Board Mountable
DC-DC Converters
IMX 35 Series
Edition 3/4.2000
9/18
Thermal Considerations
If a converter, mounted on a PCB, is located in free, quasi-
stationary air (convection cooling) at the indicated maxi-
mum ambient temperature
TA max (see table: Temperature
specifications) and is operated at its nominal input voltage
and output power, the case temperature
TC measured at
the
Measuring point of case temperature TC (see: Mechani-
cal Data) will approach the indicated value TC max after the
warm-up phase. However, the relationship between
TA and
TC depends heavily on the conditions of operation and inte-
gration into a system. The thermal conditions are influ-
enced by input voltage, output current, airflow, temperature
of surrounding components and the surfaces and proper-
ties of the printed circuit board.
TA max is therefore only an
indicative value and under practical operating conditions,
the ambient temperature
TA may be higher or lower than
this value.
Caution: The case temperature
TC measured at the:
Measuring point of case temperature TC (see: Mechani-
cal Data) may under no circumstances exceed the
specified maximum value. The installer must ensure that
under all operating conditions
TC remains within the lim-
its stated in the table:
Temperature specifications.
Short Circuit Behaviour
The current limit characteristic shuts down the converter
whenever a short circuit is applied to an output. It acts self-
protecting and automatically recovers after removal of the
overload condition (hiccup mode).
Overtemperature Protection
The converters individual power trains are protected
against possible overheating by means of an internal tem-
perature monitoring circuit. It shuts down the unit above the
internal temperature limit and attempts to automatically re-
start. This feature prevents from excessive internal tem-
perature building up which could occur under heavy over-
load conditions.
Connection in Series
The outputs of one or several single or double output power
trains may be connected in series without any precautions.
Connection in Parallel
The outputs of one or several double output power trains
(except 3.3 or 5.1 V types) with equal nominal output volt-
age can be connected in parallel. Approximate current
sharing between 2 or several power trains is ensured by
their load dependent output characteristic.
Fig. 8
Uo versus Io (typ) of units with Uo = 5.1 V.
(40 IMX 35-05D12-9).
Fig. 9
Uo1/2 versus Io1/2 of double output power trains
(i.e. 2
× 12 V). See: Block diagram 1
5.5
5.0
4.5
4.0
3.5
3.0
0
1
2
3
4
5
Io [A]
Uo [V]
05019
7
8
9
10
11
12
13
Uo [V]
0.2
0.4
0.6 0.8
1.0
1.2
1.4
1.6 1.8 Io total [A]
0
05020
Output Overvoltage Protection
The outputs of the converter are protected against overvolt-
ages by a second control loop. In the event of an overvolt-
age on one of the outputs the unit will shut down and
attempt to restart in short intervals. The main purpose of
this feature is to protect against possible overvoltages
which could occur due to a failure in the feedback control
circuit. The overvoltage protection is not designed to with-
stand externally applied overvoltages.
Typical Performance Curves
General conditions:
– TA
°C, unless T
C is specified.
– Shut down pin left open circuit.
– Trim input not connected.