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<Lx Overvoltage Limit Circuit>

XC9133 series' Lx overvoltage limit circuit monitors the Lx pin voltage.

When the Lx pin voltage exceeds than 19V (TYP.),

the IC performs the function of latching the OFF state of the driver transistor, and goes into operation suspension mode.

The suspension mode does not mean

a complete shutdown, but a state in which pulse output is suspended; therefore, the internal circuitry remains in operation.

<Maximum Duty Cycle Limit>

The XC9133 series' maximum duty cycle limit circuit monitors the duty cycle.

When the maximum duty cycle is repeated

for a certain time, the IC controls the error amplifier output so that the duty cycle of the next pulse becomes smaller than

that of the first pulse.

<CE Pin Function>

The operation of the XC9133 series will enter into the shut down mode when a low level signal is input to the CE pin.

During the shut down mode, the supply current is 0

μA (TYP.), with high impedance at the Lx pin. The IC starts its

operation with a high level signal to the CE pin.

The input to the CE/MODE pin is a CMOS input and the sink current is 0

μA (TYP.). 100μs after disable, the IC goes into suspension mode and supply current is minimal. After this, the IC will

be in stand-by mode and the supply current will be 0

μA (TYP.).

5mA

40

Ω

13.3mA

15

Ω

10mA

20

Ω

20mA

10

Ω

■OPERATIONAL EXPLANATIONS (Continued)

<Current Limit>

The current limit circuit of the XC9133 series monitors the current flowing through the N-channel MOS driver transistor

connected to the Lx pin, and features a combination of the constant-current type current limit mode and the duty cycle limit

of the next pulse.

1When the driver current is greater than a specific levels, the constant-current type current limit function operates to

turn off the pulses from the Lx pin at any given timing.

2The IC controls the next pulse to be smaller than the first pulse.

■NOTES ON USE

<Lx (Pin 1): Switch Pin>

Please connect the anode of a Schottky barrier diode and an inductor to the Lx pin.

<FB (Pin 3): Voltage Feedback Pin>

The reference voltage is 200mV (TYP.).

LEDs and a constant current value.

The resistance value can be calculated by the following equation.

constant current value

Typical example:

<CE (Pin 4): Chip Enable Pin>

An ENABLED state is reached when the CE voltage exceeds 0.65V and a DISABLED state when the CE Voltage falls below

0.2V.

Current Limit

Current Limit

The current will be off when the coil current

reached the value of the constant current limit.

Limit some duty pulses after the limit.