Datasheet
TMP421
TMP422
TMP423
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SBOS398C –JULY 2007–REVISED MAY 2012
The RC bit (bit 2) enables the resistance correction For the TMP423 only, the REN3 bit (bit 6) enables
feature for the external temperature channels. If RC = the third external measurement channel. If REN3 =
'1', series resistance correction is enabled; if RC = '0', '1', the third external channel is enabled; if REN3 =
resistance correction is disabled. Resistance '0', the third external channel is disabled.
correction should be enabled for most applications.
The temperature measurement sequence is: local
However, disabling the resistance correction may
channel, external channel 1, external channel 2,
yield slightly improved temperature measurement
external channel 3, shutdown, and delay (to set
noise performance, and reduce conversion time by
conversion rate, if necessary). The sequence starts
about 50%, which could lower power consumption
over with the local channel. If any of the channels are
when conversion rates of two per second or less are
disabled, they are bypassed in the sequence.
selected.
The LEN bit (bit 3) enables the local temperature
CONVERSION RATE REGISTER
measurement channel. If LEN = '1', the local channel
The Conversion Rate Register (pointer address 0Bh)
is enabled; if LEN = '0', the local channel is disabled.
controls the rate at which temperature conversions
The REN bit (bit 4) enables external temperature
are performed. This register adjusts the idle time
measurement for channel 1. If REN = '1', the first
between conversions but not the conversion timing
external channel is enabled; if REN = '0', the external
itself, thereby allowing the TMP421/22/23 power
channel is disabled.
dissipation to be balanced with the temperature
register update rate. Table 7 describes the
For the TMP422 and TMP423 only, the REN2 bit (bit
conversion rate options and corresponding current
5) enables the second external measurement
consumption. A one-shot command can be used
channel. If REN2 = '1', the second external channel is
during the idle time between conversions to
enabled; if REN2 = '0', the second external channel is
immediately start temperature conversions on all
disabled.
enabled channels.
Table 6. Configuration Register 2 Bit Descriptions
CONFIGURATION REGISTER 2 (Read/Write = 0Ah, POR = 1Ch for TMP421; 3Ch for TMP422; 7Ch for TMP423)
POWER-ON RESET
BIT NAME FUNCTION VALUE
7 Reserved — 0
0 = External Channel 3 Disabled 1 (TMP423)
6 REN3
1 = External Channel 3 Enabled 0 (TMP421, TMP422)
0 = External Channel 2 Disabled 1 (TMP422, TMP423)
5 REN2
1 = External Channel 2 Enabled 0 (TMP421)
0 = External Channel 1 Disabled
4 REN 1
1 = External Channel 1 Enabled
0 = Local Channel Disabled
3 LEN 1
1 = Local Channel Enabled
0 = Resistance Correction Disabled
2 RC 1
1 = Resistance Correction Enabled
1, 0 Reserved — 0
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