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IMX 7 DC/DC Series Data Sheet
7W Board Mountable Converter
REV. OCT 01, 2003
10/15
IMX SERIES
R
Vo+
Vo–
+
U
ext
–
4 k
Uref 2.5 V
control
circuit
Vi+
Vi–
R
ext1
R
ext 2
06029
Fig. 13
Output voltage control for single output units by means of
the R-input
Double output units:
The R input (Trim) input is referenced to the primary side.
The figure below shows the circuit topology. Adjustment of
the output voltage is possible by means of either an exter-
nal resistor in the range of 100...105% of Vo nom, or an ex-
ternal voltage source in the range of 75...105% of Vo nom.
R (Trim)
Vo1+
Vo2–
+
U
ext
–
Vi+
Vi–
R
ext
Vo1–
Vo2+
06030
Control
circuit
Uref 2.5 V
Fig. 14
Output voltage control for double output units by means
of the R input
a) Adjustment by means of an external resistor.
Programming of the output voltage by means of an ex-
ternal resistor Rext1 is possible within a limited range of
100...105% of Vo nom. Rext1 should be connected be-
tween the R-pin and Vi–. Connection of Rext1 to Vi+ may
damage the converter. The following table indicates suit-
able resistor values for typical output voltages under
nominal conditions (Vi nom, Io = 0.5 Io nom), with either par-
alleled outputs or equal load conditions on each output.
b) Adjustment by means of an external voltage source Vext.
For external output voltage programming in the range
75...105% of Vo nom a (0...20 V) source Vext is required,
connected to the R-pin and Vi–. The table below indi-
cates typical Vo versus Vext values under nominal condi-
tions (Vi nom, Io = 0.5 Io nom), with either paralleled outputs
or equal load conditions on each output. Applying a con-
trol voltage greater than 20 V will set the converter into a
hiccup mode. Direct paralleling of the R-pins of units
connected in parallel is feasible.
Table 7: Vext for Uo = 75...105% Vo nom;
typical values (Vi nom, Io1, 2 = 0.5 Io1/2 nom)
Vo [% Uo nom]
Vext [V]
105
0
102
1.6
95
4.5
85
9
75
13
b) Adjustment by means of an external voltage Vext be-
tween Vo– and R pins.
The control voltage range is 1.87...2.62 V and allows for
an adjustment in the range of approximately 75...105%.
(85...105% for 3.3 V outputs)
Vo 2.5 V
Vext = –––––––––
Vo nom
Attempting to adjust the output below this range will
cause the converter to shutdown (hiccup mode).
Note: Applying an external control voltage >2.75 V may
damage the converter.
Table 6: Rext1 for Vo > Vo nom;
approximate values (Vi nom, Io1, 2 = 0.5 Io1/2 nom)
Vo [% Vo nom]
Rext [k]
105...108 (107 typically)
0
105
1.5
104
5.6
103
12
102
27
101
68
100
∞