MAX4145ESD+ Datasheet MAX4145ESD+, MAX4144EEE+T, MAX4144ESD+T | P10-P12

MAX4144/MAX4145/MAX4146

High-Speed, Low-Distortion,

Differential Line Receivers

10 ______________________________________________________________________________________

Pin Description

________________Detailed Description

The MAX4144/MAX4145/MAX4146 are low-distortion,

differential line receivers that feature high bandwidths

and excellent common-mode rejection, making them

ideal for balanced, high-speed data transmission sys-

tems.

The MAX4144 has a preset gain of +2V/V and achieves

a 130MHz -3dB bandwidth, a 1000V/µs slew rate, and

common-mode rejection (CMR) of 70dB at 10MHz. The

MAX4145 and MAX4146 use a single external resistor to

set the closed-loop gain from +1V/V to +10V/V for the

MAX4145, or greater than +10V/V for the MAX4146. The

MAX4145 achieves a -3dB bandwidth of 180MHz, a

slew rate of 600V/µs, and CMR of 75dB at 10MHz when

operating in the unity-gain configuration. The MAX4146

attains a -3dB bandwidth of 70MHz, a slew rate of

800V/µs, and CMR of 90dB at 10MHz when operating

with a closed-loop gain of +10V/V.

Differential inputs make the MAX4144/MAX4145/

MAX4146 ideal for applications with high common-

mode noise, such as receiving T1 or xDSL transmis-

sions over a twisted-pair cable. Excellent differential

gain and phase, along with low noise, also suit them to

video applications and RF signal processing.

For a complete differential transmission link, use the

MAX4144/MAX4145/MAX4146 amplifiers with the

MAX4147 line driver, as shown in the

Typical Applica-

tion Circuit.

___________Applications Information

Grounding, Bypassing,

and PC Board Layout

Adhere to the following high-frequency design tech-

niques when designing the PC board for the

MAX4144/MAX4145/MAX4146.

• The printed circuit board should have at least two

layers: the signal layer and the ground plane.

• Do not use wire-wrap boards—they are too

inductive.

FUNCTIONNAME

8, 14

10, 12

1, 7

Output Reference. Connect to ground for

normal operation.

REF9

OutputOUT11

Output Sense. Connect to OUT close to

the pin for normal operation.

SENSE13

Logic Input for Shutdown Circuitry. A logic

low enables the amplifier. A logic high

disables the amplifier.

SHDN4

Noninverting Input for Gain-Set Resistor RG+—

Noninverting InputIN+6

Positive Power SupplyV

8, 14

Inverting Input for Gain-Set ResistorRG-—

No Connect. Not internally connected.N.C.

3, 5, 10,

Inverting InputIN-2

Negative Power SupplyV

1, 7

8, 14

10, 12

1, 7

MAX4146MAX4144 MAX4145

14 SO14 SO 14 SO16 QSOP 16 QSOP 16 QSOP

1, 7

3, 5, 8, 9,

12,14

1, 7

8, 9, 12,

1, 7

8, 9, 12,

3 3—

4 4 4

— 5 5

6 6 6

10, 16 10, 16 10, 16

11 11 11

13 13 13

15 15 15

MAX4144/MAX4145/MAX4146

High-Speed, Low-Distortion,

Differential Line Receivers

______________________________________________________________________________________ 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

more than 10V

, where V

is the diode’s forward volt-

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 1.4kΩ. 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

MAX4145/MAX4146, R

can be as low as 150Ω. Under

this condition, the absolute maximum input current rat-

ing might be exceeded if the differential input voltage

exceeds 5.5V (10mA x 150Ω + 10V

). In that case,

510Ω 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

(1.4kΩ).

Setting Gain (MAX4145/MAX4146)

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

gle external resistor, R

. The optimal gain range is from

+1V/V to +10V/V for the MAX4145 and +10V/V (R

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

given in the following equations:

Input Current =

V - V - 10V

IN+ IN- F

()

1.4k

IN+

IN-

IN+

IN-

MAX4144 MAX4145

MAX4146

Figure 1. Input Protection Circuits

MAX4144/MAX4145/MAX4146

High-Speed, Low-Distortion,

Differential Line Receivers

12 ______________________________________________________________________________________

Figure 2 shows the connection for R

. R

might simply

be a resistor, or it can be a complex pole-zero pair for

filter and shaping applications (Figure 9). Use surface-

mount gain-setting components to ensure stability.

Using REF and SENSE

The MAX4144/MAX4145/MAX4146 have a REF pin (nor-

mally connected to ground) and a SENSE pin (normally

connected to OUT). In some long-line applications, it

may be desirable to connect SENSE and OUT together

at the load, instead of the typical connection at the part

(Figure 3). This compensates for the long line’s resis-

tance, which otherwise leads to an IR voltage error.

When using this technique, keep the sense lines’

impedance low to minimize gain errors. Also, keep

capacitance low to maximize frequency response. The

gain of the MAX4144/MAX4145/MAX4146 output stage

is approximated by the following equation:

where ΔR

SENSE

and ΔR

REF

are the SENSE and REF

trace impedances, respectively. R is 700Ω for the

MAX4144 and MAX4145, and 100Ω for the MAX4146.

Additionally, mismatches in the SENSE and REF traces

lead to common-mode gain errors. Common-mode

gain is approximated by the following equation:

Substituting numbers for ΔR

REF

and ΔR

SENSE

into this

equation, we can see that if changes in ΔR

REF

and

ΔR

SENSE

are equal, CMR is not degraded.

Driving Capacitive Loads

The MAX4144/MAX4145/MAX4146 provide maximum

AC performance when not driving an output load

capacitance. This is the case when driving a correctly

terminated transmission line (i.e., a back-terminated

cable). In most amplifier circuits, driving large load

capacitance increases the chance of oscillations. The

amplifier’s output impedance and the load capacitor

combine to add a pole and excess phase to the loop

response. If the pole’s frequency is low enough and

phase margin is degraded sufficiently, oscillations may

occur. A second concern when driving capacitive

loads results from the amplifier’s output impedance,

R - R

R + 700

VCM

REF SENSE

ΔΔ

700 R

R 700 R

REF

ΩΔ

⎤

⎦

⎥

700 R

R 700 R

SENSE REF

REF

ΩΔ ΩΔ

ΩΔ

⎛

⎝

⎜

⎞

⎠

⎟

⎡

⎣

⎢

G = A = 1 +

1.4k

(MAX4145)

G = A = 10 +

14k

(MAX4146

)

100k 1M 10M 100M 1G

-3

-4

-5

-2

FREQUENCY (Hz)

GAIN (dB)

-1

= 10pF

= 5pF

= 15pF

Figure 4. MAX4144 Small-Signal Response with Capacitive

Load

SENSE

OUT

REF

MAX4144

MAX4145

MAX4146

Figure 3. Connection of SENSE and REF to a Remote Load

IN-

IN+

MAX4145

MAX4146

Figure 2. Connection of R

in MAX4146

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MAX4145ESD+

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Description:

Differential Amplifiers

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