Datasheet

TMP421
TMP422
TMP423
www.ti.com SBOS398C –JULY 2007–REVISED MAY 2012
The TMP422 checks the polarity of the external READ/WRITE OPERATIONS
transistor at power-on, or after software reset, by
Accessing a particular register on the TMP421/22/23
forcing current to pin 1 while connecting pin 2 to
is accomplished by writing the appropriate value to
approximately 0.6V. If the voltage on pin 1 does not
the Pointer Register. The value for the Pointer
pull up to near the V+ of the TMP422, pin 1 functions
Register is the first byte transferred after the slave
as DXP for channel 1, and the second LSB of the
address byte with the R/W bit low. Every write
slave address is '0'. If the voltage on pin 1 does pull
operation to the TMP421/22/23 requires a value for
up to near V+, the TMP422 forces current to pin 2
the Pointer Register (see Figure 17).
while connecting pin 1 to 0.6V. If the voltage on pin 2
does not pull up to near V+, the TMP422 uses pin 2
When reading from the TMP421/22/23, the last value
for DXP of channel 1, and sets the second LSB of the
stored in the Pointer Register by a write operation is
slave address to '1'. If both pins are shorted to GND
used to determine which register is read by a read
or if both pins are open, the TMP422 uses pin 1 as
operation. To change which register is read for a read
DXP and sets the address bit to '0'. This process is
operation, a new value must be written to the Pointer
then repeated for channel 2 (pins 3 and 4).
Register. This transaction is accomplished by issuing
a slave address byte with the R/W bit low, followed
If the TMP422 is to be used with transistors that are
by the Pointer Register byte; no additional data are
located on another IC (such as a CPU, DSP, or
required. The master can then generate a START
graphics processor), it is recommended to use pin 1
condition and send the slave address byte with the
or pin 3 as DXP to ensure correct address detection.
R/W bit high to initiate the read command. See
If the other IC has a lower supply voltage or is not
Figure 19 for details of this sequence. If repeated
powered when the TMP422 tries to detect the slave
reads from the same register are desired, it is not
address, a protection diode may turn on during the
necessary to continually send the Pointer Register
detection process and the TMP422 may incorrectly
bytes, because the TMP421/22/23 retain the Pointer
choose the DXP pin and corresponding slave
Register value until it is changed by the next write
address. Using pin 1 and/or pin 3 for transistors that
operation. Note that register bytes are sent MSB first,
are on other ICs ensures correct operation
followed by the LSB.
independent of supply sequencing or levels.
Read operations should be terminated by issuing a
The TMP423 has a factory-preset slave address. The
Not-Acknowledge command at the end of the last
TMP423A slave address is 1001100b, and the
byte to be read. For a single-byte operation, the
TMP423B slave address is 1001101b. The
master should leave the SDA line high during the
configuration of the DXP and DXN channels are
Acknowledge time of the first byte that is read from
independent of the address. Unused DXP channels
the slave. For a two-byte read operation, the master
can be left open or tied to GND.
must pull SDA low during the Acknowledge time of
the first byte read, and should leave SDA high during
the Acknowledge time of the second byte read from
the slave.
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