LM5068EVAL: LM5068

Irene Caponigri

Part Number: LM5068EVAL

Hello,

I'm using your evaluation board LM5068EVAL (input voltage -12V) and I've put a pull-up resistor on PWRGD pin to a 5V external voltage:

- when the output voltage is not good the voltage on PWRGD is -10.4V;

- when the output voltage is good the voltage on PWRGD is 1.2V

why, if the internal circuit on PWRGD is a open-drain, the output voltage is not able to reach the pull-up voltage (5V)?

can you help me?

Irene

over 5 years ago

0 Rakesh over 5 years ago

TI__Guru** 105211 points

Hi Irene,

Can you share me the schematic and pull-up resistor value ? Are you measuring with respect to VEE ? where is the return path of 5V external voltage connected ?

BR, Rakesh

0 Irene Caponigri over 5 years ago in reply to Rakesh

Prodigy 120 points

Hi Rakesh,

the schematic is:

where the reference voltage of 5V_standby is GND_signal;

value of R146 is 4K7 ohm

when micro_logic_en is 5V the output voltage is -12V

when micro_logic_en is 0V the output voltage is 0V;

thanks

Irene

0 Irene Caponigri over 5 years ago in reply to Rakesh

Prodigy 120 points

I've measured it respect PWRGD respect to GND.

Irene

0 Rakesh over 5 years ago in reply to Irene Caponigri

TI__Guru** 105211 points

Hi Irene,

It should be pulled to 5V level.

I have placed order for LM5068EVAL and will check as soon as I get it.

BR, Rakesh

0 Irene Caponigri over 5 years ago in reply to Rakesh

Prodigy 120 points

Hi Rakesh,

please let me know as soon as possible because I have to freeze my schematic.

When you will have the evaluation board?

Irene

0 Rakesh over 5 years ago in reply to Irene Caponigri

TI__Guru** 105211 points

Hi Irene,

I will receive EVM by 18th and will get back to you couple of days after that.

BR, Rakesh

0 Rakesh over 5 years ago in reply to Rakesh

TI__Guru** 105211 points

Hi Irene,

I have received the EVM. I will check and let you know by tomorrow.

Can you share your full schematic.

BR, Rakesh

0 Irene Caponigri over 5 years ago in reply to Rakesh

Prodigy 120 points

OK great,

following the schematic in detail.

Let me know if you need something else.

Thanks

Irene

0 Rakesh over 5 years ago in reply to Irene Caponigri

TI__Guru** 105211 points

Hi Irene,

Is between drawing correct.? 5V is applied between 5V_STDBY and GND_signal

BR, Rakesh

0 Irene Caponigri over 5 years ago in reply to Rakesh

Prodigy 120 points

Yes, I confirm you that the 5V_standby is referred to GND_signal.

Irene

0 Rakesh over 5 years ago in reply to Irene Caponigri

TI__Guru** 105211 points

Hi Irene,

I have observed similar issue on EVM. Let me check with my team about the internal details of PWRGD and get back to you early next week.

Regards, Rakesh

0 Rakesh over 5 years ago in reply to Rakesh

TI__Guru** 105211 points

Hi Irene,

The internal ESD diodes at the PWRGD (between PWRGD to VDD) is getting active because of the external 5V source leading to the voltages different than expected.

To overcome this, pull-up PWRGD to GND_Signal (as shown in datasheet) and then use external level shifter circuit. Let us know if you have follow up questions.