DATA SHEET SKY87201-11: Low Noise, Fast Transient 600 mA Step-Down Converter with Output Auto Discharge Applications Description Cellular phones The SKY87201-11 is a 2 MHz step-down converter with an input voltage range of 2.7 V to 5.5 V and output voltage as low as 0.6 V. It is optimized to react quickly to a load variation. The SKY8720111 incorporates a unique low-noise architecture that reduces ripple and spectral noise. Digital cameras Handheld instruments Microprocessor, DSP Core, I/O power PDAs and handheld computers USB devices Features Output auto discharge when disabled VIN range: 2.7 V to 5.5 V Low-noise, light-load mode Low ripple power management mode Output voltage adjustable from 0.6 V to VIN No load quiescent current: 37 μA Up to 98% efficiency Maximum output current: 600 mA Switching Frequency: 2 MHz Soft start: 150 μs The SKY87201-11 is programmable with external feedback resistors. It can deliver 600 mA of load current while maintaining a low 37 μA no-load quiescent current. The 2 MHz switching frequency minimizes the size of external components while keeping switching losses low. The SKY87201-11 is designed to maintain high efficiency throughout the operating range, which is critical for portable applications. The device has an output auto discharge feature. This enables the device to quickly discharge the output when the device is disabled (VEN = VIN to 0 V). The SKY87201-11 is provided in a small, 8-pin, 2 x 2 mm Thin Dual Flat No-Lead (STDFN) package. A typical application circuit diagram is provided in Figure 1. The pin configuration and package are shown in Figure 2. Signal pin assignment and functional pin descriptions are provided in Table 1. A functional block diagram is shown in Figure 3. Fast load transient Over-temperature protection Current limit protection 100% duty cycle low-dropout operation Shutdown current: <1 μA Available in an STDFN (8-pin, 2 x 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 201856G • Skyworks Proprietary Information • Products and Product Information Are Subject To Change Without Notice • October 9, 2013 1 DATA SHEET • SKY87201-11 LOW-NOISE STEP-DOWN CONVERTER L1 4.7 μH Input Supply Voltage 2.7 V ~ 5.5 V C1 4.7 μF VIN LX EN OUT AGND R1 118 kΩ Output Voltage 1.8 V C2 10 μF R2 59 kΩ PGND Figure 1. Typical Application Circuit Schematic N/C 1 8 EN N/C AGND PGND 2 7 3 6 OUT VIN 4 5 LX Figure 2. SKY87201-11 Pinout – 8-Pin STDFN Package (Top View) Table 1. SKY87201-11 Signal Descriptions Name Pin # N/C 1 Description Not connected. Name Pin # Description LX 5 Switching node. Connect an inductor to this pin, which is internally connected to the drain of both high- and lowside MOSFETs. N/C 2 Not connected. VIN 6 Input supply voltage for the converter. AGND 3 Non-power signal ground pin. OUT 7 Feedback input pin. This pin is connected to an external resistive divider. PGND 4 Main power ground return pin. Connect to the output and input capacitor return. EN 8 Enable pin Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 2 October 9, 2013 • Skyworks Proprietary Information • Products and Product Information Are Subject To Change Without Notice • 201856G DATA SHEET • SKY87201-11 LOW-NOISE STEP-DOWN CONVERTER VIN OUT Err Amp . DH Voltage Reference LX Logic DL EN INPUT PGND AGND S2945 Figure 3. SKY87201-11 Block Diagram Electrical and Mechanical Specifications The absolute maximum ratings of the SKY87201-11 are provided in Table 2. Electrical specifications are provided in Table 3. Typical performance characteristics of the SKY87201-11 are illustrated in Figures 4 to 25. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201856G • Skyworks Proprietary Information • Products and Product Information Are Subject To Change Without Notice • October 9, 2013 3 DATA SHEET • SKY87201-11 LOW-NOISE STEP-DOWN CONVERTER Table 2. Absolute Maximum Ratings (Note 1) Parameter Symbol Minimum Maximum Units +6.0 V Supply voltage GND VIN LX to GND VLX –0.3 VIN + 0.3 V OUT to GND VOUT –0.3 VIN + 0.3 V EN to GND VEN –0.3 VIN + 0.3 V Junction temperature TJ –40 +150 C Soldering temperature (@ leads, 10 sec) TLEAD +300 C Thermal resistance (Note 2) ΘJA 70 C/W Power dissipation (Note 2) (Note 3) PD 1.43 W Electrostatic Discharge: ESD 1500 4000 400 V V V Charged Device Model (CDM), Class 4 Human Body Model (HBM), Class 3A Machine Model (MM), Class C 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. Note 2: Mounted on an FR4 board. Note 3: Derate 14.3 mW/C above 25 C. 