FAN6520A

FAN6520A FAIRCHILD | Alldatasheet

Document overview

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Technical content

Features

• Output Range 0.8V to V IN – 0.8V Internal Reference – ±1.5% Over Line V oltage and Temperature
• Drives N-Channel MOSFETs
• Simple Single-Loop Control Design –V oltage-Mode PWM Control
• F ast Transient Response – High-Bandwidth Error Amplifier – Full 0% to 100% Duty Cycle
• Lossless, Programmable Over-current Protection – Uses Upper MOSFET’s R DS(ON)
• Small Converter Size – 300kHz Fixed Frequency Oscillator – Internal Soft-Start – 8-Lead SOIC

Applications

• P ower Supplies for PC Subsystems and Peripherals
• MCH, GTL, and AGP Supplies
• Cable Modems, Set Top Boxes, and DSL Modems
• DSP, Memory
• L ow-V oltage Distributed Power Supplies General Description The FAN6520A makes simple work out of implementing a complete control and protection scheme for a DC-DC stepdown converter. Designed to drive N-channel MOSFETs in a synchronous buck topology, the FAN6520A integrates the control, output adjustment, monitoring and protection functions into a single 8-lead package. The FAN6520A is easy to use, employs a single feedback loop, and voltage-mode control with fast transient response. The output voltage can be precisely regulated to as low as 0.8V , with a maximum tolerance of ±1.5% over temperature and line voltage variations. A fixed frequency oscillator reduces design complexity, while balancing typical application cost. The error amplifier features a 15MHz gain- bandwidth product and an 8V/µs slew rate which enables high converter bandwidth for fast transient performance. The resulting PWM duty cycles range from 0% to 100%. The IC monitors the drop across the upper MOSFET and inhibits PWM operation appropriately to protect against over-current conditions. This approach simplifies the implementation and improves efficiency by eliminating the need for a current sense resistor. The FAN6520A is rated for operation from 0° to +70°C with the FAN6520AI rated from –40° to +85°C. FAN6520A Single Synchronous Buck PWM Controller

REV. 1.0.2 8/26/04 FAN6520A PRODUCT SPECIFICATION Pin Configuration FAN6520AM 8-pin SOIC Package Pin Definitions Pin # Pin Name Pin Function Description

1 BOOT

Bootstrap Supply Input. Provides a boosted voltage to the high-side MOSFET driver. Connect to bootstrap capacitor as shown in Figure 1.

2 HDRV

High Side Gate Drive Output. Connect to the gate of the high-side power MOSFET(s). This pin is also monitored by the adaptive shoot-through protection circuitry to determine when the upper MOSFET has turned off.

3 GND

Ground. The signal and power ground for the IC. Tie this pin to the ground island/plane through the lowest impedance connection available. Connect directly to source of low-side MOSFET(s).

4 LDRV

Low Side Gate Drive Output. Connect to the gate of the low-side power MOSFET(s). This pin is also monitored by the adaptive shoot-through protection circuitry to determine when the lower MOSFET has turned off.

5 VCC

VCC. Provides bias power to the IC and the drive voltage for LDRV. Bypass with a ceramic capacitor as close to this pin as possible. 6F B Feedback. This pin is the inverting input of the internal error amplifier. Use this pin, in combination with the COMP/OCSET pin, to compensate the voltage-control feedback loop of the converter.

