IMX35 Series Data Sheet
35 Watt Quad-Output DC-DC Converters
®
Table 8: Vo versus Vext for Vo = 85 to 105% Vo nom
;
Auxiliary Functions
typical values (Vi nom, Io = 0.5 Io nom
)
Adjustable Output Voltage
Vo [% Vo nom
]
Vext [V]
As a standard feature, the IMX35 offer adjustable output
voltages in the range of 85 to 105% of Vo nom. Fig. 12 shows the
schematic diagram for the adjustment of quad-output models.
Trim [V]
Trim1 [V]
>105
102
100
95
0
0
1.5
2.5
4.25
6.2
8
1.8
2.5
4.3
6.2
8
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 (Vo1 and Vo4).
90
85
Adjustment by means of an external resistor Rext
:
Synchronization (W)
06137c
It is possible to synchronize the switching frequency of one or
more converters to an external clock signal.
Vi+
Vo1+
Vo1–
Vo2+
16
4
5
Trim
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.
15
13
+
–
Control
circuit
Vref = 2.5 V
Vext
Rext
Vi–
Vo2–
2
14
Fig. 13
Reference Output (Ref)
Output voltage control by means of the Trim input
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.
Adjustment of the output voltage by means of an external
resistor Rext is possible within the range of 100 to 105% of
Vo nom. Rext 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 (Vi nom, Io =
0.5 Io nom).
It is recommended to connect a filter capacitor (0.1 µF)
between Ref and Vi–, if Ref is used.
Shutdown
Note: Connection of Rext to Vi+ may damage the converter.
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:
Adjustment by means of an external voltage source Vext
Table 7: Rext for Vo > Vo nom
;
approximate values (Vi nom, Io = 0.5 Io nom
)
Converter operating:
Converter disabled:
2.0 to 20 V
–10 to 0.7 V
Vo [% Vo nom
]
Rext [kΩ]
Trim
Trim1
105 to 108 (107 typically)
0
0
17
110
∞
105
102
100
10
62
∞
For external output voltage adjustment in the range 85 to
105% of Vo nom a voltage source Vext (0 to 20 V) is required,
connected to Trim or Trim1 (pin 5) and Vi–. The table below
indicates typical values Vo versus Vext. 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
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