ADP1043A Analog Devices, ADP1043A Datasheet - Page 66

• Manufacturer Part Number: ADP1043A
• Description: Digital Controller for Isolated Power Supply Applications
• Manufacturer: Analog Devices

ADP1043A
ADJUSTING THE TIMING OF THE PWM OUTPUTS
To accurately adjust the timing of the PWM outputs, the follow-
ing 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.
Refer to the Resonant Mode Register Descriptions section for
more detailed information. The software GUI for the ADP1043A
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 by 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
The lowest switching frequency limit is
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
The highest switching frequency limit is
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 ADP1043A is operated in
resonant mode, the switching frequency decreases when the
sensed voltage is lower than the reference voltage. This makes
the ADP1043A capable of controlling a resonant converter in
zero-voltage switching (ZVS) mode.
Although the switching frequency is variable, the feedback
voltage sampling frequency 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).
(160 × 16 + 15) × 5 ns = 12.875 μs
1/12.875 μs = 77.7 kHz
(16 × 16 + 9) × 5 ns = 1.325 μs
1/1.325 μs = 755 kHz
Rev. 0 | Page 66 of 72
SOFT START IN RESONANT MODE
During soft start, the reference voltage of the ADP1043A 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 ADP1043A 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:
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
The highest switching frequency limit is
The threshold to enter burst mode is
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
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 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.
Threshold value for burst mode =
((Register 0x46 × 16) + Register 0x48[7:4]) +
(Register 0x4A[5:0] × 2)
(16 × 16 + 0) × 5 ns = 1.28 μs
1/1.28 μs = 781 kHz
[(16 × 16 + 0) + (8 × 2)] × 5 ns = 1.36 μs
[(16 × 16 + 0) + (8 × 2) + 16] × 5 ns = 1.44 μs