOWN DC-DC CONVERTER 8X 0.650 Pin 10 10X 0.450 10X 0.250 Pin 1 2X 0.125 4X 0.250 4X 0.750 2X 0.250 1.750 2X 0.650 Exposed soldering area 2X 0.500 4X 1.750 Notes: 1. All dimensions are in millimeters. 2. The suggested land pattern should be used as a guideline only. 3. The assembly house should use a land pattern that fits their SMT process and environment. 4. Some of the key factors that affect the land pattern and solder stencil aperture opening are solder paste size, solder stencil thickness, and reflow profile. t0587 Figure 28. SKY87203 PCB Layout Footprint Pin 1 Indicator Skyworks Part # t0293-2 Figure 29. SKY87203 Typical Case Markings (Top View) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 16 October 27, 2014 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • 202456C DATA SHEET • SKY87203: STEP-DOWN DC-DC CONVERTER 2X 0.500 ± 0.050 0.05 M C A B 4X 0.200 Min. 2 Pin 1 Indicator Chamfer 0.100 X 45° A B Pin 1 Indicator 2X 0.250 ± 0.050 0.05 M C A B 2 0.500 BSC 2X 0.200 Min. 0.05 C 2X 10X 0.350 ± 0.050 2X 10X 0.250 ± 0.050 0.10 M C A B 0.05 M C 0.05 C Bottom View Top View 0.050 C 0.850 ± 0.050 C Seating Plane 0.203 Ref. 0 – 0.05 0.080 C 10X Side View All measurements are in millimeters. S3183 Figure 30. SKY87203 12-Pin QFN Package Dimensions 4.0 ± 0.1 (P0) (Note 2) 2.0 ± 0.05 (P2) (Note 1) 1.75 ± 0.1 (E1) ø1.5 ± 0.1 (D0) X ø1.0 ± 0.25 (D1) CL X 2.30 ± 0.05 (Bo) 1.00 ± 0.05 (Ko) Y 8.00 +0.3/–0.1 Y 3.50 ± 0.05 (Note 1) 0.25 ± 0.02 (T) Pin1 Location Y 4.00 ± 0.1 (P1) 2.30 ± 0.05 (A0) 10° Max. Notes: 1. Measured from centerline of sprocket hole to centerline of pocket. 2. 10 sprocket hole pitch cumulative tolerance ±0.2. 3. ESD-surface resistivity is a maximum of 1 x 109 Ohms/square per EIA, JEDEC TNR Specification. 4. All measurements are in millimeters. CL X S3188 Figure 31. SKY87203 Tape and Reel Dimensions Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202456C • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • October 27, 2014 17 DATA SHEET • SKY87203: STEP-DOWN DC-DC CONVERTER Ordering Information Model Name SKY87203 Step-Down DC-DC Converter Manufacturing Part Number SKY87203-11-631LF Evaluation Board Part Number SKY87203-11-631LF-EVB Copyright © 2012-2014 Skyworks Solutions, Inc. All Rights Reserved. Information in this document is provided in connection with Skyworks Solutions, Inc. (“Skyworks”) products or services. These materials, including the information contained herein, are provided by Skyworks as a service to its customers and may be used for informational purposes only by the customer. Skyworks assumes no responsibility for errors or omissions in these materials or the information contained herein. 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