06/09/20

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ES51991

11,000 Counts ADC

2. Component Value Selection for ADC

For various application requirements on conversion rate and input full range, we

suggest nominal values for external components of ADC in Figure 1 to obtain better

performance. Under default condition with operating clock = 12 MHz:

(1) conversion rate = 8 times/sec

(2) reference voltage = -100 mV

(3) input signal full scale = 110 mV (sensitivity = 10 uV)

We suggest that Cint = 68 nF, Buf = 56 k

Ω

If a user selects a different conversion rate rather than default, the integration

capacitor Cint value must be changed according to the following rule for better

performance:

Cint

× (conversion rate) = (68 nF) × (8 times/sec).

A smaller Cint reduces the input full range. However a larger Cint might have

weaker noise immunity than the suggested one.

A user could enlarge the input full range by changing reference voltage (Vref) and

the amount of integration resistor (Buf). For example, if Vref & Buf are enlarged as

twice than the default values then the input full range becomes 220 mV. The input full

range can be enlarged up to 1.1V (10 times than the default case). We list general rules

in below which might be helpful in determining component values.

Buf / (reference voltage) = 56 k

Ω / (-100 mV)