ADP1053ACPZ-R7 datasheet(20/84 Pages) AD

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ADP1053

Data Sheet

Rev. A | Page 20 of 84

DIGITAL FILTERS

Channel A and Channel B each have an internal programmable

digital filter. A Type III filter architecture is implemented in both

digital filters. The low frequency gain, zero location, pole loca-

tion, and high frequency gain can all be set individually to

optimize the loop response.

It is recommended that the ADP1053 GUI be used to program

the digital filter. The GUI displays the filter and loop response in

Bode plot format. Together with the parameters from the power

stages, all stability criteria can be evaluated.

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

the filter in z-domain is

H(z)

−

204

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.

where fSW is the switching frequency.

To transfer the z-domain value to the s-domain, plug the

following equation into Equation 1:

z(s)

−

Another set of registers configures the filter parameters for light

load mode (see the Light Load Mode and Phase Shedding section).

These separate registers allow the controller to regulate properly

at different load conditions and to move smoothly between

normal mode and light load mode.

ACSNS AND INPUT FEEDFORWARD

ACSNS has a low speed, high resolution ADC. This ADC samples

at the same PWM switching frequency as Channel C. The ACSNS

ADC has an update rate of 800 Hz with 11-bit resolution. The

ACSNS value register (Register 0xFED9) provides information

for the ACSNS monitoring and flag functions.

To improve line transient performance, a feedforward function

is implemented in the ADP1053 using the ACSNS voltage. As

shown in Figure 19, the input voltage signal is filtered by an RCD

network. The ACSNS value is used to modify the output of the

digital filter, and the modified result is fed to the PWM engine.

When the ACSNS input is set to a nominal voltage of 1 V

(1280 decimal in the ACSNS value register), there is no effect

on the modulation value.

When the output of the ACSNS ADC is below 0x280 (640 deci-

mal), the feedforward function uses 0x280 as the effective input

value. This means that the digital filter modulation value can be

increased up to twice the original value.

For example, if the digital filter output remains unchanged and

the ACSNS voltage changes to 50% of its original value (under

an input voltage dip condition), the modulation value of OUTX

doubles (see Figure 18). The modulation edge is still limited

by the maximum modulation limit.

The feedforward function is optional. It can be enabled or

disabled using Bit 2 of Register 0xFE3E (for Channel A) and

ACSNS

OUTX

DIGITAL

FILTER

OUTPUT

tMOD

Figure 18. Feedforward Changes Modulation Values

ACSNS

ADC

REG 0xFED9

ACSNS

FEEDFORWARD

ADC

ACSNS

GAIN TRIM

REG 0xFE77

DIGITAL

FILTER

DPWM

ENGINE

ADP1053

Figure 19. Feedforward Configuration

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