LPC553x number of usable external ADC channels

[MartinHo]

Hi,

I have a Bard that uses the LPC15xx that we whant to "update" to the LPC553x.

THe Board uses a lot of the LPC15xx (100 pin case) resources, amount them 20 ADC input's (and 25 PWM output's!)

I attempted to map all this resources to the LPC553x, But are running in some troubles with the available ADC input's. There is a ADC channel mapped to the Opamp2Out Output's (but not the the dedicated input's), and to VREFOUT and VREFN, is it possible to use this ADC channel as inputs?

Further more I will need 1 DAC channel, this is blocking an other ADC Input (Both DAC's with output Pin are mapped over an ADC Input pin).

Martin

[xiangjun_rong]

Hi,

Regarding your question, as you have seen that the OPAMP output pin and DAC pins are shared with ADC analog channels, but both the OPAMP and DAC can be disabled, in the case, you can connect analog source to the ADC analog pins which are shared with OPAMP output pins or DAC output pins.

From the following screenshot I copied from LPC553XRM.PDF, for the LPC5536 with QFP100 package, there are total 23 single-ended analog channels,  among of them there are 9 differential channels. Of course, because the DAC output pin is shared with ADC analog channel, if you use one DAC output, the ADC analog channels you can use becomes to 22.

Regarding the PWM, there are two eFlexPWM modules, one SCTimer module and 5 Ctimer modules, the two eFlexPWM can generate at least 2*8=16 PWM channels, the SCTimer can generate 10 PWM signals, so it is okay for the PWM.

Hope it can help you

BR

XiangJun Rong

[MartinHo]

Hi XiangJun Rong

Thanks for the answer, i don't know how they count 23 Input's. If I count the pins with ADC function in the Data sheet (Capter 6.1), I'm counting 20, and this includes VREFN and VREFOUT.

My main question is can I use VREFN and/or VREFOUT as general purpose ADC Input's?

My undestanding is that at least VREFN is always used by the ADC's, so has to stay at VSS or near VSS. I didn't find any possibility to switch the ADC reference to VSS.

Best regards

Martin 

[xiangjun_rong]

Hi,

As the following screenshot in LPC553XRM.pdf, you can count the channel as the blue circle, it is 23 channels.

BR

XiangJun Rong

[MartinHo]

Hi,

Yes nice table, but the pins 14,16 and 31 are counted twice (they are usable from both ADC's, but i can't connect two inputs to 1 pin!).

Martin

[xiangjun_rong · Accepted solution]

Hi, Martin,

Pls refer to the section 46.1.3 ADC voltage reference options

If you set REFSEL[7:6]=2, the internal VDDA is connected to the Vrefh as ADC reference voltage, in the case the Vrefp/vrefn pins are not used, the pin 16 of LQFP100 will function as ADC1IN5B(ADC1 CHB5).

For the Vrefout pin, Pin 14 of LQFP100(ADC0IN5A/VREF_OUT), the Voltage Reference (VREF) is an independent module which can output adjustable reference voltage. Pls refer to Chapter 51 Voltage Reference (VREF). When the Vref module is disabled, the pin 14 will function  as ADC0IN5A channel.

Hope it can help you

BR

XiangJun Rong