COP8AME9_14 Datasheet, PDF (63/102 Pages) Texas Instruments – COP8AME9 8-Bit CMOS Flash Microcontroller with 8k Memory, Dual Op Amps, Virtual EEPROM, Temperature Sensor, 10-Bit A/D and Brownout Reset

COP8AME9, COP8ANE9
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SNOS930F – MARCH 2001 – REVISED MARCH 2013
PROGRAMMABLE GAIN AMPLIFIER
A programmable gain amplifier is located between the analog multiplexor and the input to the A/D. It supports
single ended mode only. The gain of this amplifier is selected by the ADGAIN register shown in Table 30. This
register is also used to enable the stand-alone amplifier (AMP1) on port pins B3, B4 and B5, the internal
temperature sensor, and the offset trimming configuration. Both the stand-alone amplifier and the programmable
gain amplifier will draw DC current when enabled. To minimize the amount of current drawn in the HALT mode,
the user should disable both amplifiers before entering HALT. This register is initialized to 00h on Reset.
Table 30. ADGAIN
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
EN-
AMP1
ENTS
TRIM
Reserved
GAIN2
ENAMP1 Enables stand-alone amplifier (AMP1) to port B. Enabled = 1. Disabled =0.
Bit 1
GAIN1
Bit 0
GAIN0
ENTS Enable internal temperature sensor. Enabled = 1. Disabled = 0.
TRIM Configures the programmable gain amplifier into the trimming configuration by shorting its + and − inputs
together. Enabled = 1. Disabled = 0. This bit should be set to 0 for normal use of the programmable gain
amplifier.
GAIN2:0 Controls the gain of the programmable gain amplifier. See Table 31. When performing a conversion on
the temperature sensor, a gain of 1 or 2 must be selected, depending on the operating voltage of the
device. A gain of 2 can only be used for the temperature sensor if V_CC ≥ 4.5V.
Reserved These bits are reserved and must be 0.
TRIM
0
0
0
0
0
0
0
0
1
GAIN2
0
0
0
0
1
1
1
1
X
GAIN1
0
0
1
1
0
0
1
1
X
Table 31. Gain Bit Assignments
GAIN0
0
1
0
1
0
1
0
1
X
Gain Tolerance
Not Applicable
±1
±1
±1
±2
±2
±2
±2
N/A
Amplifier disabled and bypassed.
Gain = 1
Gain = 2
Gain = 5
Gain = 10
Gain = 20
Gain = 49
Gain = 98
Gain = open loop for trimming. Amplifier is
enabled.
Programmable Gain Amplifier Settling Time
When changing channels or the gain, it's necessary to give the programmable gain amplifier time to settle before
performing an A/D conversion. This is because the input from the previous channel could have the amplifier
output near one power supply rail and the newly selected channel or gain may need to drive the output to the
other power supply rail. The amount of settling time is based on the gain of the amplifier. See Table 32. It is
recommended that the user wait 7.6 time constants (τ) before performing an A/D conversion. This should give
the amplifier time to settle within 0.5 LSB of the A/D converter. This settling time needs to be taken into effect if
either the gain is changed or if the channel is changed. Since these values are in different registers, they can't be
changed simultaneously and must be changed individually. The settling time starts whenever either one is
changed, but it's not cumulative. The user should wait the amount of settling time specified after the latter of the
channel or gain change.
GAIN
1
2
5
Table 32. Programmable Gain Amplifier Settling Times
Time Constant (τ)
Slew Rate Limited
Under-Damp Response
Under-Damp Response
Settling Time (7.6 * τ)
Slew Rate Limited
9µs
6µs
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