DATA SHEET SKY87250: 400 mA Low-Noise Step-Down Converter in a Micro-Inductor Package Applications Description Bluetooth headsets The SKY87250 SwitcherTM step-down converter delivers up to 400 mA to support an adjustable 0.6 V to VIN output from 2.7 V to 5.5 V input supply. Its low supply current, small size, and high switching frequency make the SKY87250 the ideal choice for portable applications. ® Cellular phones Digital cameras Hard disk drives PDAs and handheld computers Portable media and MP3 players USB devices Features VIN range: 2.5 V to 5.5 V Adjustable output voltage: 0.6 V to VIN Output current: 400 mA Up to 95% efficiency Low-noise, light-load architecture No load quiescent current: 40 A Switching frequency: 2.0 MHz Internal soft-start control Over-temperature and current-limit protection The SKY87250 maintains a low 40 A no-load quiescent current. The 2.0 MHz switching frequency minimizes the output capacitance requirement while keeping switching losses low. The SKY87250 feedback and control delivers excellent load regulation and transient response with a small output capacitor. The SKY87250 maintains high efficiency throughout the load range. The unique low-noise, light-load architecture produces reduced ripple and spectral noise. Over-temperature and shortcircuit protection safeguards the SKY87250 and system components from damage. The ultra-small, 8-pin, 2.4 2.4 mm DLN package footprint, integrated inductor, and minimal capacitance requirements, make the SKY87250 ideal for compact designs. Figure 1 shows the typical application circuit size comparison. A typical application circuit is shown in Figure 2. The pin configuration is shown in Figure 3. Signal pin assignments and functional pin descriptions are provided in Table 1. Shutdown current: <1 A Small 4.7 F output capacitor Temperature range: 40 C to +85 C Compact integrated micro-inductor (inductor) DLN (8-pin, 2.4 × 2.4 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. tc74 Figure 1. Typical Application Circuit Size Comparison Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201922E • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • January 6, 2015 1 DATA SHEET • SKY87250: 400 mA LOW-NOISE STEP-DOWN CONVERTER IN A MICRO-INDUCTOR PACKAGE VIN 2.7 V to 5.5 V U1 1 VOUT 5 OUT VP R1 adj 2 VIN C1 4.7 μF 4 FB R2 59 kΩ SKY87250 6 EN ON/OFF 8 N/C 3 GND C2 4.7 μF 7 PGND tc64 Figure 2. SKY87250 Typical Application Circuit VP 1 8 N/C VIN 2 7 GND FB 3 6 PGND EN 4 5 OUT tc65 Figure 3. SKY87250 8-Pin DLN (Top View) Table 1. SKY87250 Signal Descriptions Pin Name Description 1 VP Input power pin; connect to the source of the P-channel MOSFET. Connect to the input capacitor. 2 VIN Input bias voltage for the converter. 3 GND Non-power signal ground pin. 4 FB Feedback input pin. Connect this pin to an external resistive divider for adjustable output. 5 OUT DC-DC converter output. 6 EN Enable pin. A logic high enables normal operation. A logic low shuts down the converter. 7 PGND Power ground. Input power return pin; connect to the source of the N-channel MOSFET. Connect to the output and input capacitor return. 8 N/C Not internally connected. