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參數(shù)資料
| 型號： | ISO253 |
| 廠商： | Texas Instruments, Inc. |
| 英文描述： | Precision, Powered, Three-Port Isolated Buffer Amplifier(精密、三端口隔離緩沖放大器(帶變壓器）) |
| 中文描述： | 精密，技術(shù)支持，三端口隔離緩沖放大器（精密，三端口隔離緩沖放大器（帶變壓器）） |
| 文件頁數(shù)： | 7/9頁 |
| 文件大?。?/td> | 150K |
| 代理商： | ISO253 |
7
ISO253
bypass for the AC portion of this current. The power should
never be instantaneously interrupted to the ISO253 (i.e., a
break in the line to +V
S3
either by accidental or switch
means.) Normal power down of the +V
S3
supply is not
considered instantaneous. Should a rapid break in input
power occur the internal transformers voltage will rapidly
rise to maintain current flow and may cause internal damage
to the ISO253.
SYNCHRONIZED OPERATION
ISO253 can be synchronized to an external signal source.
This capability is useful in eliminating troublesome beat
frequencies in multi-channel systems and in rejecting AC
signals and their harmonics. To use this feature, tie all sync
pins together or apply an external signal to the SYNC pin.
ISO253 can be synchronized to an external oscillator over
the range 1-1.4MHz (this corresponds to a modulation fre-
quency of 500kHz to 700kHz as SYNC is internally divided
by 2).
CARRIER FREQUENCY CONSIDERATIONS
ISO253 amplifiers transmit the signal across the ISO-barrier
by a duty-cycle modulation technique. This system works
like any linear amplifier for input signals having frequencies
below one half the carrier frequency, f
C
. For signal frequen-
cies above f
C
/2, the behavior becomes more complex. The
“Signal Response vs Carrier Frequency” performance curve
describes this behavior graphically. The upper curve illus-
trates the response for input signals varying from DC to f
C
/
2. At input frequencies at or above f
C
/2, the device generates
an output signal component that varies in both amplitude
and frequency, as shown by the lower curve. The lower
horizontal scale shows the periodic variation in the fre-
quency of the output component. Note that at the carrier
frequency and its harmonics, both the frequency and ampli-
tude of the response go to zero. These characteristics can be
exploited in certain applications.
It should be noted that for the ISO253, the carrier frequency
is nominally 400kHz and the –3dB point of the amplifier is
50kHz. Spurious signals at the output are not significant
under these circumstances unless the input signal contains
significant components above 200kHz.
When periodic noise from external sources such as system
clocks and DC/DC converters is a problem, ISO253 can be
used to reject this noise. The amplifier can be synchronized
to an external frequency source, f
EXT
, placing the amplifier
response curve at one of the frequency and amplitude nulls
indicated in the “Signal Response vs Carrier Frequency”
performance curve.
ISOLATION MODE VOLTAGE
Isolation Mode Voltage (IMV) is the voltage appearing
between isolated grounds GND1 and GND2. The IMV can
induce errors at the output as indicated by the plots of IMV
vs Frequency. It should be noted that if the IMV frequency
exceeds f
C
/2, the output will display spurious outputs in a
manner similar to that described above, and the amplifier
Soft start circuitry protects the MOSFET switches during
startup. This is accomplished by holding the gate-to-source
voltage of both MOSFET switches low until the free-run-
ning oscillator is fully operational. In addition, soft start
circuitry and input current sensing also protects the switches.
This current limiting keeps the MOSFET switches operating
in their safe operating area under fault conditions or exces-
sive loads. When either of these conditions occur, the peak
input current exceeds a safe limit. The result is an approxi-
mate 5% duty cycle, 300
μ
s drive period to the MOSFET
switches. This protects the internal MOSFET switches as
well as the external load from any thermal damage. When
the fault or excessive load is removed, the converter resumes
normal operation. A delay period of approximately 50
μ
s
incorporated in the current sensing circuitry allows the
output filter capacitors to fully charge after a fault is re-
moved. This delay period corresponds to a filter capacitance
of no more than 1
μ
F at either of the output pins. This
provides full protection of the MOSFET switches and also
sufficiently filters the output ripple voltage. The current
sensing circuitry is designed to provide thermal protection
for the MOSFET switches over the operating temperature
range as well. When these conditions are exceeded, the unit
will go into its shutdown mode.
OUTPUT CURRENT RATINGS
The total current which can be drawn from each output
supply on the ISO253 is a function of the total power drawn
from all outputs. For example if three outputs are not used
then maximum current can be drawn from one output. In all
cases, the total maximum current that can be drawn from any
combination of outputs is:
I
1+
+
I
1–
+
I
2+
+
I
2–
≤
50
m
Α
+V
S3
, GND3
The waveform of the ground return current is an 800kHz
sawtooth. A capacitor between +V
S3
and GND3 provides a
FIGURE 2. External SYNC drive.
15
ISO253
16
17
+15V
15
ISO253
16
17
To Other
ISO253’s
2N3904
2N3904
TTL
SYNC
MC1472
or Equivalent
Peripheral
Driver
620
100
+5V
330
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