®

BCD20007-G Rev AD, 4-Nov-09

Page 6 of 15

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IMX7/IMS7 DC-DC Series Data Sheet

7-Watt DC-DC Converters

Input Transient Voltage Protection

In many applications transient voltages on the input of the

converter may occur and are possibly caused by short circuits

between Vi+

and Vi–, where the network inductance may

cause high energy pulses.

In order to protect the converters, transient suppressors are

fitted to the input; see table below:

Table 3: Built-in transient voltage suppressor

Model

Breakdown

Peak Power

Peak Pulse

Voltage

at 1 ms

Current

overvoltage lockout at approx. 38 V

53 V

600 W

7.7 A

100 V

1500 W

11 A

100 V

600 W

4.1 A

144 V

600 W

2.9 A

167 V

600 W

2.5 A

approx. 38 V protecting the input up to 50 V. For higher transient

voltages an external suppressor or voltage limiting circuit as, e.g.,

for IEC/EN 61000-4-5, level 2 compliance should be provided.

possible, an external limiting network such as the circuit

recommended for IEC/EN 61000-4-5, level 2 compliance, is

necessary.

To achieve IEC/EN 61000-4-5, level 2 compliance, an

additional inductor and capacitor should be provided externally

as shown in the figure below. The components should have

similar characteristics as listed in table 4.

Input Fuse and Reverse Polarity Protection

The suppressor diode on the input also provides for reverse

polarity protection by conducting current in the reverse

direction, thus protecting the converter. An external fuse is

required to limit this current. We recommend for:

– 20IMX7 and 24IMS7 a fast 2 A (F2A) fuse

– 40IMX7 and 48IMS7 a fast 1 A (F1A) fuse

– 70IMX7 a fast 0.63 A (F.63A) fuse

– 110IMX7 a fast 0.63 A (F.63A) fuse.

Inrush Current

The inrush current has been kept as low as possible by

choosing a very small input capacitance. A series resistor may

be inserted in the input line to limit this current further.

Fig. 5

ETS 300132-2 (40IMX7).

0

1

2

3

A

0

20

40

60

80 µs

04030a

4

Table 4: Components for external circuitry to comply with

IEC/EN 61000-4-5

Model

L

C

D

20IMX7

330

μH, 1 A, 0.115

Ω

68

μF, 63 V

1.5KE39A

24IMS7

330

μH, 0.6 A, 0.42

Ω

68

μF, 63 V

n.a.

40IMX7

330

μ H, 0.6 A, 0.42

Ω

68

μF, 100 V

n.a.

48IMS7

330

μ H, 0.6 A, 0.42

Ω

68

μF, 100 V

n.a.

70IMX7

1000

μ H, 0.6 A, 0.42

Ω

68

μF, 100 V

n.a.

110IMX7

330

μH, 0.2 A

200

μF, 200 V

n.a.

Note: Suppressor diode D is only necessary for 20IMX7 models.

To withstand 150 V transients according to 19 Pfl 1, applicable for

40 IMX7 models, the same external circuitry with similar

components as for IEC/EN 61000-4-5, level 2 compliance can be

used.

Fig. 4

Example for external circuitry to comply with IEC/EN

61000-4-5, level 2 (transzorb D only for 20IMX7).

Vi+

Vi–

07064

C

L

D

+

i