THS4140, THS4141

HIGHSPEED FULLY DIFFERENTIAL I/O AMPLIFIERS

SLOS320E − MAY 2000 − REVISED JANUARY 2004

19

POST OFFICE BOX 655303

PRINCIPLES OF OPERATION

power-down mode

The power-down mode is used when power saving is required. The power-down terminal (PD) found on the

THS414x is an active low terminal. If it is left as a no-connect terminal, the device will always stay on due to an

internal 50 k

V = −3.6 V). By the same calculation, the device is off below −3.6 V. It is recommended to pull the terminal to

While in the power-down state, the amplifier goes into a high-impedance state. The amplifier output impedance

is typically greater than 1 M

Ω in the power-down state.

VCC

PD

VCC−

To Internal Bias

Circuitry Control

50 k

Ω

Figure 33. Simplified Power-Down Circuit

Due to the similarity of the standard inverting amplifier configuration, the output impedance appears to be very

still connected to the circuit. Therefore, a current path is allowed between the input of the amplifier and the output

of the amplifier. An example of the closed-loop output impedance is shown in Figure 34.

Figure 34

200

1200

2200

10 k

100 k

1 M

10 M

100 M

f − Frequency − Hz

THS4141

OUTPUT IMPEDANCE (IN SHUTDOWN)

vs

FREQUENCY

VCC = ±5 V,

VI = 0.8 VPP RMS

PD = VCC−