Article Details

ID: 2038
Case Type: faq
Category: Architecture
Related To: I2C
Family: Power Manager II

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How much undershoot on the SDA pin can a POWR1220AT8 device endure without causing damaging?

The data sheet shows the Absolute Maximum Ratings for the POWR1220AT8 device. The I2C pins will have the same limits as the digital outputs OUT[5:20] but will also have a digital input buffer.

The table shows Vtri, which is the voltage applied to tri-stated pins. The I2C pins should follow the minimum values that apply to the OUT[5:20] pins which is -0.5 Volts. The table also shows that Vin has a minimum voltage of -0.5 Volts for a digital input pin. The minimum that will apply to the I2C pins will be the higher of these two values or -0.5 Volts. Voltages that are less than this value can cause permanent damage to the device.

Please note that operation of the device is not guaranteed at the Absolute Maximum Ratings. To insure valid operation of the device you should insure that values are within the Recommended Operating Conditions table limits which is -0.3 Volts. The undershoot condition should be corrected to insure that the device will operate properly. The recommended method to do this is to add a series resistor in the I2C lines leading to the POWR1220AT8 device. A typical value for a series resistor is 100 Ohms.

One other thing to check is that the undershoot is being measured accurately. Sometimes a bad ground connection of the probe measuring the voltage will cause an erroneous reading.