ADP1052ACPZ-R7 datasheet(42/113 Pages) AD

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ADP1052

Data Sheet

Rev. B | Page 42 of 113

To trim the errors introduced by the resistor divider, use the

following procedure:

1. Set the VOUT_COMMAND (Register 0x21) with the

nominal output voltage value. Set the VOUT_SCALE_

LOOP command (Register 0x29) and the VOUT_SCALE_

MONITOR command (Register 0x2A), based on the resistor

divider information.

2. Enable the power supply with the no load current. The voltage

of the VS± pins is divided down by the VS resistor divider

to give a target of 1 V at the VS± pins.

3. Adjust the VOUT_CAL_OFFSET trim (Register 0x23) to

ensure that the output voltage is exactly the target output

voltage.

4. Adjust the VS gain trim register (Register 0xFE20) when

the READ_VOUT reading in Register 0x8B is the exact

output voltage reading.

VIN TRIM (VF GAIN TRIM)

The voltage sense inputs are optimized for the VF pin signals at

1 V and cannot sense a signal greater than 1.6 V. A resistor divider

is required to divide the sensed voltage signal into a voltage of

less than 1.6 V. It is recommended that the VF voltage signal be

reduced to 1 V for best performance. The resistor divider

introduces errors, which need to be trimmed.

Use the following procedure:

1. Set the VIN_SCALE_MONITOR command in Register 0xD8

based on the resistor divider information (see Figure 22)

and the turn ratio information of the transformer

IN_SCALE_MONITOR =

PRI

SEC

where NPRI and NSEC are the turns of the primary side

and secondary side windings, respectively, of the

transformer.

2. Apply the nominal input voltage at the no load condition

to achieve a targeted voltage of approximately 1 V at the

VF pin.

3. Adjust the VF gain trim register (Register 0xFE28) when

the READ_VIN reading in Register 0x88 is the exact

nominal voltage reading.

4. Adjust the input voltage compensation multiplier

(Register 0xFE59) to make the READ_VIN reading

match the exact input voltage at full load condition.

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,

follow these 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% (such as the NCP15WF104F03RC) in parallel with an

external resistor of 16.5 kΩ, 1%, with the ADP1052. With this

NTC thermistor and resistor combination, the ADP1052 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.

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