CVA3424A Datasheet, PDF (3/4 Pages) Calogic, LLC – 185MHz CRT Driver

CORPORATION
CVA3424A / CVA3424
APPLICATIONS INFORMATION
Basic Circuit Configuration
The CVA3424 is a transimpedance amplifier with two stage
feedback amplifier configurations. Any change in input
current will be reflected as change in output voltage swing. A
resistor in series with the input will change the CVA3424 into
a voltage amplifier. The output is an emitter follower.
Because of the complementary circuitry employed, there is
no need for load or pull up resistor.
An internally bypassed capacitor is included inside the
package, however, for low frequencies an electrolytic
capacitor is recommended.
CVA3424 has an internal feedback resistor of 3.66KΩ. In the
absence of any input signal, the Vout DC is set by
Vout
(DC)
=
(1
+
RF
R_B
)
Vin
(DC)
If an input signal is applied, the gain is set by
Vout = (^RRF_x ) Vin
Input and Transfer Characteristics
An input current swing of ±4.5mA causes the output to change
by ±25V.
A resistor of 270Ω in series with the input will give a voltage
gain of -13.
Input pins are internal dc feedback nodes and thus have low
impedances. These pins must be fed from a series RC
network for high frequency emphasis.
Output Characteristics
The CVA3424 is intended to be used as the final stage of very
fast video circuits. The nominal load capacitance is 10pF. Other
values can be accommodated since the output stage is an
emitter follower and is fairly insensitive to load capacitance.
However, a wire connection of some length is unavoidable, that
causes objectionable ringing due to a resonant circuit. To avoid
this a damping resistor must be used in series with the lead
inductance. Also a resistor is necessary to protect the amplifier
against arching. A resistor of 30-50Ω will provide protection but
will slow down the response. The lead inductance may be
artificially increased by a tenth of a microHenry to obtain
desired peak. Any change in inductance will require
readjustment of damping resistor, as stated by equation (1).
R^∗ = √_CL (1)
The output of CVA3424 is not short circuit proof. Any
resistance to V+ or Ground should be >600Ω.
Thermal Characteristics
When low frequency square waves are amplified, some droop
will occur due to a large change in thermal dissipation in the
input transistors. To overcome this an R-C series feedback
network is suggested with 300kΩ and 46pF values. Under
normal operating conditions the CVA3424 will dissipate up to
6W. The maximum allowed case temperature is +90^oC. To
calculate maximum heatsink thermal resistance use equation (2).
Rth
=
(90 − 50°)
6W
=
6.7°C/W
FALL TIME
RISE TIME
BANDWIDTH
0dB
2ns/DIV
2ns/DIV
1
10
100
MHz