TMP451-Q1

SLOS877 – OCTOBER 2014

www.ti.com

7.3.1.1 Standard Binary to Decimal Temperature Data Calculation Example

High-byte conversion (for example, 0111 0011):

Convert the right-justified binary high byte to hexadecimal.

The sum equals the decimal equivalent.

0111 0011b

Low-byte conversion (for example, 0111 0000):

To convert the left-justified binary low-byte to decimal, use bits 7 through 4 and ignore bits 3 through 0

because they do not affect the value of the number.

0111b

7.3.1.2 Standard Decimal to Binary Temperature Data Calculation Example

For positive temperatures (for example, 20°C):

(20°C) / (1°C/count) = 20

→ 14h → 0001 0100

Convert the number to binary code with 8-bit, right-justified format, and MSB = 0 to denote a positive sign.

20°C is stored as 0001 0100

→ 14h.

For negative temperatures (for example, –20°C):

(|–20|) / (1°C/count) = 20

→ 14h → 0001 0100

Generate the two's complement of a negative number by complementing the absolute value binary number

and adding 1.

–20°C is stored as 1110 1100

→ ECh.

7.3.2 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 1 k

Ω of

series resistance can be cancelled by the TMP451-Q1 device, eliminating the need for additional characterization

and temperature offset correction. See Figure 5, Remote Temperature Error vs Series Resistance, for details on

the effects of series resistance on sensed remote temperature error.

7.3.3 Differential Input Capacitance

The TMP451-Q1 device tolerates differential input capacitance of up to 1000 pF with minimal change in

temperature error. The effect of capacitance on sensed remote temperature error is shown in Figure 6, Remote

Temperature Error vs Differential Capacitance.

7.3.4 Filtering

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

created by fast digital signals, and it can corrupt measurements. The TMP451-Q1 device has a built-in, 65-kHz

filter on the inputs of D+ and D– 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 of between 100 pF and 1 nF. Some

applications attain better overall accuracy with additional series resistance; however, this increased accuracy is

application-specific. When series resistance is added, the total value should not be greater than 1 k

Ω. If filtering

is required, suggested component values are 100 pF and 50

Ω on each input; exact values are application-

specific.

10

Submit Documentation Feedback

Copyright © 2014, Texas Instruments Incorporated

Product Folder Links: TMP451-Q1