AD815(RevC) 查看數據表（PDF） - Analog Devices
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AD815 Datasheet PDF : 16 Pages
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AD815
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 (VIO) which appears at the output multiplied by
the noise gain of the circuit (1 + RF/RG), noninverting input
current (IBN × RN) also multiplied by the noise gain, and the
inverting input current, which when divided between RF and RG
and subsequently multiplied by the noise gain always appear at
the output as IBI × RF. The input voltage noise of the AD815 is
less than 2 nV/√Hz. At low gains though, the inverting input
current noise times RF is the dominant noise source. Careful
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.
VOUT
=
VIO
×
1
+
RF
RG
± IBN
× RN
×
1
+
RF
RG
±
IBI
× RF
RF
RG
IBI
RN
IBN
VOUT
Figure 45. Output Offset Voltage
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, PIN, of nearly 5 watts.
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 (TJ) and various
components of θJA.
TJ = TA + PIN θJA
Equation 1
TJ
θA (JUNCTION TO
DIE MOUNT)
θ B (DIE MOUNT
TA
TO CASE)
CASE
TJ θ JC
θA + θ B = θ JC
θ CA
PIN
θ JA
TA
WHERE:
PIN = DEVICE DISSIPATION
TA = AMBIENT TEMPERATURE
TJ = JUNCTION TEMPERATURE
θ JC = THERMAL RESISTANCE – JUNCTION TO CASE
θ CA = THERMAL RESISTANCE – CASE TO AMBIENT
Figure 46. A Breakdown of Various Package Thermal
Resistances
Figure 47 gives the relationship between output voltage swing
into various loads and the power dissipated by the AD815 (PIN).
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.
f = 1kHz
4
SQUARE WAVE
3
2
1
RL = 50⍀
SINE WAVE
RL = 100⍀
RL = 200⍀
10
20
30
40
VOUT – Volts p-p
Figure 47. Total Power Dissipation vs. Differential Output
Voltage
REV. C
–11–
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