AMC7823 Datasheet, PDF (33/48 Pages) Texas Instruments – ANALOG MONITORING AND CONTROL CIRCUIT

AMC7823
www.ti.com
SLAS453A – APRIL 2005 – REVISED OCTOBER 2005
Table 7. Precision Current Source Configuration
SREF
0
0
0
0
1
1
1
1
PTS
0
1
1
1
0
1
1
1
PREFB
Don't care
0
Don't care
1
Don't care
0
Don't care
1
GREF
Don't care
1
0
1
Don't care
1 ⁽²⁾
0 ⁽²⁾
1 ⁽²⁾
I_O
0
0
0.5V/R_SET ⁽¹⁾
0.5V/R_SET ⁽¹⁾
0
0
Equation 1
Equation 1
(1) V_SET = 0.5 V.
(2) Make GREF = 1 for 2.5-V external reference; make GREF = 0 for 1.25-V external reference.
When an external reference is used, select a reference value (V_REF) close to either 1.25 V or 2.5 V, and write bit
GREF low ('0') for a 1.25-V reference, or write it high ('1') for a 2.5-V reference. These settings make a better
match to the applied external reference value. The output current can be calculated by Equation 1:
I_OUTPUT
+
V_SET
R_SET
+
ǒ_VREF
ǒ_1)GREFǓ
0.4^Ǔ
R_SET
(1)
The applied external reference voltage may deviate from the recommended values, but it is important to limit the
maximum voltage applied to the set resistor to approximately 0.5 V. Voltages greater than 0.5 V across the set
resistor reduce the specified compliance of the current source to the load.
DIGITAL I/O (See AMC Status/Configuration Register)
The AMC7823 has four special function pins: DAV, GALR, ELDAC, and CONVERT, It also has six general I/O
pins (GPIO-n). The GPIO-n pins are used as general digital I/O or analog input out-of-range indicators.
The pin DAV is an output pin that indicates the completion of ADC conversions. Bit DAVF of the AMC
Status/Configuration Register determines the status of the DAV pin. In direct-mode, after the selected group of
input channels has been converted and the ADC has been halted, bit DAVF is set to '1' and pin DAV is driven to
logic low (active). In auto-mode, each time the group of input channels has been sequentially converted, a 2-µs
pulse (low) appears on the DAV pin after the last channel of the group is converted. This conversion sequence is
repeated and the pulse is repeated.
The GALR pin is an output pin that indicates whether any of the first four analog inputs being converted are
out-of-range. Bits ALR-n of the ALR Register determine the status of GALR pin. GALR is low (or active) if any
one of the bits ALR-n is set to '1'. GALR is high (inactive) if and only if all bits are cleared to '0'. See Figure 50.
DAV Pin in Direct Mode
Bit DAVF of AMC
Status / Configuration
Register
DAV Pin
DAV Pin in Auto-Mode
[EA3:EA0] is
Converted
2-µs Pulse
Generator
DAV Pin
Bit ALR−0
Bit ALR−1
Bit ALR−2
Bit ALR−3
GALR Pin
Figure 50. DAV Pin and GALR Pin
The CONVERT pin is an input pin for the external ADC trigger signal. When bit ECNVT of the AMC
Status/Configuration Register is set to '1', the AMC7823 works in external trigger mode. The rising edge of
CONVERT starts the ADC conversion.
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