1
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
http://www.intersil.com or 407-727-9207 | Copyright Intersil Corporation 1999
HFA1115
225MHz, Low Power, Output
Limiting, Closed Loop Buffer Amplifier
The HFA1115 is a high speed closed loop Buffer featuring both
user programmable gain and output limiting. Manufactured on
Intersil's proprietary complementary bipolar UHF-1 process, the
HFA1115 also offers a wide -3dB bandwidth of 225MHz, very
fast slew rate, excellent gain flatness and high output current.
This buffer is the ideal choice for high frequency applications
requiring output limiting, especially those needing ultra fast
overload recovery times. The limiting function allows the
designer to set the maximum positive and negative output
levels, thereby protecting later stages from damage or input
saturation. The HFA1115 also allows for voltage gains of +2,
+1, and -1, without the use of external resistors. Gain
selection is accomplished via connections to the inputs, as
described in the "Application Information" text. The result is a
more flexible product, fewer part types in inventory, and more
efficient use of board space.
Compatibility with existing op amp pinouts provides flexibility
to upgrade low gain amplifiers, while decreasing component
count. Unlike most buffers, the standard pinout provides an
upgrade path, should a higher closed loop gain be needed at
a future date. For Military product, refer to the HFA1115/883
data sheet.
Pinout
HFA1115
(PDIP, SOIC)
TOP VIEW
Features
User Programmable Output Voltage Limiting
High Input Impedance . . . . . . . . . . . . . . . . . . . . . . . 1M
Differential Gain . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.02%
Differential Phase . . . . . . . . . . . . . . . . . . . . 0.03 Degrees
Wide -3dB Bandwidth (A
V
= +2) . . . . . . . . . . . . . . 225MHz
Very Fast Slew Rate (A
V
= -1) . . . . . . . . . . . . . . 1135V/
s
Low Supply Current . . . . . . . . . . . . . . . . . . . . . . . . 7.1mA
High Output Current . . . . . . . . . . . . . . . . . . . . . . . . . 60mA
Excellent Gain Accuracy . . . . . . . . . . . . . . . . . . . 0.99V/V
User Programmable For Closed-Loop Gains of +1, -1 or
+2 Without Use of External Resistors
Fast Overdrive Recovery . . . . . . . . . . . . . . . . . . . . . <1ns
Standard Operational Amplifier Pinout
Applications
Flash A/D Drivers
Video Cable Drivers
High Resolution Monitors
Professional Video Processing
Medical Imaging
Video Digitizing Boards/Systems
Battery Powered Communications
Pin Descriptions
NAME
PIN NUMBER
DESCRIPTION
NC
1
No Connection
-IN
2
Inverting Input
+IN
3
Non-Inverting Input
V-
4
Negative Supply
V
L
5
Lower Output Limit
OUT
6
Output
V+
7
Positive Supply
V
H
8
Upper Output Limit
NC
-IN
+IN
V-
1
2
3
4
8
7
6
5
V
H
V+
OUT
V
L
+
_
350
350
Ordering Information
PART NUMBER
(BRAND)
TEMP.
RANGE (
o
C)
PACKAGE
PKG.
NO.
HFA1115IP
-40 to 85
8 Ld PDIP
E8.3
HFA1115IB
(H1115I)
-40 to 85
8 Ld SOIC
M8.15
HFA11XXEVAL
High Speed Op Amp DIP Evaluation Board
September 1998
File Number
3606.4
2
Absolute Maximum Ratings
Thermal Information
Voltage Between V+ and V- . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11V
DC Input Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V
SUPPLY
Output Current (Note 2) . . . . . . . . . . . . . . . . Short Circuit Protected
ESD Rating
Human Body Model (Per MIL-STD-883 Method 3015.7) . . . .600V
Operating Conditions
Temperature Range . . . . . . . . . . . . . . . . . . . . . . . . . . -40
o
C to 85
o
C
Supply Voltage Range (Typical) . . . . . . . . . . . . . . . . . . . . 5V to 10V
Thermal Resistance (Typical, Note 1)
JA
(
o
C/W)
PDIP Package . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
130
SOIC Package . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
170
Maximum Junction Temperature (Die) . . . . . . . . . . . . . . . . . . . .175
o
C
Maximum Junction Temperature (Plastic Packages) . . . . . . .150
o
C
Maximum Storage Temperature Range . . . . . . . . . . -65
o
C to 150
o
C
Maximum Lead Temperature (Soldering 10s) . . . . . . . . . . . . 300
o
C
(SOIC - Lead Tips Only)
CAUTION: Stresses above those listed in "Absolute Maximum Ratings" may cause permanent damage to the device. This is a stress only rating and operation of the
device at these or any other conditions above those indicated in the operational sections of this specification is not implied.
NOTES:
1.
JA
is measured with the component mounted on an evaluation PC board in free air.
