Datasheet

LTC4215-1/LTC4215-3
14
421513fc
(OV pin), input undervoltage (UV pin), overcurrent circuit
breaker (SENSE
–
pin), or EN transitioning high. Writing
a logic one into the UV, OV or OC fault bits (D0-D2 in
Table 5) also latches off the GATE if their auto-retry bits
are set to false.
Normally the MOSFET is turned off with a 1mA current
pulling down the GATE pin to ground. With the MOSFET
turned off, the SOURCE and FB voltages drop as CL dis-
charges. When the FB voltage crosses below its threshold,
GPIO1 may be confi gured to pull low to indicate that the
output power is no longer good.
If the V
DD
pin falls below 2.74V for greater than 2µs or
INTV
CC
drops below 2.60V for greater than 1µs, a fast shut
down of the MOSFET is initiated. The GATE pin is pulled
down with a 450mA current to the SOURCE pin.
Overcurrent Fault
The LTC4215-1/LTC4215-3 feature an adjustable current
limit that protects against short circuits or excessive load
current. An overcurrent fault occurs when the circuit
breaker 25mV threshold has been exceeded for longer than
the 20µs (LTC4215-1) or 420µs (LTC4215-3) time-out delay.
Current limiting begins immediately when the current sense
voltage between the V
DD
and SENSE pins reaches 75mV.
The GATE pin is then brought down and regulated in order
to limit the current sense voltage to 75mV. When the 20µs
(LTC4215-1) or 420µs (LTC4215-3) circuit breaker time
out has expired, the external MOSFET is turned off and the
overcurrent fault bit D2 is set.
After the MOSFET is turned off, the TIMER capacitor
begins discharging with a 2µA pull-down current. When
the TIMER pin reaches its 0.2V threshold the MOSFET is
allowed to turn on again if the overcurrent fault has been
cleared. However, if the overcurrent auto-retry bit, A2 has
been set then the MOSFET turns on again automatically
without resetting the overcurrent fault. Use a minimum
value of 10nF for C
T
. If the TIMER pin is bypassed by tying
it to INTV
CC
, the part is allowed to turn on again after an
internal 5 second timer has expired, in the same manner
as the TIMER pin passing its 0.2V threshold.
Overvoltage Fault
An overvoltage fault occurs when either the OV pin rises
above its 1.235V threshold, or the V
DD
pin rises above its
15.6V threshold, for more than 2µs. This shuts off the GATE
with a 1mA current to ground and sets the overvoltage
present bit C0 and the overvoltage fault bit D0. If the pin
subsequently falls back below the threshold for 100ms,
the GATE is allowed to turn on again unless overvoltage
auto-retry has been disabled by clearing bit A0.
Undervoltage Fault
An undervoltage fault occurs when the UV pin falls below
its 1.235V threshold for more than 2µs. This turns off the
GATE with a 1mA current to ground and sets undervoltage
present bit C1 and undervoltage fault bit D1. If the UV pin
subsequently rises above the threshold for 100ms, the
GATE is turned on again unless undervoltage auto-retry
has been disabled by clearing bit A1. When power is ap-
plied to the device, if UV is below its 1.235V threshold after
INTV
CC
crosses its 2.64V undervoltage lockout threshold,
an undervoltage fault is logged in the fault register.
Figure 3. Short-Circuit Waveforms
APPLICATIONS INFORMATION
V
GATE
10V/DIV
V
SOURCE
10V/DIV
V
DD
10V/DIV
I
LOAD
10A/DIV
5µs/DIV
4215 F03
R
S
= 5mΩ
C
L
= 0
R
SHORT
= 1Ω
R6 = 30k
C1 = 0.1µF