LM3880 issue (Capacitor connected to Enable pin is not discharged)

joshi chintan

Other Parts Discussed in Thread: LM3880

Hello, I had ordered LM3880 for power sequencing purpose. I had connected 22uF capacitor to Enable pin. Circuit Works well, when i powered On VCC supply its gives desired delay (near by 3 seconds), but when i turned OFF the supply, Capacitor connected to ENABLE pin is unable to discharge, So How can i make capacitor discharge when supply becomes off?

over 8 years ago

0 Kaisar Ali over 8 years ago

TI__Intellectual 2010 points

Joshi,
The EN cap provides a glitch free operation and with 22uF, you are also adding ~3.6sec delay time. How does your power down sequence look like. Are you pulling down EN to ground or just turning off the VCC?

0 joshi chintan over 8 years ago in reply to Kaisar Ali

Prodigy 30 points

Hi Kaisar,

This is the circuit i had followed which was given in datasheet for power up sequence only . When i turned off the Vcc supply Capacitor(CEN) not going to discharge automatically. And thats create trouble. Because you can understand if its not discharged then when i power on VCC again, Enable delay will not generate.

0 Mathew Jacob1 over 7 years ago in reply to joshi chintan

TI__Expert 5900 points

Joshi,

There is no internal pull down for the EN pin. Since you want quite a big delay for turn on I would recommend putting a resistor divider from Vcc to EN pin. The resistor divider will set the Vcc voltage at which the part is enabled but more importantly the lower resistor will provide a path for the Cen to discharge.

Mathew

0 joshi chintan over 7 years ago in reply to Mathew Jacob1

Prodigy 30 points

Hy Mathew, I'll try your solution and will see what happen, But thanks for the solution.

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LM3880 issue (Capacitor connected to Enable pin is not discharged)