TPS54494: Rail 2 is drawing more current but OCP not triggered

Mandan Kumar

Part Number: TPS54494

Hi,

We are having a strange issue in our application.

One of the load device in our application system connected from 1V8 on rail 2 is drawing very high current (it is getting hot beyond 100degC on the thermal pad). However we do not see the OCP trigger happening.

Please see the attached schematic for the reference.

Also we have tried to simulate this scenario on the benchtop level on the same PCBA - when the load current goes beyond 3.3A, the OCP triggers and the PMIC shuts off.

Our doubt is why doesn't this happen in fault state when a load device latches and sinks more current?

Please note the following values of the rail 2 in Fault state-

Vout (after 0 Ohm resistor PN-RK73Z2BTTD ) - 1.36V

Vout (before 0Ohm resistor) - 1.457V

ac coupling 1v8 out

DC coupling 1V8 out

VFB 0.576V

Vsw switching voltage on 1V8 rail

VBST on 1V8 rail.

VPG=0V

VREG=5.6V

Can you help us to find out why this is happening? why aren't we able to see the OCP triggering in and rail switching off.

Please note that once 1V8 is shorted or Input voltage is toggled.

over 1 year ago

0 Lucia Gao over 1 year ago

TI__Mastermind 30151 points

Hi Mandan,

Pls kindly let me check and get back to you soon. Thanks!

BRs

Lucia

0 Mandan Kumar over 1 year ago in reply to Lucia Gao

Prodigy 235 points

___to add the context-

1. When 1V* or 12V is toggled i.e. when PMIC power resets the latch recovers.

2. On bench top set up the transition from 1V8 to fault is quick at 3.3A - there is no intermediate 1V46 stage however in the system integrated setup when the latch happens- it stays at 1V46.

0 Lucia Gao over 1 year ago in reply to Mandan Kumar

TI__Mastermind 30151 points

Hi Manda,

Thanks. Pls kindly let me check and I will get back to you before end of this week.

BRs

Lucia

0 Lucia Gao over 1 year ago in reply to Lucia Gao

TI__Mastermind 30151 points

Mandan Kumar

Mandan Kumar said:
One of the load device in our application system connected from 1V8 on rail 2 is drawing very high current (it is getting hot beyond 100degC on the thermal pad). However we do not see the OCP trigger happening.

What is the actual load current of rail2? For hot beyond 100C, is it the temp for TPS54494 or the downstream device?

Important considerations for this type of over-current protection: The load current is one half of the peak-to-peak inductor current higher than the over-current threshold. Also when the current is being limited, the output voltage tends to fall as the demanded load current may be higher than the current available from the converter. When the over current condition is removed, the output voltage returns to the regulated value.

Thanks!

BRs

Lucia

0 Mandan Kumar over 1 year ago in reply to Lucia Gao

Prodigy 235 points

Hi,

Load current is around 4.5A

0 Lucia Gao over 1 year ago in reply to Mandan Kumar

TI__Mastermind 30151 points

Hi Mandan,

TPS54494 rail 2 supports 2A continuous Load Current. I would not recommend 4.5A for rail2.

Thanks!

BRs

Lucia

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TPS54494: Rail 2 is drawing more current but OCP not triggered