LTC4252-1IMS8 Linear Technology, LTC4252-1IMS8 Datasheet - Page 16

• Manufacturer Part Number: LTC4252-1IMS8
• Description: IC CNTRLR HOTSWAP NEGVOLT 8-MSOP
• Manufacturer: Linear Technology
• Type: Hot-Swap Controllerr

Specifications of LTC4252-1IMS8

• Applications: General Purpose
• Internal Switch(s): No
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-TSSOP, 8-MSOP (0.118", 3.00mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: LTC42521IMS8

LTC4252-1/LTC4252-2
LTC4252A-1/LTC4252A-2
APPLICATIONS INFORMATION
conditions are met. A high-to-low transition in the UV
comparator immediately shuts down the LTC4252, pulls
the MOSFET gate low and resets the latched PWRGD high.
Overvoltage conditions detected by the OV compara-
tor will also pull GATE low, thereby shutting down the
load. However, it will not reset the circuit breaker TIMER,
PWRGD flag or shutdown cooling timer. Returning the
supply voltage to an acceptable range restarts the GATE
pin if all the interlock conditions except TIMER are met.
Only during the initial timing cycle does an OV condition
reset the TIMER.
DRAIN
Connecting an external resistor, R
DRAIN pin allows V
aged by large voltage transients. Below 5V, negligible pin
leakage allows a DRAIN low comparator to detect V
less than 2.385V (V
the GATE low comparator, sets the PWRGD flag.
If V
V
This current is scaled up 8 times during a circuit breaker
fault and is added to the nominal 230μA TIMER current.
This accelerates the fault TIMER pull-up when the MOS-
FET’s drain-source voltage exceeds V
shortens the MOSFET heating duration.
TIMER
The operation of the TIMER pin is somewhat complex as
it handles several key functions. A capacitor C
TIMER to provide timing for the LTC4252. Four different
charging and discharging modes are available at TIMER:
1) A 5.8μA slow charge; initial timing and shutdown cool-
ing delay.
2) A (230μA + 8 • I
3) A 5.8μA slow discharge; circuit breaker “cool off” and
shutdown cooling.
16
DRNCL
I
DRN
OUT
≈
and the current flowing in R
> V
V
OUT
DRNCL
R
-V
D
DRNCL
, the DRAIN pin is clamped at about
DRN
OUT
DRNL
) fast charge; circuit breaker delay.
sensing* without it being dam-
). This condition, together with
D
, to the dual function
D
DRNCL
is given by:
and effectively
T
is used at
OUT
(1)
4) Low impedance switch; resets the TIMER capacitor
after an initial timing delay, in UVLO, in UV and in OV
during initial timing.
For initial start-up, the 5.8μA pull-up is used. The low
impedance switch is turned off and the 5.8μA current
source is enabled when the interlock conditions are met.
C
When C
turns on and discharges C
and both SS and GATE are released.
CIRCUIT BREAKER TIMER OPERATION
If the SENSE pin detects more than a 50mV drop across
R
C
latches off while the LTC4252-2 starts a shutdown cooling
cycle. The LTC4252-1 remains latched off until the UV
pin is momentarily pulsed low or TIMER is momentarily
discharged low by an external switch or V
UVLO and is then restored. The circuit breaker timeout
period is given by:
If V
pin leakage current, making I
If V
the charging of C
Intermittent overloads may exceed the 50mV threshold at
SENSE, but, if their duration is sufficiently short, TIMER
will not reach 4V and the LTC4252 will not shut the external
MOSFET off. To handle this situation, the TIMER discharges
C
voltage is less than 50mV. Therefore, any intermittent
overload with V
*V
T
T
T
S
OUT
, the TIMER pin charges C
charges to 4V, the GATE pin pulls low and the LTC4252-1
charges to 4V in a time period given by:
t=
t=
slowly with a 5.8μA pull-down whenever the SENSE
OUT
OUT
as viewed by the MOSFET; i.e., V
4V •C
230μA +8 •I
5.8μA
< 5V, an internal PMOS device isolates any DRAIN
T
> V
reaches 4V (V
4V •C
DRNCL
T
OUT
T
T
during the circuit breaker fault period,
DRN
accelerates by 8 • I
> 5V and an aggregate duty cycle of
DS
TMRH
.
T
. A GATE start-up cycle begins
), the low impedance switch
T
DRN
with (230μA + 8 • I
= 0μA in Equation (3).
DRN
of Equation (1).
IN
dips below
DRN
425212fc
). If
(2)
(3)