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. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 4 October 9, 2013 • Skyworks Proprietary Information • Products and Product Information Are Subject To Change Without Notice • 201856G DATA SHEET • SKY87201-11 LOW-NOISE STEP-DOWN CONVERTER Table 3. SKY87201-11 Electrical Characteristics (Note 1) (TA = –40 C to +85 C [Typical Values @ +25 C, VIN = 3.6 V], Unless Otherwise Noted) Parameter Symbol Test Conditions Minimum Typical Maximum Units 5.5 V 2.7 V Step-Down Converter Input voltage VIN Under Voltage Lockout threshold VUVLO 2.7 VIN rising 100 Hysteresis VIN falling 1.8 IOUT = 0 mA to 600 mA, VIN = 2.7 V to 5.5 V –3 Output voltage tolerance VOUT Output voltage range VOUT Quiescent current ICQ No load Shutdown current ISHDN EN = AGND = PGND P-channel current limit ILIM mV V +3 0.6 VIN 37 % V 70 μA 1 μA 800 mA High side switch on resistance RDS(ON)H 0.35 Ω Low side switch on resistance RDS(ON)L 0.30 Ω Line regulation ΔVLINEREG VIN = 2.7 V to 5.5 V, IOUT = 600 mA 0.1 %/V Output threshold voltage accuracy VOUT 0.6 V output, No load, TA = 25 C Output leakage current IOUT 0.6 V output Output impedance ROUT >0.6 V output Start-up time TS From enable to output regulation Oscillator frequency fOSC TA = 25 C Over-temperature shutdown threshold TSD 140 C Over-temperature shutdown hysteresis THYS 15 C 591 600 609 mV 0.2 μA kΩ 250 μs 150 0.9 2.0 2.6 MHz Enable Enable threshold low VEN(L) Enable threshold high VEN(H) 0.6 1.4 Input low current IEN VIN = VOUT = 5.5 V Output discharge time TDISCHARGE VIN = 3.0 V to 5.5 V, VEN = VIN to 0 V, VOUT = 3.0 V to 0.4 V, L = 4.7 μH COUT = 22 μF –1 V V +1 μA 25 ms Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201856G • Skyworks Proprietary Information • Products and Product Information Are Subject To Change Without Notice • October 9, 2013 5 DATA SHEET • SKY87201-11 LOW-NOISE STEP-DOWN CONVERTER Typical Performance Characteristics (TA = +25 °C, Unless Otherwise Noted) 1 100 0.8 80 70 60 50 VIN = 2.7V VIN = 3.6V VIN = 4.2V 40 30 0.1 Output Error (%) Efficiency (%) 90 0.6 0.4 0.2 0 -0.2 -0.4 VIN = 2.7V VIN = 3.6V VIN = 4.2V -0.6 -0.8 -1 1 10 100 1000 0.1 1 Output Current (mA) 100 1 90 0.8 80 70 60 VIN = 3V VIN = 3.6V VIN = 4.2V VIN = 5V 40 30 0.1 1 10 100 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1 0.1 1000 1 0.8 80 70 60 VIN = 3.6V VIN = 4.2V VIN = 5V 10 100 Output Current (mA) Figure 8. Efficiency vs Output Current (VOUT = 3.3 V) 1000 Output Error (%) Efficiency (%) 1 90 1 100 VIN = 3.6V VIN = 4.2V VIN = 5V 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1 0.1 1 10 100 Output Current (mA) Figure 9. Load Regulation (VOUT = 3.3 V) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 6 1000 Figure 7. Load Regulation (VOUT = 2.5 V) 100 30 0.1 10 Output Current (mA) Figure 6. Efficiency vs Output Current (VOUT = 2.5 V) 40 1000 VIN = 3V VIN = 3.6V VIN = 4.2V VIN = 5V 0.6 Output Current (mA) 50 100 Figure 5. Load Regulation (VOUT = 1.8 V) Output Error (%) Efficiency (%) Figure 4. Efficiency vs Output Current (VOUT = 1.8 V) 50 10 Output Current (mA) October 9, 2013 • Skyworks Proprietary Information • Products and Product Information Are Subject To Change Without Notice • 201856G 1000 DATA SHEET • SKY87201-11 LOW-NOISE STEP-DOWN CONVERTER 1mA 400mA 600mA 0.4 0.3 Accuracy (%) Switching Frequency (MHz) 0.5 0.2 0.1 0 -0.1 -0.2 -0.3 -0.4 -0.5 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 2.08 2.06 2.04 2.02 2 1.98 1.96 1.94 1.92 -40 -15 10 Input Voltage (V) Figure 10. Line Regulation (VOUT = 1.8 V) 85 2.0 Output Voltage Error (%) Frequency