TIME (400 ns/div)

V

+

+

-

+

-

V

+

C = 200pF

SAMPLE

CLOCK

LMV341-N, LMV342-N, LMV344-N

SNOS990G – APRIL 2002 – REVISED MARCH 2013

www.ti.com

Figure 45 shows the schematic of a simple sample and hold circuit. When the sample clock is high the first

amplifier is in normal operation mode and the second amplifier acts as a buffer. The capacitor, which appears as

a load on the first amplifier, will be charging at this time. The voltage across the capacitor is that of the non-

inverting input of the first amplifier since it is connected as a voltage-follower. When the sample clock is low the

first amplifier is shut off, bringing the output impedance to a high value. The high impedance of this output, along

with the very high impedance on the input of the second amplifier, prevents the capacitor from discharging. There

is very little voltage droop while the first amplifier is in shutdown mode. The second amplifier, which is still in

normal operation mode and is connected as a voltage follower, also provides the voltage sampled on the

capacitor at its output.

Figure 45. Sample and Hold Circuit

Shutdown Feature

The LMV341-N is capable of being turned off in order to conserve power and increase battery life in portable

devices. Once in shutdown mode the supply current is drastically reduced, 1µA maximum, and the output will be

"tri-stated."

The device will be disabled when the shutdown pin voltage is pulled low. The shutdown pin should never be left

unconnected. Leaving the pin floating will result in an undefined operation mode and the device may oscillate

between shutdown and active modes.

The LMV341-N typically turns on 2.8µs after the shutdown voltage is pulled high. The device turns off in less

than 400ns after shutdown voltage is pulled low. Figure 46 and Figure 47 show the turn-on and turn-off time of

the LMV341-N, respectively. In order to reduce the effect of the capacitance added to the circuit by the scope

probe, in the turn-off time circuit a resistive load of 600

Ω is added. Figure 48 and Figure 49 show the test circuits

used to obtain the two plots.

Figure 46. Turn-on Time

14

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