VIPer53 - E

Transconductance error amplifier

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11

Transconductance error amplifier

The VIPer53-E includes a transconductance error amplifier. Transconductance Gm is the

Equation 8

Equation 9

Equation 10

where Gm value for VIPer53 is typically 1.4mA/V.

tolerances. An impedance Z must be connected between the COMP pin and ground in order

to accurately define the transfer function F of the error amplifier, the following equation, very

similar to the one above:

Equation 11

The error amplifier frequency response is shown in .0 for different values of a simple

resistance connected on the COMP pin. The unloaded transconductance error amplifier

the COMP pin to achieve different compensation methods. A capacitor provides an

integrator function, thus eliminating the DC static error, and a resistance in series leads to a

flat gain at higher frequency, introducing a zero level and ensuring a correct phase margin.

This configuration illustrated in Figure 22, for the schematic and Figure 23 on page 28 for

Note that a 10nF capacitor (8nF, minimum value) should always be connected to the COMP

pin to ensure a correct stability of the internal error amplifier.

The complete converter open loop transfer function can be built from both power cell and

error amplifier transfer functions. A theoretical example can be seen in Figure 24 for a

discontinuous mode flyback loaded by a simple resistor, regulated from primary side (no

Gm

∂I

COMP

∂V

DD

--------------------

=

Z

COMP

∂V

COMP

∂I

COMP

----------------------

1

Gm

----------

∂V

COMP

∂V

DD

----------------------

⋅

=

=

A

VOL

Gm

Z

COMP

⋅

=

Fs

()

Gm

Z s

()

⋅

=