LMQ61460: Supply rise time at different load condition

Amit Gade

Prodigy 70 points

Part Number: LMQ61460
Other Parts Discussed in Thread: TPSM63603EVM

Tool/software:

Hello Team,

We have requirement of +5V and -5V power supply for our design as per below specifications.

Input voltage = 12V-24V

Output voltage 1 = +5V 4A

Output voltage 2 = -5V 0.5A

We are planning to use LMQ61460AFSQRJRRQ1 for +5V and TPSM63603SRDHR for -5V (as both has same 5mS typical internal soft start)

Our question is, will both power supplies (+5V and -5V) ramp at same time as per the internal 5mS soft start circuit with different load conditions on each rail ?

for our application both supplies should ramp up simultaneously.

Do we need to implement any additional circuits to match the ramp time of both supplies?

Regards,

Amit

2 months ago

0 Niranjan Nair 2 months ago

TI__Genius 9280 points

Hi Amit,

What is the nature of the load at both +5 and -5? Is it a constant current or resistive load?

Regards,

Niranjan

0 Amit Gade 2 months ago in reply to Niranjan Nair

Prodigy 70 points

Hi Niranjan,

+5V will be for Mixed signal boards, which consist digital section with Processors, memories, USB's etc load) and Analog section which consist of Op amps and ADC's. (this +5V requires 4A current)

-5V will be for analog section for Op amps and ADC's. ( this -V requires 0.5A current)

Regards,

Amit

0 Niranjan Nair 2 months ago in reply to Amit Gade

TI__Genius 9280 points

Hi Amit,

The 5 ms value given is the typical soft start and it can vary from 3.5 to 7 ms. The difference in load would further affect the charging time of the output. Overall it will be difficult to avoid a difference of few ms between the two rails reaching their target outputs.

Is this difference manageable/ what is the maximum allowable difference?

Regards,

Niranjan

0 Niranjan Nair 2 months ago in reply to Niranjan Nair

TI__Genius 9280 points

Hi Amit,

Any update on this?

Regards,

Niranjan

0 Amit Gade 2 months ago in reply to Niranjan Nair

Prodigy 70 points

Hi Niranjan,

The few ms (2-3ms) between difference between both rails are acceptable , also I checked rise timing with LMQ61460EVM-400K for 5+V and TPSM63603EVM for -5V, it looks nearly same.

0 Amit Gade 2 months ago in reply to Niranjan Nair

Prodigy 70 points

Also , I observed there is 320mV positive peak on negative -5V supply rail with TPSM63603EVM and MBRS2H100T3G Schottky diode at output, is there any other way to clip this positive voltage more or any other Schottky diode recommendation to solve this?

Regards

Amit

0 Niranjan Nair 2 months ago in reply to Amit Gade

TI__Genius 9280 points

Hi Amit,

A Schottky diode with a lower forward voltage should reduce the peak more, though I am not sure if you will get VF less than 300 mV.

Increasing the output capacitance would also help to an extent.

Regards,

Niranjan

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LMQ61460: Supply rise time at different load condition