TPS54821: Pull down EN pin

Thanks to the reply.

I post this topic for better understanding how EN pin work with internal pull up current sources.

Refer to datasheet, TPS54821 allows user to float EN pin for enabling it by internal pull-up current source. Then...

Q1: Are these any internal pull-down resister or similar part driven by this pull-up current source, so that can generate a voltage greater than 1.21V to active the DC/DC? This will help me to calculate the external pull-down resister by 1.21V / Ip. The value much smaller than 1.21/Ip will keep EN low when these is no other current source to it.  Can I consider the external pull-down resister in parallel with the internal pull-down resister(I should be a high resister).

As soon as the logic "1" to the EN pin, additional Ih will be added to drive more higher pull-up current. Then...

Q2: What is the purpose of this Ih and how it affect the on/off control on EN pin? 

Hi,

A1: Yes, there's a default pull-up current source to make EN-pin voltage larger than 1.21V to enable the device. Once the EN logic high, Ih will be added like you said.

A2: Ih sets a hysteresis window. The EN thresholds are different when EN rising and when EN falling. That's a convenient way to avoid device repeatedly on and off when EN voltage near threshold.

Got more by the two replies.

Go back to the OD and OC issues in the original post. Same as Fig 22. in the datasheet of tps54821, EN connects to PG out which is OD gate without pull-up. I consider all the drive capability comes from down-stream 54821's pull-up current source which is uA level. 

Two tps54821s support OD connection without pull-up resister on PG. What about connecting other dc/dc's OD PG to  tps54821's EN? These is a parameter "output high leakage" on PG pin which shares the uA level current(no pull-up on PG) providing by down-stream tps54821. 

I just checked about the leakage current values of LDO tps74801 and lp5912, max. values are up to 1uA. 

I am not sure when up-stream dc/dc's/LDO's PG requests uA level or closed value without external pull-up resister on it, the PG pin is able to raise up to 1.21V. 

The same question to the status of PG low without pull-up on it. Is uA level current provided by down-stream EN pin enough to drive up-stream PG(no pull-up) LOW?

Hi,

Sorry I don't understand your questions, whether you use GPIO port control or tps74801/lp5912 PG-pin control? Please clarify your actual concerns, thank you.

Besides GPIO control issue, these is another OD/OC question in my post. It is similar to the post below in 2nd question:

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/657083/tps54821-tps54821-using-problem

I fully believe it supports connection of two tps54821 together because of Fig 22 in datasheet. What about connect other PG(without pull-up resister) to tps54821's EN? Just as LDO tps74801 and lp5912, max. values of PG's high leakage current are up to 1uA.

Hi,

Miranda will reply you later today.