8
LTC4230
4230f
FB3 (Pin 1): The FB3 (Feedback) pin is an input to the
FBCOMP3 comparator which monitors the V
CC3
output
supply voltage through an external resistor divider. If V
FB3
< 1.234V, RESET 3 pin pulls low. An internal glitch filter at
FBCOMP3’s output prevents triggering a reset condition
due to negative voltage transients. If V
FB3
> 1.237V,
RESET 3 pin goes high after exiting undervoltage lockout.
RESET 3 (Pin 2): An open-drain N-channel device whose
source connects to GND (Pin 14). This pin pulls low if the
voltage at FB3 (Pin 1) falls below the FB3 threshold
(1.234V). This pin requires an external pull-up resistor to
V
OUT3
. If an undervoltage lockout condition occurs,
RESET␣ 3 pulls low independently of FB3 to prevent false
glitches.
GATE 3 (Pin 3): The output signal at this pin is the high side
gate drive for Channel 3’s external N-channel MOSFET
pass transistor. An internal charge pump produces a 4.5V
(minimum) to 18V (maximum) gate drive voltage for V
CC1
supply voltages from 2.7V to 16.5V, respectively.
As shown in the Block Diagram for each channel, an
internal charge pump supplies a 10µA gate current and
sufficient gate voltage drive to the external MOSFET. The
internal charge pump produces a minimum 4.5V gate
drive for V
CC1
< 4.75V. For V
CC1
> 4.75V, the minimum
gate voltage drive is 9V. For V
CC1
≥ 12V, the minimum gate
voltage drive is 7V which is set by an internal zener diode
clamp connected between the GATE 3 pin and GND.
SENSE 3 (Pin 4): Circuit Breaker Sense Pin for Channel 3.
With a sense resistor placed in the power path between
V
CC3
and SENSE 3, Channel 3’s electronic circuit breaker
trips if the voltage across the sense resistor (V
CC3
–
V
SENSE3
) exceeds the thresholds set internally for SLOW
COMP3 and FAST COMP3, as shown in the Block Diagram.
The threshold for SLOW COMP3 is V
CB(SLOW)
= 50mV, and
the electronic circuit breaker trips if the voltage across
R
SENSE3
exceeds 50mV for 10µs, or for the time delay
programmed by C
FILTER
. To adjust SLOW COMP3’s delay,
please refer to the section on Adjusting SLOW COMP
n
’s
Response Time.
Under transient conditions where large step current
changes can and do occur over shorter periods of time, a
PI FU CTIO S
UUU
second (fast) comparator instead trips the electronic
circuit breaker. The threshold for FAST COMP3 is set at
V
CB(FAST)
= 150mV, and the circuit breaker trips if the
voltage across the R
SENSE3
exceeds 150mV for more than
500ns. FAST COMP3’s delay is fixed in the LTC4230 and
cannot be adjusted. To disable Channel 3’s electronic
circuit breaker, connect the V
CC3
and SENSE 3 pins
together.
V
CC3
(Pin 5): Positive Supply Input for Channel 3. V
CC3
operates from 1.7V to 15.5V (V
CC3
≤ V
CC1
– 1V) and its
supply current, I
CC3
, is typically 65µA. The master UVLO
circuit disables all three GATE
n
outputs of the LTC4230
until the voltage at V
CC3
exceeds 1.19V.
V
CC1
(Pin 6): This is the positive supply input to the
LTC4230, the power supply input for Channel 1, and the
power supply input for all three internal charge pumps.
The LTC4230 operates from 2.7V to 16.5V, and the I
CC1
supply current is typically 1.8mA. The master UVLO circuit
disables all three GATE
n
outputs of the LTC4230 if V
CC1
is
less than 2.35V. The internal charge pump outputs are
enabled when V
CC1
> 2.35V, V
CC2
> 2.15V, and
V
CC3
> 1.19V.
SENSE 1 (Pin 7): Circuit Breaker Sense Pin for Channel 1.
With a sense resistor placed in the power path between
V
CC1
and SENSE 1, Channel 1’s electronic circuit breaker
trips if the voltage across the sense resistor (V
CC1
–
V
SENSE1
) exceeds the thresholds set internally for SLOW
COMP1 and FAST COMP1, as shown in the Block Diagram.
The threshold for SLOW COMP1 is V
CB(SLOW)
= 50mV, and
the electronic circuit breaker trips if the voltage across
R
SENSE1
exceeds 50mV for 10µs, or for the time delay
programmed by C
FILTER
. To adjust SLOW COMP1’s delay,
please refer to the section on Adjusting SLOW COMP
n
’s
Response Time.
Under transient conditions where large step current changes
can and do occur over shorter periods of time, a second
(fast) comparator instead trips the electronic circuit breaker.
The threshold for FAST COMP1 is set at V
CB(FAST)
= 150mV,
and the circuit breaker trips if the voltage across the
R
SENSE1
exceeds 150mV for more than 500ns. FAST
COMP1’s delay is fixed in the LTC4230 and cannot be
adjusted. To disable Channel 1’s electronic circuit breaker,
connect the V
CC1
and SENSE 1 pins together.