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 2 January 6, 2015 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • 201922E DATA SHEET • SKY87250: 400 mA LOW-NOISE STEP-DOWN CONVERTER IN A MICRO-INDUCTOR PACKAGE Electrical and Mechanical Specifications The absolute maximum ratings and thermal information of the SKY87250 are provided in Tables 2 and 3, respectively. Electrical specifications are provided in Table 4. Typical performance characteristics of the SKY87250 are illustrated in Figures 4 through 33. Table 2. SKY87250 Absolute Maximum Ratings (Note 1) Parameter Symbol Minimum Typical Maximum Units VIN, VP 0.3 +6.0 V FB to GND VFB 0.3 VIN + 0.3 V EN to GND VEN 0.3 VIN + 0.3 V AGND to PGND VGND 0.3 +0.3 V OUT RMS current capability IOUT Input voltage and bias power to PGND 1 A 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 may result in permanent damage to the device. Table 3. SKY87250 Thermal Information Parameter Symbol Minimum Typical Maximum Units TA 40 +85 °C Operating junction temperature TJ 40 +150 °C Maximum soldering temperature (at leads, 10 seconds) TLEAD 300 °C Maximum power dissipation (Note 1, Note 2, Note 3) PD 790 mW Maximum junction-to-ambient thermal resistance (Note 1, Note 3) JA 158 °C/W Ambient temperature Note 1: Mounted on FR4 circuit board. Two-layer, 1 ounce copper. Note 2: Derate 6.3 mW/C above 40 C ambient temperature. Note 3: The thermal resistance is measured in accordance with EIA/JESD 51 series. 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 201922E • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • January 6, 2015 3 DATA SHEET • SKY87250: 400 mA LOW-NOISE STEP-DOWN CONVERTER IN A MICRO-INDUCTOR PACKAGE Table 4. SKY87250 Electrical Specifications (Note 1) (CIN = 4.7 F, COUT = 4.7 F , VIN = VP = 3.6 V, VEN = VIN, GND = PGND, TA = –40 °C to 85 °C [Typical Values are at TA = 25 °C], Unless Otherwise Noted) Parameter Symbol Test Condition VP, VIN Min Input voltage VIN Output voltage VOUT Maximum continuous output current capability IOUT No load supply current IQ No load current; not switching Shutdown current ISHDN EN = GND Input under-voltage lockout VUVLO VCC rising VIN = 2.7 V to 5.5 V, 10 mA load, TA = 25 °C 588 FB regulation threshold VFB VIN = 2.7 V to 5.5 V, 10 mA load, TA = –40 °C to 85 °C 582 IFB VFB = 1 V Line regulation ∆VOUT/VOUT VIN = 2.7 V to 5.5 V Load regulation ∆VOUT/VOUT 10 mA to 400 mA load Oscillator frequency fOSC On-time resistance RTON Off-time resistance Max 5.5 V 0.6 VIN V 400 40 mA 100 A 1.0 A 1.8 2.5 V 600 612 mV 618 mV 200 nA 0.1 % 0.3 % 2.0 MHz VP to OUT resistance (high-side MOSFET on-resistance + DCR) 800 m RTOFF VP to PGND resistance (low-side MOSFET on-resistance + DCR) 650 m Soft-start period tSS Enable rising edge to output regulation 100 s Over-temperature shutdown threshold TSHDN Hysteresis = 15 °C 140 °C EN logic level high VIH EN logic level low VIL EN input current IEN 1.4 VEN = 0 V or VIN 1.0 V 0.4 V +1.0 A Note 1: Performance is guaranteed only under the conditions listed in this table. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 4 Units 2.7 TA = 25 °C FB leakage current Typical January 6, 2015 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • 201922E DATA SHEET • SKY87250: 400 mA LOW-NOISE STEP-DOWN CONVERTER IN A MICRO-INDUCTOR PACKAGE Typical Performance Characteristics (CIN = 4.7 F, COUT = 4.7 F , VIN = VP = 3.6 V, VEN = VIN, GND = PGND, TA = –40 °C to 85 °C [Typical Values are at TA = 25 °C], Unless Otherwise Noted) 100 1.0 0.8 Output Voltage Error (%) 90 Efficiency (%) 80 70 60 50 VIN = 3.6 V VIN = 4.2 V VIN = 5.0 V VIN = 5.5 V 40 30 0.1 1 10 100 0.6 0.4 0.2 0.0 -0.2 -0.4 VIN = 3.6 V VIN = 4.2 V VIN = 5.0 V VIN = 5.5 V -0.6 -0.8 -1.0 0.1 1000 1 1.0 100 0.8 Output Voltage Error (%) 90 Efficiency (%) 80 70 60 50 VIN = 3.6 V VIN = 4.2 V VIN = 