ISL9021A

9

FN7845.3

December 20, 2012

Functional Description

The ISL9021A is a high performance low-dropout regulator (LDO)

with 250mA sourcing capability. The extra low ground current

makes this part a good choice for handheld product applications.

The device also incorporates overcurrent, thermal shutdown,

reverse current protections, and soft-start features.

Thermal shutdown protects the device against overheating.

Soft-start limits the start-up input current surges. In some

applications, the output voltage may be externally pulled higher

than the input, or the input voltage could be connected to ground,

or connected to some voltage lower than the output side. The

ISL9021A features reverse current protection; that can block the

reverse current from output to input.

Enable Control

The ISL9021A has an enable pin. When EN is low, the IC is in

shutdown mode. In this condition, all on-chip circuits are off, and

the device draws minimum current, typically less than

0.1µA(typ). Driving this pin high will turn on the device.

LDO Protections

The ISL9021A offers several protection functions, making it ideal for

use in battery-powered applications. The ISL9021A provides

short-circuit protection by limiting the output current at current limit

of 260mA (min). If the short circuit lasts long enough, the die

temperature increases, and the over-temperature protection circuit

will shut down the output. When the die temperature reaches about

+145°C, thermal protection starts to work with output being loaded

with at least 50mA. Once the die temperature drops to about

+110°C, the LDO will resume operation beginning with a soft-start.

The ISL9021A’s reverse current protection is intended to block

reverse conduction if output voltage is higher than input voltage.

Input and Output Capacitors

The ISL9021A provides a linear regulator that has low quiescent

current, fast transient response, and overall stable operation

across the recommended operating conditions. A ceramic

capacitor (X5R or X7R) with a capacitance of 1µF to 4.7µF with

an ESR up to 400m

Ω is suitable for the ISL9021A to maintain its

output stability. The ground connection of the output capacitor

should be routed directly to the GND pin of the device, and also

placed close to the IC. Similarly for the input capacitor, usually a

1µF ceramic capacitor (X5R or 7R) is suitable for most cases, but

if a large, fast rising load transient condition is expected, a higher

value input capacitor may be necessary to achieve satisfactory

performance.

Board Layout Recommendations

A good PCB layout is an important step to achieve good

performance. It is recommended to design the board with

separate ground planes for input and output, and connect both

ground planes at the GND pin of the IC. Consideration should be

taken when placing the components and routing the trace to

minimize the ground impedance, and keep the parasitic

inductance low. Usually the input/output capacitors should be

placed as close to the IC as possible with a good ground

connection.