BUF16821 datasheet(20/29 Pages) EPCOS

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OUTPUT PROTECTION

OUTX

COM

ESDCurrent

SteeringDiodes

BUF16821

SBOS428 – JULY 2008 ...................................................................................................................................................................................................... www.ti.com

The BUF16821 output stages can safely source and

sink the current levels indicated in Figure 1 and

Figure 2. However, there are other modes where

precautions must be taken to prevent to the output

stages from being damaged by excessive current

flow. The outputs (OUT1 through OUT16, VCOM1 and

VCOM2) include ESD protection diodes, as shown in

Figure 18. Normally, these diodes do not conduct and

are passive during typical device operation. Unusual

operating conditions can occur where the diodes may

conduct, potentially subjecting them to high, even

damaging current levels. These conditions are most

likely to occur when a voltage applied to an output

exceeds (VS) + 0.5V, or drops below GND – 0.5V.

One common scenario where this condition can occur

Figure 18. Output Pins ESD Protection

is when the output pin is connected to a sufficiently

Current-Steering Diodes

large capacitor, and the BUF16821 power-supply

source (VS) is suddenly removed. Removing the

power-supply

source

allows

the

capacitor

discharge through the current-steering diodes. The

energy released during the high current flow period

causes the power dissipation limits of the diode to be

exceeded. Protection against the high current flow

may be provided by placing current-limiting resistors

in series with the output, as shown in Figure 10.

Select a resistor value that restricts the current level

to the maximum rating for the particular pin.

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