10

LT1360

Capacitive Loading

The LT1360 is stable with any capacitive load. This is

accomplished by sensing the load induced output pole

and adding compensation at the amplifier gain node. As

the capacitive load increases, both the bandwidth and

phase margin decrease so there will be peaking in the

frequency domain and in the transient response as shown

in the typical performance curves.The photo of the small-

signal response with 500pF load shows 60% peaking. The

large-signal response with a 10,000pF load shows the

output slew rate being limited to 5V/

µs by the short-circuit

current. Coaxial cable can be driven directly, but for best

pulse fidelity a resistor of value equal to the characteristic

impedance of the cable (i.e., 75

Ω) should be placed in

series with the output. The other end of the cable should

be terminated with the same value resistor to ground.

Cable Driver Frequency Response

FREQUENCY (MHz)

1

–8

–6

–4

–2

0

2

100

1360 AI02

10

–

+

LT1360

510

Ω

75

Ω

OUT

75

Ω

IN

510

Ω

The LT1360 may be inserted directly into AD817, AD847,

EL2020, EL2044, and LM6361 applications improving

both DC and AC performance, provided that the nulling

circuitry is removed. The suggested nulling circuit for the

LT1360 is shown below.

Offset Nulling

1360 AI01

6

7

4

8

1

2

10k

3

–

+

LT1360

Layout and Passive Components

The LT1360 amplifier is easy to apply and tolerant of less

than ideal layouts. For maximum performance (for ex-

ample fast settling time) use a ground plane, short lead

lengths, and RF-quality bypass capacitors (0.01

µF to

0.1

µF). For high drive current applications use low ESR

bypass capacitors (1

µF to 10µF tantalum). Sockets

should be avoided when maximum frequency perfor-

mance is required, although low profile sockets can

provide reasonable performance up to 50MHz. For

more details see Design Note 50.

The parallel combination of the feedback resistor and gain

setting resistor on the inverting input can combine with

the input capacitance to form a pole which can cause

peaking or oscillations. For feedback resistors greater

than 5kW, a parallel capacitor of value

should be used to cancel the input pole and optimize

dynamic performance. For unity-gain applications where