ADP1050ACPZ-R7 datasheet(37/93 Pages) AD

37 / 93 page

ADP1050

Data Sheet

RTD AND OTP TRIM

The RTD requires two trims, one for the ADC and one for the

current source. To use the internal linearization scheme, addi-

tional trimming procedures are required.

Trimming the Current Source

10 µA, 20 µA, 30 µA, or 40 µA. Register 0xFE2D[5:0] can be

used to fine-tune the current value. By fine-tuning the internal

current source, component tolerance can be compensated and

errors can be minimized. One LSB in Bits[5:0] = 160 nA.

A decimal value of 1 adds 160 nA to the current source set by

10.08 µA to the current source set by Register 0xFE2D[7:6].

Use Register 0xFE2D[7:6] to program a value for the current

source, selecting the nearest possible option (10 µA, 20 µA, 30 µA,

or 40 µA). Then use Register 0xFE2D[5:0] to achieve the finer

step size.

For example, to use a value of 46 µA as the current source,

complete the following steps:

1. Place a known resistor (Rx) from the RTD pin to AGND.

2. Set Register 0xFE2D[7:6] to 11 binary (40 µA).

3. Increase the value of Register 0xFE2D[5:0], 1 LSB at a time,

until the voltage at the RTD pin is VRTD = 46 µA × Rx.

The current source is now calibrated and set to the factory

default value.

Trimming the ADC

The first option for trimming the ADC uses the internal

linearization scheme with 46 µA RTD current, which provides

an accurate reading, expressed in degrees Celsius, read in the

READ_TEMPERATURE command (Register 0x8D) in decimal

format.

Use an R25 = 100 kΩ, 1% accuracy NTC thermistor with beta =

4250, 1% accuracy (such as the NCP15WF104F03RC) in parallel

with an external resistor of 16.5 kΩ, 1% accuracy, with the

ADP1050. With this NTC thermistor and resistor combination,

the ADP1050 default current source trim is set to 46 µA to

achieve the best possible accuracy over temperatures ranging from

85°C to 125°C.

If an external microcontroller is used, the RTD ADC value

in Register 0xFEAB can be fed into the microcontroller, and

a different linearization scheme can be implemented in terms

of a best-fit polynomial for the selected NTC characteristics.

Rev. A | Page 36 of 92

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