LT1206_11 Datasheet, PDF (8/18 Pages) Linear Technology – 250mA/60MHz Current Feedback Amplifier Adjustable Supply Current

LT1206
Simplified Schematic
TO ALL
CURRENT
SOURCES
Q18
Q17
1.25k
+IN
SHUTDOWN
V⁺
Q2
Q1
Q5
Q6
D1
Q15
Q10
Q11
V^–
–IN
V⁺
Q9
V^–
C_{C RC}
V⁺
Q12
50Ω
COMP
OUTPUT
Q3
Q4
Q8
Q7
Q16
D2
Q14
Q13
V^–
1206 SS
Applications Information
The LT1206 is a current feedback amplifier with high output
current drive capability. The device is stable with large
capacitive loads and can easily supply the high currents
required by capacitive loads. The amplifier will drive low
impedance loads such as cables with excellent linearity
at high frequencies.
Feedback Resistor Selection
The optimum value for the feedback resistors is a function
of the operating conditions of the device, the load imped-
ance and the desired flatness of response. The Typical AC
Performance tables give the values which result in the
highest 0.1dB and 0.5dB bandwidths for various resistive
loads and operating conditions. If this level of flatness is
not required, a higher bandwidth can be obtained by use
of a lower feedback resistor. The characteristic curves of
Bandwidth vs Supply Voltage indicate feedback resistors
for peaking up to 5dB. These curves use a solid line when
the response has less than 0.5dB of peaking and a dashed
8
line when the response has 0.5dB to 5dB of peaking. The
curves stop where the response has more than 5dB of
peaking.
For resistive loads, the COMP pin should be left open (see
section on capacitive loads).
Capacitive Loads
The LT1206 includes an optional compensation network
for driving capacitive loads. This network eliminates most
of the output stage peaking associated with capacitive
loads, allowing the frequency response to be flattened.
Figure 1 shows the effect of the network on a 200pF load.
Without the optional compensation, there is a 5dB peak
at 40MHz caused by the effect of the capacitance on the
output stage. Adding a 0.01µF bypass capacitor between the
output and the COMP pins connects the compensation and
completely eliminates the peaking. A lower value feedback
resistor can now be used, resulting in a response which
1206fb