SLAZ290AC October   2012  – May 2021 MSP430F5438A , MSP430F5438A-EP

 

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6.2 ADC27

ADC Module

Category

Functional

Function

Integral and differential non-linearity exceed specifications

Description

The ADC12_A integral and differential non-linearity may exceed the limits specified in the data sheet under the following conditions:

- If the internal voltage reference generator is used

and

- If the reference voltage is not buffered off-chip

and

- If fADC12CLK > 2.7 MHz

The non-linearity can be up to tens of LSBs. This is due to the internal reference buffer providing insufficient drive for the switched capacitor array of the ADC12_A.

Workaround

(1) Turn on the output of the internal voltage reference to increase the drive strength of the reference to the ADC_12 core:

- If REFMSTR bit in REFCTL0 is 0 (allowing Shared REF to be controlled by ADC_A reference control bits)

Set ADC12REFON bit in ADC12CTL0 = 1

and

Set ADC12REFOUT bit in ADC12CTL2 = 1

- If REFMSTR bit in REFCTL0 is 1

Set REFON and REFOUT bits in REFCTL0 = 1

OR

(2) Ensure fADC12CLK < 2.7 MHz. Depending on the frequency of the source of fADC12CLK (ACLK, MCLK, SMCLK, or MODOSC), select the divider bits accordingly.

- If fADC12CLK = MODOSC

(ADC12OSC) ADC12CTL1 |= ADC12DIV_1; // Divide clock by 2

- If fADC12CLK = ACLK/SMCLK/MCLK > 2.7 MHz.

Use ADC12DIVx and/or ADC12PDIVx bits to reduce the selected clock frequency to between 0.45 MHz and 2.7 MHz.