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Message ID: 10     Entry time: Tue Jul 7 16:39:57 2009
Author: Stefan Ritt 
Subject: Power up problem and remedy 

Maybe some of you have experienced that the DRS4 chip can get pretty hot after power up. After it's initialized the first time, the power consumption goes back to normal. I finally found the cause of this problem and have a remedy. Here is the new paragraph from the updated data sheet:

During power-up, care has to be taken that the DENABLE and DWRITE signals are low. If not, the domino wave can get started before the power supply voltages are stable, which brings the DRS4 chip into a state where it draws a considerable amount of current and heats up significantly. This can be problematic if the signals are directly generated by a FPGA, since most FPGAs have internal pull-up resistors which get activated during the configuration phase of the FPGA. In such a case, the DENABLE and DWRITE signals should be connected to GND with a pull down resistor. This resistor should be much smaller than the FPGA pull-up resistor in order to keep the signals close to GND during the FPGA configuration. A typical value is 4.7 kOhm.

The attached schematics shows the location of the two required resistors.

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