40IMX7-05-8 Datasheet, PDF (10/14 Pages) Power-One – IMX7, IMS7 Series Data Sheet 7-Watt DC-DC Converters

IMX7, IMS7 Series Data Sheet
®
7-Watt DC-DC Converters
Single-output models with R-input:
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.
06029e
Vi+
Vo+
V_ref = 2.5 V ^{4 kΩ}
+
Control
logic
Vi–
R_{ext 2}
R
+
R_ext1
V_ext
Vo–
–
100 to 105% V_{o nom}. R_ext should be connected between pin
4 and Vi –. The following table indicates suitable resistor
values for typical output voltages under nominal
conditions (V_{i nom}, I_o = 0.5 I_{o nom}), with paralleled outputs or
equal load conditions on each output.
Caution: Connection of R_ext to Vi+ may damage the converter.
+
V_ext
–
Vi+
Trim
R_ext
Vi–
06089a
Control
circuit
V_ref 2.5 V
Vo1+
Vo1–
Vo2+
Vo2–
Fig. 12
Output voltage adjust for single-output models
Fig. 13
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 R_ext1 or R_ext2 shall be connected as shown in the
figure below:
Either: R_ext1 between the R pin and Vo– to achieve an
output voltage adjustment range of V_o = 75 to 100% of
V_{o nom} (85 to 100% for 3.3 V outputs):
R_ext1 ≈ 4 kΩ • –_V–_o–_n–^V_o–_mo––––_V–_o
or: R_ext2 between the R pin and Vo+ to achieve an output
voltage range of approximately V_o = 100 to 105 % of V_{o nom}:
R_ext2 ≈ 4 kΩ • _{2–.–5–V–(–}^V_{•–(}^o–_V^––_o–/2_V–.5_o–_n^V–_o–)_m––––1–) –
b) Adjustment by means of an external voltage V_ext between
Vo– and R pin.
The control voltage is 1.96 to 2.62 V and allows for
adjustment in the range of 75 to 105% of V_{o nom}.
V_ext ≈
–^V–^o–•–2–.–5–V–
V_{o nom}
Caution: Applying an external voltage >2.75 V may damage the
converter.
Note: Attempting to adjust the output below this range will cause
the converter to shut down (hiccup mode).
Double-output models with Trim input:
The Trim input (pin 4) of double-output models is referenced
to the primary side. The figure 15 shows the circuitry.
Adjustment of the output voltage is possible in the range of
100 to 105% of V_{o nom} using an external resistor, or in the range
of 75 to 105% of V_{o nom} using an external voltage source.
a) Adjustment by means of an external resistor R_ext.
Programming of the output voltage by means of an
external resistor R_ext1 is possible within a limited range of
Table 6: R_ext for V_o > V_{o nom}
approximate values (V_{i nom}, I_o1 = I_o2 = 0.5 I_{o1/2 nom})
V_o [% V_onom]
R_ext [ kΩ]
105 to 108 (107 typically)
0
105
1.5
104
5.6
103
12
102
27
101
68
100
∞
Note: Applying a control voltage greater than 20 V will set the
converter into a hiccup mode.
b) Adjustment by means of an external voltage source V_ext.
For external output voltages in the range of 75 to 105% of
V_{o nom} a voltage source V_ext (0 to 20 V) is required,
connected to the Trim-input (pin 4) and Vi–. The table
below indicates typical V_o versus V_ext values under
nominal conditions (V_{i nom}, I_o = 0.5 I_{o nom}), with paralleled
outputs or equal load conditions on each output. Direct
paralleling of the Trim-inputs of converters connected in
parallel is feasible.
Table 7: V_ext for V_o = 75 to 105% V_{o nom};
typical values (V_{i nom}, I_o1 = I_o2 = 0.5 I_{o1/2 nom})
V_o [% V_{o nom}]
V_ext [V]
≥105
0
102
1.6
95
4.5
85
9
75
13
BCD20007-G Rev AE, 14-May-2012
Page 10 of 14
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