ISL9003A

FN6299 Rev 5.00

Page 9 of 12

July 18, 2014

Block Diagram

Functional Description

The ISL9003A contains all circuitry required to implement a

high performance LDO. High performance is achieved through

a circuit that delivers fast transient response to varying load

conditions. In a quiescent condition, the ISL9003A adjusts its

biasing to achieve the lowest standby current consumption.

The device also integrates current limit protection, smart

thermal shutdown protection, and soft-start. Smart Thermal

shutdown protects the device against overheating. Soft-start

minimizes start-up input current surges without causing

excessive device turn-on time.

Power Control

The ISL9003A has an enable pin, (EN), to control power to the

LDO output. When EN is low, the device is in shutdown mode.

In this condition, all on-chip circuits are off, and the device

draws minimum current, typically less than 0.3µA. When the

EN pin goes high, the device first polls the output of the UVLO

detector to ensure that VIN voltage is at least 2.1V (typical).

Once verified, the device initiates a start-up sequence. During

the start-up sequence, trim settings are first read and latched.

Then, sequentially, the bandgap, reference voltage and current

generation circuitry turn-on. Once the references are stable,

the LDO powers-up.

During operation, whenever the VIN voltage drops below about

1.84V, the ISL9003A immediately disables the LDO output.

When VIN rises back above 2.1V (assuming the EN pin is

high), the device re-initiates its start-up sequence and LDO

operation resumes automatically.

Reference Generation

The reference generation circuitry includes a trimmed

bandgap, a trimmed voltage reference divider, a trimmed

current reference generator, and an RC noise filter. The filter

includes the external capacitor connected to the CBYP pin. A

0.01µF capacitor connected CBYP implements a 100Hz

lowpass filter, and is recommended for most high performance

greater CBYP capacitor should be used. This filters the

reference noise to below the 10Hz to 1kHz frequency band,

which is crucial in many noise-sensitive applications.

The bandgap generates a zero temperature coefficient (TC)

voltage for the regulator reference and other voltage

references required for current generation and

over-temperature detection.

A current generator provides references required for adaptive

biasing as well as references for LDO output current limit and

thermal shutdown determination.

LDO Regulation and Programmable Output Divider

The LDO Regulator is implemented with a high-gain

operational amplifier driving a PMOS pass transistor. The

design of the ISL9003A provides a regulator that has low

quiescent current, fast transient response, and overall stability

across all operating and load current conditions. LDO stability

is guaranteed for a 1µF to 4.7µF output capacitor that has a

design is performance-optimized for a 1µF capacitor. Unless

limited by the application, use of an output capacitor value

above 4.7µF is not recommended as LDO performance

improvement is minimal. Soft-start circuitry integrated into each

LDO limits the initial ramp-up rate to about 30µs/V to minimize

current surge. The ISL9003A provides short-circuit protection

by limiting the output current to about 265mA (typ).

GND

BANDGAP AND

TEMPERATURE

SENSOR

UVLO

SD

CONTROL

LOGIC

VOLTAGE AND

REFERENCE

GENERATOR

CBYP

1.0V

0.94V

0.9V

GND

SHORT CIRCUIT,

THERMAL PROTECTION,

SOFT-START

+

-