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| 型號(hào)： | PA25A |
| 廠商： | Electronic Theatre Controls, Inc. |
| 英文描述： | POWER DUAL OPERATIONAL AMPLIFIERS |
| 中文描述： | 功耗雙運(yùn)算放大器 |
| 文件頁(yè)數(shù)： | 5/5頁(yè) |
| 文件大小： | 84K |
| 代理商： | PA25A |
APEX MICROTECHNOLOGY CORPORATION
TELEPHONE (520) 690-8600
FAX (520) 888-3329
ORDERS (520) 690-8601
EMAIL prodlit@apexmicrotech.com
PA21/25/26U REV. G FEBRUARY 2000
ADDITIONAL PA26 PIN FUNCTIONS
2000 Apex Microtechnology Corp.
Figure 3 shows a bootstrap which dynamically couples the
output waveform onto the V
pin. This causes V
BOOST
to
swing positive from it's initial value, which is equal to +V
(one diode drop), an amount equal to the output. In other
words, if V
was initially 19.3, and the output swings
positive 18 Volts, the voltage on the V
pin will swing to 19.3
-0.7 + 18 or 36.6. The capacitor needs to be sized based on a
1K
impedance and the lowest frequency required by the
circuit. For example, 20Hz will require > 8uF.
I
SENSE
The I
pin is in series with the negative half of the output
stage only. Current will flow through this pin only when nega-
tive current is being outputted. The current that flows in this pin
is the same current that flows in the output (if
–
1A flows in the
output, the I
pin will have 1A of current flow, if +1A flows
in the output the I
pin will have 0 current flow).
The resistor choice is arbitrary and is selected to provide
whatever voltage drop the engineer desires, up to a maximum
of 1.0 volt. However, any voltage dropped across the resistor
will subract from the swing to rail. For instance, assume a +/
–
12 volt power supply and a load that requires +/
–
1A. With no
current sense resistor the output could swing +/
–
10.2 volts. If
a 1
resistor is used for current sense (which will drop 1 Volt
at 1 Amp) then the output could swing +10.2,
–
9.2 Volts.
Figure 4 shows the PA26 I
feature being used to obtain
a Transconductance function. In this example, amplifier "A" is
the master and amplifier "B" is the slave. Feedback from
sensing resistors R
is applied to the summing network and
scaled to the inverting input of amplifier "A" where it is com-
pared to the input voltage. The current sensing feedback
imparts a Transconductance feature to the amplifiers transfer
function. In other words, the voltage developed across the
sensing resistors is directly proportional to the output current.
Using this voltage as a feedback source allows expressing the
gain of the circuit in amperes vs input voltage. The transfer
funcion is approximately:
I
L
= (V
IN
–
V
REF
) *R
IN
/ R
FB
/ R
s
In the illustration, resistors R
IN
, R
FB
and R
S
determine gain.
V
BIAS
should be set midway between +V
s
and -V
s
, Vref is
usually ground in dual supply systems or used for level
translation in single supply systems.
MOUNTING PRECAUTIONS
1. Always use a heat sink. Even unloaded, the PA26 can
dissipate up to 3.6 watts. A thermal washer or thermal
grease should always be used.
2. Avoid bending the leads. Such action can lead to internal
damage.
3. Always fasten the tab to the heat sink before the leads are
soldered to fixed terminals.
4. Strain relief must be provided if there is any probability of
axial stress to the leads.
10
3
7
5
8
PA26A
PA26B
+V
S
≤
20V
D
B1
D
B2
C
B1
SPEAKER
C
B2
FIGURE 3. SIMPLE BOOTSTRAPPING IMPROVES POSITIVE
OUTPUT SWING. CONNECT PINS 3 AND 10 TO V
S
IF NOT
USED. TYPICAL CURRENTS ARE 12
m
A EACH.
The V
pin is the positive terminal for the load of the
second stage of the amplifier. When that terminal is connected
to a voltage greater than +V
it will provide more drive to the
upper output transistor, which is a darlington connected emit-
ter follower. This will better saturate the output transistor.
When V
is about 5 Volts greater than +V
the positive
output can swing 0.5 Volts closer to the rail. This is as much
improvement as is possible.
V
pin requires approximately 10
–
12mA of current.
Dynamically it represents 1K
impedance. The maximum
voltage that can be applied to V
is 40 volts with respect to
–
V
S
. There is no limit to the difference between +V
S
and V
BOOST
.
OPERATING
CONSIDERATIONS
PA21/25/26
PA21A/25A
V
BOOST
A
B
V
BIAS
+VS
VIN
VREF
–
VS OR GND
RS
RS
IL
RL
RIN
RIN
R
PA26
R
RFB
R
FB
FIGURE 4. I
SENSE
TRANSCONDUCTANCE BRIDGING
AMPLIFIER
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