9.4 Power Supply Recommendations

9.4.1 Transient Protection

When the external MOSFETs turn OFF during the conditions such as overvoltage cut-off, reverse current

blocking, EN/UVLO causing an interruption of the current flow, the input line inductance generates a positive

voltage spike on the input and output inductance generates a negative voltage spike on the output. The peak

amplitude of voltage spikes (transients) depends on the value of inductance in series to the input or output of

the device. These transients can exceed the Absolute Maximum Ratings of the device if steps are not taken to

address the issue.

Typical methods for addressing transients include:

• Minimizing lead length and inductance into and out of the device

• Using large PCB GND plane

• Use of a Schottky diode across the output and GND to absorb negative spikes

• A low value ceramic capacitor (C(IN) to approximately 0.1 μF) to absorb the energy and dampen the

transients.

The approximate value of input capacitance can be estimated with Equation 8.

(

)

( )

(

)

( )

( )

IN

spike Absolute

IN

Load

IN

L

V

V

I

C

=

+

´

(8)

where

• V(IN) is the nominal supply voltage

• I(LOAD) is the load current

• L(IN) equals the effective inductance seen looking into the source

• C(IN) is the capacitance present at the input

Some applications may require additional Transient Voltage Suppressor (TVS) to prevent transients from

exceeding the Absolute Maximum Ratings of the device. These transients can occur during EMC testing such as

automotive ISO7637 pulses.

The circuit implementation with optional protection components (a ceramic capacitor, TVS and schottky diode) is

shown in Figure 9-14

GND

DGATE

A

HGATE OUT

C

EN/UVLO

VIN

VOUT

LM74810

CAP

VS

ON OFF

Q1

Q2

D1

SW

R2

R1

OV

VSNS

R3

BATT_MON

CIN

COUT

D2

CVS

CVCAP

*

*

* Optional components needed for suppression of transients

Figure 9-14. Circuit Implementation with Optional Protection Components for LM7481

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LM7481

SNOSDD9 – DECEMBER 2022

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