TPS24711DGSR【PDF 26/34 页】IC CTRLR HOT SWAP 2.5-18V 10MSOP

Partof

TPS2471x

M

1

ToLoad

GND

GATE

romSource

R

GATE

1k

C

GATE

-

I

30 A

GATE

RS

t

I

C

V

?/DIV>

D

=

?/DIV>

-

?/DIV>

TPS24710,TPS24711

TPS24712,TPS24713

SLVSAL2E JANUARY 2011REVISED NOVEMBER 2013

www.ti.com

To select the gate capacitance, use Equation 15. I

GATE

is the nominal gate charge current. This equation

assumes that the MOSFET C

GD

is the controlling element as the gate and output voltage rise. C

GD

is non-linear

with applied V

DG

. An averaged estimate may be made using the MOSFET V

GS

vs Q

G

curve. Divide the charge

accumulated during the plateau region by the plateau V

GS

to get C

RS

.

(15)

Figure 36. Gate Capacitor (dV/dt) Control Inrush Mode.

ADDITIONAL DESIGN CONSIDERATIONS

Use of PG/PGb

Use the PG/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 TPS24710/11/12/13 output characteristic and the dc/dc converter input characteristic if

the converter starts while C

OUT

is still charging; the PG/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 TPS24710/11/12/13 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 M

1

is recommended if V

GS

of M

1

is rated below 12

V. 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

Gate voltage overstress and abnormally large fault current spikes can be caused by large gate capacitance. An

external gate clamp Zener diode is recommended to assist the internal Zener if the total gate capacitance of M

1

exceeds about 4000 pF. When gate capacitor dV/dt control is used, a 1-k?resistor in series with C

GATE

is

recommended (see Figure 36). If the series R-C combination is used for MOSFETs with C

ISS

less than 3000 pF,

then a Zener diode is not necessary.

26

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