Does anyone use the LPC176* uPs?
I need to know how much current the ADC/DAC VREFP pin uses, and I can't find that anywhere. You'd think they might spec that.
They recommend filtering it, but the eval board uses a ferrite bead.
torsdag den 9. januar 2020 kl. 02.06.09 UTC+1 skrev John Larkin:
google says,
"The input impedance of Vref is around 7k Ohms, so this should be taken into consideration when using a voltage divider on this input."
Thanks. I did search the NXP community posts, with various keywords, and didn't find that one.
I can probably use a 50 ohm series resistor.
It may need a capacitor to handle pulse currents.
Sure, all my voltage reference noise filters involve capacitors somewhere.
Maybe I'll provide a separate voltage reference for the uP ADC, a local bandgap and cap. Then I can digitize and check the *other* reference. 3V for the uP, 2.5 for everything else.
This will be a lithium niobate EO modulator driver, with a very expensive (over $200) distributed amplifier chip. It has a lot of sequencing requirements and a lot of protections.
We use that series of parts. Always place some capacitance across the A/D input to analog Vss.... Usually this is my 1st order low pass anyway.
For Vref+ I just use a small resistance and a capacitor. 1 Ohm or a few more does pretty well.
OK, sounds like a few ohms, 10 or so maybe, and a pretty big ceramic cap would be OK.
Or my dedicated 3V bandgap running at a few mA.
The NXP data sheets are weird. They specify the analog power and reference currents in various shutdown modes, but not operating.
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