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ADUM3190

High Stability Isolated Error Amplifier

Analog Devices 

Data Sheet

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 has the effect of making the latching PWM com-

parator 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.

PWM CONTROLLER

OSC

VREF

ERROR

AMP

LATCHING

PWM

FB COMP

CURRENT

SENSE

VIN

POWER

STAGE

LO DCR

VOUT

CO +

ESR

EAOUT2

COMP

C1

COMPENSATION

NETWORK

C2 R2

OP AMP –IN

+IN

ADuM3190 1.225V REFOUT

Figure 23. Application Block Diagram 1

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 L and Output Filter C components create a

double pole; the op amp has a pole at 10 MHz (see Figure 21),

and the linear isolator has a pole at 400 kHz (see Figure 21 and

Figure 22).

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 com-

ponents 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 enough 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.

In an application where the 5 V minimum output of the EAOUT2

pin is not enough to drive the COMP pin of some PWM con-

trollers, for example, controllers that operate with 6 V or more

of COMP pin voltage, use EAOUT2 to drive the FB pin of the error

amplifier of the PWM controller (see Figure 24). The typical VREF

voltage level of PWM controllers is approximately 1.25 V or

2.5 V, setting the reference level for the FB pin. In Figure 24, the

ADuM3190

EAOUT2 output is used for a PWM controller with a 2.5 V

reference.

PWM CONTROLLER

OSC

VREF

ERROR

AMP

LATCHING

PWM

FB COMP

CURRENT

SENSE

VIN

POWER

STAGE

EAOUT2

C1 COMPENSATION

C2 R2

NETWORK

COMP

OP AMP

LO

–IN

+IN

DCR VOUT

CO +

ESR

ADuM3190 1.225V REFOUT

Figure 24. Application Block Diagram 2

As shown in Figure 24, the ADuM3190 op amp has the feed-

back voltage from the VOUT output divider is connected to the

+IN pin, and the +1.225 V reference voltage connected to the

−IN pin. This configuration produces a low going ADuM3190

COMP pin when the VOUT voltage drops from a load step. The

EAOUT2 pin follows the COMP pin, going low and connecting to

the PWM controller FB pin. The error amplifier of the PWM

controller has a reference (VREF) at the noninverting input,

which, when the FB pin is low, makes the COMP pin of the

error amplifier output go high. A high at the COMP pin 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 application block diagrams (see Figure 23 and Figure 24)

show two different ways to use the ADuM3190 to provide iso-

lated feedback in the control loop of an isolated dc-to-dc converter.

In both figures, the loop is closed at approximately the 1.225 V

reference voltage, providing ±1% accuracy over temperature. The

ADuM3190 op amp has a high gain bandwidth of 10 MHz to

allow the dc-to-dc converter to operate at high switching speeds,

enabling smaller values for the Output Filter L and Output Filter C

components.

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 25.

The output voltage is determined by the following equation,

where VREF = 1.225 V:

VOUT = VREF × (R1 + R2)/R2

(1)

Rev. 0 | Page 13 of 16

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