ADP1046AACPZ-R7 datasheet(17/88 Pages) AD

17 / 88 page

Data Sheet

ADP1046A

Rev. 0 | Page 17 of 88

VS2 OPERATION (VS2)

VS2 is used in conjunction with VS1 to control the OrFET gate

drive turn-on. The VS2 sense point on the power rail needs an

external resistor divider to bring the nominal common-mode

signal to 1 V at the VS2 pin (see Figure 17).

The resistor divider is necessary because the VS2 ADC input

range is 0 V to 1.6 V. This divided-down signal is internally fed

into the VS2 ADC. The output of the VS2 ADC goes to the VS2

voltage value register (Register 0x16). The VS2 signal is never used

for the control loop but is used to control the turn-on and turn-off

of the OrFET (see the OrFET Control (GATE Pin) section) as

well as the voltage continuity flag. If the OrFET function of the

ADP1046A is not used, it is recommended that the VS2 input

be connected directly to PGND. The VS2 value is updated in

VS3 OPERATION (VS3+, VS3−)

VS3± is used for the monitoring and protection of the remote

load voltage. VS3± is a fully differential input that is the main

feedback sense point for the power supply control loop. The

VS3± sense point on the power rail needs an external resistor

divider to bring the nominal common-mode signal to 1 V at

the VS3± pins (see Figure 17). The resistor divider is necessary

because the VS3 ADC input range is 0 V to 1.6 V. This divided-

down signal is internally fed into a high frequency (HF) ADC.

The output of the VS3 ADC goes to the digital filter and is also

updated in Register 0x17 every 10 ms. The HF ADC is also the

high frequency feedback loop for the power supply.

VOLTAGE LINE FEEDFORWARD AND ACSNS

The ADP1046A supports voltage line feedforward control to

improve line transient performance. The ACSNS value is used

to divide the output of the digital filter, and the result is fed into

the PWM engine. The input voltage signal can be sensed at the

secondary winding of the isolation transformer and must be

filtered by an RCD network to eliminate the voltage spike at the

switch node (see Figure 19).

ACSNS

ADC

0V TO 1.6V

ACSNS

FEEDFORWARD

ADC

0.6V TO 1.6V

PROGRAMMABLE

ACTION (REG 0x0D[3:0])

FEEDFORWARD

GAIN

(REG 0x75[1:0])

DPWM

ENGINE

DIGITAL

FILTER

ACSNS GAIN TRIM

(REG 0x5E)

0.45V

1/x

FROM

SECONDARY

WINDING

Figure 19. Feedforward Configuration

The ACSNS voltage must be set to 1 V when the nominal input

voltage is applied. The ACSNS ADC sampling period is 10 µs;

therefore, the decision to modify the PWM outputs based on

input voltage is performed at this rate.

The feedforward scheme modifies the modulation value based

on the ACSNS voltage. When the ACSNS input is 1 V, the line

feedforward has no effect. For example, if the digital filter output

remains unchanged and the ACSNS voltage changes to 50% of

its original value (still higher than 0.5 V), the modulation of the

falling edge of OUTx doubles and vice versa (see Figure 20). The

voltage line feedforward function is optional and is programmable

using Register 0x75.

ACSNS

DIGITAL

FILTER

OUTPUT

OUTx

tMODULATION

Figure 20. Feedforward Control on Modulation

The ACSNS level comparator is also connected on the same pin

and flags an ACSNS fault when the voltage on the pin is below

0.45 V within each switching period. The ACSNS level comparator

is used to detect whether the node is switching.

DIGITAL FILTER

The loop response of the power supply can be changed using the

internal programmable digital filter. A Type 3 filter architecture

has been implemented. To tailor the loop response to the specific

application, the low frequency gain, zero location, pole location,

and high frequency gain can all be set individually (see the Digital

Filter Programming Registers section). It is recommended that

the Analog Devices, Inc., software GUI be used to program the

filter. The software GUI displays the filter response in Bode plot

format and can be used to calculate all stability criteria for the

power supply.

From the sensed voltage to the duty cycle, the transfer function

of the filter in z-domain is as follows:













−













−

H(z)

202

where:

a = filter_pole_register_value/256.

b = filter_zero_register_value/256.

c = high_frequency_gain_register_value.

d = low_frequency_gain_register_value.

m = 1 when 48.8 kHz ≤ fSW < 97.7 kHz.

m = 2 when 97.7 kHz ≤ fSW < 195.3 kHz.

m = 4 when 195.3 kHz ≤ fSW < 390.6 kHz.

m = 8 when 390.6 kHz ≤ fSW.

fSW is the switching frequency.

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