5.0 V VIN = 5.5 V 40 1 10 100 0.6 0.4 0.2 0.0 -0.2 -0.4 VIN = 3.6 V VIN = 4.2 V VIN = 5.0 V VIN = 5.5 V -0.6 -0.8 -1.0 0.1 1000 1 Output Current (mA) 90 0.8 Output Voltage Error (%) 1.0 80 70 60 50 VIN = 2.7 V VIN = 3.6 V VIN = 4.2 V VIN = 5.0 V VIN = 5.5 V 40 30 10 100 1000 Figure 7. Load Regulation (VOUT = 2.5 V, R3 = 0 , C3 = 0 pF) 100 1 10 Output Current (mA) Figure 6. Efficiency vs Load (VOUT = 2.5 V, R3 = 0 , C3 = 0 pF) Efficiency (%) 1000 Figure 5. Load Regulation (VOUT = 3.3 V, R3 = 0 , C3 = 0 pF) Figure 4. Efficiency vs Load (VOUT = 3.3 V, R3 = 0 , C3 = 0 pF) 20 0.1 100 Output Current (mA) Output Current (mA) 30 0.1 10 100 Output Current (mA) Figure 8. Efficiency vs Load (VOUT = 1.8 V, R3 = 0 , C3 = 0 pF) VIN = 2.7 V VIN = 3.6 V VIN = 4.2 V VIN = 5.0 V VIN = 5.5 V 0.6 0.4 0.2 0.0 -0.2 -0.4 -0.6 -0.8 1000 -1.0 0.1 1 10 100 1000 Output Current (mA) Figure 9. Load Regulation (VOUT = 1.8 V, R3 = 0 , C3 = 0 pF) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201922E • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • January 6, 2015 5 DATA SHEET • SKY87250: 400 mA LOW-NOISE STEP-DOWN CONVERTER IN A MICRO-INDUCTOR PACKAGE 1.0 90 0.8 Output Voltage Error (%) 100 Efficiency (%) 80 70 60 50 VIN = 2.7 V VIN = 3.6 V VIN = 4.2 V VIN = 5.0 V VIN = 5.5 V 40 30 20 0.1 1 10 100 VIN = 2.7 V VIN = 3.6 V VIN = 4.2 V VIN = 5.0 V VIN = 5.5 V 0.6 0.4 0.2 0.0 -0.2 -0.4 -0.6 -0.8 -1.0 0.1 1000 1 Figure 10. Efficiency vs Load (VOUT = 1.8 V, R3 = 500 , C3 = 100 pF) 90 0.8 Output Voltage Error (%) 1.0 Efficiency (%) 80 70 60 50 VIN = 2.7 V VIN = 3.6 V VIN = 4.2 V VIN = 5.0 V VIN = 5.5 V 40 30 10 100 VIN = 2.7 V VIN = 3.6 V VIN = 4.2 V VIN = 5.0 V VIN = 5.5 V 0.6 0.4 0.2 0.0 -0.2 -0.4 -0.6 -0.8 -1.0 0.1 1000 1 Figure 12. Efficiency vs Load (VOUT = 1.2 V, R3 = 0 , C3 = 0 pF) 100 3.0 2.0 1.0 Output Voltage Error (%) IOUT = 1 mA IOUT = 10 mA IOUT = 50 mA IOUT = 100 mA IOUT = 200 mA IOUT = 400 mA 0.0 -1.0 -2.0 -25 0 25 50 75 Temperature (°C) Figure 14. Output Voltage Error vs Temperature (VIN = 3.6 V, VOUT = 1.8 V, R3 = 0 , C3 = 0 pF) 100 IOUT = 1 mA IOUT = 10 mA IOUT = 50 mA IOUT = 100 mA IOUT = 200 mA IOUT = 400 mA 2.0 1.0 0.0 -1.0 -2.0 -3.0 -50 -25 0 25 50 75 Temperature (°C) Figure 15. Output Voltage Error vs Temperature (VIN = 3.6 V, VOUT = 1.8 V, R3 = 0 , C3 = 0 pF) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 6 1000 Figure 13. Load Regulation (VOUT = 1.2 V, R3 = 0 , C3 = 0 pF) 3.0 Output Voltage Error (%) 10 Output Current (mA) Output Current (mA) -3.0 -50 1000 Figure 11. Load Regulation (VOUT = 1.8 V, R3 = 500 , C3 = 100 pF) 100 1 100 Output Current (mA) Output Current (mA) 20 0.1 10 January 6, 2015 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • 201922E 100 DATA SHEET • SKY87250: 400 mA LOW-NOISE STEP-DOWN CONVERTER IN A MICRO-INDUCTOR PACKAGE 3.0 IOUT = 0.1 mA IOUT = 1 mA IOUT = 10 mA IOUT = 50 mA IOUT = 100 mA IOUT = 200 mA IOUT = 400 mA 2.0 1.0 0.0 Output Voltage Error (%) Output Voltage Error (%) 3.0 -1.0 -2.0 -3.0 -50 -25 0 25 50 75 1.0 0.0 -1.0 -2.0 -3.0 -50 100 IOUT = 0.1 mA IOUT = 1 mA IOUT = 10 mA IOUT = 50 mA IOUT = 100 mA IOUT = 200 mA IOUT = 400 mA 2.0 -25 0 Temperature (°C) 0.2 0.0 0.8 -0.2 -0.4 -0.6 0.6 0.4 0.2 0.0 -0.4 -0.6 -0.8 -1.0 2.5 -1.0 2.5 3.5 4.0 4.5 5.0 5.5 Input Voltage (V) 3.5 4.0 4.5 5.0 5.5 Figure 19. Line Regulation (VOUT = 1.8 V, R3 = 0 , C3 = 0 pF) 1.0 4 0.6 0.4 IOUT = 100 mA IOUT = 200 mA IOUT = 400 mA 0.2 0.0 -0.2 -0.4 -0.6 -0.8 3.5 4.0 4.5 5.0 Input Voltage (V) Figure 20. Line Regulation (VOUT = 2.5 V, R3 = 0 , C3 = 0 pF) 3 2 1 0 0.6 0.4 Output Current (bottom) (A) IOUT = 0.1 mA IOUT = 1 mA IOUT = 10 mA IOUT = 50 mA Enable Voltage (top) (V) Output Voltage (middle) (V) 0.8 Output Voltage Error (%) 3.0 Input Voltage (V) Figure 18. Line Regulation (VOUT = 1.8 V, R3 = 500 , C3 = 100 pF) -1.0 3.0 IOUT = 1 mA IOUT = 10 mA IOUT = 50 mA IOUT = 100 mA IOUT = 200 mA IOUT = 400 mA -0.2 -0.8 3.0 100 1.0 IOUT = 0.1 mA IOUT = 1 mA IOUT = 10 mA IOUT = 50 mA IOUT = 100 mA IOUT = 200 mA IOUT = 400 mA Output Voltage Error (%) Output Voltage Error (%) 0.4 75 Figure 17. Output Voltage Error vs Temperature (VIN = 4.2 V, VOUT = 3.3 V, R3 = 0 , C3 = 0 pF) 1.0 0.6 50 Temperature (°C) Figure 16. Output Voltage Error vs Temperature (VIN = 3.6 V, VOUT = 2.5 V, R3 = 0 , C3 = 0 pF) 0.8 25 0.2 0.0 5.5 Time (50 μs/div) Figure 21. Soft Start (VIN = 3.6 V, VOUT = 1.8 V, IOUT = 400 mA) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201922E • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • January 6, 2015 7 DATA SHEET • SKY87250: 400 mA LOW-NOISE STEP-DOWN CONVERTER IN A MICRO-INDUCTOR PACKAGE 4 2.02 Frequency Variation (%) Switching Frequency (MHz) 3 2.00 1.98 1.96 1.94 2 1 0 -1 -2 -3 1.92 -40 -20 0 20 40 60 80 -4 2.7 100 3.1 3.5 Temperature (°C) 4.7 5.5 1.2 70 1.1 VIH and VIL (V) 60 50 40 30 85 °C 25 °C –40 °C 20 10 2.5 3.0 3.5 4.0 4.5 5.0 5.5 1.0 0.9 VIH VIL 0.8 0.7 0.6 2.5 6.0 Input Voltage (V) 3.0 3.5 4.0 4.5 5.0 5.5 6.0 Input Voltage (V) Figure 24. Input Current vs Input Voltage Figure 25. Enable Threshold vs Input Voltage 1.4 2.2 1.3 2.0 1.2 1.6 1.4 0.6 0.4 0.2 0.2 0.0 0.0 Time (50 μs/div) Time (50 μs/div) Figure 26. Load Transient Response (40 mA to 400 mA, VIN = 3.6 V, VOUT = 1.2 V, COUT = 4.7 F, C3 = 0 pF, R3 = 0 ) Figure 27. Load Transient Response (40 mA to 400 mA, VIN = 3.6 V, VOUT = 1.8 V, COUT = 4.7 F, C3 = 100 pF, R3 = 500 ) January 6, 2015 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • 201922E Output Current (bottom) (A) 0.6 0.4 Output Current (bottom) (A) 1.0 Output Voltage (top) (V) 1.8 1.1 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 8 5.1 Figure 23. Switching Frequency vs Input Voltage (VOUT = 1.8 V, IOUT = 400 mA) 80 Input Current (μA) 4.3 Input Voltage (V) Figure 22. Switching Frequency vs Temperature (VIN = 3.6 V, VOUT = 1.8 V, IOUT = 400 mA) Output Voltage (top) (V) 3.9 4.8 2.0 4.2 1.8 3.6 0.6 1.4 0.4 3.0 1.30 1.25 0.2 1.20 0.0 1.15 Output Voltage (bottom) (V) 1.6 Input Voltage (top) (V) 2.2 Output Current (bottom) (A) Output Voltage (top) (V) DATA SHEET • SKY87250: 400 mA LOW-NOISE STEP-DOWN CONVERTER IN A MICRO-INDUCTOR PACKAGE Time (50 μs/div) Time (100 μs/div) Figure 28. Load Transient Response (40 mA to 400 mA, VIN = 3.6 V, VOUT = 1.8 V, COUT = 4.7 F, C3 = 0 pF, R3 = 0 ) Figure 29. Line Transient Response (VIN = 3.6 V to 4.2 V, VOUT = 1.2 V, IOUT = 400 mA, COUT = 4.7 F, C3 = 0 pF, R3 = 0 ) 4.8 4.2 4.2 3.6 3.6 2.0 1.9 3.0 2.0 1.9 1.8 1.8 1.7 1.7 1.6 1.6 Output Voltage (bottom) (V) 3.0 Input Voltage (top) (V) 4.8 Output Voltage (bottom) (V) Input Voltage (top) (V) 1.10 Time (100 μs/div) Time (100 μs/div) Figure 30. Line Transient Response (VIN = 3.6 V to 4.2 V, VOUT = 1.8 V, IOUT = 400 mA, COUT = 4.7 F, C3 = 100 pF, R3 = 500 ) Figure 31. Line Transient Response (VIN = 3.6 V to 4.2 V, VOUT = 1.8 V, IOUT = 400 mA, COUT = 4.7 F, C3 = 0 pF, R3 = 0 ) 1.84 1.84 1.78 0.10 0.05 Output Voltage (top) (V) Output Voltage (top) (V) 1.80 1.78 0.8 0.6 Inductor Current (bottom) (A) 1.82 1.80 Inductor Current (bottom) (A) 1.82 0.4 0.00 0.2 0.0 Time (5 μs/div) Time (200 ns/div) Figure 32. Output Ripple (VIN = 3.6 V, VOUT = 1.8 V, IOUT = 1 mA) Figure 33. Output Ripple (VIN = 3.6 V, VOUT = 1.8 V, IOUT = 400 mA) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201922E • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • January 6, 2015 9 DATA SHEET • SKY87250: 400 mA LOW-NOISE STEP-DOWN CONVERTER IN A MICRO-INDUCTOR PACKAGE VIN VP Slope Comp FB Comp DH Error Amp. 1 μH Logic OUT Ref 0.6 V DL EN Input GND PGND tc66 Figure 34. SKY87250 Functional Block Diagram Functional Description The SKY87250 is a high performance 400 mA, 2.0 MHz monolithic step-down converter with an integrated microinductor. It is designed with the goal of minimizing external component requirements and optimizing efficiency over the complete load range. The converter operates at 2.0 MHz, which minimizes the ceramic output capacitor requirement. The device is designed to operate with an output voltage as low as 0.6 V over an input voltage range of 2.7 V to 5.5 V. Power devices are sized for 400 mA current capability while maintaining up to 95% efficiency. At dropout, the regulator's duty cycle increases to 100% and the output voltage tracks the input voltage minus the load drop across the on-time resistance (RTON). A high-DC gain error amplifier with internal compensation controls the output. It provides excellent transient response and load/line regulation. Soft start eliminates any output voltage overshoot when the enable or the input voltage is applied. A functional block diagram is shown in Figure 34. Integrated Power Inductor The SKY87250 integrates the power inductor within the package. Therefore, no external power inductor is needed. Control Loop The SKY87250 is a 400 mA, 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 over 50%. The peak current mode loop appears as a voltageprogrammed current source in parallel with the output capacitor. The output of the voltage error amplifier programs the current mode loop for the necessary peak switch current to force a constant output voltage for all load and line conditions. Internal loop compensation terminates the transconductance voltage error amplifier output. The error amplifier reference is fixed at 0.6 V. Soft Start/Enable Soft start ramps the reference voltage when the input voltage and enable input are valid. The controlled output slew-rate limits the current surge seen at the input and eliminates output voltage overshoot. When the EN pin is pulled low, it forces the SKY87250 into a low-power, non-switching state. The total input current during shutdown is less than 1 A. Current Limit and Over-Temperature Protection For overload conditions, the peak input current is limited. As load impedance decreases and the output voltage falls closer to zero, more power is dissipated internally, raising the device temperature. Thermal protection completely disables switching when internal dissipation becomes excessive, protecting the device from damage. The junction over-temperature threshold is 140°C with 15°C of hysteresis. