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AD5170 Datasheet

I2C Digital Potentiometer

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AD5170
I2C CONTROLLER PROGRAMMING
Write Bit Patterns
1
SCL
91
91
9
SDA
START BY
MASTER
0 1 0 1 1 AD1 AD0 R/W
A0 SD T 0 OW X X X
D7 D6 D5 D4 D3 D2 D1 D0
ACK BY
AD5170
ACK BY
AD5170
ACK BY
AD5170
FRAME 1
SLAVE ADDRESS BYTE
FRAME 2
INSTRUCTION BYTE
FRAME 3
DATA BYTE
STOP BY
MASTER
Figure 45. Writing Data to the RDAC Register
Read Bit Pattern
1
SCL
91
91
9
SDA
START BY
MASTER
0 1 0 1 1 AD1 AD0 R/W
D7 D6 D5 D4 D3 D2 D1 D0
E1 E0 X X X X X X
ACK BY
AD5170
ACK BY
MASTER
NO ACK
BY MASTER
FRAME 1
SLAVE ADDRESS BYTE
FRAME 2
DATA BYTE
FRAME 3
VALIDATION BYTE
STOP BY
MASTER
Figure 46. Reading Data from the RDAC Register
I2C-COMPATIBLE, 2-WIRE SERIAL BUS
The following section describes how the 2-wire, I2C serial bus
protocol operates (see Figure 45 and Figure 46).
The master initiates a data transfer by establishing a start con-
dition, which is when a high-to-low transition on the SDA line
occurs while SCL is high (see Figure 45). The following byte is
the slave address byte, which consists of the slave address followed
by an R/W bit (this bit determines whether data is read from or
written to the slave device). AD0 and AD1 are configurable address
bits that allow up to four devices on one bus (see Table 9).
The slave address corresponding to the transmitted address bits
responds by pulling the SDA line low during the ninth clock
pulse (this is called the acknowledge bit). At this stage, all other
devices on the bus remain idle while the selected device waits
for data to be written to, or read from, its serial register. If the
R/W bit is high, the master reads from the slave device. If the
R/W bit is low, the master writes to the slave device.
In write mode, the second byte is the instruction byte. The first
MSB of the instruction byte, 2T, is the second trim enable bit.
A logic low selects the first array of the fuses, and a logic high
selects the second array of the fuses. This means that after blowing
the fuses with Trim 1, the user still has another chance to blow
them again with Trim 2. Note that using Trim 2 before Trim 1
effectively disables Trim 1 and, in turn, allows only one-time
programming.
The second MSB, SD, is a shutdown bit. A logic high causes an
open circuit at Terminal A and shorts the wiper to Terminal B.
This operation yields almost 0 Ω in rheostat mode or 0 V in
potentiometer mode. Note that the shutdown operation does
not disturb the contents of the register. When brought out of
shutdown, the previous setting is applied to the RDAC. In
addition, new settings can be programmed during shutdown.
When the part is returned from shutdown, the corresponding
VR setting is applied to the RDAC.
The third MSB, T, is the OTP programming bit. A logic high
blows the polyfuses and programs the resistor setting perma-
nently. For example, if the user wants to blow the first array
of fuses, the instruction byte is 00100XXX. To blow the second
array of fuses, the instruction byte is 10100XXX. A logic low of
the T bit simply allows the device to act as a typical volatile digital
potentiometer.
The fourth MSB must always be Logic 0.
The fifth MSB, OW, is an overwrite bit. When raised to a logic
high, OW allows the RDAC setting to be changed even after the
internal fuses are blown. However, when OW is returned to
Logic 0, the position of the RDAC returns to the setting prior to
the overwrite. Because OW is not static, if the device is powered
off and on, the RDAC presets to midscale or to the setting at
which the fuses were blown, depending on whether the fuses
are permanently set.
The remainder of the bits in the instruction byte are don’t care
bits (see Figure 45).
After acknowledging the instruction byte, the last byte in write
mode is the data byte. Data is transmitted over the serial bus in
sequences of nine clock pulses (eight data bits followed by an
acknowledge bit). The transitions on the SDA line must occur
during the low period of SCL and remain stable during the high
period of SCL (see Figure 2).
In read mode, the data byte follows immediately after the
acknowledgment of the slave address byte. Data is transmitted
over the serial bus in sequences of nine clock pulses (a slight
difference from write mode, with eight data bits followed by an
acknowledge bit). Similarly, transitions on the SDA line must
occur during the low period of SCL and remain stable during
the high period of SCL (see Figure 46).
Following the data byte, the validation byte contains two valida-
tion bits, E0 and E1. These bits signify the status of the one-time
programming (see Figure 46).
Rev. G | Page 21 of 24
Analog Devices
Analog Devices



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