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 kΩ
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 kΩ / (-100 mV)
6
06/09/20
CYRUSTEK [ Cyrustek corporation ]
