Datasheet

=h
eff
1.008 300´
300 N
ADJUST
-
N =300
ADJUST
-
300 1.008´
h
eff
=V V
BE2 BE1
-
hkT
q
ln
I
2
I
1
TMP421
TMP422
TMP423
SBOS398C –JULY 2007–REVISED MAY 2012 www.ti.com
Table 7. Conversion Rate Register
CONVERSION RATE REGISTER (Read/Write = 0Bh, POR = 07h)
AVERAGE I
Q
(TYP) (μA)
R7 R6 R5 R4 R3 R2 R1 R0 CONVERSIONS/SEC V+ = 2.7V V+ = 5.5V
0 0 0 0 0 0 0 0 0.0625 11 32
0 0 0 0 0 0 0 1 0.125 17 38
0 0 0 0 0 0 1 0 0.25 28 49
0 0 0 0 0 0 1 1 0.5 47 69
0 0 0 0 0 1 0 0 1 80 103
0 0 0 0 0 1 0 1 2 128 155
0 0 0 0 0 1 1 0 4
(1)
190 220
0 0 0 0 0 1 1 1 8
(2)
373 413
(1) Conversion rate shown is for only one or two enabled measurement channels. When three channels are enabled, the conversion rate is
2 and 2/3 conversions-per-second. When four channels are enabled, the conversion rate is 2 per second.
(2) Conversion rate shown is for only one enabled measurement channel. When two channels are enabled, the conversion rate is 4
conversions-per-second. When three channels are enabled, the conversion rate is 2 and 2/3 conversions-per-second. When four
channels are enabled, the conversion rate is 2 conversions-per-second.
The value η in Equation 1 is a characteristic of the
ONE-SHOT CONVERSION
particular transistor used for the remote channel. The
power-on reset value for the TMP421/22/23 is η =
When the TMP421/22/23 are in shutdown mode
1.008. The value in the η-Factor Correction Register
(SD = 1 in the Configuration Register 1), a single
may be used to adjust the effective η-factor according
conversion is started on all enabled channels by
to Equation 2 and Equation 3.
writing any value to the One-Shot Start Register,
pointer address 0Fh. This write operation starts one
conversion; the TMP421/22/23 return to shutdown
mode when that conversion completes. The value of
(2)
the data sent in the write command is irrelevant and
is not stored by the TMP421/22/23. When the
TMP421/22/23 are in shutdown mode, the conversion
sequence currently in process must be completed
(3)
before a one-shot command can be issued. One-shot
The η-correction value must be stored in two's-
commands issued during a conversion are ignored.
complement format, yielding an effective data range
from –128 to +127. The n-correction value may be
η-FACTOR CORRECTION REGISTER
written to and read from pointer address 21h. The η-
The TMP421/22/23 allow for a different η-factor value
correction value for the second remote channel
to be used for converting remote channel
(TMP422 and TMP423) may be written and read from
measurements to temperature. The remote channel
pointer address 22h. The η-correction value for the
uses sequential current excitation to extract a
third remote channel (TMP423 only) may be written
differential V
BE
voltage measurement to determine
to and read from pointer address 23h. The register
the temperature of the remote transistor. Equation 1
power-on reset value is 00h, thus having no effect
describes this voltage and temperature.
unless the register is written to.
(1)
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