Z86D990 Datasheet, PDF (37/102 Pages) Zilog, Inc. – Low-Voltage Micro controllers with ADC

Z86D990/Z86D991 OTP and Z86L99X ROM
Low-Voltage Microcontrollers with ADC
30
Filter response
0
2
4
6
8
10
12
14
16
18
20
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
log10(f)
Figure 15. Low-Pass Filter (with 8-MHz Crystal)
The sampling frequency of the modulator f_ADC can be selected between f_SCLK and
f_SCLK/2 (bit1 from ADCCTRL). Reducing the clock frequency lowers the power
dissipated in the ADC block.
The ADC can be enabled or disabled. When enabled, the Σ∆ converter tracks the
input voltage. When switching between the channels (step response), the
required time to reach the final value is given by the time constant of the low-pass
filter:
T_delay
=
----2----
f_3db
=
-------------2--------------
0.0021f_ADC
=
--9---5---2--
f_ADC
When available, the reference for the ADC is set externally with the V_ref+ and V_ref-
pins. The output code represents the following ratio:
D_out
=
---^V----ⁱ--ⁿ---–-----^V----^R---^e--^f--^---
V_Ref+ – V_Ref-
×
256
PS003807-1002
PRELIMINARY