TPS2480PW datasheet(26/60 Pages) TI2

26 / 60 page

TPS2480

TPS2481

SLUS939B – APRIL 2010 – REVISED DECEMBER 2010

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Additional Design Considerations

Use of PG

Use the PG pin to control and sequence a downstream DC/DC converter. If this is not done a long time delay

may be needed to allow CO to fully charge before the converter starts.

Output Clamp Diode

Inductive loads on the output may drive the OUT pin below GND when the circuit is unplugged or during current

limit. The OUT pin ratings can be maintained with a small diode such as an S1B, between the TPS2480/81 OUT

to GND pins.

Gate Clamp Diode

The TPS2480/81 has a relatively well-regulated gate voltage of 12 V to 16 V, even at low supply voltages. A

small clamp Zener from gate to source of M1, such as a BZX84C7V5, is recommended if VGS of M1 is rated

below this.

High Gate Capacitance Applications

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

clamp Zener diode is recommended if the total gate capacitance of M1 exceeds 4000 pF. When gate capacitor

dV/dT control is used, a 1-k

Ω resistor in series with CG is recommended, as shown in Figure 17. If the series R-C

combination is used for MOSFETs with CISS less than 3000 pF, then a Zener is not required.

Input Transient Protection

The maximum recommended bus voltage is lower than the absolute maximum voltage ratings on VINP and

VINM solely to provide margin for transients on the bus. The TPS2480 will operate properly up to the absolute

maximum voltage ratings on VINP and VINM.

Hotswap systems experience positive transients on their input during hotplug or rapid turnoff with high current

due to inductance in the input circuit. These same systems experience negative transients on the output during

rapid turnoff with high current due to inductance in the output circuit. The TPS2480 may not require operational

voltage margin below the absolute maximum if it is operated from a non-inductive input. An example is an

application where the TPS2480 is used as an output protector with a large input capacitance located directly at

the input terminals.

Transient protection, e.g. a TVS diode (transient voltage suppressor, a type of Zener diode), may be required on

the input in addition to a bypass capacitor if the system design does not inherently limit transient voltages below

the absolute maximum ratings. An example of this is a system with significant input inductance. If a TVS is

required, it must protect to the absolute maximum ratings at the worst case clamping current.

An output voltage clamp diode may be required on the output to limit negative transients if the local output

capacitance does not adequately control it. An example of this is a system with significant output bus inductance

and little local capacitance. Select a schottky diode with low forward voltage at the anticipated current during an

output short.

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