TPS2480_1 Datasheet, PDF (24/54 Pages) Texas Instruments – Positive Voltage Intelligent Protection Device Hotswap Controller and I2C Current Monitor

TPS2480
TPS2481
SLUS939A – APRIL 2010 – REVISED JUNE 2010
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Alternative Inrush Designs
Gate Capacitor (dV/dt) Control
The TPS2480/81 can be configured to provide a linear dV/dt turn on characteristic. The load capacitor charging
current I_CHARGE, is controlled by a single capacitor from the GATE terminal to ground. M1 operates as a source
follower (following the gate voltage) in this implementation. Choose a charge time, t_ON, based on the load
capacitor, C_O input voltage V_I, and desired charge current. When power limiting is used (V_PROG < V_REF) choose
I_CHARGE to be less than P_LIM /V_VCC to prevent the fault timer from starting. The fault timer starts only if power or
current limit is invoked.
C ´V
t = ^{O VCC}
ON
I
CHARGE
(26)
Use the following equation to select the gate capacitance, C_G. C_ISS is the gate capacitance of M1, and I_GATE is
the TPS2480/81 nominal gate charge current. As shown in Figure 17, a series resistor of about 1 kΩ should be
used in series with C_G.
C_G
=
I_GATE ´ t_ON
V_VCC
- C_ISS
(27)
If neither power nor current limit faults are invoked during turn on, C_T can be chosen for fast transient turn off
response using the M1 SOA curve. Choose the single pulse time conservatively from the M1 SOA curve using
maximum operating voltage and maximum trip current.
PROG Inrush Control
A capacitor can be connected from the PROG pin to ground to reduce the initial current step seen in Figure 12.
This method maintains a relatively fast turn-on time without the drawbacks of a gate-to-ground capacitor that
include increased short circuit response time and less predictable gate clamping.
24
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