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ADP1053 View Datasheet(PDF) - Analog Devices

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ADP1053 Datasheet PDF : 84 Pages
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ADP1053
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) =
d
×
z
+
c
zb
×
204.8 × m z 1 5.12 z a
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) = 2 fS + s
2 fS 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.
Data Sheet
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
Register 0xFE3F (for Channel B).
ACSNS
DIGITAL
FILTER
OUTPUT
OUTX
tMOD
tMOD
tS
tS
Figure 18. Feedforward Changes Modulation Values
ACSNS
ADC
REG 0xFED9
ACSNS
GAIN TRIM
REG 0xFE77
ADP1053
R1
VX
ACSNS
FEEDFORWARD
1
X
ADC
R2
DIGITAL
FILTER
DPWM
ENGINE
Figure 19. Feedforward Configuration
Rev. A | Page 20 of 84
 

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