LT1206C Linear Technology, LT1206C Datasheet - Page 9

• Manufacturer Part Number: LT1206C
• Description: 250mA/60MHz Current Feedback Amplifier
• Manufacturer: Linear Technology

A
which is flat to 0.35dB to 30MHz. The network has the
greatest effect for C
graph of Maximum Capacitive Load vs Feedback Resistor
can be used to select the appropriate value of feedback
resistor. The values shown are for 0.5dB and 5dB peaking
at a gain of 2 with no resistive load. This is a worst case
condition, as the amplifier is more stable at higher gains
and with some resistive load in parallel with the capaci-
tance. Also shown is the – 3dB bandwidth with the sug-
gested feedback resistor vs the load capacitance.
Although the optional compensation works well with
capacitive loads, it simply reduces the bandwidth when it
is connected with resistive loads. For instance, with a 30
load, the bandwidth drops from 55MHz to 35MHz when
the compensation is connected. Hence, the compensation
was made optional. To disconnect the optional compensa-
tion, leave the COMP pin open.
Shutdown/Current Set
If the shutdown feature is not used, the SHUTDOWN pin
must be connected to ground or V
The shutdown pin can be used to either turn off the biasing
for the amplifier, reducing the quiescent current to less
than 200 A, or to control the quiescent current in normal
operation.
The total bias current in the LT1206 is controlled by the
current flowing out of the shutdown pin. When the shut-
down pin is open or driven to the positive supply, the part
is shut down. In the shutdown mode, the output looks like
PPLICATI
–2
–4
–6
–8
12
10
8
6
4
2
0
1
V
S
NO COMPENSATION
= ±15V
O
U
L
COMPENSATION
in the range of 0pF to 1000pF. The
S
FREQUENCY (MHz)
R
Figure 1.
F
R
= 1.2k
F
COMPENSATION
I FOR ATIO
= 2k
U
10
R
F
= 2k
–
W
.
LT1206 • F01
100
U
a 40pF capacitor and the supply current is typically 100 A.
The shutdown pin is referenced to the positive supply
through an internal bias circuit (see the simplified sche-
matic). An easy way to force shutdown is to use open drain
(collector) logic. The circuit shown in Figure 2 uses a
74C904 buffer to interface between 5V logic and the
LT1206. The switching time between the active and shut-
down states is less than 1 s. A 24k pull-up resistor
speeds up the turn-off time and insures that the LT1206
is completely turned off. Because the pin is referenced to
the positive supply, the logic used should have a break-
down voltage of greater than the positive supply voltage.
No other circuitry is necessary as the internal circuit
limits the shutdown pin current to about 500 A. Figure 3
shows the resulting waveforms.
A
R
R
V
F
L
ENABLE
= 1
= 825
= 50
Figure 3. Shutdown Operation
Figure 2. Shutdown Interface
R
V
V
PU
IN
5V
IN
= 1V
= 24k
74C906
P-P
–
+
LT1206
S/D
–15V
15V
15V
24k
LT1206 • F02
R
R
F
G
V
OUT
LT1206 • F3
LT1206
9