9
FN9217.4
March 11, 2008
Block Diagram
Functional Description
The ISL9000 contains 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 ISL9000 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 ISL9000 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 LDOs power-up in their specified
sequence.
Soft-start circuitry integrated into each LDO limits the initial
ramp-up rate to about 30µs/V to minimize current surge.
VO2
LDO
ERROR
AMPLIFIER
IS1 1VQEN1
LDO-1
LDO-2
POR
COMPARATOR
VOK1
POR1
VREF
TRIM
VIN
VO1
VO2
POR2
POR1
GND
EN2
EN1
CONTROL
LOGIC
POR2
DELAY
POR1
DELAY
VOLTAGE
REFERENCE
GENERATOR
BANDGAP AND
TEMPERATURE
SENSOR
UVLO
VOK2
VOK1
1.00V
0.94V
0.90V
IS1
IS2
QEN1
QEN2
VO1
VO2
100k100k
CPOR
CBYP
VO1
~1.0V
VOK2
POR2
ISL9000