7 COMP/

COMP/OCSET/SD. This is a multiplexed pin. During operation, the output of the error amplifier drives this pin. During a short period of time following power-on reset (POR), this pin is used to determine the over-current threshold of the converter. Pulling COMP/OCSET to a level below 0.8V disables the controller. Disabling the controller causes the oscillator to stop, the HDRV and LDRV outputs to be held low, and the soft-start circuitry to re-arm. 8S W Switch Node Input. Connect as shown in Figure 1. The SW pin provides return for the high-side bootstrapped driver, is a sense point for the adaptive shoot-thru protection, and is used for monitoring the drop across Q1’s R DS(ON) for current limit. FAN6520A SW COMP/OCSET/SD FB VCC BOOT HDRV GND LDRV

REV. 1.0.2 8/26/04 FAN6520A PRODUCT SPECIFICATION Absolute Maximum Ratings Absolute maximum ratings are the values beyond which the device may be damaged or have its useful life impaired. Functional operation under these conditions is not implied. Thermal Information Recommended Operating Conditions Parameter Min. Max. Units VCC to GND 6V VBOOT to GND 15 V HDRV (V BOOT – V SW ) 6V LDRV 0.5 6 V SW to PGND Continuous 0.5 6 V Transient ( t < 50nsec, F < 500kHz) 37 V All other pins 5.5 V Parameter Min. Typ. Max. Units Storage Temperature –65 150 °C Lead Soldering Temperature, 10 seconds 300 °C Vapor Phase, 60 seconds 215 °C Infrared, 15 seconds 220 °C Power Dissipation (P D ), T A = 25°C 715 mW Thermal Resistance – Junction to Case θ JC 40 °C/W Thermal Resistance – Junction to Ambient θ JA 140 °C/W Parameter Conditions Min. Typ. Max. Units Supply Voltage VCC VCC to PGND 4.5 5 5.5 V Ambient Temperature (T A )F AN6520A 07 0 ° C FAN6520AI 40 85 °C Junction Temperature (T J 40 125 °C

PRODUCT SPECIFICATION FAN6520A REV. 1.0.2 8/26/04 Electrical Specifications VCC = 5V, and TA = 25°C using circuit in Figure 1 unless otherwise noted. The • denotes specifications which apply over the full operating temperature range. Notes: 1. All limits at operating temperature extremes are guaranteed by design, characterization and statistical quality control. 2. AC specifications guaranteed by design/characterization (not production tested). Parameter Symbol Conditions Min. Typ. Max. Units Supply Current VCC Current I VCC HDRV, LDRV open • 1.5 2.4 3.8 mA Power-On Reset Rising VCC POR Threshold POR • 4.00 4.22 4.45 V VCC POR Threshold Hysteresis 170 mV Oscillator Frequency F OSC FAN6520A • 250 300 340 kHz FAN6520AI • 230 300 340 kHz Ramp Amplitude V OSC

• 1.5 Vp-p Reference Reference Voltage V REF T A = 0 to 70°C • 788 800 812 mV FAN6520AI • 780 800 820 mV Error Amplifier DC Gain 88 dB Gain – Bandwidth Product GBWP 15 MHz Slew Rate S/R 8 V/µs Gate Drivers HDRV pull-up resistance R HUP 2.5 Ω HDRV pull-down resistance R HDN 2.0 Ω LDRV pull-up resistance R LUP 2.5 Ω LDRV pull-down resistance R LDN 1.0 Ω Protection/Disable OCSET Current Source I OCSET FAN6520A • 17 20 22 µ A FAN6520AI • 14 20 24 µ A Disable Threshold V DISABLE 800 mV

Over-current Protection (OCP) sample and hold operation. the POR function initiates the soft-start operation. current trip level (see Typical Application diagram). The FAN6520A then samples this voltage at the COMP pin. power for the conditions shown in Figure 3 is only 1.5W. Figure 3. Over-Current Operation from the specification table. I is the output inductor ripple current. )” under Component Selection. An overcurrent trip cycles the soft-start function. entire startup sequence typically takes about 11ms.

Figure 8. Asymptotic Bode Plot of Converter Gain function of the switching frequency and the ripple current. rate (di/dt) and the magnitude of the transient load current. perform better than a single large case capacitor. transient is the time required to change the inductor current. response time can minimize the output capacitance required. output levels for the worst case response time.

