AD816 Просмотр технического описания (PDF) - Analog Devices
Номер в каталоге
Компоненты Описание
производитель
AD816 Datasheet PDF : 16 Pages
| |||
AD816
PRINTED CIRCUIT BOARD LAYOUT
CONSIDERATIONS
As to be expected for a wideband amplifier, PC board parasitics
can affect the overall closed-loop performance. Of concern are
stray capacitances at the output and the inverting input nodes. If
a ground plane is to be used on the same side of the board as
the signal traces, a space (5 mm min) should be left around the
signal lines to minimize coupling.
POWER SUPPLY BYPASSING
Adequate power supply bypassing can be critical when optimiz-
ing the performance of a high frequency circuit. Inductance in
the power supply leads can form resonant circuits that produce
peaking in the amplifier’s response. In addition, if large current
transients must be delivered to the load, then bypass capacitors
(typically greater than 1 µF) will be required to provide the best
settling time and lowest distortion. A parallel combination of
10.0 µF and 0.1 µF is recommended. Under some low frequency
applications, a bypass capacitance of greater than 10 µF may be
necessary. Due to the large load currents delivered by the AD816,
special consideration must be given to careful bypassing. The
ground returns on both supply bypass capacitors as well as signal
common must be “star” connected as shown in Figure 44.
+VS
+IN
DRIVER A
RF
RG
(OPTIONAL)
RF
DRIVER B
–IN
+OUT
–OUT
OUT
RECEIVER A
IN
RF
RG
RF
RG
OUT
IN
RECEIVER B
–VS
Figure 44. Signal Ground Connected in “Star”
Configuration
POWER CONSIDERATIONS
The 500 mA drive capability of the AD816 driver enables it to
drive a 50 Ω load at 40 V p-p when it is configured as a dif-
ferential driver. This implies a power dissipation, PIN, of nearly
5 watts. To ensure reliability, the junction temperature of the
AD816 should be maintained at less than 175°C. For this rea-
son, the AD816 will require some form of heat sinking in most
applications. The thermal diagram of Figure 45 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 POWER DISSIPATION
TA = AMBIENT TEMPERATURE
TJ = JUNCTION TEMPERATURE
θ JC = THERMAL RESISTANCE – JUNCTION TO CASE
θ CA = THERMAL RESISTANCE – CASE TO AMBIENT
Figure 45. A Breakdown of Various Package Thermal
Resistances
Figure 46 gives the relationship between output voltage swing
into various loads and the power dissipated by the AD816 (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. When the power dissipation
requirements are known, Equation 1 and the graph on Figure 47
can be used to choose an appropriate heat sinking configuration.
f = 1kHz
VS = ؎15V
4
SQUARE WAVE
3
2
1
RL = 50⍀
SINE WAVE
RL = 100⍀
RL = 200⍀
10
20
30
40
VOUT – Volts p-p
Figure 46. Total Power Dissipation vs Differential Driver
Output Voltage
–12–
REV. B
Share Link: 