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 10 January 6, 2015 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • 201922E DATA SHEET • SKY87250: 400 mA LOW-NOISE STEP-DOWN CONVERTER IN A MICRO-INDUCTOR PACKAGE Under-Voltage Lockout (UVLO) Internal bias of all circuits is controlled using the VIN bias supply input. UVLO guarantees sufficient VIN bias and proper operation of all internal circuitry before activation. Application Information Input Capacitor Selection Select a 4.7 F to 22 F X7R or X5R ceramic capacitor for the input. To estimate the required input capacitor size, determine the acceptable input voltage ripple level (VPP) and solve for CIN. C IN D 1 D VPP ESR f SW I OUT D VOUT VIN The peak ripple voltage occurs when VIN = 2 VOUT (50% duty cycle), resulting in a minimum output capacitance recommendation: 1 V 4 PP ESR f SW I OUT The maximum input capacitor RMS current is: I RMS I OUT D 1 D I OUT VOUT VOUT 1 VIN VIN Output Capacitor Selection The output voltage droop due to a load transient (ILOAD) 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: COUT The calculated value varies with input voltage and is a maximum when VIN is twice the output voltage. The input capacitor provides a low impedance loop for the edges of pulsed current drawn by the SKY87250. X7R and X5R ceramic capacitors are ideal for this function due to their low Equivalent Series Resistance (ESR) and Equivalent Series Inductance (ESL). To minimize stray parasitic inductance, the capacitor should be placed as closely as possible to the SKY87250. 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 layer detail (see C1 in Figure 35). A laboratory test set-up 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 low-ESR ceramic input capacitor, can create a high-Q 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 ceramic. This dampens the high Q network and stabilizes the system. The output capacitor limits the output ripple and provides holdup during large load transitions. A 4.7 F to 10 F X5R or X7R ceramic capacitor provides sufficient bulk capacitance to stabilize the output during large load transitions and has the ESR and ESL characteristics necessary for low output ripple. Where D is the duty cycle and fSW is the switching frequency. C IN 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. 3 I LOAD VDROOP f SW Once the average inductor current increases to the DC load level, the output voltage recovers. The above equation 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 F. 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: I RMS ( MAX) 1 2 3 VOUT VIN ( MAX ) VOUT L f SW VIN ( MAX ) Where L = 1 H and fSW = 2.0 MHz. 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. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201922E • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • January 6, 2015 11 DATA SHEET • SKY87250: 400 mA LOW-NOISE STEP-DOWN CONVERTER IN A MICRO-INDUCTOR PACKAGE 2 PTOTAL I OUT RTON D RTOFF 1 D Feedback Resistor Selection Resistors R1 and R2 in Figure 35 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 suggested value for R2 is 59 k. Decreased resistor values are necessary to maintain noise immunity on the FB pin, resulting in increased quiescent current. Table 5 summarizes the resistor values for various output voltages. With an enhanced transient response for extreme pulsed load applications, an external feed-forward capacitor and series feedback resistor (C3 and R3 in Figure 4) can be added, and usually use 100 pF capacitor as C3 and 500 resister as R3. The feedback resistor value can be calculated using the following equation: V 1.8V R1 OUT 1 R 2 1 59 k 118 k V 0 . 