LTC4211
11
4211fc
For more information www.linear.com/LTC4211
PIN FUNCTIONS
(8-Lead Package/10-Lead Package)
clamps at the GATE pin determine the gate drive voltage
(∆V
GATE
= V
GATE
– V
CC
). The charge pump produces a
minimum 4.5V of ∆V
GATE
for supplies in the range of 2.7V
≤ V
CC
< 4.75V. For 4.75V ≤ V
CC
≤ 12V the ∆V
GATE
is limited
by zener clamp Z1 connected between the GATE and V
CC
pins. The ∆V
GATE
is typically at 12V and with guaranteed
minimum value of 10V. For V
CC
> 12V, the Zener clamp
Z2 begins to set the limitation for ∆V
GATE
. Z2 clamps the
gate voltage to ground to 26V typically. The minimum Z2’s
clamp voltage is 23V. This effectively sets ∆V
GATE
to 8V
minimum at V
CC
= 15V.
SENSE (Pin 7/Pin 8): Circuit Breaker Set Pin. With a sense
resistor placed in the power path between V
CC
and SENSE,
the LTC4211’s electronic circuit breaker trips if the voltage
across the sense resistor exceeds the thresholds set inter
-
nally for the SLOW COMP and the FAST COMP, as shown in
the Block Diagram. The threshold for the SLOW COMP is
V
CB(SLOW)
= 50mV, and the electronic circuit breaker trips
if the voltage across the sense resistor exceeds 50mV for
20µs. The SLOW COMP delay is fixed in the S8/MS8 ver
-
sion and adjustable in the MS version of the LTC4211. To
adjust the SLOW COMP’s delay, please refer to the section
on Adjusting SLOW COMP’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 the FAST COMP is set at
V
CB(FAST)
= 150mV, and the circuit breaker trips if the
voltage across the sense resistor exceeds 150mV for
more than 300ns. The FAST COMP’s delay is fixed in the
LTC4211 and cannot be adjusted. To disable the electronic
circuit breaker, connect the V
CC
and SENSE pins together.
V
CC
(Pin 8/Pin 9): This is the positive supply input to
the LTC4211. The LTC4211 operates from 2.5V < V
CC
<
16.5V, and the supply current is typically 1mA. An internal
undervoltage lockout circuit disables the device until the
voltage at V
CC
exceeds 2.3V.
FAULT (Not available on S8/MS8, Pin 10 MS): FAULT is
both an input and an output. Connected to this pin are
an analog comparator (COMP6) and an open-drain N-
channel FET. During normal operation, if COMP6 is driven
below 1.236V, the electronic circuit breaker trips and the
GATE pin pulls low. Typically, a 10k pull-up resistor con
-
nects to the FAULT pin. This pull-up is required to allow
the LTC4211 to begin a second timing cycle (V
FAULT
>
1.286) and start-up properly. This also allows the use of
the FAULT pin as a status output. Under normal operating
conditions, the FAULT output is a logic high. Two condi
-
tions cause an active low on FAUL
T: (1) the LTC4211’s
electronic circuit breaker trips because of an output short
circuit causing a fast output overcurrent transient (FAST
COMP trips circuit breaker); or (2) V
FILTER
> 1.236V. The
FAULT output is driven to logic low and is latched logic
low until the ON pin is driven to logic low for 150µs (the
t
RESET
duration).
FILTER (Not available S8/MS8, Pin 3 MS): Overcurrent
Fault Timing Pin and Overvoltage Fault Set pin. With a
capacitor connected from this pin to ground, the SLOW
COMP’s response time can be adjusted. In the S8/MS8
version of the LTC4211, the FILTER pin is not available
and the delay time from overcurrent detect to GATE OFF
is fixed at 20µs.
