®
IMX35 Series Data Sheet
35 Watt Quad-Output DC-DC Converters
Auxiliary Functions
Adjustable Output Voltage
As a standard feature, the IMX35 offer adjustable output
voltages in the range of 85 to 105% of
V
o nom
. Fig. 12 shows the
schematic diagram for the adjustment of quad-output models.
All models with equal output voltages have a Trim input at pin
5 referenced to the primary side, influencing all outputs simul-
taneously. Models with different output voltages exhibit a
Trim1 input, influencing only the first power train (V
o1
and
V
o4
).
Adjustment by means of an external resistor
R
ext
:
Table 8: V
o
versus V
ext
for V
o
= 85 to 105% V
o nom
;
typical values (V
i nom
, I
o
= 0.5 I
o nom
)
V
o
[%
V
o nom
]
Trim [V]
>105
102
100
95
90
85
0
1.8
2.5
4.3
6.2
8
V
ext
[V]
Trim1 [V]
0
1.5
2.5
4.25
6.2
8
Synchronization (W)
06137c
Vi+
Trim
+
V
ext
–
R
ext
Vi–
4
5
16
15
Vo1+
Vo1–
Vo2+
It is possible to synchronize the switching frequency of one or
more converters to an external clock signal.
This logic input W can be used to synchronize the oscillator to
an external frequency source. This signal is edge-triggered
with TTL thresholds and requires a source frequency of 490 to
540 kHz (duty cycle 10 to 90%). The external source frequency
is internally divided by 2 to define the switching frequency of
the converter. If unused, this pin can be connected to V1– (pin
2) or left open-circuit.
Control
circuit
V
ref
= 2.5 V
2
13
14
Vo2–
Fig. 13
Output voltage control by means of the Trim input
Adjustment of the output voltage by means of an external
resistor
R
ext
is possible within the range of 100 to 105% of
V
o nom
.
R
ext
should be connected between Trim (pin 5) and Vi–
(pin 2). The following table indicates suitable resistor values for
typical output voltages under nominal conditions (V
i nom
,
I
o
=
0.5
I
o nom
).
Note: Connection of
R
ext
to Vi+ may damage the converter.
Reference Output (Ref)
The converter provides a stable 5 V (±0.1 V) reference signal
on pin 7 (Ref). The output is protected by a 1 kΩ resistor. The
signal may be used also in conjunction with the Trim input (pin
5) as a limited external voltage reference.
It is recommended to connect a filter capacitor (0 .1 µF)
between Ref and Vi–, if Ref is used.
Shutdown
The outputs of the converters may be enabled or disabled by
means of a logic signal (TTL, CMOS, etc.) applied to shut-
down (pin 8). If the shutdown function is not required, pin 8
should be left open-circuit:
Converter operating:
Converter disabled:
2.0 to 20 V
–10 to 0 .7 V
Adjustment by means of an external voltage source
V
ext
Table 7: R
ext
for V
o
> V
o nom
;
approximate values (V
i nom
, I
o
= 0.5 I
o nom
)
V
o
[%
V
o nom
]
Tr i m
105 to 108 (107 typically)
105
102
100
0
10
62
R
ext
[kΩ]
Ω
Trim1
0
17
110
∞
∞
For external output voltage adjustment in the range 85 to
105% of
V
o nom
a voltage source
V
ext
(0 to 20 V) is required,
connected to Trim or Trim1 (pin 5) and Vi–. The table below
indicates typical values
V
o
versus
V
ext
. Applying a control
voltage of 15 to 20 V will set the converter into the hiccup
mode. Direct paralleling of the Trim pins of converters of the
same type connected in parallel is feasible.
BCD20009-G Rev AC, 06-May-2013
Page 9 of 15
POWER-ONE [ POWER-ONE ]
