Hi,
I'm using TP51916 on a new design with DDR3.
At startup, PGOOD is pulsing high, 1.2ms, then goes low as captured below.
As PGOOD is controling the board reset, the complete board is held in reset.
The output voltage is measured to be 1,345V. DDR3L requires 1,35V. So it's fine for my application.
The reference voltage is 1,348V. This is less than 1% error.
The datasheet says that PGOOD unvalidates when output voltage deviates more than +/-16% of the ref voltage. That is not my case.
The part is configured in mode 3: DCAP2 / 500kHz.
I have also made a screenshoot of the pulse on the mode PIN at startup.
The voltage is 490 mV. According to the table p7, this is inline with mode 3.
Below is a screen capture of the output noise, when the device is loaded at 3 Amps.
I was expecting to see 500kHz pulses. That is not obvious on the screen shot.
Lastely, I'm sharing the schematics.
I have simulated the design with Webench.
Everything is fine there. Unfortunately, I cannot probe the PGOOD indicator in the simulator.
When I manually disable the device (forcing S3 and S5 low) then re-enabling the device, PGOOD behaves the same.
I have asked my local TI support for a TPS51916 demo board to perform comparison.
Any ideas about the reason that makes PGOOD going low?
Regards,
Pierre
