TMP400 datasheet(11/25 Pages) TI

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RESOLUTION REGISTER

CONVERSION RATE REGISTER

N-FACTOR CORRECTION REGISTER

BE2

BE1

nkT

(1)

ONE-SHOT (OS)

eff

1.008

300

(300

)

ADJUST

(2)

=300 -

ADJUST

300

1.008

neff

(3)

TMP400

SBOS404 – DECEMBER 2007

conversion. This mode is useful to reduce power

consumption

the

TMP400

when

continuous

The RES1 and RES0 bits (resolution bits 1 and 0,

temperature monitoring is not required. When the

respectively) of the Resolution Register set the

configuration register is read, the OS bit always reads

resolution of the local temperature measurement

'0'

channel. Remote temperature measurement channel

resolution is not affected. Changing the local channel

resolution also affects the conversion time and rate of

the TMP400. The Resolution Register is set by

The Conversion Rate Register controls the rate at

writing to pointer address 1Ah and is read by reading

which temperature conversions are performed. This

from pointer address 1Ah. Table 5 shows the

resolution bits for the Resolution Register.

not the conversion timing itself, thereby allowing the

TMP400 power dissipation to be balanced with the

Table 5. Resolution Register: Local Channel

temperature register update rate. Table 6 shows the

Programmable Resolution

conversion rate options and corresponding current

consumption. By default, the TMP400 converts every

RESOLUTION REGISTER

four seconds.

(Read = 1Ah, Write = 1Ah, POR = 18h)

CONVERSION

RES1

RES0

RESOLUTION

TIME (Typical)

9 Bits (0.5

°C)

12.5ms

The TMP400 allows for a different n-factor value to

10 Bits (0.25

°C)

25ms

used

for

converting

remote

channel

measurements to temperature. The remote channel

11 Bits (0.125

°C)

50ms

uses

sequential

current

excitation

extract

12 Bits (0.0625

°C)

100ms

differential VBE voltage measurement to determine

the temperature of the remote transistor. Equation 1

Bits 3 and 4 of the Resolution Register must always

relates this voltage and temperature.

be set to ‘1’. Bits 5 through 7 of the Resolution

reset value of this register is 18h. Resistance

correction (RC) is not automatically enabled on

power-on; see the Series Resistance Cancellation

The value n in Equation 1 is a characteristic of the

section for information on RC.

particular transistor used for the remote channel. The

default value for the TMP400 is n = 1.008. The value

in the N-Factor Correction Register may be used to

The TMP400 features a One-Shot Temperature

adjust the effective n-factor according to Equation 2

Measurement Mode. When the device is in Shutdown

and Equation 3.

Mode, writing a ‘1’ to the OS bit starts a single

temperature conversion. The device returns to the

shutdown state at the completion of the single

Table 6. Conversion Rate Register

CONVERSION RATE REGISTER (Read = 04h, Write = 0Ah, POR = 02h)

AVERAGE IQ (TYP)

(

µA)

CONVERSION/SEC

VS = 2.7V VS = 5.5V

0.0625

0.125

0.25

0.5

103

128

155

190

220

07h to 0Fh

373

413

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