Internal pull-up of CHIP_EN

hfcheng
Posts: 2
Joined: Mon Aug 31, 2015 6:09 pm

Internal pull-up of CHIP_EN

Postby hfcheng » Tue Sep 01, 2015 12:04 pm

Hello,

Could you confirm whether the internal pull-up exists for the CHIP_EN pin?
From English datasheet, Section 2.2.2 it is said there is an internal pull-up but Chinese version of the data does not say so.

Thanks.

BuGless
Posts: 10
Joined: Wed Sep 09, 2015 1:28 am

Re: Internal pull-up of CHIP_EN

Postby BuGless » Thu Sep 17, 2015 9:01 pm

When reading between the lines, I'm guessing that the pin indeed *has* an internal pull-up, however...

These internal pull-ups (on all of those pins where they are) probably are reasonably weak (I'm guessing >50kohm).
So that implies that they work perfectly fine if pins are non-critical and left dangling *without* copper attached.
However, the CHIP_EN and nRESET pins are both critical, and usually have some copper attached due to you wanting to control them from the outside. The copper attached to the pins is subject to RF-spike-reception, and thus is able to pull that pin down momentarily despite the weak pull-up present.

So I'd recommend not relying on the internal pull-up for critical pins like CHIP_EN and nRESET. Other pins could be relied upon, if they have no copper attached only.

YimingLi
Posts: 59
Joined: Sun May 03, 2015 5:36 pm

Re: Internal pull-up of CHIP_EN

Postby YimingLi » Mon Sep 28, 2015 12:46 pm

Well according to my experience, the chip_en has no internal pullup and MUST have an external pullup. If there is no external pullup the chip will not work just like in a powered off status. However, there is a good enough pullup in the nRESET pin therefore a float to nRESET will be OK enough. In a customised module(http://www.ebay.com/itm/282162857143) and http://www.ebay.com/itm/282162896341, even a long wire of net nRESET is routed to the two external connectors but without any pullup, it is quite stable as well, quite immune to some external interference.
Last edited by YimingLi on Tue Sep 20, 2016 1:17 pm, edited 1 time in total.

BuGless
Posts: 10
Joined: Wed Sep 09, 2015 1:28 am

Re: Internal pull-up of CHIP_EN

Postby BuGless » Thu Oct 01, 2015 3:58 pm

Did you try to measure the internal nRESET pull-up?
(I.e. attach a capacitor, and then measure the time it takes to charge it?)

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