Datasheet

OUT VCC
CHG
C V
t
I
´
D =
GATE GATE ISS
VCC
t
C I C
V
æ ö
D
= ´ -
ç ÷
è ø
Partof
TPS2470x
M
1
ToLoad
GND
GATE
FromSource
R
GATE
1kΩ
C
GATE
S0509-03
I
30 A
GATE
μ
TPS24700
TPS24701
www.ti.com
SLVSAL3B MARCH 2011 REVISED MAY 2011
The TPS24700/1 can be used in applications that expect a constant inrush current. This current is controlled by a
capacitor connected from the GATE terminal to GND. A resistor of 1 k placed in series with this capacitor
prevents it from slowing a fast-turnoff event. In this mode of operation, M1 operates as a source follower, and the
slew rate of the output voltage approximately equals the slew rate of the gate voltage (see Figure 32).
To implement a constant-inrush-current circuit, choose the time to charge, t, using Equation 9,
(9)
where C
OUT
is the output capacitance, V
VCC
is the input voltage, and I
CHG
is the desired C
OUT
charge current.
To select the gate capacitance use Equation 10.
(10)
Figure 32. Gate Capacitor (dV/dt) Control Inrush Mode
ADDITIONAL DESIGN CONSIDERATIONS
Use of PGb
Use the PGb pin to control and coordinate a downstream dc/dc converter. If this is not done, then a long time
delay is needed to allow C
OUT
to fully charge before the converter starts. An undesirable latch-up condition can
be created between the TPS24700/1 output characteristic and the dc/dc converter input characteristic if the
converter starts while C
OUT
is still charging; the PGb pin is one way to avoid this.
Output Clamp Diode
Inductive loads on the output may drive the OUT pin below GND when the circuit is unplugged or during a
current-limit event. The OUT pin ratings can be satisfied by connecting a diode from OUT to GND. The diode
should be selected to control the negative voltage at the full short-circuit current. Schottky diodes are generally
recommended for this application.
Gate Clamp Diode
The TPS24700/1 has a relatively well-regulated gate voltage of 12 V to 15.5 V with a supply voltage V
VCC
higher
than 4 V. A small clamp Zener from gate to source of M1 is recommended. A series resistance of several
hundred ohms or a series silicon diode is recommended to prevent the output capacitance from discharging
through the gate driver to ground.
High-Gate-Capacitance Applications
Copyright © 2011, Texas Instruments Incorporated Submit Documentation Feedback 21
Product Folder Link(s): TPS24700 TPS24701