ADUM3190 Просмотр технического описания (PDF) - Analog Devices
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ADUM3190 Datasheet PDF : 16 Pages
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ADuM3190
Data Sheet
APPLICATIONS INFORMATION
THEORY OF OPERATION
In the test circuits of the ADuM3190 (see Figure 18 through
Figure 20), external supply voltages from 3 V to 20 V are
provided to the VDD1 and VDD2 pins, and internal regulators
provide 3.0 V to operate the internal circuits of each side of the
ADuM3190. An internal precision 1.225 V reference provides
the reference for the ±1% accuracy of the isolated error amplifier.
UVLO circuits monitor the VDDx supplies to turn on the internal
circuits when the 2.8 V rising threshold is met and to turn off
the error amplifier outputs to a high impedance state when VDDx
falls below 2.6 V.
approximately 100 kHz, but the circuit is more stable with a phase
shift of approximately −120°, which yields a stable 60° phase
margin.
This circuit is used for accuracy tests only, not for real-world
applications, because it has a 680 Ω resistor across the isolation
barrier to close the loop for the error amplifier; this resistor
causes leakage current to flow across the isolation barrier. For
this test circuit only, GND1 must be connected to GND2 to create a
return for the leakage current created by the 680 Ω resistor
connection.
AMPLITUDE (dB)
The op amp on the right side of the device has a noninverting
+IN pin and an inverting −IN pin available for connecting a
feedback voltage in an isolated dc-to-dc converter output, usually
through a voltage divider. The COMP pin is the op amp output,
which can be used to attach resistor and capacitor components in
a compensation network. The COMP pin internally drives the Tx
transmitter block, which converts the op amp output voltage
into an encoded output that is used to drive the digital isolator
transformer.
On the left side of the ADuM3190, the transformer output
PWM signal is decoded by the Rx block, which converts the
signal into a voltage that drives an amplifier block; the amplifier
block produces the error amplifier output available at the EAOUT
pin. The EAOUT pin can deliver ±3 mA and has a voltage level
between 0.4 V and 2.4 V, which is typically used to drive the
input of a PWM controller in a dc-to-dc circuit.
For applications that need more output voltage to drive their
controllers, Figure 19 illustrates the use of the EAOUT2 pin output
which delivers up to ±1 mA with an output voltage of 0.6 V to 4.8 V
for an output that has a pull-up resistor to a 5 V supply. If the
EAOUT2 pull-up resistor connects to a 10 V to 20 V supply, the
output is specified to a minimum of 5.0 V to allow use with a
PWM controller requiring a minimum input operation of 5 V.
ACCURACY CIRCUIT OPERATION
100
OP AMP AND
LINEAR ISOLATOR
LINEAR ISOLATOR
POLE AT 400kHz
100
1k
10k 100k
OP AMP
ALONE
FREQUENCY
1M 10M (Hz)
PHASE (°)
LINEAR
ISOLATOR
100
1k
10k 100k 1M 10M FREQUENCY
(Hz)
–90
–180
Figure 21. Bode Plot 1
AMPLITUDE (dB)
100
OP AMP AND
LINEAR ISOLATOR
LINEAR ISOLATOR
POLE AT 400kHz
INTEGRATOR
CONFIGURATION
OP AMP
ALONE
FREQUENCY
100
1k
10k 100k 1M 10M (Hz)
PHASE (°)
100
1k
10k 100k 1M 10M FREQUENCY
(Hz)
–90
–180
See Figure 18 and Figure 19 for stability of the accuracy circuits.
The op amp on the right side of the ADuM3190, from the −IN
pin to the COMP pin, has a unity-gain bandwidth (UGBW) of
Figure 22. Bode Plot 2
10 MHz. Figure 21, Bode Plot 1, shows a dashed line for the op
APPLICATION BLOCK DIAGRAM
amp alone and its 10 MHz pole.
Figure 23 shows a typical application, an isolated error amplifier
Figure 21 also shows the linear isolator alone (the blocks from
in primary side control, for the ADuM3190. The op amp of the
the op amp output to the ADuM3190 output, labeled as the
ADuM3190 is used as the error amplifier for the feedback of the
linear isolator), which introduces a pole at approximately
output voltage, VOUT, using a resistor divider to the −IN pin of
400 kHz. This total Bode plot of the op amp and linear isolator
the op amp. This configuration inverts the output signal at the
shows that the phase shift is approximately −180° from the −IN
COMP pin when compared to the +IN pin, which is connected
pin to the EAOUT pin before the crossover frequency. Because a
to the internal 1.225 V reference. For example, when the output
−180° phase shift can make the system unstable, adding an inte-
voltage, VOUT, falls due to a load step, the divider voltage at the
grator configuration, as shown in the test circuits in Figure 18 and
−IN pin falls below the +IN reference voltage, causing the COMP
Figure 19, consisting of a 2.2 nF capacitor and a 680 Ω resistor,
pin output signal to go high. The COMP output of the op amp
helps to make the system stable. In Figure 22, Bode Plot 2 with an
is encoded and then decoded back by the digital isolator trans-
integrator configuration added, the system crosses over 0 dB at
former block to a signal that drives the output of the ADuM3190
Rev. 0 | Page 12 of 16
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