TPS23753AEVM-004: design discussion

user4979999

Prodigy 690 points

Part Number: TPS23753AEVM-004

Hi,

Here’re some questions from customer about TPS23753A-004EVM.

1. For the original EVM which is synchronous MOS at secondary side, why it will be CCM even load=0A? What’s the gate turn on/off criteria? When changed secondary MOS to diode SBR10U45SP5-13, it will into DCM when light load.

[MOS]0A

[Diode]0.5A

2.Why the VCS signal will be negative when using synchronous MOS at load=0A?

3. When use diode and the load=0A, we will see the gate like below(until load add to 20ma, then gate become stable and fixed frequency), Is that unstable?

(ignore channel 3, there's no gate due to diode)

[0A]

[20mA]

thanks.

over 6 years ago

0 Darwin Fernandez over 6 years ago

TI__Mastermind 41770 points

Hi Lynn,

1. Synchronous allows reverse current this is why is stays at CCM. A diode would block the reverse current.
2. Same as #1
3. This is not unstable, this is normal behavior. At no load, it's possible the converter will pulse skip because there is no need to turn on the primary FET to charge the transformer. Therefore it could skip pulses. The frequency of the pulses will be relative to the amount of output cap. At some point, as you add load, it allows the output cap to discharge so the DCDC will need to have longer pulses to transfer the energy.

0 user4979999 over 6 years ago in reply to Darwin Fernandez

TI__Prodigy 690 points

Hi Darwin,

thanks for feedback. customer wonder the pwm on/off criteria details, can you explain the block diagram? The gate will stop switching when VCTL<VZDC? And the VCS>VCSMAX also stop switching?

0 Darwin Fernandez over 6 years ago in reply to user4979999

TI__Mastermind 41770 points

Hi Lynn,

Yes this is correct. Also when there is no more gate drive (VC < VCUVLO) and the PWM controller will stop switching.

Power management

Power management forum

TPS23753AEVM-004: design discussion

1. For the original EVM which is synchronous MOS at secondary side, why it will be CCM even load=0A? What’s the gate turn on/off criteria? When changed secondary MOS to diode SBR10U45SP5-13, it will into DCM when light load.

2.Why the VCS signal will be negative when using synchronous MOS at load=0A?

3. When use diode and the load=0A, we will see the gate like below(until load add to 20ma, then gate become stable and fixed frequency), Is that unstable?