LM7480 datasheet(32/44 Pages) TI

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

shown in Figure 10-29

GND

DGATE

HGATE OUT

EN/UVLO

VIN

VOUT

LM7480x

CAP

ON OFF

VSNS

BATT_MON

CIN

COUT

CVS

CVCAP

* Optional components needed for suppression of transients

Figure 10-29. Circuit Implementation with Optional Protection Components for LM7480

10.5.2 TVS Selection for 12-V Battery Systems

In selecting the TVS, important specifications are breakdown voltage and clamping voltage. The breakdown

voltage of the TVS+ should be higher than 24-V jump start voltage and 35-V suppressed load dump voltage

and less than the maximum ratings of LM7480 (65 V). The breakdown voltage of TVS- should be beyond than

maximum reverse battery voltage –16 V, so that the TVS- is not damaged due to long time exposure to reverse

connected battery.

Clamping voltage is the voltage the TVS diode clamps in high current pulse situations and this voltage is much

higher than the breakdown voltage. In the case of an ISO 7637-2 pulse 1, the input voltage goes up to –150 V

with a generator impedance of 10 Ω. This translates to 15 A flowing through the TVS - and the voltage across

the TVS would be close to its clamping voltage.

The next criterion is that the absolute maximum rating of cathode to anode voltage of the LM7480 (85 V) and

the maximum VDS rating MOSFET are not exceeded. In the design example, 60-V rated MOSFET is chosen and

maximum limit on the cathode to anode voltage is 60 V.

During ISO 7637-2 pulse 1, the anode of LM7480 is pulled down by the ISO pulse, clamped by TVS- and the

MOSFET Q1 is turned off quickly to prevent reverse current from discharging the bulk output capacitors. When

the MOSFET turns off, the cathode to anode voltage seen is equal to (TVS Clamping voltage + Output capacitor

voltage). If the maximum voltage on output capacitor is 16 V (maximum battery voltage), then the clamping

voltage of the TVS- should not exceed, (60 V – 16) V = –44 V.

The SMBJ33CA TVS diode can be used for 12-V battery protection application. The breakdown voltage of 36.7

V meets the jump start, load dump requirements on the positive side and 16-V reverse battery connection on the

negative side. During ISO 7637-2 pulse 1 test, the SMBJ33CA clamps at –44 V with 12 A of peak surge current

as shown in and it meets the clamping voltage ≤ 44 V.

SMBJ series of TVS' are rated up to 600-W peak pulse power levels and are sufficient for ISO 7637-2 pulses.

10.5.3 TVS Selection for 24-V Battery Systems

For 24-V battery protection application, the TVS and MOSFET in Figure 10-1 needs to be changed to suit 24-V

battery requirements.

The breakdown voltage of the TVS+ should be higher than 48-V jump start voltage, less than the absolute

maximum ratings of anode and enable pin of LM7480 (70 V) and should withstand 65-V suppressed load dump.

The breakdown voltage of TVS- should be lower than maximum reverse battery voltage –32 V, so that the TVS-

is not damaged due to long time exposure to reverse connected battery.

LM7480

SNOSDD8 – DECEMBER 2022

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