CY8C28xxx PSoC Programmable System-on-Chip TRM, Document No. 001-52594 Rev. *G
511
29. Internal Voltage Reference
This chapter discusses the Internal Voltage Reference and its associated register. The internal voltage reference provides an
absolute value of 1.3 V to a variety of subsystems in the PSoC device. For a quick reference of all PSoC
®
registers in address
order, refer to the
Register Details chapter on page 125
.
29.1
Architectural Description
The Internal Voltage Reference is made up of two blocks: a
bandgap voltage generator and a buffer with sample and
hold. The bandgap voltage generator is a typical (V
BE
+ K
V
T
) design.
The buffer circuit provides gain to the 1.20 V bandgap volt-
age, to produce a 1.30 V reference. A simplified
is illustrated in
. The connection between ampli-
fier and capacitor is made through a CMOS switch, allowing
the reference voltage to be used by the system while the ref-
erence circuit is powered down. The voltage reference is
trimmed to 1.30 V at room temperature.
A temperature proportional voltage is also produced in this
block for use in temperature sensing.
Figure 29-1. Voltage Reference Schematic
29.2
Register Definitions
The following register is associated with the Internal Voltage Reference. The Internal Voltage Reference is trimmed for gain
and temperature coefficient using the BDG_TR register. The register description below has an associated register table
showing the bit structure. The bits that are grayed out in the table are reserved bits and are not detailed in the register
description that follows. Reserved bits should always be written with a value of ‘0’.
29.2.1
BDG_TR Register
The Bandgap Trim Register (BDG_TR) is used to adjust the
bandgap and add an RC filter to AGND.
Depending on how many analog columns your PSoC device
has (see the Cols. column in the register table above), only
certain bits are accessible to be read or written.
Bit 6: AGNDBYP.
When set, this bit adds an RC filter to
AGND. (R is an internal 8.1K resistor and C is external to
the PSoC device on P2[4].)
Bits 5 and 4: TC[1:0].
These bits are for setting the tem-
perature coefficient inside the bandgap voltage generator.
10b is the design center for ‘0’ TC.
It is strongly recommended that the user not alter the
value of these bits.
Bits 3 to 0: V[3:0].
These bits are for setting the gain in the
reference buffer. Sixteen steps of 4 mV are available. 1000b
is the design center for 1.30 V.
It is strongly recommended that the user not alter the
value of these bits.
For additional information, refer to the
V
BG
+
-
S + H
V
REF
Add.
Name
Cols.
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Access
1,EAh
4, 2
AGNDBYP
TC[1:0]
V[3:0]
RW : 00
Summary of Contents for CY8C28 series
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