BOOT) and the internal diode, as shown in Figure 1. where FSW is switching frequency (in kHz). Where QG1 is total gate charge of Q1 for its applied VGS. Figure 9. Driver Dissipation Model RG is the polysilicon gate resistance, internal to the FET. in Synchronous Buck Converters. LDRV is dissipation of the lower FET driver.

12 REV. 1.0.2 8/26/04 FAN6520A PRODUCT SPECIFICATION Low-Side Losses Q2, however, switches on or off with its parallel shottky diode conducting, therefore VDS ≈ 0.5V . Since PSW is proportional to VDS, Q2’s switching losses are negligible and we can select Q2 based on RDS(ON) only. Conduction losses for Q2 are given by: PCOND = (1-D) × IOUT 2 × RDS(ON) (18) where RDS(ON) is the RDS(ON) of the MOSFET at the highest operating junction temperature and is the minimum duty cycle for the converter. Since DMIN < 20% for portable computers, (1-D) ≈ 1 produces a conservative result, further simplifying the calculation. The maximum power dissipation (P D(MAX) ) is a function of the maximum allowable die temperature of the low-side MOSFET, the θ J-A, and the maximum allowable ambient temperature rise: θJ-A, depends primarily on the amount of PCB area that can be devoted to heat sinking (see Fairchild app note AN-1029 for SO-8 MOSFET thermal information). D VOUT VIN PD MAX() TJ MAX() TA MAX()– θJA–

Figure 12. 5V to 1.5V 15A DC-DC Converter

14 REV. 1.0.2 8/26/04 FAN6520A PRODUCT SPECIFICATION Dimensional Outline Drawing 0.15+0.10 -0.05 (R0.10) 0.70±0.20 (1.04)

1.75 MAX

1.45+0.05 -0.20 (R0.10) 0.501.27 SEE DETAIL A NOTES: UNLESS OTHERWISE SPECIFIED A) THIS PACKAGE CONFORMS TO JEDEC MS-012, VARIATION AA, ISSUE C, DATED MAY 1990. B) ALL DIMENSIONS ARE IN MILLIMETERS. C) DIMENSIONS DO NOT INCLUDE MOLD FLASH OR BURRS. D) STANDARD LEAD FINISH: 200 MICROINCHES / 5.08 MICRONS MIN. LEAD/TIN (SOLDER) ON COPPER. LAND PATTERN RECOMMENDATION 0.36 SEATING PLANE 0.10 C C GAGE PLANE 3.81 0.25 0.19 1.00 6.75 4.75 DETAIL A (0.33) 1.27 6.00 PIN ONE INDICATOR CM B A0.25 3.90±0.10 0.51 0.35 B 4.90±0.10 3.81 A SCALE: 2:1 0.50

0.25 X 45°

8/26/04 0.0m 001 Stock#DS505602 2004 Fairchild Semiconductor Corporation LIFE SUPPORT POLICY FAIRCHILD’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and (c) whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury of the user. 2. A critical component in any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. www.fairchildsemi.com DISCLAIMER FAIRCHILD SEMICONDUCTOR RESERVES THE RIGHT TO MAKE CHANGES WITHOUT FURTHER NOTICE TO ANY PRODUCTS HEREIN TO IMPROVE RELIABILITY, FUNCTION OR DESIGN. FAIRCHILD DOES NOT ASSUME ANY LIABILITY ARISING OUT OF THE APPLICATION OR USE OF ANY PRODUCT OR CIRCUIT DESCRIBED HEREIN; NEITHER DOES IT CONVEY ANY LICENSE UNDER ITS PATENT RIGHTS, NOR THE RIGHTS OF OTHERS. PRODUCT SPECIFICATION FAN6520A

Ordering Information

Part Number Temperature Range Package Packing FAN6520AM 0°C to 70°C SOIC-8 Rails FAN6520AMX 0°C to 70°C SOIC-8 Tape and Reel FAN6520AIM –40°C to 85°C SOIC-8 Rails FAN6520AIMX –40°C to 85°C SOIC-8 Tape and Reel