Variation (%) 60 Figure 11. Switching Frequency vs Temperature (VOUT = 1.8 V, IOUT = 1 A) 4 3 2 1 0 -1 -2 VOUT = 1.8V VOUT = 3V -3 -4 2.7 3.1 3.5 3.9 4.3 4.7 5.1 1.0 0.0 -1.0 -2.0 -40 5.5 -20 0 Input Voltage (V) 40 60 80 100 Figure 13. Output Voltage Error vs Temperature (VIN= 3.6 V, VOUT = 1.8 V, IOUT = 400 mA) 60 550 55 120°C 100°C 85°C 25°C 500 50 RDS(ON) (mΩ Ω) 45 40 35 30 25 85°C 25C -40°C 20 15 10 2.7 20 Temperature (°C) Figure 12. Frequency Variation vs Input Voltage Supply Current (µA) 35 Input Voltage (V) 3.1 3.5 3.9 4.3 4.7 5.1 450 400 350 300 250 5.5 Input Voltage (V) Figure 14. No Load Quiescent Current vs Input Voltage (VOUT = 1.8 V) 200 2.5 3 3.5 4 4.5 5 5.5 6 Input Voltage (V) Figure 15. P-Channel RDS(ON) vs Input Voltage Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201856G • Skyworks Proprietary Information • Products and Product Information Are Subject To Change Without Notice • October 9, 2013 7 DATA SHEET • SKY87201-11 LOW-NOISE STEP-DOWN CONVERTER 1.9 RDS(ON) (mΩ Ω) 450 Output Voltage (top) (V) 120°C 100°C 85°C 25°C 500 400 350 300 250 200 2.5 1.8 1.7 300mA 1.6 1mA 1.5 1.4 1.3 300mA 1.2 1mA 1.1 3 3.5 4 4.5 5 5.5 6 Output and Inductor Current (100mA/div) 550 Time (50µs/div) Input Voltage (V) Output Voltage (top) (V) 1.75 1.7 400mA 300mA 1.65 1.6 400mA 1.55 300mA 1.5 1.85 1.8 1.75 1.7 300mA Time (50µs/div) Figure 19. Load Transient (VIN= 3.6 V, VOUT = 1.8 V, COUT = 10 μF, CFF = 0 pF) 1.7 300mA 1.65 300mA 400mA 1.5 Time (50µs/div) Figure 20. Load Transient (VIN= 3.6 V, VOUT = 1.8 V, COUT = 10 μF, CFF = 100 pF) Input Voltage (top) (V) Output Voltage (top) (V) 1.75 4.8 1.92 4.2 1.9 3.6 1.88 3 1.86 2.4 1.84 1.8 1.82 1.2 1.8 0.6 1.78 0 1.76 Time (50µs/div) Figure 21. Line Transient (VOUT= 1.8 V, VIN = 3.6 V to 4.2 V, IOUT = 400 mA, CFF = 0 pF) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 8 Output Voltage (bottom) (V) 1.8 Output and Inductor Current (100mA/div) 1.85 1.55 400mA 1.5 Figure 18. Load Transient (VIN= 3.6 V, VOUT = 1.8 V, COUT = 4.7 μF, CFF = 0 pF) 1.6 300mA 1.6 1.55 Time (50µs/div) 400mA 400mA 1.65 Output and Inductor Current (100mA/div) 1.8 Output and Inductor Current (100mA/div) 1.85 Figure 17. Load Transient (VIN= 3.6 V, VOUT = 1.8 V, COUT = 10 μF, CFF = 100 pF) Output Voltage (top) (V) Figure 16. N-Channel RDS(ON) vs Input Voltage October 9, 2013 • Skyworks Proprietary Information • Products and Product Information Are Subject To Change Without Notice • 201856G 0.35 0.01 0.3 -0.01 0.2 -0.02 0.15 -0.03 0.1 -0.04 0.05 -0.05 0 -0.06 -0.05 1 -0.01 0.8 -0.02 0.6 -0.03 0.4 -0.04 0.2 -0.05 0 -0.2 Time (200ns/div) 4 3 2 1 0 0.5 0 -0.5 Figure 23. Output Ripple (VOUT= 1.8 V, VIN = 3.6 V, IOUT = 400 mA, CFF = 0 pF) Input Current (bottom) (A) Enable Voltage (top) (V) Output Voltage (middle) (V) 1.2 -0.06 Figure 22. Output Ripple (VOUT= 1.8 V, VIN = 3.6 V, IOUT = 1 mA, CFF = 0 pF) Figure 24. Soft Start (VIN= 3.6 V, VOUT = 1.8 V, IOUT = 400 mA) 1.4 0.01 0 Time (10µs/div) Time (100µs/div) 0.02 Inductor Current (bottom) (A) 0.25 0 Output Voltage (top) (V) 0.02 Inductor Current (bottom) (A) Output Voltage (top) (V) DATA SHEET • SKY87201-11 LOW-NOISE STEP-DOWN CONVERTER EN 2V/div VOUT 2V/div 4ms/div Figure 25. Discharge Time (CIN= 2.2 μF, COUT = 2.2 μF, L = 4.7 μH, R1 = 236 kΩ, R2 = 59 kΩ) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201856G • Skyworks Proprietary Information • Products and Product Information Are Subject To Change Without Notice • October 9, 2013 9 DATA SHEET • SKY87201-11 LOW-NOISE STEP-DOWN CONVERTER Functional Description The SKY87201-11 is a high performance, 600 mA, 2 MHz monolithic step-down converter. It has been designed to minimize external component size and optimize efficiency over the complete load range with reduced ripple and spectral noise. Apart from the small bypass input capacitor, only a small L-C filter is required at the output. Typically, a 4.7 μH inductor is recommended for a 1.8 V output converter (see Table 4). The SKY87201-11 can be programmed with external feedback to any voltage, ranging from 