READ VOLTAGE AND/OR CURRENT DATA BYTES
The ADM1191 can be set up to provide information in three
different ways (see the Write Command Byte section). Depending
on how the device is configured, the following data can be read
out of the device after a conversion (or conversions).
Voltage and Current Readback
The ADM1191 digitizes both voltage and current. Three bytes
are read out of the device in the format shown in Table 12.
Table 12. Voltage and Current Readback
Byte Contents B7 B6 B5 B4 B3 B2 B1 B0
1
Voltage V11 V10 V9 V8 V7 V6 V5 V4
MSBs
2
Current I11 I10 I9 I8 I7 I6 I5 I4
MSBs
3
LSBs
V3 V2 V1 V0 I3 I2 I1 I0
Voltage Readback
The ADM1191 digitizes voltage only. Two bytes are read out of
the device in the format shown in Table 13.
Table 13. Voltage Only Readback Format
Byte Contents
B7 B6 B5 B4 B3 B2 B1 B0
1 Voltage MSBs V11 V10 V9 V8 V7 V6 V5 V4
2 Voltage LSBs V3 V2 V1 V0 0 0 0 0
Current Readback
The ADM1191 digitizes current only. Two bytes are read out of
the device in the format shown in Table 14.
Table 14. Current Only Readback Format
Byte Contents
B7 B6 B5 B4 B3 B2 B1 B0
1 Current MSBs I11 I10 I9 I8 I7 I6 I5 I4
2 Current LSBs I3 I2 I1 I0 0 0 0 0
The following series of events occurs when the master receives
three bytes (voltage and current data) from the slave device:
1. The master device asserts a start condition on SDA.
2. The master sends the 7-bit slave address, followed by the
read bit (high).
3. The addressed slave device asserts an acknowledge on SDA.
4. The master receives the first data byte.
5. The master asserts an acknowledge on SDA.
6. The master receives the second data byte.
7. The master asserts an acknowledge on SDA.
8. The master receives the third data byte.
9. The master asserts a no acknowledge on SDA.
10. The master asserts a stop condition on SDA, and the
transaction ends.
ADM1191
For cases where the master is reading voltage only or current
only, only two data bytes are read. Step 7 and Step 8 are not
required.
1
2
3 4 5 6 7 8 9 10
S
SLAVE
ADDRESS
R
A
DATA 1
A
DATA 2
A
DATA 3
N
P
Figure 22. Three-Byte Read from ADM1191
1
2
3
4
5
6
78
S
SLAVE
ADDRESS
RA
REGISTER
ADDRESS
A
REGISTER
DATA
N
P
Figure 23. Two-Byte Read from ADM1191
Converting ADC Codes to Voltage and Current Readings
The following equations can be used to convert ADC codes
representing voltage and current from the ADM1175 12-bit
ADC into actual voltage and current values.
Voltage = (VFULLSCALE/4096) × Code
where:
VFULLSCALE = 6.65 (7:2 range) or 26.52 (14:1 range).
Code is the ADC voltage code read from the device (Bit V0
to Bit V11).
Current = ((IFULLSCALE/4096) × Code)/Sense Resistor
where:
IFULLSCALE = 105.84 mV.
Code is the ADC current code read from the device (Bit I0 to
Bit I11).
Read Status Register
A single register of status data can also be read from the
ADM1191.
1. The master device asserts a start condition on SDA.
2. The master sends the 7-bit slave address, followed by the
read bit (high).
3. The addressed slave device asserts an acknowledge on SDA.
4. The master receives the status byte.
5. The master asserts an acknowledge on SDA.
1
2
34 5
S
SLAVE
ADDRESS
R
A
DATA 1
A
Figure 24. Status Read from ADM1191
Table 15 shows the ADM1191 status registers in detail. Note
that Bit 1, Bit 3, and Bit 5 are cleared by writing to Bit 4 of the
ALERT_EN register (CLEAR).
Rev. 0 | Page 13 of 16