ADP1046AACPZ-R7 datasheet(34/88 Pages) AD

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ADP1046A

Data Sheet

Rev. 0 | Page 34 of 88

VOLTAGE CALIBRATION AND TRIM

The voltage sense inputs are optimized for sensing signals at

1 V (the usable input range is 1.4 V). In a 12 V system, a 12:1

resistor divider is required to reduce the 12 V signal to below

1.4 V. It is recommended that the output voltage of the power

supply be reduced to 1 V at this pin for best performance. The

tolerance of the resistor divider introduces errors that need to

be trimmed. The ADP1046A has enough trim range to trim out

errors introduced by resistors with a tolerance of 0.5% or better.

The VS1, VS2, and VS3 ADCs produce a digital code equal to

VSx/1.6 × 4096. The ADCs output a digital word of 2560

decimal (0xA00) in Bits[15:4] of Register 0x15, Register 0x16,

and Register 0x17 when there is exactly 1 V at their inputs.

OUTPUT VOLTAGE SETTING (VS3+, VS3− TRIM)

The VS3± inputs require a gain trim. Set the output regulation

point to 100% of the nominal value (Register 0x31 = 0xA0).

Enable the power supply with no-load current. The power

supply output voltage is divided down by the VS3 resistor

divider to give 1 V across the VS3+ and VS3− differential input

pins. The VS3 trim register (Register 0x3A) is adjusted until

the output voltage is at the desired value. This step should be

performed before any other trim routine. The VS3 voltage

value in Register 0x17[15:4] reads 2560 decimal (0xA00).

VS1 TRIM

The VS1 input requires a gain trim. Enable the power supply

with no-load current. It is recommended that the VS1 voltage

be divided down by the VS1 resistor divider to give 1 V at the

VS1 pin. The VS1 trim register (Register 0x38) is adjusted until

the VS1 value in Register 0x15[15:4] reads 2560 decimal (0xA00).

VS2 TRIM

The VS2 input requires a gain trim. Enable the power supply

with no-load current. It is recommended that the VS2 voltage

be divided down by the VS2 resistor divider to give 1 V at the

VS2 pin. The VS2 trim register (Register 0x39) is adjusted until

the VS2 value in Register 0x16[15:4] reads 2560 decimal (0xA00).

RTD/OTP TRIM

The RTD input requires two trims: one for the current source

and one for the ADC. To use the internal linearization scheme,

additional trimming procedures are required.

Trimming the Current Source

Bits[7:6] of Register 0x11 set the value of the current source to

10 µA, 20 µA, 30 µA, or 40 µA. Bits[5:0] of Register 0x11 can be

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

current source, component tolerance can be compensated for

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

Bits[7:6]; a decimal value of 63 adds 63 × 160 nA = 10.08 µA

to the current source set by Bits[7:6].

To program a value for the current source, select the nearest

possible option (10 µA, 20 µA, 30 µA, or 40 µA) using

the finer step size.

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

follow these steps:

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

2. Set Register 0x11[7:6] to 11 (40 µA).

3. Increase the value of Register 0x11[5:0] one LSB at a time

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

The current source is now calibrated and is set to the factory

default value.

Trimming the ADC

Due to the nonlinear nature of the thermistor, two trimming

options can be used.

Using the Internal Linearization Scheme

The first option uses the internal linearization scheme with

46 µA RTD current, which provides an accurate reading in °C

read in Register 0x1B in decimal format.

A 100 kΩ, 1% NTC thermistor with beta = 4250, 1% (such as

the NCP15WF104F03RC) in parallel with an external resistor of

16.5 kΩ, 1%, should be used with the ADP1046A. With this NTC

thermistor and resistor combination, the ADP1046A 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 code in

linearization scheme can be implemented in terms of a best-fit

polynomial for the selected NTC characteristics.

ADP1046AACPZ-R7 数据表(PDF) 34 Page - Analog Devices

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