0.6 V to the input voltage (VIN). An additional feed-forward capacitor can also be added to the external feedback loop to provide improved transient response. At dropout, the converter duty cycle increases to 100 percent and the output voltage tracks the input voltage minus the RDS(ON) drop of the P-channel high-side MOSFET. The input voltage range is 2.7 V to 5.5 V. The converter efficiency has been optimized for all load conditions, ranging from no load to 600 mA. constant output voltage for all load and line conditions. Internal loop compensation terminates the transconductance voltage error amplifier output. Soft Start/Enable Soft start limits the current surge seen at the input and eliminates output voltage overshoot. When pulled low, the enable input forces the SKY87201-11 into a low-power, non-switching state. The total input current during shutdown is less than 1 μA. Current Limit and Over-Temperature Protection For overload conditions, the peak input current is limited. To minimize power dissipation and stresses under current limit and short-circuit conditions, switching is terminated after entering current limit for a series of pulses. Switching is terminated for seven consecutive clock cycles after a current limit has been sensed for a series of four consecutive clock cycles. The internal error amplifier and compensation provides excellent transient response, load, and line regulation. Soft start eliminates any output voltage overshoot when the enable or the input voltage is applied. Thermal protection completely disables switching when internal dissipation becomes excessive. The junction over-temperature threshold is 140 °C with 15 °C of hysteresis. Once an overtemperature or over-current fault condition is removed, the output voltage automatically recovers. Control Loop Under-Voltage Lockout The SKY87201-11 is a peak current mode step-down converter. The current through the P-channel MOSFET (high side) is sensed for current loop control, as well as short circuit and overload protection. A fixed slope compensation signal is added to the sensed current to maintain stability for duty cycles greater than 50 percent. The peak current mode loop appears as a voltageprogrammed current source in parallel with the output capacitor. Internal bias of all circuits is controlled using the the VIN input. Under-Voltage Lockout (UVLO) guarantees sufficient VIN bias and proper operation of all internal circuitry before activation. The output of the voltage error amplifier programs the current mode loop for the necessary peak switch current to force a Output Auto Discharge When the SKY87201-11 is disabled (VEN =VIN to 0 V), the output is quickly discharged (refer to Figure 26). LX 150Ω EN PGND Figure 26. Output Auto Discharge Circuit Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 10 October 9, 2013 • Skyworks Proprietary Information • Products and Product Information Are Subject To Change Without Notice • 201856G DATA SHEET • SKY87201-11 LOW-NOISE STEP-DOWN CONVERTER Evaluation Board Layout 3. The feedback trace or OUT pin should be separate from any power trace and connected as close as possible to the load point. Sensing along a high-current load trace degrades DC load regulation. If external feedback resistors are used, they should be placed as close as possible to the OUT pin to minimize the length of the high impedance feedback trace. The SKY87201-11 Evaluation Board is used to test the performance of the SKY87201-11 Step-Down Converter. An Evaluation Board schematic diagram is provided in Figure 27. Component values for the SKY87201-11 Evaluation Board are listed in Table 4. Typical surface mount inductors and capacitors are listed in Tables 5 and 6, respectively. Table 7 provides the Bill of Materials (BOM) for Evaluation Board components. 