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Internal reference generator not accurate

Bjarte Hetland
Prodigy 10 points

Other Parts Discussed in Thread: MSP430F2619S-HT, MSP430F2619

Hello,

I am using the msp430F2619S-HT MCU and I am trying to get 2.5V internal reference from internal reference generator, but what I see on Vref+ pin is only 2.239V. My code is:

#include "msp430F2619.h"

 

void main(void)

{

 WDTCTL = WDTPW+WDTHOLD;                              // Stop watchdog timer

 ADC12CTL0 |= REF2_5V;                                          // reference generator voltage 1 = 2.5V; 0 = 1.5V

 ADC12CTL0 |= REFON;                                             // reference generator ON

 

 while(1){}                                                                       // MAIN LOOP

 

}

When I tried to get 1.5V clearing the REF2_5V bit I have got 1.479V on Vref+ pin.

I am powering my board from JTAG (3.04V) but I tried also external supply voltage (3.668V) and I received 2.471V on Vref+ pin.

It is not normal, because I should receive 2.5 even when my Vcc is 3V, that says datasheet.

I am using MSP-TS430PM64 standalone ZIF socket target board and here you can find schematics http://focus.ti.com/lit/ug/slau278f/slau278f.pdf

What could be the reason for that I don't receiveing accurate 2.5 voltage?

 

 

  • 0
    Guru 227245 points

    The internal reference shouldn't be below 2.4V if VCC is 3V.

    However, the reference requires a 10µF tantalum and 100nF ceramic capacitor to AVSS. Without these capacitors, the reference is very distorted and what you read on a multimeter is an averaged value over noise and oscillation effects. If you look at the reference with a scope, you'll see what really happens.

    On the board schematics, the 10µF is marked as 'not assembled' and there is no 100nF ceramic at all.

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