TPS54335A: TPS54335ADRCT

SIDDHARTH MOHAN

Genius 3205 points

Part Number: TPS54335A
Other Parts Discussed in Thread: TPS54308

Hi All,

We are facing an issue on a current design and seek your urgent help using TPS54335ADRCT.

Details:

The regulator is configured so as to have Vin=5v, Vout =4.5v Iload = 2A.

The switching regulator TPS54335ADRCT is fed by a 5V switching regulator which is sourced by the a power supply (5V @3A)

Due to loading & IR drop the voltage fed to the TPS54335ADRCT is about 4.8Volts.

The output of the TPS54335ADRCT fluctuates at around 28Hz with is voltage waveform from 0.8 to 4.5V (a square wave)

The output tracks the input.

TI webench calculator won’t provide a solution for a Vin of 5V @ 2A output with Vout=4.5V

We need some help in reviewing this SW regulator on high loads & temperature stress.

over 7 years ago

0 Vental Mao over 7 years ago

TI__Expert 5745 points

pls upload your schematic and layout.

I think the main reason is the V(boot-PH) is less than 2.1V. If the V(BOOT-PH) ≥ 3 V, the min off-time can be 0

0 SIDDHARTH MOHAN over 7 years ago in reply to Vental Mao

Genius 3205 points

thanks for the reply, i can send you my tina schematic , please provide email id.

0 SIDDHARTH MOHAN over 7 years ago in reply to Vental Mao

Genius 3205 points

also can you please detail a bit on which off time are you referring to when mentioning V(BOOT-PH) ≥ 3 V, the min off-time can be 0

0 Vental Mao over 7 years ago in reply to SIDDHARTH MOHAN

TI__Expert 5745 points

0 SIDDHARTH MOHAN over 7 years ago in reply to Vental Mao

Genius 3205 points

thanks Vental i am unable to understand the consequences of this. can you please details a bit.

0 Vental Mao over 7 years ago in reply to SIDDHARTH MOHAN

TI__Expert 5745 points

When the voltage between BOOT and PH pins drops below the BOOT-PH UVLO threshold, which is 2.1 V (typical), the high-side MOSFET turns off and the low-side MOSFET turns on(this time called off-time), allowing the boot capacitor to recharge, the Vout will drop.

In your application, the Vout is close to Vin, the Duty is big which also means the off-time is very short. So the boot cap charge time (off-time) is too samll and can't provide enough energy to open Hi-side MOS during the Duty*Fsw.

0 SIDDHARTH MOHAN over 7 years ago in reply to Vental Mao

Genius 3205 points

thanks Vental so what is the consequences of not being able to open the Hi-side MOS during the Duty*Fsw ?

0 Vental Mao over 7 years ago in reply to SIDDHARTH MOHAN

TI__Expert 5745 points

if H-side MOS can't turn on, the Vout will drop, and after the boot cap charge to above 2.1V, the H-side MOS turn on, the Vout will increase again.

0 SIDDHARTH MOHAN over 7 years ago in reply to Vental Mao

Genius 3205 points

Thanks for the reply, i am uanble to change the configuration at present because my input source can't give more than 5v in current application , so is there a solution out to this pleasE?

0 SIDDHARTH MOHAN over 7 years ago in reply to SIDDHARTH MOHAN

Genius 3205 points

Hi Can anyone let me know a pin equivalent part that has low rds of the FETs so to support the configuration of Vin=5v, Vout=4.5v, Iload = 2A

0 Vental Mao over 7 years ago in reply to SIDDHARTH MOHAN

TI__Expert 5745 points

Try TPS54308

Or use the WEBENCH to find your need

0 SIDDHARTH MOHAN over 7 years ago in reply to Vental Mao

Genius 3205 points

thanks for the reply, is this pin to pin compatible ?

0 Vental Mao over 7 years ago in reply to SIDDHARTH MOHAN

TI__Expert 5745 points

No, tps54308 is more easy to use with 6-pin

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TPS54335A: TPS54335ADRCT