Board Mountable
DC-DC Converters
IMX 35 Series
Edition 1/01.2001
12/18
Synchronisation (W)
This logic input can be used to synchronise the oscillator to
an external frequency source. The input is edge triggered
with TTL thresholds, and requires a source frequency of
490...540 kHz (duty cycle 10...90%). The external source
frequency is internally divided by 2 to define the switching
frequency of the converter. If unused, this pin can be con-
nected to V1– (pin 2) or left open-circuit.
Reference (Ref)
The signal output provides a stable 5 V (
±0.1 V) reference
signal on pin Ref. It is protected by a 1 k
resistor. This sig-
nal may be used also in conjunction with the Trim input pin
5 (primary side) as a limited external voltage reference.
Then we recommend to connect a filter capacitor (0.1
F)
between Ref and Vi–.
Shut Down Function
The outputs of the converters may be enabled or disabled
by means of a logic signal (TTL, CMOS, etc.) applied to the
shut down pin. If the shut down function is not required then
it should be left open-circuit.
Converter operating:
2.0...20 V
Converter shut down:
–10...0.7 V
Programmable Input Undervoltage Lockout PUL
A special feature of these units is the accurate undervoltage
lockout function which protects the units (and the system)
from large currents caused by operation at low voltages.
This ensures easier start-up in distributed power systems.
Table 7: Turn on and turn off voltage
Type
Trigger level
Hysteresis
Units
20 IMX 35
7...8
≤0.5
V
40 IMX 35
14...15.5
≤1
See:
Electrical input data for a description of the turn on
turn off voltage levels of the various types.
The under voltage lockout levels may be programmed by
use of an external resistor to pull up the preset level as indi-
cated in table 8. (see:
Fig. 15).
Table 8: Typical values for Rext and the respective lockout
voltage for input voltage.
20 IMX 35
40 IMX 35
RPUL [k]
Ui min [V]
RPUL [k]
Ui min [V]
∞≤8
∞≤15.5
39
10
43
22
19
12
16
26
13
14
10
28
9.1
16
0
32