AD815 Analog Devices, AD815 Datasheet - Page 11

• Manufacturer Part Number: AD815
• Description: High Output Current Differential Driver
• Manufacturer: Analog Devices

Specifications of AD815

• -3db Bandwidth: 120MHz
• Slew Rate: 900V/µs
• Vos: 10mV
• Ib: 2µA
• # Opamps Per Pkg: 2
• Input Noise (nv/rthz): 1.85nV/rtHz
• Vcc-vee: 10V to 36V
• Isy Per Amplifier: 40mA
• Packages: DDPAK,SIP,SOIC

REV. C
DC ERRORS AND NOISE
There are three major noise and offset terms to consider in
a current feedback amplifier. For offset errors refer to the
equation below. For noise error the terms are root-sum-squared
to give a net output error. In the circuit below (Figure 45), they
are input offset (V
the noise gain of the circuit (1 + R
current (I
inverting input current, which when divided between R
and subsequently multiplied by the noise gain always appear at
the output as I
less than 2 nV/√Hz. At low gains though, the inverting input
current noise times R
layout and device matching contribute to better offset and
drift specifications for the AD815 compared to many other
current feedback amplifiers. The typical performance curves
in conjunction with the equations below can be used to predict
the performance of the AD815 in any application.
POWER CONSIDERATIONS
The 500 mA drive capability of the AD815 enables it to drive
a 50 Ω load at 40 V p-p when it is configured as a differential
driver. This implies a power dissipation, P
To ensure reliability, the junction temperature of the AD815
should be maintained at less than 175°C. For this reason, the
AD815 will require some form of heat sinking in most appli-
cations. The thermal diagram of Figure 46 gives the basic
relationship between junction temperature (T
components of θ
V
OUT
T
J
=
= V
BN
T
A
× R
IO
Figure 45. Output Offset Voltage
BI
+
× 1 +
N
× R
P
JA
) also multiplied by the noise gain, and the



IN
IO
R
R
.
N
G
) which appears at the output multiplied by
F
. The input voltage noise of the AD815 is
θ
F
R
R
J
A
is the dominant noise source. Careful
G
F
I
I
BN
BI

 ± I

BN
R
F
× R
F
/R
N
G
), noninverting input
× 1 +



IN
, of nearly 5 watts.
R
R
V
J
OUT
G
) and various
F

 ± I

Equation 1
BI
F
and R
× R
F
G
–11–
Figure 47 gives the relationship between output voltage swing
into various loads and the power dissipated by the AD815 (P
This data is given for both sine wave and square wave (worst
case) conditions. It should be noted that these graphs are for
mostly resistive (phase < ±10°) loads.
Figure 47. Total Power Dissipation vs. Differential Output
Voltage
Figure 46. A Breakdown of Various Package Thermal
Resistances
4
3
2
1
P
IN
T
WHERE:
A
f = 1kHz
P
T
T
θ
θ
IN
A
J
JC
CA
= JUNCTION TEMPERATURE
= AMBIENT TEMPERATURE
= DEVICE DISSIPATION
= THERMAL RESISTANCE – JUNCTION TO CASE
T
= THERMAL RESISTANCE – CASE TO AMBIENT
SQUARE WAVE
J
T
J
10
CASE
θ
JC
θ
JA
V
20
OUT
θ
– Volts p-p
A
θ
+
θ
B
CA
θ
SINE WAVE
θ
B
(DIE MOUNT
TO CASE)
A
=
30
(JUNCTION TO
DIE MOUNT)
θ
R
R
JC
R
L
T
L
L
A
= 200
= 100
= 50
40
AD815
IN
).