4. The resistance of the trace from the load return to PGND should be kept to a minimum. This helps to minimize any error in DC regulation due to differences in the potential of the internal signal ground and the power ground. A high density, small footprint layout can be achieved using an inexpensive, miniature, non-shielded, high DCR inductor. The suggested PCB layout for the SKY87201-11 is shown in Figures 28 and 29. The following guidelines should be used to help ensure a proper layout. 1. The input capacitor (C1) should connect as close as possible to VIN and PGND. 2. C2 and L1 should be connected as close as possible. The connection of L1 to the LX pin should be as short as possible. Input Voltage 6 8 × C1 4.7 μF 1 4 VIN LX EN OUT N/C N/C AGND PGND Output Voltage 5 L1 4.7 μH 7 2 R1 118 kΩ × C3 DNI C2 4.7 μF 3 R2 59 kΩ GND GND VIN JP1 1 2 3 EN GND GND Figure 27. SKY87201-11 Evaluation Board Schematic Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201856G • Skyworks Proprietary Information • Products and Product Information Are Subject To Change Without Notice • October 9, 2013 11 DATA SHEET • SKY87201-11 LOW-NOISE STEP-DOWN CONVERTER Table 4. Evaluation Board Component Values VOUT (V) R2 = 59 kΩ R1 (kΩ) R2 =221 kΩ R1 (kΩ) L1 (μH) 0.80 19.6 75.0 2.2 0.90 29.4 113 2.2 1.00 39.2 150 2.2 1.10 49.9 187 2.2 1.20 59.0 221 2.2 1.30 68.1 261 2.2 1.40 78.7 301 4.7 1.50 88.7 332 4.7 1.80 118.0 442 4.7 1.85 124.0 464 4.7 2.00 137.0 523 6.8 2.50 187.0 715 6.8 3.30 267.0 1000 6.8 Table 5. Typical Surface Mount Inductors Max DC Current (A) DCR (Ω) CDRH3D16-2R2 2.2 1.20 0.072 3.8x3.8x1.8 Shielded CDRH3D16-4R7 4.7 0.90 0.105 3.8x3.8x1.8 Shielded Part # Sumida Coiltronics Type Inductance (μH) Manufacturer Size, lxwxh (mm) CDRH3D16-6R8 6.8 0.73 0.170 3.8x3.8x1.8 Shielded SD3118-4R7 4.7 0.98 0.122 3.1x3.1x1.85 Shielded SD3118-6R8 6.8 0.82 0.175 3.1x3.1x1.85 Shielded VLS3015T-4R7MR99 4.7 0.99 0.136 3.0x3.0x1.5 Shielded VLS3015T-6R8MR86 6.8 0.86 0.176 3.0x3.0x1.5 Shielded Wurth 744042006 6.8 1.25 0.100 4.8x4.8x1.8 Shielded Taiyo Yuden MAKK2016T4R7M 4.7 1.20 0.308 2.0x1.6x1.0 Shielded TDK Table 6. Surface Mount Capacitors Manufacturer Murata Part # Value (μF) Voltage (V) Temp. Coefficient Case GRM219R61A475KE19 4.7 10 X5R 0805 GRM21BR60J106KE19 10 6.3 X5R 0805 GRM188R60J475KE19 4.7 6.3 X5R 0603 GRM219R61A106KE44 10 10 X5R 0805 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 12 October 9, 2013 • Skyworks Proprietary Information • Products and Product Information Are Subject To Change Without Notice • 201856G DATA SHEET • SKY87201-11 LOW-NOISE STEP-DOWN CONVERTER Table 7. Evaluation Board Bill of Materials (STDFN Package) Component C1, C2 Part Number GRM188R60J475KE19 Manufacturer Murata Description Ceramic capacitors, 4.7 μF, 0603, X5R, 6.3 V, 10% L1 CDRH3D16-4R7 Sumida 4.7 μH inductor, 105 mΩ, 0.9 A, 20% R1 RC0603FR-0759KL Yageo 59 kΩ resistor, 1/10 W, 1%, 0603, SMD R2 RC0603FR-07118KL Yageo 118 kΩ resistor, 1/10 W, 1%, 0603, SMD Figure 28. SKY87201-11 Evaluation Board Component Side Layout Figure 29. SKY87201-11 Evaluation Board Solder Side Layout Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201856G • Skyworks Proprietary Information • Products and Product Information Are Subject To Change Without Notice • October 9, 2013 13 DATA SHEET • SKY87201-11 LOW-NOISE STEP-DOWN CONVERTER Application Information C IN Inductor Selection The step-down converter uses peak current mode control with slope compensation to maintain stability for duty cycles greater than 50 percent. The output inductor value must be selected so the inductor current down-slope meets the internal slope compensation requirements. The internal slope compensation of the SKY87201-11 is 0.24 A/μs (see Equation 1). This equates to a slope compensation that is 75 percent of the inductor current down-slope for a 1.5 V output and 4.7 μH inductor. 