2. Output is protected for short circuits to ground. Brief short circuits to ground will not degrade reliability, however, continuous (100% duty cycle)
output current should not exceed 30mA for maximum reliability.
Electrical Specifications
V
SUPPLY
=
5V, A
V
= +1, R
L
= 100
, Unless Otherwise Specified
PARAMETER
TEST
CONDITIONS
(NOTE 3)
TEST
LEVEL
TEMP.
(
o
C)
MIN
TYP
MAX
UNITS
INPUT CHARACTERISTICS
Output Offset Voltage
A
25
-
2
10
mV
A
Full
-
3
15
mV
Average Output Offset Voltage Drift
B
Full
-
22
70
V/
o
C
Common-Mode Rejection Ratio
V
CM
=
1.8V
A
25
42
45
-
dB
V
CM
=
1.8V
A
85
40
44
-
dB
V
CM
=
1.2V
A
-40
40
45
-
dB
Power Supply Rejection Ratio
V
PS
=
1.8V
A
25
45
49
-
dB
V
PS
=
1.8V
A
85
43
48
-
dB
V
PS
=
1.2V
A
-40
43
48
-
dB
Non-Inverting Input Bias Current
A
25
-
1
15
A
A
Full
-
3
25
A
Non-Inverting Input Bias Current Drift
B
Full
-
30
80
nA/
o
C
Non-Inverting Input Bias Current Power
Supply Sensitivity
V
PS
=
1.25V
A
25
-
0.5
1
A/V
A
Full
-
-
3
A/V
Non-Inverting Input Resistance
V
CM
=
1.8V
A
25
0.8
1.1
-
M
V
CM
=
1.8V
A
85
0.5
1.4
-
M
V
CM
=
1.2V
A
-40
0.5
1.3
-
M
Inverting Input Resistance
C
25
280
350
420
Input Capacitance
C
25
-
1.6
-
pF
Input Voltage Common Mode Range
(Implied by V
IO
CMRR and +R
IN
Tests)
A
25, 85
1.8
2.4
-
V
A
-40
1.2
1.7
-
V
Input Noise Voltage Density (Note 4)
f = 100kHz
B
25
-
7
-
nV/
Hz
Non-Inverting Input Noise Current Density
(Note 4)
f = 100kHz
B
25
-
3.6
-
pA/
Hz
HFA1115
3
TRANSFER CHARACTERISTICS
Gain
A
V
= -1
A
25
-0.98
-0.996
-1.02
V/V
A
Full
-0.975
-1.000
-1.025
V/V
A
V
= +1
A
25
0.98
0.992
1.02
V/V
A
Full
0.975
0.993
1.025
V/V
A
V
= +2
A
25
1.96
1.988
2.04
V/V
A
Full
1.95
1.990
2.05
V/V
AC CHARACTERISTICS
-3dB Bandwidth
(V
OUT
= 0.2V
P-P
, Note 4)
A
V
= -1
B
25
-
225
-
MHz
A
V
= +1, +R
S
= 620
B
25
-
200
-
MHz
A
V
= +2
B
25
-
225
-
MHz
Full Power Bandwidth
(V
OUT
= 5V
P-P
at A
V
= +2/-1,
4V
P-P
at A
V
= +1, Note 4)
A
V
= -1
B
25
-
157
-
MHz
A
V
= +1, +R
S
= 620
B
25
-
140
-
MHz
A
V
= +2
B
25
-
125
-
MHz
Gain Flatness
(to 25MHz, V
OUT
= 0.2V
P-P
, Note 4)
A
V
= +1, +R
S
= 620
B
25
-
0.1
-
dB
A
V
= +2
B
25
-
0.04
-
dB
Gain Flatness
(to 50MHz, V
OUT
= 0.2V
P-P
, Note 4)
A
V
= +1, +R
S
= 620
B
25
-
0.25
-
dB
A
V
= +2
B
25
-
0.1
-
dB
OUTPUT CHARACTERISTICS
Output Voltage Swing (Note 4)
A
V
= -1, R
L
= 100
A
25
3.0
3.2
-
V
A
Full
2.8
3.0
-
V
Output Current (Note 4)
A
V
= -1, R
L
= 50
A
25, 85
50
55
-
mA
A
-40
28
42
-
mA
Output Short Circuit Current
B
25
-
90
-
mA
Output Resistance (Note 4)
DC, A
V
= +2
B
25
-
0.07
-
Second Harmonic Distortion
(A
V
= +2, V
OUT
= 2V
P-P
)
10MHz
B
25
-
-50
-
dBc
20MHz
B
25
-
-45
-
dBc
Third Harmonic Distortion
(A
V
= +2, V
OUT
= 2V
P-P
)
10MHz
B
25
-
-50
-
dBc
20MHz
B
25
-
-45
-
dBc
TRANSIENT RESPONSE A
V
= +2, Unless Otherwise Specified
Rise and Fall Times
(V
OUT
= 0.5V
P-P
, Note 4)
Rise Time
B
25
-
1.7
-
ns
Fall Time
B
25
-
1.9
-
ns
Overshoot
(V
OUT
= 0.5V
P-P
, V
IN
t
RISE
= 2.5ns)
+OS
B
25
-
0
-
%
-OS
B
25
-
0
-
%
Slew Rate
(V
OUT
= 5V
P-P
, A
V
= -1)
+SR
B
25
-
1660
-
V/
s
-SR (Note 5)
B
25
-
1135
-
V/
s
Slew Rate
(V
OUT
= 4V
P-P
, A
V
= +1, +R
S
= 620
)
+SR
B
25
-
1125
-
V/
s
-SR (Note 5)
B
25
-
800
-
V/
s
Electrical Specifications
V
SUPPLY
=
5V, A
V
= +1, R
L
= 100
, Unless Otherwise Specified (Continued)
PARAMETER
TEST
CONDITIONS
(NOTE 3)
TEST
LEVEL
TEMP.
