STEP-DOWN, SYNCHRONOUS PWM CONTROL SWITCHING REGULATOR CONTROLLER

S-8533 Series

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3. ON/OFF Pin (Shutdown Pin)

This pin is used to activate and deactivate the step-down operation.

When the ON/OFF pin is set to “L”, all the internal circuits stop working, and substantial savings in current

The ON/OFF pin is configured as shown in

Figure 8. Since pull-up or pull-down is not performed internally,

operation where the ON/OFF pin is in a floating state should be avoided. Application of a voltage of 0.3 to 1.8 V to

the pin should also be avoided lest the current consumption increases. When the ON/OFF pin is not used, it should

be connected to the VIN pin.

ON/OFF

Figure 8 ON/OFF Pin Structure

ON/OFF Pin

CR Oscillation

Circuit

Output

Voltage

“H”

Active

Set value

“L”

Non-active

Open

4. 100% Duty Cycle

The S-8533 Series operates with a maximum duty cycle of 100%. The switching transistor can be kept on to supply

current to the load continually, even in cases where the input voltage falls below the preset output voltage value.

The output voltage under these circumstances is equal to the subtraction of the lowering due to the DC resistance

of the coil and the on-resistance of the switching transistor from the input voltage.

5. Back-Flow Current

Since the S-8533 Series performs PWM synchronous rectification under a light load, current flows backward in the

Figure 9). Pay attention

to the maximum back-flow current value, which can be calculated from the following expressions.

Figure 10, flows backward.

current is absorbed by the input capacitor. The input capacitor is indispensable to reduce back-flow current to the

power source.