0.75 Vo 0.75 1.5 V m 0.24 A / s L 4.7 H 0.75 Vo 0.75 Vo 3 s / A Vo m 0.24 A / s (2) 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. Some inductors may meet the peak and average current ratings yet result in excessive losses due to a high Direct Current Resistance (DCR). Always consider the losses associated with DCR and the affect on the total converter efficiency when selecting an inductor. The 4.7 μH CDRH3D16 series inductor selected from Sumida has a 105 mW DCR and a 900 mA DC current rating. At full load, the inductor DC loss is 17 mW, which gives a 2.8 percent loss in efficiency for a 400 mA, 1.5 V output. Input Capacitor Select a 2.2 μF to 10 μF X7R or X5R ceramic capacitor for the input. To estimate the required input capacitor size, determine the acceptable input ripple level (VPP) and solve for CIN (see Equations 3, 4, and 5). The calculated value varies with input voltage and is a maximum when VIN is double the output voltage. 1 for V IN 2 VO 4 VO V 1 O V IN V IN For VIN = 2 × VO: (3) (4) IO 2 The term VO/VIN x (1 – VO/VIN) appears in both the input voltage ripple and input capacitor RMS current equations and is a maximum when VO is twice VIN. This is why the input voltage ripple and the input capacitor RMS current ripple are a maximum at a 50 percent duty cycle. The input capacitor provides a low impedance loop for the edges of pulsed current drawn by the SKY87201-11. Low ESR/ESL X7R and X5R ceramic capacitors are ideal for this function. To minimize stray inductance, the capacitor should be placed as closely as possible to the device. This keeps the high frequency content of the input current localized, minimizing EMI and input voltage ripple. The proper placement of the input capacitor (C1) can be seen in the Evaluation Board layout in Figure 28. A laboratory test setup typically consists of two long wires running from the bench power supply to the Evaluation Board input voltage pins. The inductance of these wires, along with the lowESR ceramic input capacitor, can create a high Q network that may affect converter performance. This problem often becomes apparent in the form of excessive ringing in the output voltage during load transients. Errors in the loop phase and gain measurements can also result. Since the inductance of a short PCB trace feeding the input voltage is significantly lower than the power leads from the bench power supply, most applications do not exhibit this problem. In applications where the input power source lead inductance cannot be reduced to a level that does not affect the converter performance, a high ESR tantalum or aluminum electrolytic should be placed in parallel with the low ESR/ESL bypass Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 14 (6) 1 D 1 D 0.5 2 2 I RMS ( MAX ) Table 4 displays inductor values for the SKY87201-11. Vo V 1 o V IN VIN I RMS I O VO V 1 O V IN V IN In this case, a standard 6.8 μH values is selected. C IN The maximum input capacitor RMS current is calculated using Equation 6: The input capacitor RMS ripple current varies with the input and output voltage and is always less than or equal to half of the total DC load current as follows: 3 s / A 2.5 V 7.5 H Vo V 1 O V IN V IN V PP I ESR FS O (5) Always examine the ceramic capacitor DC voltage coefficient characteristics when selecting the proper value. For example, the capacitance of a 10 μF, 6.3 V, X5R ceramic capacitor with 5.0 V DC applied is actually about 6 μF. (1) This is the internal slope compensation for the SKY87201-11. When externally programming the output voltage to 2.5 V, the calculated inductance is 7.5 μH (from Equation 2). L 1 V PP I ESR 4 FS O October 9, 2013 • Skyworks Proprietary Information • Products and Product Information Are Subject To Change Without Notice • 201856G DATA SHEET • SKY87201-11 LOW-NOISE STEP-DOWN CONVERTER ceramic. This dampens the high Q network and stabilizes the system. Output Capacitor The output capacitor limits the output ripple and provides holdup during large load transitions. A 4.7 μF to 10 μF X5R or X7R ceramic capacitor typically provides sufficient bulk capacitance to stabilize the output during large load transitions and has the ESR and ESL characteristics necessary for low output ripple. The output voltage droop due to a load transient is dominated by the capacitance of the ceramic output capacitor. During a step increase in load current, the ceramic output capacitor alone