ha5025ip Intersil Corporation, ha5025ip Datasheet - Page 6

• Manufacturer Part Number: ha5025ip
• Description: Quad, 125mhz Video Current Feedback Amplifier
• Manufacturer: Intersil Corporation

Application Information
Optimum Feedback Resistor
The plots of inverting and non-inverting frequency response,
see Figure 8 and Figure 9 in the typical performance section,
illustrate the performance of the HA5025 in various closed
loop gain configurations. Although the 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 amplifier’s unique
relationship between bandwidth and R
amplifiers require a feedback resistor, even for unity gain
applications, and R
compensation capacitor, sets the dominant pole of the
frequency response. Thus, the amplifier’s bandwidth is
inversely proportional to R
for a 1000 R
application decreases stability, resulting in excessive peaking
and overshoot. At higher gains the amplifier is more stable, so
R
The following table lists recommended R
gains, and the expected bandwidth.
PC Board Layout
The frequency response of this amplifier depends greatly on
the amount of care taken in designing the PC board. The
use of low inductance components such as chip resistors
and chip capacitors is strongly recommended. If leaded
components are used the leads must be kept short
especially for the power supply decoupling components and
those components connected to the inverting input.
Attention must be given to decoupling the power supplies. A
large value (10 F) tantalum or electrolytic capacitor in
parallel with a small value (0.1 F) chip capacitor works well
in most cases.
A ground plane is strongly recommended to control noise.
Care must also be taken to minimize the capacitance to
ground seen by the amplifier’s inverting input (-IN). The larger
this capacitance, the worse the gain peaking, resulting in
pulse overshoot and possible instability. It is recommended
that the ground plane be removed under traces connected to
F
can be decreased in a trade-off of stability for bandwidth.
GAIN
(A
+10
-10
+1
+2
+5
-1
CL
)
F
at a gain of +1. Decreasing R
F
, in conjunction with the internal
R
1000
1000
750
681
383
750
F
( )
F
. The HA5025 design is optimized
6
F
. All current feedback
F
BANDWIDTH
values for various
F
(MHz)
in a unity gain
100
125
95
52
65
22
HA5025
-IN, and that connections to -IN be kept as short as possible to
minimize the capacitance from this node to ground.
Driving Capacitive Loads
Capacitive loads will degrade the amplifier’s phase margin
resulting in frequency response peaking and possible
oscillations. In most cases the oscillation can be avoided by
placing an isolation resistor (R) in series with the output as
shown in Figure 6.
The selection criteria for the isolation resistor is highly
dependent on the load, but 27 has been determined to be
a good starting value.
Power Dissipation Considerations
Due to the high supply current inherent in quad amplifiers,
care must be taken to insure that the maximum junction
temperature (T
exceeded. Figure 7 shows the maximum ambient temperature
versus supply voltage for the available package styles (PDIP,
SOIC). At V
may be operated over the full industrial range of -40
85
into account output power, be performed by the designer.
FIGURE 6. PLACEMENT OF THE OUTPUT ISOLATION
FIGURE 7. MAXIMUM OPERATING AMBIENT TEMPERATURE
o
C. It is recommended that thermal calculations, which take
130
120
110
100
90
80
70
60
50
40
30
20
10
V
IN
S
5
RESISTOR, R
vs SUPPLY VOLTAGE
= 5V quiescent operation both package styles
J
, see Absolute Maximum Ratings) is not
R
100
T
R
I
7
SUPPLY VOLTAGE ( V)
SOIC
+
-
9
R
R
F
PDIP
11
C
L
13
V
o
OUT
C to
15