1

DATASHEET

2.5A Regulator with Integrated High-side MOSFET for

Synchronous Buck or Boost Buck Converter

ISL85403

The ISL85403 is a 40V, 2.5A synchronous buck or boost buck

controller with a high-side MOSFET and low-side driver

integrated. In buck mode, the ISL85403 supports a wide input

range of 3V to 40V. In boost-buck mode, the input range can

be extended down to 2.5V and output regulation can be

electronics to remain on in low input voltage conditions.

The ISL85403 has a 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 preregulator followed by a buck

controlled by the same IC, which greatly expands the operating

input voltage range down to 2.5V or lower (Refer to “Typical

Application Schematic III - Boost Buck Converter” on page 6).

The ISL85403 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; also, the hiccup overcurrent mode is also

implemented to guarantee reliable operations under harsh

short conditions.

The ISL85403 has comprehensive protections against various

faults including overvoltage and over-temperature protections,

etc.

Related Literature

• AN1960, “ISL85403DEMO1Z Demonstration Board User

Guide”

• UG010, “ISL85403EVAL2Z Evaluation Board User Guide”

Features

• Buck mode: input voltage range 3V to 40V (refer to “Input

Voltage” on page 15 for more details)

• Boost mode expands operating input voltage lower than

2.5V (refer to “Input Voltage” on page 15 for more details)

• Selectable forced PWM mode or PFM mode

• 300µA IC quiescent current (PFM, no load); 180µA input

• Less than 5µA (MAX) shutdown input current (IC disabled)

• Operational topologies

-Synchronous buck

-Non-synchronous buck

- Two-stage boost buck

- Non-inverting single inductor buck boost

• 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

ISL85403

VCC

SGND

MODE

BOOT

VIN

PHASE

PGND

FS

EXT_BOOST

EN

FB

COMP

VIN

AUXVCC

LGATE

ILIMIT

SS

SYNC

PGOOD

ISL85403

50

55

60

65

70

75

80

85

90

95

100

0.1m

1m

10m

100m

1.0

2.5

LOAD CURRENT (A)

March 13, 2015

FN8631.1

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

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