supplies the load current until the loop responds. Within two or three switching cycles, the loop responds and the inductor current increases to match the load current demand. The relationship of the output voltage droop during the three switching cycles to the output capacitance can be estimated by Equation 7: COUT 3 I LOAD V DROOP FS (7) Once the average inductor current increases to the DC load level, the output voltage recovers. Equation 7 establishes a limit on the minimum value for the output capacitor with respect to load transients. The internal voltage loop compensation also limits the minimum output capacitor value to 4.7 μF. This is due to its effect on the loop crossover frequency (bandwidth), phase margin, and gain margin. Increased output capacitance reduces the crossover frequency with greater phase margin. The maximum output capacitor RMS ripple current is given by Equation 8: I RMS ( MAX ) 1 2 3 VOUT VIN ( MAX ) VOUT L F VIN ( MAX ) (8) Dissipation due to the RMS current in the ceramic output capacitor ESR is typically minimal, resulting in less than a few degrees rise in hot-spot temperature. Adjustable Output Resistor Selection For applications that require an adjustable output voltage, the SKY87201-11 can be externally programmed. Resistors R1 and R2 shown in the schematic diagram (see Figure 27) program the output to regulate at a voltage higher than 0.6 V. To limit the bias current required for the external feedback resistor string while maintaining good noise immunity, the minimum suggested value for R2 is 59 kΩ (see Equation 9). Although a larger value will further reduce quiescent current, it will also increase the impedance of the feedback node, making it more sensitive to external noise and interference. Table 8 summarizes the resistor values for various output voltages with R2 set to either 59 kΩ for good noise immunity or 221 kΩ for reduced, no-load input current. V 1.5 V R1 OUT 1 R 2 1 59 k 88.5 k V 0 . 6 V REF (9) The SKY87201-11, combined with an external feed-forward capacitor (C3 in Figure 27), delivers enhanced transient response for extreme pulsed load applications. The addition of the feedforward capacitor typically requires a larger C2 output capacitor for stability. Thermal Calculations There are three types of losses associated with the SKY87201-11 step-down converter: switching losses, conduction losses, and quiescent current losses. Conduction losses are associated with the RDS(ON) characteristics of the power output switching devices. Switching losses are dominated by the gate charge of the power output switching devices. At full load, assuming Continuous Conduction Mode (CCM), a simplified form of the losses is given by Equation 10: PTOTAL I O 2 ( RDSON ( HS ) VO RDSON ( LS ) [ VIN VO ]) VIN (10) ( t SW F I O I Q ) VIN Where IQ is the step-down converter quiescent current. The term tSW is used to estimate the full load step-down converter switching losses. For the condition where the step-down converter is in dropout at 100 percent duty cycle, the total device dissipation reduces to: PTOTAL I O 2 RDSON ( HS ) I Q VIN Since RDS(ON), the quiescent current, and switching losses all vary with input voltage, the total losses should be investigated over the complete input voltage range. Given the total losses, the maximum junction temperature can be derived from the thermal resistance (ΘJA), which is 70 °C/W as shown by Equation 11: TJ ( MAX ) PTOTAL JA TA (11) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201856G • Skyworks Proprietary Information • Products and Product Information Are Subject To Change Without Notice • October 9, 2013 15 DATA SHEET • SKY87201-11 LOW-NOISE STEP-DOWN CONVERTER Table 8. Resistor Selection for Different Output Voltage Settings VOUT (V) R2 = 59 kΩ R2 = 221 kΩ R1 (kΩ) R1 0.80 19.6 75K 0.90 29.4 113K 1.00 39.2 150K 1.10 49.9 187K 1.20 59.0 221K 1.30 68.1 261K 1.40 78.7 301K 1.50 88.7 332K 1.80 118.0 442K 1.85 124.0 464K 2.00 137.0 523K 2.50 187.0 715K 3.30 267.0 1.00M Step-Down Converter Design