9
LT1357
TYPICAL PERFORMANCE CHARACTERISTICS
U
W
Large-Signal Transient
(A
V
= 1, C
L
= 10,000pF)
Large-Signal Transient
(A
V
= –1)
1357 TA34 1357 TA35
1357 TA36
Large-Signal Transient
(A
V
= 1)
APPLICATIONS INFORMATION
WUU
U
The LT1357 may be inserted directly into many high
speed amplifier applications improving both DC and AC
performance, provided that the nulling circuitry is
removed. The suggested nulling circuit for the LT1357 is
shown below.
Offset Nulling
1357 AI01
6
7
V
+
V
–
4
8
1
2
10k
3
–
+
LT1357
Layout and Passive Components
The LT1357 amplifier is easy to apply and tolerant of less
than ideal layouts. For maximum performance (for
example, fast settling time) use a ground plane, short lead
lengths and RF-quality bypass capacitors (0.01µF to 0.1µF).
For high drive current applications use low ESR bypass
capacitors (1µF to 10µF tantalum). Sockets should be
avoided when maximum frequency performance 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 5kΩ, a parallel capacitor of value
C
F
> (R
G
• C
IN
)/R
F
should be used to cancel the input pole and optimize
dynamic performance. For unity-gain applications where
a large feedback resistor is used, C
F
should be greater
than or equal to C
IN
.
Capacitive Loading
The LT1357 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 1000pF load shows 50% 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., 75Ω) should be placed in
