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ADP1046AW Datasheet(PDF) 35 Page - Analog Devices

Part No. ADP1046AW
Description  Digital Controller for Isolated
Download  88 Pages
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Maker  AD [Analog Devices]
Homepage  http://www.analog.com

ADP1046AW Datasheet(HTML) 35 Page - Analog Devices

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Data Sheet
Rev. 0 | Page 35 of 88
Using the OTP Value
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 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.
To use this procedure, the temperatures and equivalent resistances
of the NTC thermistor and parallel resistor combination must
be known.
In Figure 45, T2 is the OTP threshold that sets the OTP flag,
and T1 is the temperature at which the OTP flag is cleared.
Figure 45. RTD Pin Voltage, ADC Code, and Temperature
The following procedure should be used:
1. Adjust the desired RTD current source, IRTD, as described
in the Trimming the Current Source section.
2. Set the temperature to the OTP threshold.
3. Adjust the offset trim registers (Register 0x1C and
Register 0x20) until the reading in Register 0x1A is
the same as V2 (in mV).
4. Set the OTP threshold (Register 0x2F) to the value of V2.
5. Set the temperature to the hysteresis point where the OTP
flag is cleared.
6. Adjust the temperature gain trim register (Register 0x2B)
until the correct voltage is seen in Register 0x1A.
The ADC is now trimmed and is linear between the two
temperatures of interest.
This procedure achieves the most accurate OTP because it takes
into account the part-to-part variations of the ADP1046AW and
the tolerances of the thermistor being used.
The ACSNS feedforward ADC (see Figure 19) is used for
voltage line feedforward and cannot be trimmed by the user.
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 19).
To trim the ACSNS ADC, the user can reverse-calculate the
primary voltage as follows:
VPRIMARY = Vx × (R1 + R2)/R2 × (N1/N2)
Vx is the voltage at the ACSNS pin.
N1/N2 is the turns ratio.
The ACSNS gain trim register (Register 0x5E) is adjusted until
this calculated voltage is equal to the desired primary input
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).
ADC Code = Vx/1.6 × 4096
where Vx is the voltage at the ACSNS pin.
The resistors in Figure 19 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.

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