5

FN3955.5

June 1, 2006

Application Information

Optimum Feedback Resistor

Although a current feedback amplifier’s bandwidth

dependency on closed loop gain isn’t as severe as that of a

voltage feedback amplifier, there can be an appreciable

decrease in bandwidth at higher gains. This decrease may be

minimized by taking advantage of the current feedback

current feedback amplifiers require a feedback resistor, even

internal compensation capacitor, sets the dominant pole of the

frequency response. Thus, the amplifier’s bandwidth is

stability, resulting in excessive peaking and overshoot (Note:

Capacitive feedback will cause the same problems due to the

feedback impedance decrease at higher frequencies). At

be decreased in a trade-off of stability for bandwidth.

gains, and the expected bandwidth. For a gain of +1, a

peaking and increase stability.

Non-inverting Input Source Impedance

For best operation, the DC source impedance seen by the

non-inverting input should be

≥50Ω. This is especially

important in inverting gain configurations where the non-

inverting input would normally be connected directly to GND.

DISABLE Input TTL Compatibility

The HFA1145 derives an internal GND reference for the

digital circuitry as long as the power supplies are

symmetrical about GND. With symmetrical supplies the

0.8)/2) is 1.4V, which ensures the TTL compatibility of the

DISABLE input. If asymmetrical supplies (e.g. +10V, 0V) are

utilized, the switching threshold becomes:

DISABLE Input Logic High Current

A

Full

-

1

15

μA

Output Disable Time (Note 6)

B25

-

35

-

ns

Output Enable Time (Note 6)

B

25

-

180

-

ns

Disabled Output Capacitance

B

25

-

2.5

-

pF

Disabled Output Leakage

AFull

-

3

10

μA

Off Isolation

At 5MHz

B

25

-

-75

-

dB

At 25MHz

B

25

-

-60

-

dB

POWER SUPPLY CHARACTERISTICS

Power Supply Range

C

25

±4.5

-

±5.5

V

Power Supply Current (Note 6)

A

25

-

5.8

6.1

mA

A

Full

-

5.9

6.3

mA

NOTES:

3. Test Level: A. Production Tested; B. Typical or Guaranteed Limit Based on Characterization; C. Design Typical for Information Only.

condition. See the “Application Information” section for details.

5. Slew rates are asymmetrical if the output swings below GND (e.g. a bipolar signal). Positive unipolar output signals have symmetric positive and

negative slew rates comparable to the +SR specification. See the “Application Information” section, and the pulse response graphs for details.

6. See Typical Performance Curves for more information.

Electrical Specifications

PARAMETER

TEST CONDITIONS

(NOTE 3)

TEST

LEVEL

TEMP. (°C)

MIN

TYP

MAX

UNITS

GAIN

BANDWIDTH

(MHz)

-1

425

300

+1

270

+2

510

330

+5

200

300

+10

180

130

V

TH

V+

V-

+

2

-------------------

1.4V

+

=

HFA1145