DATASHEET NOT RECOMMENDED FOR NEW DESIGNS RECOMMENDED REPLACEMENT PART ISL85403 ISL85402 FN7640 Rev 1.00 2.5A Regulator with Integrated High-Side MOSFET for Synchronous Buck or April 25, 2013 Boost Buck Converter The ISL85402 is a synchronous buck controller with a 125m Features high-side MOSFET and low-side driver integrated. The ISL85402 Buck Mode: Input Voltage Range 3V to 36V (Refer to Input supports a wide input range of 3V to 36V in buck mode. It Voltage on page 13 for more details) supports 2.5A continuous load under conditions of 5V V , V OUT IN range of 8V to 36V, 500kHz and +105C ambient temperature Boost Mode Expands Operating Input Voltage Lower Than with still air. For any specific application, the actual maximum 2.5V (Refer to Input Voltage on page 13 for more details) output current depends upon the die temperature not exceeding Selectable Forced PWM Mode or PFM Mode +125C with the power dissipated in the IC, which is related to input 300A IC Quiescent Current (PFM, No Load) 180A Input voltage, output voltage, duty cycle, switching frequency, board layout Quiescent Current (PFM, No Load, V Connected to OUT and ambient temperature, etc. Refer to Output Current on page 14 AUXVCC) for more details. Less than 3A Shut Down Input Current (IC Disabled) The ISL85402 has a flexible selection of operation modes of Operational Topologies forced PWM mode and PFM mode. In PFM mode, the -Synchronous Buck quiescent input current is as low as 180A (AUXVCC connected to V ). The load boundary between PFM and PWM can be -Non-Synchronous Buck OUT programmed to cover wide applications. - Two-Stage Boost Buck The low-side driver can be either used to drive an external low-side Programmable Frequency from 200kHz to 2.2MHz and MOSFET for a synchronous buck, or left unused for a standard Frequency Synchronization Capability non-synchronous buck. The low-side driver can also be used to 1% Tight Voltage Regulation Accuracy drive a boost converter as a pre-regulator followed by a buck Reliable Overcurrent Protection controlled by the same IC, which greatly expands the operating input voltage range down to 2.5V or lower (Refer to Typical - Temperature Compensated Current Sense Application Schematic III - Boost Buck Converter on page 5). - Cycle-by-Cycle Current Limiting with Frequency Foldback - Hiccup Mode for Worst Case Short Condition The ISL85402 offers the most robust current protections. It uses peak current mode control with cycle-by-cycle current 20 Ld 4x4 QFN Package limiting. It is implemented with frequency foldback under Pb-Free (RoHS Compliant) current limit condition besides that, the hiccup overcurrent mode is also implemented to guarantee reliable operations Applications under harsh short conditions. General Purpose The ISL85402 has comprehensive protections against various faults 24V Bus Power including overvoltage and over-temperature protections, etc. Battery Power Point of Load Embedded Processor and I/O Supplies 100 95 6V V IN 90 PGOOD EN V 12V V VIN IN 85 IN MODE 80 SYNC BOOT 36V V AUXVCC IN 75 24V V IN VCC V OUT 70 ISL85402 PHASE ILIMIT 65 LGATE SS 60 PGND 55 EXT BOOST FB FS 50 SGND COMP 0.1m 1m 10m 100m 1.0 2.5 LOAD CURRENT (A) FIGURE 2. EFFICIENCY, SYNCHRONOUS BUCK, PFM MODE, FIGURE 1. TYPICAL APPLICATION V 5V, T = +25C OUT A FN7640 Rev 1.00 Page 1 of 22 April 25, 2013 EFFICIENCY (%)ISL85402 ISL85402 Pin Configuration (20 LD QFN) TOP VIEW 20 19 18 17 16 1 15 EN BOOT 2 14 PGND FS 21 Thermal Pad 3 13 SS LGATE PAD21 4 12 SYNC FB 5 11 COMP EXT BOOST 6 7 8 9 10 Functional Pin Descriptions PIN NAME PIN DESCRIPTION EN 1 The controller is enabled when this pin is left floating or pulled HIGH. The IC is disabled when this pin is pulled LOW. Range: 0V to 5.5V. FS 2 Connecting this pin to VCC, or GND, or leaving it open will force the IC to have 500kHz switching frequency. The oscillator switching frequency can also be programmed by adjusting the resistor from this pin to GND. SS 3 Connect a capacitor from this pin to ground. This capacitor, along with an internal 5A current source, sets the soft-start interval of the converter. Also, this pin can be used to track a ramp on this pin. FB 4 This pin is the inverting input of the voltage feedback error amplifier. With a properly selected resistor divider connected from V to FB, the output voltage can be set to any voltage between the power rail (reduced by maximum duty cycle and voltage OUT drop) and the 0.8V reference. Loop compensation is achieved by connecting an RC network across COMP and FB. The FB pin is also monitored for overvoltage events. COMP 5 Output of the voltage feedback error amplifier. ILIMIT 6 Programmable current limit pin. With this pin connected to the VCC pin, or to GND, or left open, the current limiting threshold is set to default of 3.6A the current limiting threshold can be programmed with a resistor from this pin to GND. MODE 7 Mode selection pin. Pull this pin to GND for forced PWM mode to have it floating or connected to VCC will enable PFM mode when the peak inductor current is below the default threshold of 700mA. The current boundary threshold between PFM and PWM can also be programmed with a resistor at this pin to ground. Check for more details in the PFM Mode Operation on page 13. PGOOD 8 PGOOD is an open drain output that will be pulled low immediately under the events when the output is out of regulation (OV or UV) or when the EN pin is pulled low. PGOOD is equipped with a fixed delay of 1000 cycles upon output power-up (V > 90%). O PHASE 9, 10 These pins are the PHASE nodes that should be connected to the output inductor. These pins are connected to the source of the high-side N-channel MOSFET. EXT BOOST 11 This pin is used to set boost mode and monitor the battery voltage that is the input of the boost converter. After VCC POR, the controller will detect the voltage on this pin if voltage on this pin is below 200mV, the controller is set in synchronous/non-synchronous buck mode and will latch in this state unless VCC is below POR falling threshold if the voltage on this pin after VCC POR is above 200mV, the controller is set in boost mode and latch in this state. In boost mode, the low-side driver output PWM with same duty cycle with upper-side driver to drive the boost switch. In boost mode, this pin is used to monitor input voltage through a resistor divider. By setting the resistor divider, the high threshold and hysteresis can be programmed. When voltage on this pin is above 0.8V, the PWM output (LGATE) for the boost converter is disabled, and when voltage on this pin is below 0.8V minus the hysteresis, the boost PWM is enabled. In boost mode operation, PFM is disabled when boost PWM is enabled. Check the Boost Converter Operation on page 14 for more details. FN7640 Rev 1.00 Page 2 of 22 April 25, 2013 AUXVCC ILIMIT VCC MODE SGND PGOOD PHASE VIN PHASE VIN