GD32W51x User Manual
911
6.
Charge transfer
ASW_0 and ASW_1 are closed and PIN0 is configured to input floating to transfer charge
from C
x
to C
s
. The transfer time should be configured (see Register Section for detail) to
ensure the full transfer after that the voltage of C
x
and C
s
will be equal.
7.
Buffer Time3
Buffer time with ASW_0 and ASW_1 open, PIN0 is configured to input floating.
8.
Compare
ASW_0, ASW_1 and PIN0 remain the configuration of Step7. At this step, the voltage of
sample pin PIN1 is compared to a threshold called
V
th
. If voltage of PIN1 is lower than V
th
,
the sequence returns to Step2 and continues, otherwise, the sequence ends.
The voltage of sample pin V
s
is zero after initial step and increases after each charge cycle,
Figure 26-3. Voltage of a sample pin during charge-transfer sequence.
A
larger C
x
will cause a greater increase during a cycle. The sequence stops when V
s
reaches V
th
. Each group has a counter which records the number of cycles performed on it
to reach V
th
. At the end of charge-transfer sequence, the group counter is read out to estimate
the C
x
, i.e. a smaller counter values indicates a larger C
x
.
Figure 26-3. Voltage of a sample pin during charge-transfer sequence
26.3.4.
Charge transfer sequence FSM
A hardware Finite-state machine (FSM) is designed in chip to perform the charge transfer
sequence described in the previous section as shown in
Figure 26-4. FSM flow of a charge-
0
3.3
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
Cycle Number
V
th
Vs