HA5004 Datasheet, PDF (6/8 Pages) Harris Corporation – 100MHz Current Feedback Amplifier

HA-5004
Application Information
Theory Of Operation
The HA-5004 is a high performance amplifier that uses
current feedback to achieve its outstanding performance.
Although it is externally configured like an ordinary op amp
in most applications, its internal operation is significantly
different.
Inside the HA-5004, there is a unity gain buffer from the non-
inverting (+) input to the inverting-input (as suggested by the
circuit symbol), and the inverting terminal is a low
impedance point. Error currents are sensed at the inverting
input and amplified; a small change in input current
produces a large change in output voltage. The ratio of
output voltage delta due to input current delta is the
transimpedance of the device.
Steady state current at the inverting input is very small
because the transimpedance is large. The voltage across
the input terminals is nearly zero due to the buffer amplifier.
These two properties are similar to standard op amps and
likewise simplify circuit analysis.
Resistor Selection
The HA-5004 is optimized for a feedback resistor of 250Ω,
regardless of gain configuration. It is important to note that
this resistor is required even for unity gain applications;
higher gain settings use a second resistor like regular op
amp circuits as shown in Figure 2 below.
+5V
10kΩ
THERMAL OVERLOAD
V_IN
100
-15V
249Ω
8 NC
OE ⁷
9 GND
TOI ⁶
10 TOL
11 ₊
12 ^-
13 V_EE
14 V_C-
V_CC 5
4 ^{- 5kΩ}
3 ^BAL
+
2
V_{C+ 1}
100Ω
+15V
R_F
249Ω
V_OUT
capacitors from each supply to ground are recommended,
typically a 0.01µF ceramic in parallel with a 4.7µF
electrolytic.
Current Limit
No internal current limiting is provided for the HA-5004 in
order to maximize bandwidth and slew rate. However, power
is supplied separately to the output stage via pins 1 (V_C+)
and 14 (V_C-) so that external current limiting resistors may
be used. If required, 100Ω resistors to each supply rail are
recommended.
Enable/Disable and Thermal
Overload Operation
The HA-5004 operates normally with a TTL low state on pin
7 (OE) but it may be disabled manually by a TTL high state
at this input. When disabled, the output and inverting-input
go to a high impedance state and the circuit is electrically
debiased, reducing supply current by about 5mA. It is
important to keep the differential input voltage below the
absolute maximum rating of 5V when the device is disabled.
If the power dissipation becomes excessive and chip
temperature exceeds approximately 180^oC, the HA-5004 will
automatically disable itself. The thermal overload condition
will be indicated by a low state at the TOL output on pin 10.
(TOL is also low for manual shutdown via pin 7). Automatic
thermal shutdown can be bypassed by a TTL high state on
Thermal Overload Inhibit (TOI) pin 6. See the truth table for a
summary of operation.
Offset Adjustment
Offset voltage may be nulled with a 5kΩ potentiometer
between pins 3 and 4, center tapped to the positive supply.
Setting the slider towards pin 3 (+BAL) increases output
voltage; towards pin 4 (-BAL) decreases output voltage.
Offset can be adjusted by about ±10mV with a 5K pot; this
range is extended with a lower resistance potentiometer.
FIGURE 2. TYPICAL APPLICATION CIRCUIT, A_V = +2
Power Supplies
The HA-5004 will operate over a wide range of supply
voltages with excellent performance. Supplies may be either
single-ended or split, ranging from 6V (±3V) to 36V (±18V).
Appropriate reduction in input and output signal excursion is
necessary for operation at lower supply voltages. Bypass
6