Data Sheet ADuM3190
Rev. A | Page 15 of 18
The gain, offset, and linearity of EAOUT and EAOUT2 are specified
in Table 1 using this test circuit. When designing applications
for voltage monitoring using an isolated amplifier, review these
specifications, noting that the 1% accuracy specifications for the
isolated error amplifier do not apply. In addition, the EAOUT circuit
in Figure 29 is shown with an optional external RC low-pass filter
with a corner frequency of 500 kHz, which can reduce the 3 MHz
output noise from the internal voltage to the PWM converter.
APPLICATION BLOCK DIAGRAM
Figure 32 shows a typical application for the ADuM3190: an
isolated error amplifier in primary side control.
Figure 32. Application Block Diagram
The op amp of the ADuM3190 is used as the error amplifier for
the feedback of the output voltage, VOUT, using a resistor divider
to the −IN pin of the op amp. This configuration inverts the
output signal at the COMP pin when compared to the +IN pin,
which is connected to the internal 1.225 V reference.
For example, when the output voltage, VOUT, falls due to a load
step, the divider voltage at the −IN pin falls below the +IN ref-
erence voltage, causing the COMP pin output signal to go high.
The COMP output of the op amp is encoded and then decoded
by the digital isolator transformer block to a signal that drives the
output of the ADuM3190 high. The output of the ADuM3190
drives the COMP pin of the PWM controller, which is designed
to reset the PWM latch output to low only when its COMP pin is
low. A high at the COMP pin of the PWM controller causes the
latching PWM comparator to produce a PWM duty cycle output.
This PWM duty cycle output drives the power stage to increase
the VOUT voltage until it returns to regulation.
The power stage output is filtered by output capacitance and, in
some applications, by an inductor. Various elements contribute to
the gain and phase of the control loop and the resulting stability.
The output filter components (LO and CO) create a double pole;
the op amp has a pole at 10 MHz (see Figure 30), and the linear
isolator has a pole at 400 kHz (see Figure 30 and Figure 31).
The output capacitor and its ESR can add a zero at a frequency
that is dependent on the component type and values. With the
ADuM3190 providing the error amplifier, a compensation network
is provided from the −IN pin to the COMP pin to compensate
the control loop for stability. The compensation network values
depend on both the application and the components that are
selected; information about the component network values is
provided in the data sheet of the selected PWM controller.
The ADuM3190 has two different error amplifier outputs:
EAOUT and EAOUT2. The EAOUT output, which can drive ±3 mA,
has a guaranteed maximum high output voltage of at least 2.4 V,
which may not be sufficient to drive the COMP pin of some
PWM controllers. The EAOUT2 pin can drive ±1 mA and has an
output range that guarantees 5.0 V for a VDD1 voltage range of
10 V to 20 V, which works well with the COMP pin of many
PWM controllers.
Figure 32 shows how to use the ADuM3190 to provide isolated
feedback in the control loop of an isolated dc-to-dc converter. In
this application block diagram, the loop is closed at approxi-
mately the 1.225 V reference voltage, providing ±1% accuracy
over temperature. The ADuM3190 op amp has a high gain band-
width of 10 MHz to allow the dc-to-dc converter to operate at
high switching speeds, enabling smaller values for the output
filter components (LO and CO).
The 400 kHz bandwidth of the ADuM3190 error amplifier output
offers faster loop response for better transient response than the
typical shunt regulator and optocoupler solutions, which typically
have bandwidths of only 25 kHz to 50 kHz maximum.
SETTING THE OUTPUT VOLTAGE
The output voltage in the application circuit can be set with two
resistors in a voltage divider, as shown in Figure 33.
The output voltage is determined by the following equation
where VREF = 1.225 V.
VOUT = VREF × (R1 + R2)/R2 (1)
Figure 33. Setting the Output Voltage
DOSA MODULE APPLICATION
Figure 34 is a block diagram of a Distributed-power Open
Standards Alliance (DOSA) circuit using the ADuM3190.
The block diagram shows how to use the ADuM3190 1.225 V
reference and the error amp in a DOSA standard power supply
module circuit to produce output voltage settings using a
combination of resistors.
The ADuM3190 1.225 V reference is specified for ±1% over the
−40°C to +125°C temperature range. See Table 10 to select the
resistor values to set the output voltage of the module. Two
different ranges of VOUT can be implemented, VOUT > 1.5 V or
VOUT < 1.5 V, depending on the required module.
–IN
+IN
REF
OUT
1.225V
OSC
LATCHING
PWM
V
REF
FB COMP
EA
OUT2
ERROR
AMP
CURRENT
SENSE
POWER
STAGE
VIN
VOUT
C
1
COMPENSATION
NETWORK
L
O
C
O
ESR
DCR
C
2
COMPR
2
+
ADuM3190
PWM CONTROLLER
OP AMP
11335-008
V
REF
1.225V
V
IN
= 0.35V TO 1.5V
ADuM3190
–IN R
1
V
OUT
ISOLATED DC-TO-DC S UP PLY
R
2
+IN
REF
OUT
ERROR
AMP
11335-010