LTC4252C-2_15 Datasheet, PDF (23/36 Pages) Linear Technology – Negative Voltage Hot Swap Controllers

LTC4252B-1/LTC4252B-2
LTC4252C-1/LTC4252C-2
APPLICATIONS INFORMATION
UV CLEARS V_UVHI, CHECK OV < V_OVHI, GATE < V_GATEL, SENSE < V_CB, SS < 20 • V_OS AND TIMER < V_TMRL
TIMER CLEARS V_TMRL, CHECK GATE < V_GATEL, SENSE < V_CB AND SS < 20 • V_OS
1
2
GND – V_EE OR
(–48RTN) – (–48V)
3 4 56 7 8 9 1011
UV/OV
V_UVHI
V_IN
TIMER
GATE
SS
V_LKO
V_GATEL
SENSE
5.8µA
V_TMRH
V_TMRL
230µA + 8 • I_DRN
5.8µA
58µA
58µA
V_IN – V_GATEH
20 • (V_ACL + V_OS)
20 • (V_CB + V_OS)
20 • V_OS
V_ACL
V_CB
5.8µA
V_OUT
DRAIN
V_DRNCL
V_DRNL
PWRGD
INITIAL TIMING
GATE
START-UP
4252B12 F10
Figure 10. Power-Up Timing with a Short Pin (All Waveforms Are Referenced to V_EE)
satisfied before a GATE start-up cycle begins. SS ramps up
as dictated by R_SS • C_SS; GATE is held low by the analog
current limit amplifier until SS crosses 20 • V_OS. Upon
releasing GATE, 58µA sources into the external MOSFET
gate and compensation network. When the GATE voltage
reaches the MOSFET’s threshold, current begins flowing
into the load capacitor at time point 5. At time point 6,
load current reaches the SS control level and the analog
current limit loop activates. Between time points 6 and 8,
the GATE voltage is servoed, the SENSE voltage is regulated
at V_ACL(t) and soft-start limits the slew rate of the load
current. If the SENSE voltage (V_SENSE – V_EE) reaches the
V_CB threshold at time point 7, the circuit breaker TIMER
activates. The TIMER capacitor, C_T, is charged by a (230µA
+ 8 • I_DRN) current pull-up. As the load capacitor nears full
charge, load current begins to decline. At point 8, the load
current falls and the SENSE voltage drops below V_ACL(t).
The analog current limit loop shuts off and the GATE pin
ramps further. At time point 9, the SENSE voltage drops
below V_CB and the fault TIMER cycle ends, followed by a
5.8µA discharge cycle (cool off). When GATE ramps past
V_GATEH threshold at time point 10, PWRGD pulls low.
At time point 11, GATE reaches its maximum voltage as
determined by V_IN.
4252b12f
23