ADP-I2C-USB-Z View Datasheet(PDF) - Analog Devices
Part Name
Description
Manufacturer
ADP-I2C-USB-Z Datasheet PDF : 108 Pages
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ADP1051
Data Sheet
If the digital compensator output remains unchanged and the VF
voltage changes to 200% of its original value (still smaller than 1.6 V),
the modulation of the OUTx edges that are configured for
modulation is divided by 2 (see Figure 23). Register 0xFE3D[3:2] is
used to program the optional input voltage feedforward function.
The VF pin also has a low speed, high resolution Σ-Δ ADC. The
ADC has an update rate of 800 Hz with 11-bit resolution. The
ADC output value is stored in Register 0xFEAC and converted
to the READ_VIN command (Register 0x88). This value provides
information for the input voltage monitoring and flag functions.
VF
DIGITAL
FILTER
OUTPUT
OUTx
tMODULATION
tS
tMODULATION
tS
Figure 23. Closed-Loop Input Voltage Feedforward Changes Modulation
Values
OPEN-LOOP INPUT VOLTAGE FEEDFORWARD
OPERATION
The ADP1051 can run in open-loop input voltage feedforward
operation mode. In this mode, the input voltage is sensed as the
feedforward signal for generation of the PWM outputs.
As shown in Figure 24, the digital compensator output is modified
by a programmable modulation reference. The VF value, which
represents the input voltage, is fed into the feedforward ADC to
divide the modulation reference. The result of this division is then
fed into the PWM engine. The duty cycle value is in inverse
proportion to the input voltage.
Using the following equations:
D = VIN _ NOM × (tREF × fSW)
VIN
and
VOUT =
VIN × D
n
the output voltage can be derived by
( ) VOUT = VIN _ NOM × tREF × f SW
n
where:
D is the duty cycle value.
VIN_NOM is the nominal input voltage.
VIN is the input voltage.
tREF is the modulation reference, which is set by Register 0xFE63
and Register 0xFE64.
fSW is the switching frequency.
VOUT is the output voltage.
n is the turn ratio of the main transformer.
In the equation to derive VOUT, the input voltage, VIN, is cancelled out.
Therefore, the output voltage does not change when the input
voltage changes.
Register 0xFE63 and Register 0xFE64 set the modulation reference,
based on the target output voltage and the nominal input voltage at
which the VF pin voltage is 1 V (see Figure 24).
FROM THE VIN
SENSE CIRCUIT
VIN_UV_FAULT
FLAG REG 0x7C[4]
READ_VIN
REG 0x88
Σ-Δ
ADC
0V TO 1.6V VF
VIN_LOW
FLAG REG 0x7C[3] REG 0xFE29[5]
1/x
REG 0x35,
REG 0x36
FEED-
FORWARD
ADC
0.5V TO 1.6V
DPWM
ENGINE
MODULATION
REFERENCE
REG 0xFE63 AND REG 0xFE64
Figure 24. Open-Loop Feedforward Operation
The PWM settings of open-loop input voltage feedforward operation
are similar to those of general closed-loop operation. The falling edge
timings, rising edge timings, and modulation are set in the same
manner as for closed-loop operation, by using Register 0xFE3E to
Register 0xFE52. Register 0xFE09[4:3] sets the soft start speed of the
modulation edges. Register 0xFE3D[6] enables open-loop feed-
forward operation. Register 0xFE3D[7] is used to enable the soft
start procedure of open-loop feedforward operation.
The flag settings of open-loop feedforward operation are also similar
to those of general closed-loop operation.
Because the output voltage is not regulated in the same manner as
closed-loop operation, some settings, such as the VOUT setting, the
digital compensator settings, and the constant current mode
setting, are not functional. Other settings can be programmed in
a manner that is similar to general closed-loop operation.
Rev. B | Page 22 of 108
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