IMX7/IMS7 DC-DC Series Data Sheet
7-Watt DC-DC Converters
®
Single-output models with R-input:
Adjustment of the output voltage is possible in the range of
100 to 105% of Vo nom using an external resistor, or in the range
of 75 to 105% of Vo nom using an external voltage source.
The R input (pin 13) is referenced to the secondary side of the
converter. Adjustment of the output voltage is possible by
means of either an external resistor or a voltage source.
06089a
06131
Vi+
Vo1+
Vo1–
Vo2+
Vo+
Vi+
Vi–
Trim
Rext1
+
–
Control
circuit
R
Vext
Rext
Vi–
V
ref 2.5 V
Rext2
Vo2–
Vo–
Fig. 13
Output voltage control with external resistor
Fig. 15
Output voltage adjust for double-output models
a) Adjustment by means of an external resistor:
Depending upon the value of the required output voltage,
a resistor Rext1 or Rext2 shall be connected as shown in the
figure below:
a) Adjustment by means of an external resistor Rext
.
Programming of the output voltage by means of an
external resistor Rext1 is possible within a limited range of
100 to 105% Vo nom. Rext should be connected between pin
4 and Vi–. The following table indicates suitable resistor
values for typical output voltages under nominal
conditions (Vi nom, Io = 0.5 Io nom), with paralleled outputs or
equal load conditions on each output.
Either: Rext1 between the R pin and Vo– to achieve an
output voltage adjustment range of Vo = 75 to 100% of
Vo nom (85 to 100% for 3.3 V outputs):
Vo
Rext1 ≈ 4 kΩ • –––––––––
V
o nom – Vo
Caution: Connection of Rext to Vi+ may damage the converter.
or: Rext2 between the R pin and Vo+ to achieve an output
voltage range of approximately Vo = 100 to 105% of Vo nom
:
Table 6: Rext for Vo > Vo nom
approximate values (Vi nom, Io1 = Io2 = 0.5 Io1/2 nom
)
(Vo – 2.5 V)
Rext2 ≈ 4 kΩ • ––––––––––––––––––
2.5 V • (Vo/Vo nom – 1)
Vo [% Vo nom
]
Rext [kΩ]
105 to 108 (107 typically)
0
b) Adjustment by means of an external voltage Vext between
Vo– and R pin.
105
104
103
102
101
100
1.5
5.6
12
27
68
∞
The control voltage is 1.96 to 2.62 V and allows for
adjustment in the range of 75 to 105% of Vo nom
.
Vo • 2.5 V
Vext ≈ ––––––––
Vo nom
Caution: Applying an external voltage >2.75 V may damage the
converter.
b) Adjustment by means of an external voltage source Vext
.
For external output voltages in the range of 75 to 105% of
Vo nom a voltage source Vext (0 to 20 V) is required,
connected to the Trim-input (pin 4) and Vi–. The table
below indicates typical Vo versus Vext values under
nominal conditions (Vi nom, Io = 0.5 Io nom), with paralleled
outputs or equal load conditions on each output. Direct
paralleling of the Trim-inputs of converters connected in
parallel is feasible.
Note: Attempting to adjust the output below this range will cause
the converter to shut down (hiccup mode).
06029b
Vi+
Vo+
Rext2
4 kΩ
Vref = 2.5 V
R
+
-
Control
logic
Note: Applying a control voltage greater than 20 V will set the
converter into a hiccup mode.
Vext
Rext1
Vi–
Vo-
Table 7: Vext for Vo = 75 to 105% Vo nom
;
typical values (Vi nom, Io1 = Io2 = 0.5 Io1/2 nom
)
Fig. 14
Vo [% Vo nom
]
Vext [V]
Output voltage adjust for single-output models
≥105
102
95
85
75
0
1.6
4.5
9
Double-output models with Trim input:
The Trim input (pin 4) of double-output models is referenced
to the primary side. The figure below shows the circuitry.
13
BCD20007-G Rev AD, 4-Nov-09
Page 10 of 15
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