6 V REF Table 5. Adjustable Resistor Values for Step-Down Converter R1 (k) (R2 = 59 k) VOUT (V) R1 (k) (R2 = 221 k) 0.8 19.6 75 0.9 29.4 113 1.0 39.2 150 1.1 49.9 187 1.2 59 221 1.3 68.1 261 1.4 78.7 301 1.5 88.7 332 1.8 118 442 2.5 187 698 3.3 267 1000 Thermal Calculations There are many types of losses in the internal micro-inductor including the losses in the inductor core material, losses in the inductor from skin effects, magnetic field losses of the neighboring windings, and radiation losses. To simplify the calculation, the total inductor losses can be combined into the losses in the DC winding resistance of the inductor. There are three types of losses associated with the SKY87250 step-down converter: switching losses, conduction losses, and quiescent current losses. Conduction losses are associated with the on-resistance characteristics of the power output switching devices and the DC winding resistance (DCR) of the internal micro-inductor. Switching losses are dominated by the gate charge of the power output switching devices. At full load, assuming a Continuous Conduction Mode (CCM), a simplified form of the losses is given by: t DRV f SW I OUT I Q VIN Where D = VOUT/VIN, RTON is the high-side MOSFET onresistance plus inductor DCR, RTOFF is the low-side MOSFET onresistance plus inductor DCR, IQ is the step-down converter quiescent current, and tDRV is used to estimate the full load step-down converter switching losses. Since RTON, RTOFF, quiescent current, and switching losses all vary with the 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 JA for the package which is 158 °C/W. TJ(MAX) PTOTAL JA TA Layout Considerations The following guidelines should be used to help ensure a proper layout: The input capacitor (C1) should be connected directly between the VP and PGND pins. The output capacitor and analog ground should be connected together to minimize any DC regulation errors caused by ground potential differences. The output-sense connection to the FB pin should be separated from any power trace. Route the output-sense trace as close as possible to the load point to avoid additional load regulation errors. Sensing along a high-current load trace will degrade DC load regulation. Place the feedback components near the FB pin to minimize the high-impedance feedback trace length. Avoid routing the feedback trace directly under the package to avoid EMI coupled noise. Connect the N/C pin to the power ground plane to enhance thermal impedance, and use vias directly under the package to ground planes on the bottom or internal PCB layers to help distribute the heat. Evaluation Board Description The SKY87250 Evaluation Board schematic diagram is provided in Figure 35. The PCB layer details are shown in Figure 36. Component values for the SKY87250 Evaluation Board are listed in Table 6. Package Information The PCB layout footprint for the SKY87250 is provided in Figure 37. Package dimensions are shown in Figure 38, and tape and reel dimensions are provided in Figure 39. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 12 January 6, 2015 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • 201922E DATA SHEET • SKY87250: 400 mA LOW-NOISE STEP-DOWN CONVERTER IN A MICRO-INDUCTOR PACKAGE VIN 2.7 V to 5.5 V VOUT U1 1 2 C1 4.7 μF EN VP OUT 5 R1 adj. VIN 4 FB R3 Short SKY87250 3 2 6 EN GND N/C PGND 3 C3 optional R2 59 kΩ C2 4.7 μF 1 8 7 tc67 Figure 35. SKY87250 Evaluation Board Schematic (b) Bottom Side (a) Top Side (L1 not required; shown for size comparison only) tc68 Figure 36. SKY87250 Evaluation Board Layer Details Table 6. SKY87250 Evaluation Board Bill of Materials (BOM) Component Part Number Description Manufacturer U1 SKY87250 400mA