A/D Converter Reference Voltage - Holtek HT67F2350 Manual

Bit 1~0 PGAGS1~PGAGS0: PGA gain select
00: Gain=1
01: Gain=1.667 – V
10: Gain=2.5 – V
11: Gain=3.333 – V
These bits are used to select the PGA gain. Note that here the gain is guaranteed only
when the PGA input voltage is equal to 1.2V.
• VBGRC Register
Bit 7
Name —
R/W —
POR —
Bit 7~1 Unimplemented, read as "0"
Bit 0 VBGREN: Bandgap reference voltage control
0: Disable
1: Enable
This bit is used to enable the internal Bandgap reference circuit. The internal Bandgap
reference circuit should first be enabled before the V
used. A specific start-up time is necessary for the Bandgap circuit to become stable and
accurate.

A/D Converter Reference Voltage

The actual reference voltage supply to the A/D Converter can be supplied from the positive power
supply pin, AVDD, an external reference source supplied on pin VREF or an internal reference
voltage V determined by the SAVRS1~SAVRS0 bits in the SADC2 register. The internal reference
R
voltage is amplified through a programmable gain amplifier, PGA, which is controlled by the
ADPGAEN bit in the SADC2 register. The PGA gain can be equal to 1, 1.667, 2.5 or 3.333 and
selected using the PGAGS1~PGAGS0 bits in the SADC2 register. The PGA input can come from
the external reference input pin, VREFI, or an internal Bandgap reference voltage, V
by the PGAIS bit in the SADC2 register. As the VREFI and VREF pin both are pin-shared with
other functions, when the VREFI or VREF pin is selected as the reference voltage pin, the VREFI
or VREF pin-shared function selection bits should first be properly configured to disable other
pin-shared functions. However, if the internal reference signal is selected as the reference source,
the external reference input from the VREFI or VREF pin will automatically be switched off by
hardware.
Note that the internal Bandgap reference circuit should first be enabled before the V
to be used. A specific start-up time is necessary for the Bandgap circuit to become stable and
accurate.
Rev. 1.60
Advanced A/D Flash MCU with LCD & EEPROM
=2V as V =1.2V
R RI
=3V as V =1.2V
R RI
=4V as V =1.2V
R RI
6 5 4
— — —
— — —
— — —
172
HT67F2350/HT67F2360
HT67F2370/HT67F2390
3 2 1
— — — VBGREN
— — —
— — —
voltage is selected to be
BGREF
, selected
BGREF
is selected
BGREF
May 16, 2019
0
R/W
0