THS6092SLASH3 datasheet(27/46 Pages) TI1

27 / 46 page

THS6042, THS6043

350 mA, ±12 V ADSL CPE LINE DRIVERS

SLOS264G − MARCH 2000 − REVISED DECEMBER 2001

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

APPLICATION INFORMATION

shutdown control

The THS6043 is essentially the same amplifier as the THS6042. The only difference is the added flexibility of

a shutdown circuit. When the shutdown pin signal is low, the THS6043 is active. But, when a shutdown pin is

high (

≥2 V), the THS6043 is turned off. The shutdown logic is not latched and should always have a signal

applied to it. To help ensure a fixed logic state, an internal 50 k

Ω resistor to GND is utilized. An external resistor,

such as a 3.3 k

Ω, to GND may be added to help improve noise immunity within harsh environments. If no

external resistor is utilized and SHDN pin is left unconnected, the THS6043 defaults to a power-on state. A

simplified circuit can be seen in Figure 47.

+VCC

To Internal

Bias Circuitry

Control

−VCC

GND

50 k

Ω

SHDN

Figure 47. Simplified THS6043 Shutdown Control Circuit

One aspect of the shutdown feature, which is often over-looked, is that the amplifier does not have a large output

impedance while in shutdown mode. This is due to the RF and RG resistors. This effect is true for any amplifier

connected as an amplifier with gains >1. The internal circuitry may be powered down and in a high-impedance

state, but the resistors are always there. This allows the signal to flow through these resistors and into the ground

connection. Figure 48 shows the results of the output impedance with no feedback resistor and a typically

configured amplifier.

0.01

0.1

100

1000

10 K

100 K

1 M

10 M

100 M

1 G

f − Frequency − Hz

Open Loop

VCC = ±5 V to ±15 V

Gain = −8

RF = 750 Ω

Figure 48. Output Impedance In Shutdown Mode

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