MP023GS datasheet(14/23 Pages) MPS

14 / 23 page

MP023 – PRIMARY-SIDE CC/CV CONTROLLER

MP023 Rev. 1.1

www.MonolithicPower.com

7/18/2016

MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.

VIPK

VLimit-Max

fS_L

fS-min

VLimit-Min

fS_H

Figure 5: Peak Current Modulation

In the event that the external current sensing

resistor is shorted, the maximum turn-on time is

limited internally at tONmax. If this maximum

limitation is reached, the IC enters protection

mode.

Constant Voltage (CV) Operation

The MP023 detects the auxiliary winding

voltage from FB and operates in constant

voltage (CV) mode to regulate the output

voltage.

The auxiliary voltage can be calculated with

Equation (5):

aux

V(V

V )



(5)

Where VD is the forward drop voltage of the

secondary diode.

During the conduction time of the secondary

diode, the difference between the output

voltage and the voltage on the secondary

winding is not constant since VD varies with the

current

flowing

through

the

diode.

compensate for the voltage drop difference, the

sampling time decreases gradually from tFBS-Max

to tFBS-Min as the current limitation folds back

from VLimit-Max to VLimit-Min (see Figure 6).

Figure 6: FB Voltage Sampling Point

The FB sampling time is also customizable with

different resistor values connected to CS (see

Figure 7). Please refer to EC table for details.

Figure 7: External Resistor for Sampling Time

Customization

Choose a sampling time toward the end of the

secondary diode conduction period to improve

the accuracy of the CV regulation. The CV

regulation loop then generates the switching

frequency to regulate the output voltage based

on the sampled voltage.

Constant Current (CC) Operation

Figure

shows

the

secondary

current

waveforms.

Figure 8: Secondary Current Waveform

In constant current (CC) operation, the CC loop

control function remains at a fixed ratio between

the secondary diode on time (tons) and the

secondary diode off time (toffs) by charging or

discharging the internal capacitance. The fixed

ratio limits the maximum duty of the secondary

side diode on time, as shown in Equation (6):

ons

SMax

ons

offs







(6)

For applications with varying output voltages,

the DS-Max can be customized with CP. If CP is

connected with a capacitor directly or shorted to

GND, the DS-Max remains at a default value of

0.4. However, if CP is connected with a resistor

(Figure 9), several choices are available based

on the different resistances.

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