ICE3A1065 Datasheet, PDF(16/32 Page) Infineon Technologies AG – Off-Line SMPS Current Mode Controller with integrated 650V Startup Cell/ Depletion CoolMOS™

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ICE3A1065 Datasheet, PDF (16/32 Pages) Infineon Technologies AG – Off-Line SMPS Current Mode Controller with integrated 650V Startup Cell/ Depletion CoolMOS™

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CoolSETâ¢-F3

Functional Description

via the gate G2. The external Soft Start capacitor can

now be charged further by the integrated pull up

resistor RSoftS. The comparator C3 releases the gates

G5 and G6 once VSofts has exceeded 5.4V. Therefore

there is no entering of Auto Restart Mode possible

during this charging time of the external capacitor

CSoftS. The same procedure happens to the external

Soft Start capacitor if a low load condition is detected

by comparator C5 when VFB is falling below 1.32V.

Only after VSoftS has exceeded 5.4V and VFB is still

below 1.32V Active Burst Mode is entered.

3.6.2

Active Burst Mode

The controller provides Active Burst Mode for low load

conditions at VOUT. Active Burst Mode increases

significantly the efficiency at light load conditions while

supporting a low ripple on VOUT and fast response on

load jumps. During Active Burst Mode which is

controlled only by the FB signal the IC is always active

and can therefore immediately response on fast

changes at the FB signal. The Startup Cell is kept

switched off to avoid increased power losses for the

self supply.

SoftS

6.5V

RSoftS

Internal Bias

4.4V

The Active Burst Mode is located in the Control Unit.

Figure 18 shows the related components.

3.6.2.1 Entering Active Burst Mode

The FB signal is always observed by the comparator

C5 if the voltage level falls below 1.32V. In that case the

switch S1 is released which allows the capacitor CSoftS

to be charged starting from the clamped voltage level

at 4.4V in normal operating mode. If VSoftS exceeds

5.4V the comparator C3 releases the gate G6 to enter

the Active Burst Mode. The time window that is

generated by combining the FB and SoftS signals with

gate G6 avoids a sudden entering of the Active Burst

Mode due to large load jumps. This time window can be

adjusted by the external capacitor CSoftS.

After entering Active Burst Mode a burst flag is set and

the internal bias is switched off in order to reduce the

current consumption of the IC down to approx. 1.05mA.

In this Off State Phase the IC is no longer self supplied

so that therefore CVCC has to provide the VCC current

(see Figure 19). Furthermore gate G11 is then released

to start the next burst cycle once VFB has 3.4V

exceeded.

It has to be ensured by the application that the VCC

remains above the Undervoltage Lockout Level of 8.5V

to avoid that the Startup Cell is accidentally switched

on. Otherwise power losses are significantly increased.

The minimum VCC level during Active Burst Mode is

depending on the load conditions and the application.

The lowest VCC level is reached at no load conditions

at VOUT.

5.4V

4.8V

1.32V

Current

Limiting

G10

Active

Burst

Mode

C6a

4.0V

C6b

G11

3.4V

Control Unit

Figure 18 Active Burst Mode

3.6.2.2 Working in Active Burst Mode

After entering the Active Burst Mode the FB voltage

rises as VOUT starts to decrease due to the inactive

PWM section. Comparator C6a observes the FB signal

if the voltage level 4V is exceeded. In that case the

internal circuit is again activated by the internal Bias to

start with switching. As now in Active Burst Mode the

gate G10 is released the current limit is only 0.257V to

reduce the conduction losses and to avoid audible

noise. If the load at VOUT is still below the starting level

for the Active Burst Mode the FB signal decreases

down to 3.4V. At this level C6b deactivates again the

internal circuit by switching off the internal Bias. The

gate G11 is released as after entering Active Burst

Mode the burst flag is set. If working in Active Burst

Mode the FB voltage is changing like a saw tooth

between 3.4V and 4V (see Figure 19).

3.6.2.3 Leaving Active Burst Mode

The FB voltage immediately increases if there is a high

load jump. This is observed by comparator C4. As the

current limit is ca. 26% during Active Burst Mode a

certain load jump is needed that FB can exceed 4.8V.

At this time C4 resets the Active Burst Mode which also

Version 2.3

02 Apr 2013

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