9
FN6437.2
September 1, 2015
Block Diagram
Functional Description
The ISL9011A contains all circuitry required to implement
two high performance LDOs. High performance is achieved
through a circuit that delivers fast transient response to
varying load conditions. In a quiescent condition, the
ISL9011A adjusts its biasing to achieve the lowest standby
current consumption.
The device also integrates current limit protection, smart
thermal shutdown protection, staged turn-on and soft-start.
Smart Thermal shutdown protects the device against
overheating. Staged turn-on and soft-start minimize start-up
input current surges without causing excessive device
turn-on time.
Power Control
The ISL9011A has two separate enable pins (EN1 and EN2)
to individually control power to each of the LDO outputs.
When both EN1 and EN2 are low, the device is in shutdown
mode. During this condition, all on-chip circuits are off, and
the device draws minimum current, typically less than 0.1µA.
When one or both of the enable pins are asserted, the
device first polls the output of the UVLO detector to ensure
that VIN voltage is at least about 2.1V. 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 power-up. Once the references are
stable, a fast-start circuit quickly charges the external
reference bypass capacitor (connected to the CBYP pin) to
the proper operating voltage. After the bypass capacitor has
been charged, the LDO’s power-up.
If EN1 is brought high, and EN2 goes high before the VO1
output stabilizes, the ISL9011A delays the VO2 turn-on until
the VO1 output reaches its target level.
If EN2 is brought high, and EN1 goes high before VO2 starts
its output ramp, then VO1 turns on first and the ISL9011A
LDO
ERROR
AMPLIFIER
IS1
1V
QEN1
LDO-1
LDO-2
VREF
TRIM
VIN
VO1
VO2
CBYPGND
EN2
EN1
CONTROL
LOGIC
VOLTAGE
REFERENCE
GENERATOR
BANDGAP AND
TEMPERATURE
SENSOR
UVLO
1.00V
IS1
IS2
QEN1
QEN2
VO1
~1.0V
ISL9011A
