ADP1050ACPZ-R7 datasheet(30/93 Pages) AD

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Data Sheet

ADP1050

TEMPERATURE READING

The RTD pin (Pin 20) is set up for use with an external negative

temperature coefficient (NTC) thermistor. The RTD pin has an

internal programmable current source. An ADC monitors the

voltage on the RTD pin. The RTD ADC has an input range of

1.6 V. The raw data is stored in Register 0xFEAB. It is a 12-bit

reading, which means that the LSB size is 1.6 V/4096 = 390.625 μV.

Using Register 0xFE2D[7:6], an internal precision current source

can be configured to generate a 10 μA, 20 μA, 30 μA, or 40 μA

current. This current source can be trimmed, by means of an

internal DAC, to compensate for thermistor accuracy. To set the

current source to the factory default value of 46 μA, write 0xE6

to Register 0xFE2D.

The output of the RTD ADC is linearly proportional to the voltage

on the RTD pin; however, thermistors exhibit a nonlinear function

of resistance vs. temperature. Therefore, it is necessary to perform

postprocessing on the RTD ADC reading to accurately read the

temperature.

By connecting an external resistor in parallel with the NTC ther-

mistor, linearization is achieved. Figure 31 shows the RTD and

OTP operation. Using the factory default value of 46 μA and

the linearization scheme, the temperature, expressed in degrees

Celsius (°C), can be read directly via the READ_TEMPERATURE

command (Register 0x8D). The temperature reading is derived

from the RTD ADC output, and it is updated every 10 ms. The

ADP1050 implements a linearization scheme that is based on a

preselected combination of external components and current

selection (see the Temperature Linearization Scheme section).

Optionally, the user can process the RTD reading and perform

postprocessing in the form of a lookup table or polynomial

equation to match the specific NTC thermistor used.

In this case, the external resistor in parallel is not needed. With an

internal current source of 46 μA, the equation to calculate the

ADC code at a certain NTC value (RX) is given by the following

formula:

ADC CODE = 46 μA × RX/390.7 μV

For example, at 60°C, the NTC thermistor connected to the

RTD pin is 21.82 kΩ. Therefore,

RTD ADC CODE = 46 μA × 21.82 kΩ/390.7 μV = 2570

For the overtemperature function, the RTD threshold (in volts)

can be transferred through the OT_FAULT_LIMIT command in

Temperature Linearization Scheme section.

Alternatively, the temperature reading and overtemperature

protection function can be implemented by applying an external

analog temperature sensor, such as the STLM20. See Figure 30

for more information. Using this solution, the temperature sense

range can be as low as −40°C. To facilitate this approach, disable

the internal current source by writing 0x00 to Register 0xFE2D and

setting Register 0xFE2B[2]. The temperature reading in degrees

Celsius can be derived by the following formula:

T = 159.65 −

CODE

ADC

where the ADC CODE is the reading in Register 0xFEAB[15:4].

The recommended values of R1 and R2 are 20 kΩ and 10 kΩ,

respectively.

RTD

ADC

RTD TEMPERATURE

VALUE REGISTER

10kΩ

10µA/20µA/30µA/40µA

REG 0xFEAB[15:4]

20kΩ

STLM20

VOUT

GND

Figure 30. Temperature Sensing by an Analog Temperature Sensor

RTD

ADC

100kΩ

NTC

OT_FAULT_LIMIT

REG 0x4F

RTD TEMPERATURE

VALUE REGISTER

OT_FAULT

RESPONSE

16.5kΩ

10µA/20µA/30µA/40µA

REG 0xFEAB[15:4]

SIGNAL

CONDITIONING

TEMPERATURE

VALUE IN

CELSIUS

READ_TEMPERATURE

REG 0x8D

OT_FAULT FLAG

REG 0x7D[7]

PGOOD

OT_FAULT_RESPONSE

REG 0x50

Figure 31. RTD and OTP Operation

Rev. A | Page 29 of 92

ADP1050ACPZ-R7 数据表(PDF) 30 Page - Analog Devices

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