High-Speed, Low-Distortion,

Differential Line Receivers

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11

• Do not use IC sockets—they increase parasitic

capacitance and inductance.

• Use surface-mount power-supply bypass capacitors

instead of through-hole capacitors. Their shorter

lead lengths reduce parasitic inductance, leading to

superior high-frequency performance.

• Keep signal lines as short and as straight as possi-

ble. Do not make 90° turns; round all corners.

• The ground plane should be as free from voids as

possible.

Output Short-Circuit Protection

Under short-circuit conditions to ground, limit the out-

put current to 120mA. This level is low enough that a

short to ground of moderate duration will not cause per-

manent damage to the chip. However, a short to either

supply will significantly increase power dissipation, and

will cause permanent damage. The high output current

capability is an advantage in systems that transmit a

signal to several loads.

Input Protection Circuitry

The MAX4144/MAX4145/MAX4146 include internal pro-

tection circuitry that prevents damage to the precision

input stage from large differential input voltages. This

protection circuitry consists of five back-to-back

Schottky protection diodes between IN+ and RG+, and

IN- and RG- (Figure 1). The diodes limit the differential

voltage applied to the amplifiers’ internal circuitry to no

age drop (about 0.4V at +25°C).

For a large differential input voltage (exceeding 4V), the

MAX4145/MAX4146 input bias current (at IN+ and IN-)

increases according to the following equation:

The MAX4144 has an internal gain-setting resistor val-

ued at 1.4k

Ω. A differential input voltage as high as 10V

will cause only 4.3mA to flow—much less than the

10mA absolute maximum rating. However, in the

this condition, the absolute maximum input current rat-

ing might be exceeded if the differential input voltage

exceeds 5.5V (10mA x 150

510

Ω resistors can be placed at IN+ and IN- to limit the

current without degrading performance.

Shutdown Mode

The MAX4144/MAX4145/MAX4146 can be put into low-

power shutdown mode by bringing SHDN high. The

amplifier output is high impedance in this mode; thus

the impedance at OUT is that of the feedback resistors

(1.4k

Ω).

Setting Gain (MAX4145/MAX4146)

The MAX4145/MAX4146 ’s gain is determined by a sin-

open) to +100V/V for the MAX4146. The gain (in V/V) is

given in the following equations:

Input Current =

V

- V

- 10V

R

IN+

IN-

F

G

(

)

1.4k

IN+

IN-

IN+

IN-

MAX4144

MAX4145

MAX4146

Figure 1. Input Protection Circuits