=

heff

1.008

300

´

300

N

ADJUST

-

N

=300

ADJUST

-

300

1.008

´

heff

=

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 IQ (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 VBE 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)

16

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