LMH6703_16 Datasheet, PDF (14/26 Pages) Texas Instruments – 1.2 GHz, Low Distortion Op Amp with Shutdown

LMH6703
SNOSAF2E – FEBRUARY 2005 – REVISED MAY 2016
Device Functional Modes (continued)
8.3.3 Enable/Disable
SUPPLY
MID-POINT
20 k:
PIN 6
V⁺
BIAS CIRCUITRY 20 k: ^PULL-UP
RESISTOR
V⁺ - V^-
2
Q₂ Q₁
20 k:
PIN 5
SD
I TAIL
PIN 2
V^-
NOTE: PINS 2, 5, 6 ARE EXTERNAL
Figure 28. SD Pin Simplified Schematic
(SOT-23 Pinout Shown)
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For 5-V supplies only, the LMH6703 has a TTL logic compatible disable function. Apply a logic low (< 0.8 V) to
the SD pin and the LMH6703 is disabled. Apply a logic high (> 2.0 V), or let the pin float and the LMH6703 is
enabled. Voltage, not current, at the Shutdown pin (SD) determines the enable/disable state. Care must be
exercised to prevent the shutdown pin voltage from going more than 0.8 V below the midpoint of the supply
voltages (0V with split supplies, V⁺/2 with single supply biasing). Doing so could cause transistor Q1 to Zener
resulting in damage to the disable circuit (See Figure 28). The core amplifier is unaffected by this, but the
shutdown operation could become permanently slower as a result.
Disabled, the LMH6703 inputs and output become high impedances. While disabled the LMH6703 quiescent
current is approximately 200 µA. Because of the pull up resistor on the shutdown circuit, the I_CC and I_EE currents
(positive and negative supply currents respectively) are not balanced in the disabled state. The positive supply
current (I_CC) is approximately 300 µA while the negative supply current (I_EE) is only 200 µA. The remaining I_EE
current of 100 µA flows through the shutdown pin.
The disable function can be used to create analog switches or multiplexers. Implement a single analog switch
with one LMH6703 positioned between an input and output. Create an analog multiplexer with several
LMH6703s and tie the outputs together.
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