CMMDW24S5-4000 Wall Industries,Inc., CMMDW24S5-4000 Datasheet - Page 5

• Manufacturer Part Number: CMMDW24S5-4000
• Description: 20w Dc/dc Chassis Mount Converter 9-36 Vdc Input 5 Vdc Single Output At 4000ma
• Manufacturer: Wall Industries,Inc.

TECHNICAL DATASHEET
CMMDW24S5-4000
Rev. A
DESIGN CONSIDERATIONS:
Output Over Current Protection
When excessive output current occurs in the system, circuit protection is required on all power supplies. Normally,
overload current is maintained at approximately 140% of rated current for the CMMDW single output series.
Hiccup mode is a method of operation in a power supply whose purpose is to protect the power supply from being
damaged during an over-current fault condition. It also enables the power supply to restart when the fault is
removed. There are other ways of protecting the power supply when it is over loaded such as maximum current
limiting or current fold-back methods.
One of the problems resulting from over current is that excessive heat may be generated in power devices;
especially MOSFET and Schottky diodes and the temperature of those devices may exceed their specified limits. A
protection mechanism has to be used to prevent those power devices from being damaged.
The operation of hiccup is as follows. When the current sense circuit sees an over current event, the controller
shuts off the power supply for a given time and then tries to start up the power supply again. If the over load
condition has been removed, the power supply will start up and operate normally; otherwise, the controller will see
another over current event and shut off the power supply again repeating the previous cycle. Hiccup operation has
none of the drawbacks of the other two protection methods, although its circuit is more complicated because it
requires a timing circuit. The excess heat due to over load lasts for only a short duration in the hiccup cycle, hence
the junction temperature of the power devices is much lower.
The hiccup operation can be done in various ways. For example, one can start the hiccup operation any time an
over current event is detected, or prohibit hiccup during a designated start-up which is usually larger than during
normal operation and it is easier for an over current event to be detected, or prohibit hiccup during a designated
start-up interval (usually a few milliseconds). The reason for the latter operation is that during start-up the power
supply needs to provide extra current to charge up the output capacitor thus the current demand is usually larger
than during normal operation making it easier for an over current event to occur. If the power supply starts to
hiccup once there is over current it might never start up successfully. Hiccup mode protection will give the best
protection for a power supply against over current situations since it will limit the average current to the load at a
low level reducing power dissipation and case temperature in the power devices.
Output Over Voltage Protection
The output over voltage protection consists of an output Zener diode that monitors the voltage on the output
terminals. If the voltage on the output terminals exceeds the over voltage protection threshold, then the Zener diode
will clamp the output voltage.
Short Circuit Protection
Continuous, hiccup, and auto-recovery mode. The average current during this condition will be very low and the
device is still safe in this condition.
Input Source Impedance
The power module should be connected to a low impedance input source. Highly inductive source impedance can
affect the stability of the power module. Input external L-C filter is recommended to minimize input reflected
ripple current. The inductor is simulated source impedance of 12µH and capacitor is Nippon chemi-con KZE series
220µF/100V. The capacitor must be connected as close as possible to the input terminals of the power module for
lower impedance.
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