MV1002SC

7

2.1 Starting sequence

The MV1002SC starts up when a voltage equal to or exceeding the starting voltage (Vcc_start) is supplied to the Vcc

pin from an external power supply. To ensure stable operations, the signal should be sent to the REF pin when the Vcc

voltage is equal to or greater than the Vcc_start.

Figure 3 shows an example of a starting operation in the Vcc->REF sequence, using the circuit configuration shown in

Figure 1.

In a normal start operation, oscillations start when the Vcc voltage reaches Vcc_start. As the output voltage rises, the

Svin voltage crosses the Svout voltage, enabling zero current detection. (Figure 3(a) Starting operation OK)

When it is difficult to charge the output capacitor—for instance, when the resistance of the gate resistor R4 is large or

when the resistance of a dummy resistor connected in parallel with LED is small—the output voltage may not rise after

oscillation has started and zero current detection may be disabled. When zero current detection cannot be performed, the

IC is forcibly switched over to the restart operation, in which the minimum on-time and maximum off-time are used, instead

of the normal peak current detection operation. When zero current detection is left disabled, the restart operation

continues and LED will not light. (Figure 3(b) Starting operation NG)

Be sure to measure the Svin and Svout voltages at the start of the actual apparatus to confirm that zero current

detection is enabled.

Figure 3(a) Starting operation OK

Figure 3(b) Starting operation NG

Vi

Vcc

Svout

Svin

Vcc_start=7.2V

Vo

Io

定格電流

Gate

Svin

Svout

IL

REF

Vth_REF

Rated current

Rated current

CAT.No.1A0202-2E