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 400mΩ 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.
