TPS546C23: Duty cycle parametr

Gia

Part Number: TPS546C23

Hello. I use TPS546C23 in the recommended scheme
V1n=12V ,Vout=5V , F=500kHz, L=300nH (IHLP5050EZERR33M5A), Cout=4*220mkF (16V)
1. If there is no load ,
   Pin=2.8W, Vout=5V, duty cycle = 43% (???) (Pic_1)
   Why the duty cycle is not equal to minimum?
2. Load = 0.5 ohm
   Pin=53W, Vout=5V (!), duty cycle = 43% (???) (Pic_2)
   Why is the duty cycle not changed?
What's wrong?

Pic_1

Pic_2

over 5 years ago

0 JohnTucker over 5 years ago

TI__Guru**** 191445 points

Gia,

Duty cycle is approximately equal to Vout / Vin. So for your case D = 5/12 = .42 = 42%. there will be some slight loss n the switching FETs that will cause the observed duty cycle to be higher than the ideal of Vin/Vout as you observe.

0 Gia over 5 years ago in reply to JohnTucker

Prodigy 160 points

Thanks.
But there is another question.
1.Here is the TINA model for a load=120W (pic3)
2.Here is the TINA model for a load=2.5W (pic4)
3.Here is the TINA model for a no load, there is no generation on the SW output (pin8--12)
4.And when there is no load , the inductance is very hot, and the input power consumption is equal to 2.5W

Pic3

pic4

0 Peter James Miller over 5 years ago in reply to Gia

TI__Guru 56925 points

Gia,

2.8W of input power (233mA input current) seems unusually high for a 5V output with the TPS546C23 running at 500kHz. The simulation waveforms appear to be showing the TPS546C23 operating in discontinuous conduction mode with no low-side FET on-time. This only occurs at the very beginning of soft-start in the TPS546C23 and not through normal operation. I will ask the TINA modeling team to look into the issue.

0 Gia over 5 years ago in reply to Peter James Miller

Prodigy 160 points

Thanks. There are another question.

In the program TINA , if Pout=10-150W . Pin<0.1W

Error ???

0 JohnTucker over 5 years ago in reply to Gia

TI__Guru**** 191445 points

Gia,

That model does not support modeling of input current.

Power management

Power management forum

TPS546C23: Duty cycle parametr