Document Number: 002-08393 Rev.*A

Page 21 of 37

MB39C601

9. Various Protection Circuits

9.1

Under Voltage Lockout Protection (UVLO)

The under voltage lockout protection (UVLO) protects IC from malfunction and protects the system from destruction/deterioration

during the transient state and momentary drop due to start up for the power supply pin voltage (VDD). The voltage decrease of the

VDD pin is detected with comparator, and output HS DRIVER is turned off and output DRIVER is turned off, and the switching is

stopped.The system returns if the VDD pin becomes more than the threshold voltage of the UVLO circuit.

9.2

Over Voltage Proteciton (OVP)

When LED is in the state of open and the output voltage rises too much, the voltage of Auxiliary Winding and the voltage of the

TZE pin rise. The over voltage is detected by sampling this voltage of the TZE pin. When TZE pin voltage rises more than the

threshold voltage of OVP, the over voltage is detected. Output HS DRIVER is turned off, and output DRIVER is turned off, and the

switching is stopped. (latch-off)

If the VDD pin becomes below the voltage of Fault Latch Reset, OVP is released.

9.3

Over Load Protection (OL)

When the cathode or the anode of LED is short to GND and it becomes an overloaded status at switching frequency control, the

current does not flow into Rs and there is no current feedback to IFB. The current of the FB pin detects the overload with 1.5µA or

Shutdown/retry

…

MB39C601 becomes two states of switching on for 250ms and switching off for 750ms. These

states are repeated. If it is not OL status, it returns.

Latch-off

…

The switching is continued for 250ms. If it does not return from OL states for this period, output HS

DRIVER is turned off, and output DRIVER is turned off, and the switching is stopped. If it returns

from OL states after this time and the switching is still stopped (latch-off) and the VDD pin

becomes below the voltage of Fault Latch Reset, Latch is released.

Over Load Protection Sequencing

9.4

Over Temperature Protection (OTP)

The over temperature protection (OTP) is a function to protect IC from the thermal destruction.When the junction temperature

reaches +150°C,output HS DRIVER is turn off, and output DRIVER is turned off, and the switching is stopped.It returns again when

the junction temperature falls to +125°C (automatic recovery).