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CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.

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2.5A Regulator with Integrated High-Side MOSFET for

Synchronous Buck or Boost Buck Converter

ISL85402

The ISL85402 is a synchronous buck controller with a 125mΩ

high-side MOSFET and low-side driver integrated. The ISL85402

supports a wide input voltage range from 3V to 36V. Regarding the

output current capability from the thermal perspective, the

ISL85402 can typically support continuous load of 2.5A under

ambient temperature with still air. For any specific application, the

actual maximum output current depends upon the die temperature

not exceeding +125°C with the power dissipated in the IC, which is

related to input voltage, output voltage, duty cycle, switching

frequency, board layout and ambient temperature, etc. Refer to

“Output Current” on page 13 for more details.

The ISL85402 has flexible selection of operation modes of

forced PWM mode and PFM mode. In PFM mode, the

quiescent input current is as low as 180µA (AUXVCC connected

programmed to cover wide applications.

The low-side driver can be either used to drive an external low-side

MOSFET for a synchronous buck, or left unused for a standard

non-synchronous buck. The low-side driver can also be used to

drive a boost converter as a pre-regulator followed by a buck

controlled by the same IC, which greatly expands the operating

input voltage range down to 3V or lower (Refer to “Typical

Application Schematic III - Boost Buck Converter” on page 5).

The ISL85402 offers the most robust current protections. It

uses peak current mode control with cycle-by-cycle current

limiting. It is implemented with frequency foldback under

current limit condition; besides that, the hiccup overcurrent

mode is also implemented to guarantee reliable operations

under harsh short conditions.

The ISL85402 has comprehensive protections against various faults

including overvoltage and over-temperature protections, etc.

Features

• Ultra Wide Input Voltage Range 3V to 36V

• Optional Mode Operation

- Forced PWM Mode

- Selectable PFM with Programmable PFM/PWM Boundary

• 300µA IC Quiescent Current (PFM, No Load); 180µA Input

AUXVCC)

• Less than 3µA Standby Input Current (IC Disabled)

• Operational Topologies

-Synchronous Buck

-Non-Synchronous Buck

- Two-Stage Boost Buck

• Programmable Frequency from 200kHz to 2.2MHz and

Frequency Synchronization Capability

• Reliable Overcurrent Protection

- Temperature Compensated Current Sense

- Cycle-by-Cycle Current Limiting with Frequency Foldback

- Hiccup Mode for Worst Case Short Condition

• 20 Ld 4x4 QFN Package

• Pb-Free (RoHS Compliant)

Applications

•General Purpose

• 24V Bus Power

•Battery Power

• Point of Load

• Embedded Processor and I/O Supplies

FIGURE 1. TYPICAL APPLICATION

FIGURE 2. EFFICIENCY, SYNCHRONOUS BUCK, PFM MODE,

VOUT

ISL85402

VCC

SGND

MODE

BOOT

VIN

PHASE

PGND

FS

EXT_BOOST

EN

FB

COMP

VIN

AUXVCC

LGATE

ILIMIT

SS

SYNC

PGOOD

50

55

60

65

70

75

80

85

90

95

100

0.1m

1m

10m

100m

1.0

2.5

LOAD CURRENT (A)

September 29, 2011

FN7640.0