ADP1046ACPZ-R7 datasheet(35/96 Pages) AD

35 / 96 page

Data Sheet

ADP1046

Rev. 0 | Page 35 of 96

Using the OTP Value

The ADC is now trimmed and is linear between the two

temperatures of interest.

The second option does not use the linearization scheme.

Instead, the user programs an RTD current and sets the OTP

threshold in millivolts. Due to the nonlinear nature of the NTC

thermistor, it is best to use a resistor in parallel with the NTC

thermistor to aid in the linearization of the voltage seen at the

RTD pin.

This procedure achieves the most accurate OTP because it takes

into account the part-to-part variations of the ADP1046 and the

tolerances of the thermistor being used.

ACSNS CALIBRATION AND TRIM

The ACSNS feedforward ADC (see Figure 18) is used for

voltage line feedforward and cannot be trimmed by the user.

This procedure trims out the errors/tolerances in the NTC therm-

istor and the external resistor. Calculation of the parallel resistor

can be done by knowing the NTC resistance characteristic across

various temperatures.

The ACSNS slow ADC requires a gain trim. Enable the power

supply with full load current at the nominal input voltage. The

secondary peak reverse voltage on the output rectifiers is

filtered by an external RCD circuit (see Figure 18).

To use this procedure, the temperatures and equivalent resistances

of the NTC thermistor and parallel resistor combination must

be known.

To trim the ACSNS ADC, the user can reverse-calculate the

primary voltage as follows:

In Figure 44, T2 is the OTP threshold that sets the OTP flag,

and T1 is the temperature at which the OTP flag is cleared.

VPRIMARY = Vx × (R1 + R2)/R2 × (N1/N2)

where:

Vx is the voltage at the ACSNS pin.

N1/N2 is the turns ratio.

RTD PIN

VOLTAGE

ADC CODE

TEMPERATURE

RTD PIN VOLTAGE

The ACSNS gain trim register (Register 0x5E) is adjusted until

this calculated voltage is equal to the desired primary input

voltage.

Another way to trim the ACSNS ADC uses the average second-

ary voltage. With known values for the nominal input voltage,

transformer turns ratio, and resistor dividers at the ACSNS pin,

the ACSNS gain trim register (Register 0x5E) is adjusted to give

code 2560 decimal (0xA00).

Figure 44. RTD Pin Voltage, ADC Code, and Temperature

The following procedure should be used:

Adjust the desired RTD current source, IRTD, as described

in the Trimming the Current Source section.

Set the temperature to the OTP threshold.

ADC Code = Vx/1.6 × 4096

where Vx is the voltage at the ACSNS pin.

Adjust the offset trim registers (Register 0x1C and Register

0x20) until the reading in Register 0x1A is the same as V2

(in mV).

The resistors in Figure 18 are sized such that the first time

constant, RC, is long enough to prevent overcharging of the

capacitor (roughly 200 ns in a typical application), whereas the

second time constant, (R1 + R2) × C, is long enough to keep the

average voltage constant during the rectifier off time.

Set the OTP threshold (Register 0x2F) to the value of V2.

Set the temperature to the hysteresis point where the OTP

flag is cleared.

Adjust the temperature gain trim register (Register 0x2B)

until the correct voltage is seen in Register 0x1A.

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