IX9908 datasheet(8/10 Pages) IXYS

8 / 10 page

INTEGRATED CIRCUITS DIVISION

IX9908

www.ixysic.com

R01

The variation in AC line voltage is sensed by way of

the auxiliary winding and an internal clamp and

current sense circuit. When Q1 is on, a negative

voltage proportional to the line voltage is coupled to

the auxiliary winding; the IC will hold the ZCV pin very

close to ground during this time. The line voltage is

thus sensed indirectly through the current in RZCV1.

This current is given by:

The device uses IZCV to vary the VCS limit as shown in

Figure 4. The actual implementation is digital and is

shown below:

Figure 5. VCS vs. IZC

2.3.4 Protection Functions

The IX9908 provides comprehensive protection

features. They are summarized in the table below:

OUTPUT OVER-VOLTAGE

During the Q1 off-time the auxiliary winding voltage

(VAUX) will swing positive and in proportion to the

secondary voltage. VAUX is connected to ZCV through

a resistor divider. If the voltage at ZCV exceeds a

preset threshold (VZCVOVP) for longer than the blanking

time (tZCVOVP), then the IC is latched off.

SHORTED WINDING

If the voltage at CS exceeds a preset threshold

(VCSSW) during Q1 on time the device is latched off.

OVER-TEMPERATURE

If the die temperature exceeds 140°C, then the device

will enter the Auto-Restart Mode.

VCC OVER-VOLTAGE / UNDER-VOLTAGE

The IC continuously monitors the VCC voltage. In case

of an over-voltage, Q1 is turned off (GD=L) and VCC

will begin to fall. Once VCC goes below VVCC_off (10.5V

nominal), the startup circuit is activated, and begins to

charge CVCC. When VCC exceeds VVCC_on (18.0V

nominal), the device initiates a new soft-start. For an

under-voltage the operation is the same except that

the sequence begins with VCC < VVCC_off so GD=L and

the startup circuit is activated. This operation

describes the Auto-Restart Mode.

During Latch-Off Mode, VCC also cycles between

VVCC_off and VVCC_on, but GD remains low, and no

soft-start is initiated. The line voltage must be turned

off and on again to begin normal operation.

IZCV =

VIN • Na

RZCV1 • Np

ZC (µA)

200

600

1000

1400

1800

2200

0.60

0.65

0.70

0.75

0.80

0.85

0.90

0.95

1.00

1.05

CS vs. IZC

Fault Condition

Action Taken

Output Over-Voltage

GD Latched Off

Shorted Winding

GD Latched Off

Over-Temperature

Auto-Restart Mode

VCC Over-Voltage

Auto-Restart Mode

VCC Under-Voltage

Auto-Restart Mode

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