ISL9008A Intersil Corporation, ISL9008A Datasheet - Page 9

• Manufacturer Part Number: ISL9008A
• Description: Low Noise LDO
• Manufacturer: Intersil Corporation

Functional Description
The ISL9008A 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 ISL9008A 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 ISL9008A 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 ISL9008A 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 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 ISL9008A 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
tolerance better than 20% and ESR less than 200m
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.
9
Ω
. The
ISL9008A
Soft-start circuitry integrated into each LDO limits the initial
ramp-up rate to about 30μs/V to minimize current surge. The
ISL9008A provides short-circuit protection by limiting the output
current to about 265mA (typ).
The LDO uses an independently trimmed 1V reference as its
input. An internal resistor divider drops the LDO output voltage
down to 1V. This is compared to the 1V reference for regulation.
The resistor division ratio is programmed in the factory.
Overheat Detection
The bandgap outputs a proportional-to-temperature current that
is indicative of the temperature of the silicon. This current is
compared with references to determine if the device is in
danger of damage due to overheating. When the die
temperature reaches about +140°C, the LDO momentarily
shuts down until the die cools sufficiently. In the overheat
condition, if the LDO sources more than 50mA it will be shut off.
Once the die temperature falls back below about +110°C, the
disabled LDO is re-enabled and soft-start automatically takes
place.
April 16, 2007
FN6300.2