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参数资料
型号： ST72C171K2B6
厂商： STMICROELECTRONICS
元件分类： 微控制器/微处理器
英文描述： 8-BIT, FLASH, 8 MHz, MICROCONTROLLER, PDIP32
封装： SHRINK, PLASTIC, DIP-32
文件页数： 88/152页
文件大小： 2156K
代理商： ST72C171K2B6
ST72C171
40/152
OP-AMP MODULE (Cont’d)
7.3.4 Autozero Mode
When the following description refers to both OA1
or OA2, x stands for 1 or 2.
In order to eliminate the ADC errors due to the
SPGA offset voltage, this voltage may be deter-
mined, prior to the A/D conversion (at power on or
periodically) and stored in RAM. The stored value
may be used afterwards to eliminate the errors of
any A/D conversion that uses the SPGA (ADC
zooming). The measurement may be done inde-
pendently for OA1 and OA2.
The measurement algorithm has 3 steps:
1. The SPGA is in repeater mode (NSx[1:0] = 01),
with the lowest gain (Gx[2:0]=000), the autoze-
roing switch is left open (AZx = 0). The positive
input of the op-amp is connected to a DC value,
using the VRx reference voltage generator
(PSx[1:0] = 00), and the output is sent to the
ADC. Under these conditions, the ADC meas-
ures the value:
Vo = VRx -Voff
of the SPGA output.
2. Set the gain (G) according the application
requirement. The AZx bit is set to 1. The output
voltage of the SPGA becomes:
V’o = VRx - Voff - G * Voff
3.Voff calculated with 1) - 2)
Voff =( Vo- V’o) /G
As the offset voltage of the SPGAs may vary with
the common mode voltage value, the measure-
ment must be done choosing VRx to match the ap-
plication conditions. Alternatively, nine measure-
ments may be done with the noninverting input
voltage varying between 0 and VDDA in 1/8 VDD
steps, in order to fully characterise the offset volt-
age of the op-amp.
7.3.5 Comparator mode with Interrupts
The 2 SPGAs can be configured in comparator
mode (GX[2:0]=111). In this case the positive in-
put can be connected to the internal reference
voltage. The negative input can be used to receive
the analog voltage to be compared with the volt-
age connected to the positive input.
By means of a Schmitt trigger, the SPGA output is
readable as a logical level in the OAxVR bit in the
OAIRR register. These bits are read only.
An interrupt request remains pending as long as
the output value (OAxVR) is equal to the corre-
sponding polarity bit (OAxPR) and when the inter-
rupt enable bit (OAxIE) is set. There is one inter-
rupt vector for each SPGA.
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相关代理商/技术参数
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