Summit Microelectronics - Applications Note 23

This application note was jointly authored by Summit Microelectronics and SynQor.

Tech Support: Applications Note 23
SMH4804 and SMT4004 Telecom Reference Design Using SynQor® DC/DC Converters

The layout of the HTML version of the application note follows the page breaks in the PDF version. To navigate, you may click on a page number (below) to jump to another other page. You may also download/view the entire application note in PDF format [PDF format].

00 1 2 3 4 5 6 7 8 9 10 11 12 13 Next -->

SMH4804 and SMT4004 Telecom Reference Design Using SynQor® DC/DC Converters

PAGE 4

Figure 3- The maximum PGx# sequence delay can be increased by adding the components shown. Be careful not to exceed the 1mA maximum output current of the 5VREF output pin.

Increasing the PGx# Delay Times for SynQor^® DC/DC converters
The maximum programmable PGx# delay time for the SMH4804 is 160mS. Increased delay times are simple to implement, requiring a few external passive components and a logic gate (see Figure 3). The addition of these components makes it possible to utilize the additional delay inherent to the SynQor DC/DC converters. The SynQor devices introduce a 200 mSec delay from the time 48V is applied to the time the output is enabled.

Any of the SMH4804 PG2#-PG4# may be disabled by deasserting the ENPGA-ENPGC inputs (ENPGx = logic low). ENPGA is associated with the PG2# output, ENPGB with the PG3# output, etc (see the SMH4804 Block Diagram in the data sheet). The circuit shown in Figure 3 adds an additional delay to the PG2#-PG4# outputs according to the formula:

Where:
TDEL = additional delay introduced (seconds).
RDEL = value of the resistor from the PGx# output to the Schmitt-trigger input (ohms).
CDEL = value of the capacitor from the Schmitt-trigger input to ground (ohms).

In the example shown, outputs (PG2#-PG4#) are delayed an additional amount of time by the product of the 1uF capacitor times the 220kohm resistor or 220mS. Assuming the SMH4804 is programmed for the maximum PGx# delay, the total delay time is 160mS (maximum programmable delay time) plus 220mS or 380mS.

00 1 2 3 4 5 6 7 8 9 10 11 12 13 Next -->

SUMMIT Microelectronics, Inc. reserves the right to make changes to the products contained in this publication in order to improve design, performance or reliability. SUMMIT Microelectronics, Inc. assumes no responsibility for the use of any circuits described herein, conveys no license under any patent or other right, and makes no representation that the circuits are free of patent infringement. Charts and schedules contained herein reflect representative operating parameters, and may vary depending upon a user's specific application. While the information in this publication has been carefully checked, SUMMIT Microelectronics, Inc. shall not be liable for any damages arising as a result of any error or omission.

SUMMIT Microelectronics, Inc. does not recommend the use of any of its products in life support or aviation applications where the failure or malfunction of the product can reasonably be expected to cause any failure of either system or to significantly affect their safety or effectiveness. Products are not authorized for use in such applications unless SUMMIT Microelectronics, Inc. receives written assurances, to its satisfaction, that: (a) the risk of injury or damage has been minimized; (b) the user assumes all such risks; and (c) potential liability of SUMMIT Microelectronics, Inc. is adequately protected under the circumstances.

Revision 1.1 - This document supersedes all previous versions. Please check the Summit Microelectronics Inc. web site at www.summitmicro.com for updates.

I2C is a trademark of Philips Corporation.
SynQor® is a registered trademark of SynQor, Inc.

Copyright © 2003 SUMMIT MICROELECTRONICS, Inc.
Power Management for Communications™


	Tech Support: Applications Note 23 SMH4804 and SMT4004 Telecom Reference Design Using SynQor® DC/DC Converters