TMP9R01DGSSLASHEM datasheet(18/45 Pages) TI2

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7.3.2 Decoding Temperature Data

The TMP9R01-SEP and TMP9R01-SP temperature registers use a 12-bit format. The 12 bits are aligned to the

left side, or most significant side, of the 16-bit word. The four unused bits are on the right side, or the least

significant side. For this reason, a shift is needed to discard the extra bits. 2’s complement is employed to

describe negative temperatures. C code can easily convert the 2’s complement data when the data is typecast

into the correct signed data type. Q notation describes the number of bits that represent a fractional result. 4 bits

of fractional data, known as Q4, offers 0.0625°C resolution.

Table 7-3. 12-Bit Q4 Encoding Parameters

Parameter

Value

Bits

Resolution

0.0625

Range (+)

127.9375

Range (-)

-128

First Byte Integer C

Yes

25˚C

0x1900

Table 7-4. 12-Bit Q4 Bit Values

Sign

0.5

0.25

0.125 0.0625

-128

1/2

1/4

1/8

1/16

-27

2-1

2-2

2-3

2-4

/* 12-bit format has 4 bits discarded by right shift

q4 is 0.062500 resolution

the following bytes represent 24.5C */

uint8_t byte1 = 0x18;

uint8_t byte2 = 0x80;

float f = (((int8_t) byte1 << 8 | byte2) >> 4) * 0.0625f;

int mC = (((int8_t) byte1 << 8 | byte2) >> 4) * 1000 >> 4;

int C = (int8_t) byte1;

7.3.3 Series Resistance Cancellation

Series resistance cancellation automatically eliminates the temperature error caused by the resistance of the

routing to the remote transistor or by the resistors of the optional external low-pass filter. A total of up to 1kΩ of

series resistance can be cancelled by the TMP9R01-SEP and TMP9R01-SP devices, thus eliminating the need

for additional characterization and temperature offset correction. See Figure 6-4 and Figure 6-5 for details on the

effects of series resistance on sensed remote temperature error.

7.3.4 Differential Input Capacitance

The TMP9R01-SEP and TMP9R01-SP devices tolerate differential input capacitance of up to 1000pF with

minimal change in temperature error. The effect of capacitance on the sensed remote temperature error is

illustrated in Figure 6-8 (Remote Temperature Error vs Differential Capacitance).

7.3.5 Filtering

Remote junction temperature sensors are typically implemented in a noisy environment. Noise is most often

created by fast digital signals that can corrupt measurements. The TMP9R01-SEP and TMP9R01-SP devices

have a built-in, 65kHz filter on the D+ and D– inputs to minimize the effects of noise. However, a bypass

capacitor placed differentially across the inputs of the remote temperature sensor is recommended to make the

application more robust against unwanted coupled signals. For this capacitor, select a value between 100pF

TMP9R01-SEP, TMP9R01-SP

SNIS238A – JULY 2025 – REVISED JULY 2026

www.ti.com

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