(
o
C)
MIN
TYP
MAX
UNITS
HFA1115
4
Application Information
Relevant Application Notes
The following Application Notes pertain to the HFA1115:
AN9653-Use and Application of Output Limiting
Amplifiers
AN9752-Sync Stripper and Sync Inserter for
Composite Video
These publications may be obtained from Intersil's web site
(http://www.intersil.com) or via our AnswerFax system.
HFA1115 Advantages
The HFA1115 features a novel design which allows the user
to select from three closed loop gains, without any external
components. The result is a more flexible product, fewer part
types in inventory, and more efficient use of board space.
Implementing a gain of 2, cable driver with this IC eliminates
the two gain setting resistors, which frees up board space for
termination resistors.
Like most newer high performance amplifiers, the HFA1115
is a current feedback amplifier (CFA). CFAs offer high
bandwidth and slew rate at low supply currents, but can be
difficult to use because of their sensitivity to feedback
capacitance and parasitics on the inverting input (summing
node). The HFA1115 eliminates these concerns by bringing
the gain setting resistors on-chip. This yields the optimum
placement and value of the feedback resistor, while
minimizing feedback and summing node parasitics. Because
there is no access to the summing node, the PCB parasitics
do not impact performance at gains of +2 or -1 (see "Unity
Gain Considerations" for discussion of parasitic impact on
unity gain performance).
Slew Rate
(V
OUT
= 5V
P-P
, A
V
= +2)
+SR
B
25
-
1265
-
V/
s
-SR (Note 5)
B
25
-
870
-
V/
s
Settling Time
(V
OUT
= +2V to 0V step, Note 4)
To 0.1%
B
25
-
23
-
ns
To 0.05%
B
25
-
33
-
ns
To 0.02%
B
25
-
45
-
ns
VIDEO CHARACTERISTICS
Differential Gain
f = 3.58MHz, A
V
= +2,
R
L
= 150
B
25
-
0.02
-
%
Differential Phase
f = 3.58MHz, A
V
= +2,
R
L
= 150
B
25
-
0.03
-
Degrees
OUTPUT LIMITING CHARACTERISTICS A
V
= +2, V
H
= +1V, V
L
= -1V, Unless Otherwise Specified
Limit Accuracy (Note 4)
V
IN
=
1.6V, A
V
= -1
A
Full
-125
-70
125
mV
Overdrive Recovery Time (Note 4)
V
IN
=
1V
B
25
-
0.8
-
ns
Negative Limit Range
B
25
-5.0 to +2.5
V
Positive Limit Range
B
25
-2.5 to +5.0
V
Limit Input Bias Current
A
Full
-
85
200
A
Limit Input Bandwidth
C
25
-
100
-
MHz
POWER SUPPLY CHARACTERISTICS
Power Supply Range
C
25
4.5
-
5.5
V
Power Supply Current (Note 4)
A
25
6.6
6.9
7.1
mA
A
Full
-
7.1
7.3
mA
NOTE:
3. Test Level: A. Production Tested; B. Typical or Guaranteed Limit Based on Characterization; C. Design Typical for Information Only.
4. See Typical Performance Curves for more information.
5. Slew rates are asymmetrical if the output swings below GND (e.g., a bipolar signal). Positive unipolar output signals have symmetric positive and
negative slew rates comparable to the +SR specification. See the "Application Information" section, and the pulse response graphs for details.
Electrical Specifications
V
SUPPLY
=
5V, A
V
= +1, R
L
= 100
, Unless Otherwise Specified (Continued)
PARAMETER
TEST
CONDITIONS
(NOTE 3)
TEST
LEVEL
TEMP.
