LMH6642Q-Q1_15 Datasheet, PDF (22/34 Pages) Texas Instruments – Low Power, 130 MHz, 75 mA Rail-to-Rail Output Amplifiers

LMH6642Q-Q1, LMH6643Q-Q1
SNOSC61C – JANUARY 2012 – REVISED SEPTEMBER 2014
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Circuit Description (continued)
8.1.2 Input and Output Topology
All input / output pins are protected against excessive voltages by ESD diodes connected to V⁺ and V^- rails (see
Figure 56). These diodes start conducting when the input / output pin voltage approaches 1V_be beyond V⁺ or V^-
to protect against over voltage. These diodes are normally reverse biased. Further protection of the inputs is
provided by the two resistors (R in Figure 56), in conjunction with the string of anti-parallel diodes connected
between both bases of the input stage. The combination of these resistors and diodes reduces excessive
differential input voltages approaching 2V_be. The most common situation when this occurs is when the device is
used as a comparator (or with little or no feedback) and the device inputs no longer follow each other. In such a
case, the diodes may conduct. As a consequence, input current increases and the differential input voltage is
clamped. It is important to make sure that the subsequent current flow through the device input pins does not
violate the Absolute Maximum Ratings of the device. To limit the current through this protection circuit, extra
series resistors can be placed. Together with the built-in series resistors of several hundred ohms, these external
resistors can limit the input current to a safe number (i.e. < 10mA). Be aware that these input series resistors
may impact the switching speed of the device and could slow down the device.
V+
V+
R
IN+
V+
R
IN-
V-
V-
Figure 56. Input Equivalent Circuit
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