ADDC02808PB(Rev0) View Datasheet(PDF) - Analog Devices
Part Name
Description
Manufacturer
ADDC02808PB Datasheet PDF : 20 Pages
| |||
ADDC02808PB
not have the response depicted in the last section. This is
8
because the feedback integrator will not have had time to return
to its normal state, and so the converter’s ability to respond to a
7
positive step change in load current will be reduced. The
maximum negative going deviation in the output voltage under
6
this circumstance will then be greater than is shown in the
5
figures of that section.
Should this situation arise, one approach would be to step the
4
load current down to an intermediate value (e.g., 4 A) at the
end of the power pulse, and then let this current decay to a
3
smaller value (e.g., 0.1 A) with a time constant in the 100 µs to
2
200 µs range. This should permit a rapid return to a steady state
condition at the end of the power pulse without requiring a large
1
OBSOLETE average load current during the low power portion of the cycle.
PIN CONNECTIONS
Pins 1 and 2 (؎SENSE)
Pins 1 and 2 must always be connected for proper operation,
although failure to make these connections will not be cata-
strophic to the converter under normal operating conditions.
Pin 1 must always be connected to the output return and Pin 2
must always be connected to +VOUT. These connections can
be made at any one of the output pins of the converter, or
remotely at the load. A remote connection at the load can
adjust for voltage drops of as much as 0.25 V dc between the
converter and the load.
Long remote sense leads can affect converter stability, although
this condition is rare. The impedance of the long power leads
between the converter and the remote sense point could affect
the converter’s unity gain crossover frequency and phase margin.
99
98
97
96
95
OUTPUT VOLTAGE – %
Figure 30. External Resistor Value for Reducing Output
Voltage
5
4
3
2
1
Consult factory if long remote sense leads are to be used.
0
Pin 3 (ADJUST)
An adjustment pin is provided so that the user can change the
101
102
103
104
105
OUTPUT VOLTAGE – %
nominal output voltage during the prototype stage. Since very
low temperature coefficient resistors are used to set the output
voltage and maintain tight regulation over temperature, using
standard external resistors to adjust the output voltage will
loosen output regulation over temperature. Furthermore, since
the status trip point is not changed when the output voltage is
adjusted using external resistors, the status line will no longer
trip at the standard levels of the newly adjusted output voltage.
If necessary, modified standard units can be ordered with the
Figure 31. External Resistor for Increasing Output Voltage
Pin 4 (STATUS)
Pin 4 is active high referenced to –SENSE (Pin 1), indicating
that the output voltage is typically within ± 5%. The pin is both
pulled up and down by internal circuitry. Figures 32 and 33
show the typical source and sink capabilities of the status
output. Refer to the paragraphs describing Pin 3 (ADJUST) for
effect on status trip point.
necessary changes made inside the package at the factory. The
5
ADJUST function is sensitive to noise, and care should be
taken in the routing of connections.
To make the output voltage higher, place a resistor from
4
ADJUST (Pin 3) to –SENSE (Pin 1). To make the output
voltage lower, place a resistor from ADJUST (Pin 3) to
3
+SENSE (Pin 2). Figures 30 and 31 show resistor values for a
± 5% change in output voltage.
2
With regard to the range that the output voltage can be adjusted
by the user, there are two concerns. As the output voltage is
raised it may become difficult to maintain regulation at full
1
power and low input voltage. As the output voltage is lowered,
it may become difficult to maintain regulation at minimum
power and high input line.
0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
IOH – mA
Figure 32. Source Capability of Status Output
REV. 0
–11–
Share Link: 