CY8C28xxx PSoC Programmable System-on-Chip TRM, Document No. 001-52594 Rev. *G
421
21. Analog Reference
This chapter discusses the Analog Reference generator and its associated register. The reference generator establishes a
set of three internally fixed reference voltages for AGND, RefHi, and RefLo. For PSoC
®
devices with one analog column, a
fixed analog ground (AGND) of Vdd/2 is supplied. For a quick reference of all PSoC registers in address order, refer to the
Register Details chapter on page 125
.
21.1
Architectural Description
The PSoC device is a single supply part, with no negative
voltage available or applicable. Depending on the number of
analog columns in your PSoC device (refer to the table titled
“PSoC Device Characteristics” on page 387
),
shows the analog reference control schematic.
Analog ground (AGND) is constructed near mid-supply. This
ground is routed to all analog blocks and separately buffered
within each block. Note that there may be a small offset volt-
age between buffered analog grounds. RefHi and RefLo sig-
nals are generated, buffered, and routed to the analog
blocks. RefHi and RefLo are used to set the conversion
range (that is, span) of
converters. RefHi and RefLo can also be
used to set thresholds in comparators for four and two col-
umn PSoC devices.
The reference array supplies voltage to all blocks and cur-
rent to the Switched Capacitor blocks. At higher block clock
rates, there is increased reference current demand; the ref-
erence power should be set equal to the highest power level
of the analog blocks used.
Figure 21-1. Analog Reference Structure
Figure 21-2. Analog Reference Control Schematic
Vss
VAGND
AGND
RefHi
RefLo
V
RefHi
V
RefLo
RefHi to
Analog
Blocks
Vdd
Vss
RefLo to
Analog
Blocks
AGND
(Vdd/2)
1 Analog Column
Vbandgap
Vdd/2
P2[6]
Vdd
Vss
RefHi to
Analog
Blocks
RefLo to
Analog
Blocks
AGND
P2[4] (External Cap)
Vbandgap
P2[4]
x1
x1
x1.6
x2
4 and 2 Analog Columns
R
R
8.1K
0.4K
Summary of Contents for CY8C28 series
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