(
o
C)
MIN
TYP
MAX
UNITS
HFA1115
5
The HFA1115's closed loop gain implementation provides
better gain accuracy, lower offset and output impedance,
and better distortion compared with open loop buffers.
Closed Loop Gain Selection
This "buffer" operates in closed loop gains of -1, +1, or +2, and
gain selection is accomplished via connections to the
inputs.
Applying the input signal to +IN and floating -IN selects a gain
of +1 (see next section for layout caveats), while grounding -IN
selects a gain of +2. A gain of -1 is obtained by applying the
input signal to -IN with +IN grounded through a 50
resistor.
The table below summarizes these connections:
Unity Gain Considerations
Unity gain selection is accomplished by floating the -Input of
the HFA1115. Anything that tends to short the -Input to GND,
such as stray capacitance at high frequencies, will cause the
amplifier gain to increase toward a gain of +2. The result is
excessive high frequency peaking, and possible instability.
Even the minimal amount of capacitance associated with
attaching the -Input lead to the PCB results in approximately
3dB of gain peaking. At a minimum this requires due care to
ensure the minimum capacitance at the -Input connection.
.
Table 1 lists five alternate methods for configuring the
HFA1115 as a unity gain buffer, and the corresponding
performance. The implementations vary in complexity and
involve performance trade-offs. The easiest approach to
implement is simply shorting the two input pins together, and
applying the input signal to this common node. The amplifier
bandwidth drops from 400MHz to 200MHz, but excellent
gain flatness is the benefit. Another drawback to this
approach is that the amplifier input noise voltage and input
offset voltage terms see a gain of +2, resulting in higher
noise and output offset voltages. Alternately, a 100pF
capacitor between the inputs shorts them only at high
frequencies, which prevents the increased output offset
voltage but delivers less gain flatness.
Another straightforward approach is to add a 620
resistor
in series with the positive input. This resistor and the
HFA1115 input capacitance form a low pass filter which rolls
off the signal bandwidth before gain peaking occurs. This
configuration was employed to obtain the datasheet AC and
transient parameters for a gain of +1.
Non-inverting Input Source Impedance
For best operation, the DC source impedance seen by the
non-inverting input should be
50
.
This is especially
important in inverting gain configurations where the non-
inverting input would normally be connected directly to GND.
Pulse Undershoot and Asymmetrical Slew Rates
The HFA1115 utilizes a quasi-complementary output stage to
achieve high output current while minimizing quiescent supply
current. In this approach, a composite device replaces the
traditional PNP pulldown transistor. The composite device
switches modes after crossing 0V, resulting in added
distortion for signals swinging below ground, and an
increased undershoot on the negative portion of the output
waveform (see Figures 9, 13, and 17). This undershoot isn't
present for small bipolar signals, or large positive signals.
Another artifact of the composite device is asymmetrical slew
rates for output signals with a negative voltage component.
The slew rate degrades as the output signal crosses through
0V (see Figures 9, 13, and 17), resulting in a slower overall
negative slew rate. Positive only signals have symmetrical
slew rates as illustrated in the large signal positive pulse
response graphs (see Figures 7, 11, and 15).
PC Board Layout
This amplifier's frequency response depends greatly on the
care taken in designing the PC board. The use of low
inductance components such as chip resistors and chip
capacitors is strongly recommended, while a solid
ground plane is a must!
Attention should be given to decoupling the power supplies.
A large value (10
F) tantalum in parallel with a small value
(0.1
F) chip capacitor works well in most cases.
Terminated microstrip signal lines are recommended at the input
and output of the device. Capacitance directly on the output
must be minimized, or isolated as discussed in the next section.
For unity gain applications, care must also be taken to
minimize the capacitance to ground at the amplifier's
inverting input. At higher frequencies this capacitance tends
to short the -INPUT to GND, resulting in a closed loop gain
which increases with frequency. This causes excessive high
frequency peaking and potentially other problems as well.
An example of a good high frequency layout is the
Evaluation Board shown in Figure 2.
GAIN
(A
V
)
CONNECTIONS
+INPUT (PIN 3)
-INPUT (PIN 2)
-1
50
to GND
Input
+1
Input
NC (Floating)
+2
Input
GND
TABLE 1. UNITY GAIN PERFORMANCE FOR VARIOUS
IMPLEMENTATIONS
APPROACH
PEAK-
ING
(dB)
BW
(MHz)
+SR/-SR
(V/
s)
0.1dB
GAIN
FLATNESS
(MHz)
Remove Pin 2
2.5
400
1200/850
20
+R
S
= 620
0.6
170
1125/800
25
+R
S
= 620
and
Remove Pin 2
0
165
1050/775
65
Short Pins 2, 3
0
200
875/550
45
100pF cap. be-
tween pins 2, 3
0.2
190
900/550
19
HFA1115
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