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ADP1046AW Datasheet(PDF) 83 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
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ADP1046AW Datasheet(HTML) 83 Page - Analog Devices

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Data Sheet
ADP1046AW
Rev. 0 | Page 83 of 88
ADJUSTING THE TIMING OF THE PWM OUTPUTS
To accurately adjust the timing of the PWM outputs, the
following registers can be used to set the dead time and delays
of the PWM outputs: Register 0x41, Register 0x43, Register 0x45,
Register 0x47, Register 0x49, Register 0x4B, Register 0x4D,
Register 0x4F, Register 0x51, Register 0x53, Register 0x55, and
Register 0x57. The resolution for adjusting the dead time is 5 ns.
See the Resonant Mode Register Descriptions section for more
information. The software GUI for the ADP1046AW can be used
to set the frequency limit registers, as well as all other settings
related to the resonant mode of operation.
FREQUENCY LIMIT SETTING
The minimum frequency is set by Register 0x42 and the first
four bits of Register 0x44.
For example, Register 0x42 is set to 0xA0 (160 decimal) and
Bits[7:4] of Register 0x44 are set to 0xF (15 decimal).
The maximum switching cycle is
(160 × 16 + 15) × 5 ns = 12.875 μs
The lowest switching frequency limit is
1/12.875 μs = 77.7 kHz
The maximum frequency is set by Register 0x46 and by
Bits[7:4] of Register 0x48.
For example, Register 0x46 is set to 0x10 (16 decimal) and
Bits[7:4] of Register 0x48 are set to 0x9 (9 decimal).
The minimum switching cycle is
(16 × 16 + 9) × 5 ns = 1.325 μs
The highest switching frequency limit is
1/1.325 μs = 755 kHz
FEEDBACK CONTROL IN RESONANT MODE
In contrast to a traditional fixed frequency PWM converter, the
output voltage of a resonant converter is regulated by changing
the switching frequency. When the ADP1046AW is operated in
resonant mode, the switching frequency decreases when the
sensed voltage is lower than the reference voltage. This makes
the ADP1046AW capable of controlling a resonant converter in
zero-voltage switching (ZVS) mode.
Although the switching frequency is variable, the high
frequency feedback voltage sampling frequency (VS3± pins)
is fixed at 400 kHz. The parameters of the feedback filter are
based on this frequency. The method for calculating the filter
parameters (gains, zeros, and poles) is the same as that for the
fixed frequency PWM mode (see the Digital Filter section).
SOFT START IN RESONANT MODE
During soft start, the reference voltage of the ADP1046AW ramps
up. With the feedback loop closed, the switching frequency is
reduced from the highest limit to a regulation value. The soft
start timing settings and the filter settings are the same as those
for the fixed frequency PWM mode (see the Soft Start section).
LIGHT LOAD OPERATION (BURST MODE)
To control the converter at very light load, the ADP1046AW
can operate in burst mode. Burst mode can be enabled or
disabled using Bits[7:6] of Register 0x4A. When the desired
switching frequency is higher than the burst mode threshold,
the part enters burst mode. The threshold is determined by the
maximum frequency and the burst mode offset setting.
The threshold value used to enter burst mode is determined
as follows:
Threshold value for burst mode =
((Register 0x46 × 16) + Register 0x48[7:4]) +
(Register 0x4A[5:0] × 2)
The threshold value used to exit burst mode is determined
by the entrance value plus 0x10.
For example, Register 0x46 is set to 0x10 (16 decimal), Bits[7:4]
of Register 0x48 are set to 0, and Bits[5:0] of Register 0x4A are
set to 0x8 (8 decimal).
The minimum switching cycle is
(16 × 16 + 0) × 5 ns = 1.28 μs
The highest switching frequency limit is
1/1.28 μs = 781 kHz
The threshold to enter burst mode is
[(16 × 16 + 0) + (8 × 2)] × 5 ns = 1.36 μs
When the desired switching frequency is higher than
1/1.36 μs = 735 kHz, the PWM outputs are shut down
and the part enters burst mode.
The threshold to exit burst mode is
[(16 × 16 + 0) + (8 × 2) + 16] × 5 ns = 1.44 μs
Therefore, when the desired switching frequency becomes lower
than 1/1.44 μs = 694 kHz, the PWM signals are reenabled, and
the part exits burst mode.
OUTAUX PIN IN RESONANT MODE
In resonant mode, the OUTAUX pin cannot be used as a control
signal. However, OUTAUX can be used as a fixed frequency
PWM signal with a fixed duty cycle.
PROTECTIONS IN RESONANT MODE
All of the flags and protections that are available in resonant mode
behave in the same manner as in fixed frequency PWM mode.


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