TLC080IP datasheet(19/53 Pages) TI1

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TLC080 , TLC081, TLC082

TLC083, TLC084, TLC085, TLC08xA

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SLOS254F

– JUNE 1999 – REVISED DECEMBER 2011

Shutdown Function

Three members of the TLC08x family (TLC080/3/5) have a shutdown terminal (SHDN) for conserving battery life

in portable applications. When the shutdown terminal is tied low, the supply current is reduced to

125

µA/channel, the amplifier is disabled, and the outputs are placed in a high-impedance mode. To enable the

amplifier, the shutdown terminal can either be left floating or pulled high. When the shutdown terminal is left

floating, care should be taken to ensure that parasitic leakage current at the shutdown terminal does not

inadvertently place the operational amplifier into shutdown. The shutdown terminal threshold is always

referenced to the voltage on the GND terminal of the device. Therefore, when operating the device with split

supply voltages (e.g.

±2.5 V), the shutdown terminal needs to be pulled to VDD– (not system ground) to disable

the operational amplifier.

The amplifier

’s output with a shutdown pulse is shown in Figure 43 and Figure 44. The amplifier is powered with

a single 5-V supply and is configured as noninverting with a gain of 5. The amplifier turnon and turnoff times are

measured from the 50% point of the shutdown pulse to the 50% point of the output waveform. The times for the

single, dual, and quad are listed in the data tables.

Figure 37 through Figure 40 show the amplifiers forward and reverse isolation in shutdown. The operational

amplifier is configured as a voltage follower (AV = 1). The isolation performance is plotted across frequency using

0.1 VPP, 2.5 VPP, and 5 VPP input signals at ±2.5 V supplies and 0.1 VPP, 8 VPP, and 12 VPP input signals at ±6 V

supplies.

Circuit Layout Considerations

To achieve the levels of high performance of the TLC08x, follow proper printed-circuit board design techniques.

A general set of guidelines is given in the following.

•

Ground planes

– It is highly recommended that a ground plane be used on the board to provide all

components with a low inductive ground connection. However, in the areas of the amplifier inputs and output,

the ground plane can be removed to minimize the stray capacitance.

•

Proper power supply decoupling

– Use a 6.8-µF tantalum capacitor in parallel with a 0.1-µF ceramic capacitor

on each supply terminal. It may be possible to share the tantalum among several amplifiers depending on the

application, but a 0.1-

µF ceramic capacitor should always be used on the supply terminal of every amplifier.

In addition, the 0.1-

µF capacitor should be placed as close as possible to the supply terminal. As this distance

increases, the inductance in the connecting trace makes the capacitor less effective. The designer should

strive for distances of less than 0.1 inches between the device power terminals and the ceramic capacitors.

•

Sockets

– Sockets can be used but are not recommended. The additional lead inductance in the socket pins

will often lead to stability problems. Surface-mount packages soldered directly to the printed-circuit board is

the best implementation.

•

Short trace runs/compact part placements

– Optimum high performance is achieved when stray series

inductance has been minimized. To realize this, the circuit layout should be made as compact as possible,

thereby minimizing the length of all trace runs. Particular attention should be paid to the inverting input of the

amplifier. Its length should be kept as short as possible. This will help to minimize stray capacitance at the

input of the amplifier.

•

Surface-mount passive components

– Using surface-mount passive components is recommended for high

performance amplifier circuits for several reasons. First, because of the extremely low lead inductance of

surface-mount components, the problem with stray series inductance is greatly reduced. Second, the small

size of surface-mount components naturally leads to a more compact layout thereby minimizing both stray

inductance and capacitance. If leaded components are used, it is recommended that the lead lengths be kept

as short as possible.

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