Board Mountable
DC-DC Converters
IMS 7 Series
Edition 6/4.2000
9/16
R
Vo+
Vo–
+
U
ext
–
4 k
Uref 2.5 V
control
circuit
Vi+
Vi–
R
ext1
R
ext 2
06029
Fig. 16
Output voltage control for single output units by means of
the R-input
Double output units:
The R input (Trim) is referenced to the primary side. The fig-
ure below shows the circuit topology. Adjustment of the out-
put voltage is possible by means of either an external resis-
tor in the range of 100...105% of
Uo nom, or an external volt-
age source in the range of 75...105% of
Uo nom.
R (Trim)
Vo1+
Vo2–
+
U
ext
–
Vi+
Vi–
R
ext
Vo1–
Vo2+
06132
Control
circuit
Fig. 17
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 exter-
nal resistor
Rext1 is possible within a limited range of
100...105% of
Uo nom. Rext1 should be connected between
the R-pin and Vi–. Connection of
Rext1 to Vi+ may dam-
age the converter. The following table indicates suitable
resistor values for typical output voltages under nominal
conditions (
Ui nom, Io = 0.5 Io nom), with either paralleled
outputs or equal load conditions on each output.
Table 6: Rext1 for Uo > Uo nom;
approximate values (Ui nom, Io1, 2 = 0.5 Io1/2 nom)
Uo [% Uo nom]
Rext [k]
105...108 (107 typically)
0
105
1.5
104
5.6
103
12
102
27
101
68
100
∞
b) Adjustment by means of an external voltage source
Uext.
For external output voltage programming in the range
75...105% of
Uo nom a (0...20 V) source Uext is required,
connected to the R-pin and Vi–.The table below indicates
typical
Uo versus Uext values under nominal conditions
(
Ui nom, Io = 0.5 Io nom), with either paralleled outputs or
equal load conditions on each output. Applying a control
voltage >20 V will set the converter into a hiccup mode.
Direct paralleling of the R-pins of units connected in par-
allel is feasible.
Table 7: Uext for Uo = 75...105% Uo nom;
typical values (Ui nom, Io1, 2 = 0.5 Io1/2 nom)
Uo [% Uo nom]
Uext [V]
≥105
0
102
1.6
95
4.5
85
9
75
13
b) Adjustment by means of an external voltage
Uext 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)
Uo 2.5 V
Uext ≈ –––––––––
Uo 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.