Description
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18.1 Description
The operational amplifier is connected to the I/O pins as follows:
• The positive input pin is connected to P0_0.
• The negative input pin is connected to P0_1.
• The output is connected to P0_2.
The pins used by the operational amplifier must be configured as analog pins, by setting bits APCFG[2:0]
to 1. The OPAMPC.EN bit is used to enable/disable the operational amplifier. When power mode 2/3 is
entered, the operational amplifier is shut down automatically and must be restarted when entering PM0
again.
18.2 Calibration
The operational amplifier must be calibrated. A calibration is started by writing 1 to OPAMPC.CAL. During
calibration, OPAMPS.CAL_BUSY is 1. A new calibration is not accepted before OPAMPS.CAL_BUSY goes
low. Every time after enabling the operational amplifier, calibration must be performed.
18.3 Clock Source
The operational amplifier uses a divided version of the system clock. The division factor depends on which
clock source is used, HSOSC or XOSC. While the operational amplifier is enabled, the clock source
should not be changed.
18.4 Registers
This section describes the registers for the operational amplifier.
A
OPAMPMC (CC2530/CC2531: 0x61A6. CC2540: 0x61AD) – Operational Amplifier Mode Control
Bit Name Reset R/W Description
7:2 – 0000 00 R/W Reserved. Always write 0000 00.
1:0
MODE
00 R/W Operational amplifier mode
00 and 01: Non-chop mode – Higher offset (~500 µV), but no chopper ripple.
Use in conjunction with Mode 10 if offset cancellation is required. Offset for
these two modes is the opposite of the offset seen in Mode 10.
10: Non-chop mode – Higher offset (~500 µV), but no chopper ripple. Use in
conjunction with Mode 00 or Mode 01 to double sample and correct for the
offset by averaging the two samples.
11: Chop mode – Very low offset (~ 50 µV), and very low noise (1/f noise
shifted to 1 MHz due to chopping), and 1 MHz ripple
OPAMPC (0x62C0) – Operational Amplifier Control
Bit Name Reset R/W Description
7:2 – 0000 00 R0 Reserved
1
CAL
0 W1/R0
Start calibration. Calibration only starts if OPAMPC.EN is 1.
0
EN
0 R/W Operational amplifier enable
OPAMPS (0x62C1) – Operational Amplifier Status
Bit Name Reset R/W Description
7:1 – 0000 000 R0 Reserved
0
CAL_BUSY
0 R Calibration in progress
174
Operational Amplifier SWRU191C–April 2009–Revised January 2012
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