Example I RMS Specifications VO = 1.8 V @ 400 mA (adjustable using 0.6 V version), pulsed load ΔILOAD = 300 mA VIN = 2.7 V to 4.2 V (3.6 V nominal) 1 2 3 1 2 3 VOUT V IN ( MAX ) VOUT L1 F V IN ( MAX ) 1.8 V 4.2 V 1.8 V 32 mArms 4.7 H 2.0 MHz 4.2 V Pesr esr I RMS 2 5 m 32 mA2 6 W FS = 2 MHz TA = 85 °C Input Capacitor Input ripple VPP = 25 mV 1.8 V Output Inductor L1 = 3 μs/A x VO2 = 3 μs/A x 1.8 V = 5.4 μH (use 4.7 μH, see Table 4) C IN 1 1 2.17 F V PP 25 mV 4 FS 4 2.0 MHz 5 m ESR 0.4 A I O For Sumida inductor CDRH3D16, 4.7 μH, DCR = 105 mΩ I L1 V VO 1 O VIN L1 FS I PKL1 I O 1.8 V 1.8 V 4.7 H 2.0 MHz 1 4.2 V I L1 2 109 mA 0.4 A 0.055 A 0.455 A PL1 I O 2 DCR 0.4 A 2 105 m 17 mW VDROOP = 0.1 V 3 I LOAD 3 0.3 A 4.5 F V DROOP FS 0.1V 2 MHz (use 2.2 μF) I RMS IO 0.2 Arms 2 Pesr esr I RMS 2 5 m 0.2 A2 0.2 mW SKY87201-11 Losses PTOTAL 1.8 V Output Capacitor COUT I O 2 ( RDSON ( HS ) VO RDSON ( LS ) [ VIN VO ]) VIN ( t sw F I O I Q ) VIN (use 4.7 μF) 0.4 2 ( 0.725 1.8 V 0.7 [ 4.2 V 1.8 V ] 4.2 V ( 5 ns 2.0 MHz 0.4 A 70 A ) 4.2 V 131 mW T J ( MAX ) T A JA PLOSS 85 o C 70 o C / W 131 mW 94.2 o C Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 16 October 9, 2013 • Skyworks Proprietary Information • Products and Product Information Are Subject To Change Without Notice • 201856G DATA SHEET • SKY87201-11 LOW-NOISE STEP-DOWN CONVERTER Package and Handling Information 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. The SKY87201-11 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, document number 200164. Production quantities of this product are shipped in a standard tape and reel format. Package Dimensions Typical case markings are shown in Figure 30. Package dimensions for the 8-pin STDFN package are shown in Figure 31. Tape and reel dimensions are provided in Figure 32. Care must be taken when attaching this product, whether it is done manually or in a production solder reflow environment. Pin 1 Indicator Skyworks Part # Figure 30. Typical Case Markings (Top View) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 17 October 9, 2013 • Skyworks Proprietary Information • Products and Product Information Are Subject To Change Without Notice • 201856G DATA SHEET • SKY87201-11 LOW-NOISE STEP-DOWN CONVERTER 0.90 +0.10/–0.15 C 2 0.20 Ref Seating Plane A B 0.45 +0.05/–0.07 Exposed Pad Detail A 0.02 +0.03/–0.02 Pin 1 Indicator -B- 2 0.15 C 2X 8X 3 0.85 +0.05/–0.07 Detail C 0.08 C 0.15 C 2X 1.70 +0.10/–0.15 Detail B 2 Places 0.55 + 0.05/–0.04 0.10 C Top View Side View Bottom View R0.12 Typ 0.25 0.30 ± 0.10 -A- 0.25 +0.05/–0.07 CL R0.20 Pin 1 Indicator 0.5 5 0.10 M C A B 0.05 M C Detail C Scale: 40x 8 Places Detail B Detail A Scale: 20x Scale: 10x All measurements are in millimeters. Dimensioning and tolerancing according to ASME Y14.5M-1994. Coplanarity applies to the exposed heat sink slug as well as the terminals.. Dimension applies to metalized terminal and is measured between 0.15 mm and 0.30 mm from terminal tip. S1945a Figure 33. SKY87201-11 8-Pin STDFN Package Dimensions 4.0 ± 0.1 2.00 ± 0.05 1.5 ± 0.1 3.50 ± 0.05 1.75 ± 0.1 2.3 ± 0.1 0.29 ± 0.06 2.3 ± 0.1 4.0 ± 0.1 Pin 1 Indicator S3093 Figure 34. SKY87201-11 Tape and Reel Dimensions Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 18 October 9, 2013 • Skyworks Proprietary Information • Products and Product Information Are Subject To Change Without Notice • 201856G 8.1 ± 0.2 0.75 ± 0.1 DATA SHEET • SKY87201-11 LOW-NOISE STEP-DOWN CONVERTER Ordering Information Model Name SKY87201-11 Low-Noise, Step-Down Converter with Output Auto Discharge Manufacturing Part Number SKY87201-11-370LF Evaluation Board Part Number SKY87201-11-370LF-EVB Copyright © 2012 Skyworks Solutions, Inc. All Rights Reserved. Information in this document is provided in connection with Skyworks Solutions, Inc. 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Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201856G • Skyworks Proprietary Information • Products and Product Information Are Subject To Change Without Notice • October 9, 2013 19