Souce Current vs. V

OUT

20080711

Application Notes

CIRCUIT DESCRIPTION

The LMV116 and LMV118 are based on National Semicon-

ductor’s proprietary VIP10 dielectrically isolated bipolar pro-

cess.

The LMV116 and LMV118 architecture features the follow-

ing:

•

Complimentary bipolar devices with exceptionally high f

t

(

∼8GHz) even under low supply voltage (2.7V) and low

Collector bias current.

•

Common Emitter push-pull output stage capable of 20mA

output current (at 0.5V from the supply rails) while con-

suming only 600µA of total supply current. This architec-

ture allows output to reach within milli-volts of either

supply rail at light loads.

•

Consistent performance from any supply voltage (2.7V-

10V) with little variation with supply voltage for the most

important specifications (e.g. BW, SR, I

MICRO-POWER SHUTDOWN

The LMV118 can be shutdown to save power and reduce its

supply current to less than 50µA guaranteed, by applying a

voltage to the SD pin. The SD pin is “active high” and needs

to be tied to V

−

(

≤20kΩ) will result in normal operation. Shutdown is guaran-

teed when SD pin is 0.4V or less from V

supply voltage and temperature.

In the shutdown mode, essentially all internal device biasing

is turned off in order to minimize supply current flow and the

output goes into Hi-Z (high impedance) mode. Complete

device Turn-on and Turn-off times vary considerably relative

to the output loading conditions, output voltage, and input

impedance, but is generally limited to less than 1µs (see

tables for actual data).

During shutdown, the input stage has an equivalent circuit as

shown below in Figure 1

As can be seen above, in shutdown, there may be current

flow through the internal diodes shown, caused by input

potential, if present. This current may flow through the exter-

nal feedback resistor and result in an apparent output signal.

In most shutdown applications the presence of this output is

inconsequential. However, if the output is “forced” by another

device such as in a multiplexer, the other device will need to

conduct the current described in order to maintain the output

potential.

To keep the output at or near ground during shutdown when

there is no other device to hold the output low, a switch

(transistor) could be used to shunt the output to ground.

Figure 2 shows a circuit where a NPN bipolar is used to keep

the output near ground (

∼80mV):

20080756

FIGURE 1. LMV118 Equivalent Input in Shutdown Mode

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