VIPer50A-E/ASP-E

5 Operation Description

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The soft start feature can be implemented on the COMP pin through a simple capacitor which

will be also used as the compensation network. In this case, the regulation loop bandwidth is

rather low, because of the large value of this capacitor. In case a large regulation loop

bandwidth is mandatory, the schematics of (see Figure 17) can be used. It mixes a high

performance compensation network together with a separate high value soft start capacitor.

Both soft start time and regulation loop bandwidth can be adjusted separately.

If the device is intentionally shut down by tying the COMP pin to ground, the device is also

This voltage can be used for supplying external functions, provided that their consumption does

not exceed 0.5mA. (see Figure 18) shows a typical application of this function, with a latched

shutdown. Once the "Shutdown" signal has been activated, the device remains in the Off state

until the input voltage is removed.

5.4

Transconductance Error Amplifier

The VIPer50A-E/ASP-E includes a transconductance error amplifier. Transconductance Gm is

An impedance Z can be connected between the COMP pin and ground in order to define the

transfer function F of the error amplifier more accurately, according to the following equation

(very similar to the one above):

The error amplifier frequency response is reported in Figure 10. for different values of a simple

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

pin to achieve different compensation level. A capacitor will provide an integrator function, thus

eliminating the DC static error, and a resistance in series leads to a flat gain at higher

frequency, insuring a correct phase margin. This configuration is illustrated in Figure 20

As shown in Figure 19 an additional noise filtering capacitor of 2.2nF is generally needed to

avoid any high frequency interference.

Is also possible to implement a slope compensation when working in continuous mode with

duty cycle higher than 50%. Figure 21 shows such a configuration. Note: R1 and C2 build the

classical compensation network, and Q1 is injecting the slope compensation with the correct

polarity from the oscillator sawtooth.

G

m

∂l

COMP

∂V

DD

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

=

Z

CO MP

∂

V

CO MP

∂

I

COMP

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

1

G

m

--------

∂

V

COMP

∂V

DD

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

×

=

=