low noise step-down converter, 2.4 mm 2.4 mm Skyworks C1, C2 GRM188R60J475KE19D MLCC cap, 4.7 F/6.3 V, 0603 Murata C3 UMK105CG101JV-F 100 pF/50 V, 0402, optional Taiyo Yuden R1 Carbon film resistor 59 k, 1%, 0201 R2 Carbon film resistor adjustable (see Table 5), 1%, 0201 R3 Carbon film resistor 0 , 1%, 0201 Yageo Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201922E • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • January 6, 2015 13 DATA SHEET • SKY87250: 400 mA LOW-NOISE STEP-DOWN CONVERTER IN A MICRO-INDUCTOR PACKAGE 8X 0.35 mm Pin 8 8X 0.465 mm 2.7 mm Package outline Pin 1 0.6 mm pitch tc69 Figure 37. SKY87250 PCB Layout Footprint (Top View) Top 2.4 8x SMT pad A B C 0.1 B C Pin 8 C 2.4 B 0.9 ± 0.1 0.15 A B C 0.1 0.525 ± 0.050 (0.125) 0.45 ± 0.05 2x (0.05) (0.05) (0.05) (0.05) 0.35 ± 0.05 Metal pad edge 0.265 ± 0.100 0.35 ± 0.05 Detail B Pad Scale: 2x 1x this rotation 1x rotated 180º Detail A Pad Scale: 2x 4x this rotation 4x rotated 180º 0.35 ± 0.05 (0.05) Metal pad edge 0.265 ± 0.100 0.265 ± 0.100 0.525 ± 0.050 (0.125) Detail C Pad Scale: 2x 1x this rotation 1x rotated 180º All measurements are in millimeters. Figure 38. SKY87250 8-pin DLN2424 Package Dimensions Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 14 Pin 1 Bottom View Side View Top View A 4X 0.3 A 4X 0.9 Pin 1 Indicator Metal pad edge 8x 1.15 January 6, 2015 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • 201922E tc70 DATA SHEET • SKY87250: 400 mA LOW-NOISE STEP-DOWN CONVERTER IN A MICRO-INDUCTOR PACKAGE B’ ± 4.00 ± 0.10 2.60 ± 0.05 (Bo) 3.50 ± 0.05 05 0. 0. Ty 10 A A’ B Pin 1 0 ø1.0 R p. 8.00 ± 0.30 5 .5 ø1 2.00 ± 0.05 1.75± 0.10 0.30 ± 0.05 Min. 4.00 ± 0.10 1.20 ± 0.10 (Ko) SECTION B-B’ 2.60 ± 0.05 (Ao) SECTION A-A’ Notes: 1. Carrier tapes must meet all requirements of Skyworks GP01-D233 procurement Spec for tape and reel shipping. 2. Carrier tape shall be black conductive polystyrene. 3. Cover tape shall be transparent conductive material. 4. ESD-surface resistivity shall meet GP01-D233. 5. 10 sprocket hole pitch cumulative tolerance: ±0.20 mm. 6. Ao & Bo measured on plane 0.30 mm above the bottom of the pocket. 7. All measurements are in millimeters. 8. Part No. : 3M115401 (Please indicate on purchase order). tc456 Figure 39. SKY87250 Carrier Tape Dimensions SKY87250 Design Example Specifications VOUT = 1.8 V @ 400 mA VIN = 5 V fSW = 2.0 MHz RTON = 800 m RTOFF = 650 m TA = 85 °C SKY87250 Losses All values assume 85°C ambient temperature and thermal resistance of 158 °C/W in the package. PTOTAL 2 I OUT RTON VOUT RTOFF VIN VOUT t DRV f SW I OUT I Q VIN VIN 0.4 A2 0.8 Ω 1.8V 0.65 Ω 5V 1.8V 5 ns 2 MHz 0.4 A 45 μA 5V 5V 120 mW TJ(MAX) PLOSS JA TA 158C / W 120mW 85C 104C Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 201922E • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • January 6, 2015 15 DATA SHEET • SKY87250: 400 mA LOW-NOISE STEP-DOWN CONVERTER IN A MICRO-INDUCTOR PACKAGE Ordering Information Model Name SKY87250: 400 mA Low-Noise Step-Down Converter in a Micro-Inductor Package Manufacturing Part Number SKY87250-11 Evaluation Board Part Number SKY87250-11-EVB Copyright © 2012-2015 Skyworks Solutions, Inc. All Rights Reserved. Information in this document is provided in connection with Skyworks Solutions, Inc. (“Skyworks”) products or services. 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Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 16 January 6, 2015 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • 201922E