IMX70, IMY70 Series Data Sheet
70 to 90 Watt DC-DC Converters
BCD.00002 Rev AH, 17-Aug-2015 Page 10 of 15
MELCHER
The Power Partners.
Auxiliary Functions
Adjustable Output Voltage
As a standard feature, the converters offer adjustable output
voltages by using the control input R. Fig. 10 shows the
schematic diagram of the circuitry. If the control input is left
open-circuit, the output voltage is set to Vo nom.
Note: For output voltages Vo > Vo nom, the minimum input voltage
Vi min (see Electr. Input Data) increases proportionally to Vo/Vo nom.
Fig. 11
Output voltage control by means of the R input
The R-input is referenced to the secondary side of the
converter. Adjustment of Vo (or Vo1) is possible by means of
either an external resistor or a voltage source.
a) Adjustment by means of an external resistor Rext.
Depending upon the value of the required output voltage,
the resistor shall be connected:
either: Between the R-pin and Vo– (or Vo1) to achieve an
output voltage adjustment range of Vo ≈ 80 to 100 % of
Vo nom. Single-output models can be trimmed to Vo ≈ 0 V.
Vo
Rext1 ≈ 4 kΩ • –––––––––
Vo nom – Vo
or: Between the R-pin and Vo+ (or Vo1+) to achieve an
output voltage range of Vo ≈ 100 to 105% of Vo nom.
(Vo – 2.5 V)
Rext2 ≈ 4 kΩ • –––––––––– ––––––––
2.5 V • (Vo/Vo nom – 1)
b) Adjustment by means of an external voltage Vext between
Vo– (or Vo1–) and the R-pin.
The control voltage range is 1.96 to 2.62 V and allows for
adjustment in the range of Vo ≈ 80 to 105% of Vo nom. Single-
output models can be trimmed to Vo ≈ 0 V.
Vo • 2.5 V
Vext ≈ ––––––––
Vo nom
Note: Single-output models can be trimmed up to 110% of Vo nom.
Note: Applying a higher external control voltage as needed for the
max. trim range may damage the converter.
Reference Output (Ref)
The converter provides a stable 5 V (±0.25 V) reference signal
on pin 7 (Ref). The output is protected by a 1 kΩ resistor.
Note: It is recommended to connect a filter capacitor (0.1 µF)
between Ref and Vi–, if Ref is used.
Current Sharing (T)
This feature is available for single-output models. Several
parallel connected converters will share their current evenly by
interconnecting the T pins (pin 11).
Note: This feature allows connecting the outputs together through
ORing diodes to achieve redundancy. We recommend Schottky
diodes mounted onto the same heat sink (for thermal balancing).
Sense Lines
The sense inputs of single-output models allow for compensat-
ing a voltage drop up to 1 V (0.6 V for models with Vo nom = 5.1 V).
Synchronization (W)
Double-output models can be synchronized to an external TTL
signal (220 ±10 kHz, duty cycle 10 – 15%). Due to the higher
switching frequency, the efficiency will slightly drop.
Note: If this feature is not used, W (pin 6) can be connected to Vi–
(pin 2) or left open-circuit.
Shutdown (S
_D
_)
The outputs of the converters may be enabled or disabled by a
logic signal (TTL, CMOS, etc.) applied between the shutdown
pin 8 and Vi –. If the shutdown function is not required, pin 8
should be left open-circuit. Voltage on pin 8:
Converter operating: 2.0 to 20 V
Converter disabled: –0.7 to +0.7 V
Progr. Input Voltage Lockout PUL
A special feature of these converters is the adjustable under-
voltage lockout function, protecting the converter (and system)
from high currents caused by operation at too low input volt-
age. This ensures easier start-up in distributed power systems.
The undervoltage lockout level can be programmed by an
external resistor RPUL (between PUL and Vi–) to increase the
preset levels, as indicated in the table below (with hysteresis).
The overvoltage lockout (OVL) cannot be varied.
R
Vo+
Vo–
+
V
ex
–
4 kΩ
V
ref
= 2.5 V
Control
logic R
ext1
R
ext2
06029e
Vi–
Vi+
+
Table 9: Typical values for RPUL and the respective turn-on
input voltage Vi LO.
24IMX70 RPUL [kΩΩ
ΩΩ
Ω] 40IMX70 RPUL [kΩΩ
ΩΩ
Ω]
ViLO [V] single-op. double-op. Vi LO [ V ] single-op. double-op.
14 ∞∞24 ∞∞
16 40.5 120
18 19.8 62
20 12.8 41
110IMY70 RPUL [kΩΩ
ΩΩ
Ω]RPUL [kΩΩ
ΩΩ
Ω]
Vi LO [V] single-output double-output
46 ∞∞
50 68 270
57 25.5 110
61 18 82
Table 8: Turn-on and shutdown voltage (pin 1 left open)
Model Turn -on level Hysteresis OVL Unit
24IMX70 13.5 – 14.5 typ. 2.5 41 – 43 V
40IMX70 22 – 23.5
110IMY70 44.5 – 47.5 typ. 6 160 – 175