TPS40090: External Error amplifier to Idroop

Tried this on eval board and it looks like max limit is 0.812V, follow up question is , can i connect external error amp. out to comp pin. If yes, where should i tie FB and Idroop pin.

Hi

Team is working on this and will get back to your next monday.

Regards

Yihe

Hello, 

What is the purpose of not using the internal 700mV reference? I think the internal IDROOP current source circuit is limited to 0.8V. 

Regards

We have external error amplifier. We are not planning to use internal Vref is because we need to change our setpoint/reference at different levels instead of one single reference, application is constant current (at different current levels). Question i have is, can i feed the external error directly to comp pin and connect FB pin to Vref and leave Idroop and Vref unconnected.

Hello,

The internal error amplifier is not configured in high impedance. Connecting an external amplifier may cause problem. You may try on an EVM board.

Regards 

Tired connecting external error amplifier to the comp pin, it looks like it is able to take the external error amp input to the comp pin.

Datasheet shows VOH=2.9V and VOL=0.5V. Could you let me know what the minimum error voltage we could feed to the comp pin. We could not feed voltage <1.4V to the comp pin, output shuts down <1.4V.

Hello, 

When the error amplifier is in open loop V+ > V-, VCOMP is high (VOH = 2.9V at 1mA sourcing) and V+ > V-, VCOMP is low (VOL = 0.5V at 1mA sinking).

Are you trying to apply external voltage at COMP pin? and this voltage does not go below 1.4V. Did you measure the COMP voltage before forcing and external voltage?

Regards

I am applying external voltage to comp pin, i can provide <1.4V, but what my question was, if i try applying lower than 1.4V, output shutdown, it looks like min voltage on comp pin is 1.4V to get any PWM/duty cycle, is this correct?

That is right. If VCOMP < 1.4V, PWM output is low.

Regards

Thank you for confirming, is this specified in the datasheet anywhere?