Dual Sample and Hold
309
SNIU028A – February 2016 – Revised April 2016
Copyright © 2016, Texas Instruments Incorporated
ADC12 Overview
•
From this table, it can be seen that the location of the “moving zero” determines the number of
selected channel. Since only one channel at a time can be selected, the only valid values for
BYPASS_EN[2:0] are 6, 5 and 3.
•
The “Dual Sampled Channel” must be placed in the sequence anywhere after the “converting channel”.
•
Simultaneous sampling of the “Converted channel” with the “sample and hold channel” is determined
by setting the bits SEQ0_SH, SEQ2_SH and SEQ04_SH in ADCSEQSEL registers. For example if
SEQ4_SH is set, then one of the channels (0, 1 or 2) will be sampled together with channel 4 sampling
time.
•
Only channels CH0, CH2 and CH4 can be selected as “Converting channels” in UCD3138. Therefore
setting of SEQx_SH bits on any channel other than CH-0, CH-2 and CH-4 is not effective.
8.14.1 ADC Control Register (ADCCTRL)
Address 0x00040000
Figure 8-14. ADC Control Register (ADCCTRL)
12
11
10
8
7
4
ADC_SEL_
REF
ADC_
ROUND
BYPASS_EN
MAX_CONV
R/W-0
R/W-0
R/W-111
R/W-0000
LEGEND: R/W = Read/Write; R = Read only; -
n
= value after reset
Table 8-4. ADC Control Register (ADCCTRL) Register Field Descriptions
Bit
Field
Type
Reset
Description
12
ADC_SEL_REF
R/W
0
11
ADC_ROUND
R/W
0
10-8
BYPASS_EN
R/W
111
Bypasses the dual sample and hold circuitry, Bit 10 controls ADC Channel 2, Bit 9
controls ADC Channel 1 and Bit 8 controls ADC Channel 0
0 = Enables the Dual Sample and Hold circuitry
1 = Disables the Dual Sample and Hold circuitry (Default)
7-4
MAX_CONV
R/W
0000
8.15 Usage of Sample and Hold Circuitry for High Impedance Measurement
In UCD3138, there is another solution to this problem: use dual sample and hold circuitry. The dual
sample and hold circuitry are designed to enable the sampling of two channels together, thus it’s suitable
for power measurement, which requires that the sampling of voltage and current are in phase. There is
only one conversion unit in UCD3138 ADC. But there are two S/H units to enable dual sample and hold
function. The first one is the normal one we used for all channels. The second one shown in
is
the dual sample and hold S/H. If dual sample and hold function is enabled, two S/H units will work
simultaneously. There is an S/H buffer inside the circuitry which makes the source impedance much
lower. Thus this circuitry can be used for high impedance node measurement as well.
SEQx = y selects channel y to be converted in sequence x of the first S/H unit.
SEQx_SH = 1 enables the dual sample and hold S/H to sample at the same time as channel y.
BYPASS_EN selects the dual sample and hold channel. This register has 3 bits. 1 means bypass and 0
means connect to the S/H buffer. As shown in
.