Input:

Input:

Output:

Output:

Current:

Current:

ackage:

18-36 V

18-36 V

3.3 V

3.3 V

25 A

(82.5W)

Quarter-brick

Quarter-brick

T

pecification

Product # PQ24033QGA25

Phone 1-888-567-9596

www.synqor.com

Doc.# 005-2QG233D Rev. B

08/17/06

Page 11

APPLICATION CONSIDERATIONS

Input System Instability: This condition can occur

because any DC/DC converter appears incrementally as a

negative resistance load. A detailed application note titled

“Input System Instability” is available on the SynQor web site

(www.synqor.com) which provides an understanding of why

this instability arises, and shows the preferred solution for cor-

recting it.

Application Circuits: Figure D below provides a typical cir-

cuit diagram which details the input filtering and voltage trim-

ming.

Input Filtering and External Capacitance: Figure E

below provides a diagram showing the internal input filter com-

ponents. This filter dramatically reduces input terminal ripple

current, which otherwise could exceed the rating of an external

electrolytic input capacitor. The recommended external input

capacitance is specified in the “Input Characteristics” section.

More detailed information is available in the application note

titled “EMI Characteristics” on the SynQor website.

Startup Inhibit Period: The Startup Inhibit Period ensures

that the converter will remain off for at least 200ms when it is

shut down for any reason. When an output short is present,

this generates a 5Hz "hiccup mode," which prevents the con-

verter from overheating. In all, there are seven ways that the

converter can be shut down, initiating a Startup Inhibit Period:

• Input Under-Voltage Lockout

• Input Over-Voltage Shutdown (not present in Quarter-brick)

• Output Over-Voltage Protection

• Over Temperature Shutdown

• Current Limit

• Short Circuit Protection

• Turned off by the ON/OFF input

Figure F shows three turn-on scenarios, where a Startup Inhibit

old, the unit is disabled by the Input Under-Voltage Lockout fea-

ture. When the input voltage rises above the UVL threshold, the

Input Under-Voltage Lockout is released, and a Startup Inhibit

External

Input

Filter

Trim

L

C

or

ON/OFF

Electrolytic

Capacitor

100µF

Figure D: Typical application circuit (negative logic unit, permanently enabled).