value of pull down resistor

K_S_Lin — Mon, 19 Sep 2016 03:21:49 GMT

hi supporters,

customer is designing LPC11U37 and needs to know below four numbers(strong pull-up、strong pull-down、weak pull-up and weak pull-down) which datasheet doesn't explain it, please help to provide this thanks.

Re: value of pull down resistor

rolfmeeser — Mon, 19 Sep 2016 10:29:16 GMT

Hi KS,

It's the weak pull-up and pull-down what is meant by the terms pull-up and pull-down resistor throughout the user manual and data sheet.

The strong pull-up and pull-down in the block diagram you've posted represent the push-pull output stage of the pin! They are never referred to as pull-up or pull-down anywhere else in user manual or data sheet.

Technically both are MOSFET's with a certain ON resistance when enabled.

The (weak) pull-up and pull-down MOSFET's are equivalent (typically) to a resistor of 60k. The data sheet contains an incorrect non-linear V-I characteristic of the pull-up and pull-down (figures 19/20 in data sheet 2.2). This non-linear behaviour applies to older chip generations (e.g. early LPC1114) only. On LPC11U37 both pull-up and pull-down are almost perfectly linear resistors over the whole input voltage range (0...VDD).

As for the push-pull output stage (the strong version), the MOSFET's also act like linear resistors of typically 50 Ohms (max 100 Ohms) while in their operating area (which we specify up to 4 mA current). They are short-circuit protected, so they will saturate when output current becomes to high.

See figures 17/18 for the typical values, table 5 for the worst case values. Note that the high-side driver of the PIO0_7 output stage is different as it can drive several times the current of a standard port pin.

Regards,

Rolf

Re: value of pull down resistor

K_S_Lin — Tue, 04 Oct 2016 03:32:49 GMT

got it, thanks Rolf.

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