isl97701 Intersil Corporation, isl97701 Datasheet - Page 7

• Manufacturer Part Number: isl97701
• Description: Boost Regulator With Integrated Schottky And Input Disconnect Switch
• Manufacturer: Intersil Corporation

Function Overview
The ISL97701 is a high frequency, high efficiency boost
regulator which operates in constant frequency PWM mode.
The boost converter generates a stable, higher output
voltage from a variable, low voltage input source (e.g. L-Ion
battery). The output voltage level is defined from the
feedback resistor network in Equation 1.
VOUT
The switching frequency is either generated from the fixed
1MHz internal oscillator or provided externally at the
synchronization pin in the range from 600kHz to 1.4MHz.
The compensation network and soft-start functions are built
in with fixed parameters without any need for further external
components.
To stop battery discharge into the output load when disabled
the inductor is disconnected from the input supply with a low
on resistance power switch.
Built in fault protection monitors inductor current and output
voltage as well as junction temperature in order to interrupt
the high current circuit path through the inductor and diode in
the event of a load failure.
Low logic input thresholds allow the ISL97701 to interface
directly to micro controllers with lower supply voltage.
Alternatively the internal pull-up resistors on all logic inputs
provide level shifting when driven from open collector outputs.
Description of Operation
Enable Pin (active low) - NEN
If NEN is high the ISL97701 shuts down all its internal
functions and deactivates its I/So. Only the internal pull-up
resistor at NEN remains active. If NEN is high the input
disconnect switch between VDD and VDDOUT interrupts the
circuit path from the input voltage VDD through inductor and
diode to the output load at V
supply current in VDD is typically less than 0.1µA.
Pin Descriptions
NUMBER
PIN
10
1
2
3
4
5
6
7
8
9
=
------------------------------ -
R2 ∗ Vref
(
R1
+
PIN NAME
R2
VDDOUT
NSYNC
V
FB
GND
GND
VDD
NEN
NC
)
FB
OUT
LX
Ground
Protection Switch Output
Supply Input
Synchronization Input (Falling Edge)
Feedback Input
Do Not Connect
Ground
Enable Input (Active Low)
Boost Output Voltage
Boost FET
OUT
7
. If shut down the total
PIN FUNCTION
(EQ. 1)
ISL97701
When NEN is driven low the ISL97701 begins with the
start-up sequence.
Start-Up Sequence
After pin NEN is pulled low or a restart is triggered from Fault
Control during operation, the ISL97701 goes through a start-
up sequence with the following six states: Soft Inrush ->
VDDOUT Enable -> Soft Boost 25 -> Soft Boost 50 -> Soft
Boost 75 -> Normal.
If the sequence has completed, the ISL97701 stays in the
“Normal” state until NEN is high again or any fault is detected.
SOFT INRUSH: STATE DURATION ~2.048MS
The switch at VDDOUT is configured as current source and
provides a limited current through the inductor to pre-charge
the capacitor at V
VDDOUT ENABLE: STATE DURATION ~128µS
The switch at VDDOUT is fully enabled and connects the
inductor to VDD with a low on-resistance.
SOFT BOOST 25 -> 50 -> 75: STATE DURATION
3X ~2.048MS
The boost regulator begins to switch at LX.
The LX current limit increases in three steps representing
25%, 50% and 75% of its final value.
NORMAL
If no fault was detected Normal state is entered ~8.256ms
after NEN is pulled low.
The LX current limit steps up to 100%.
In all states Fault Control can force the sequence to restart
or even to shut down (see Table 1).
Fault Control
The input voltage at VDD, current in the VDD
voltage at V
continuously monitored and can either restart the start-up
INRUSH
SOFT
FIGURE 14. FAULT CONTROL SEQUENCE
OUT
V(NEN)
25
and junction temperature T
OUT
VDD
.
50
OUT
75
ENABLE
NORMAL
J
V(V
OUT
I(VDD)
are
OUT
switch,
April 23, 2007
)
FN6474.0