AP3015 datasheet(8/11 Pages) BCDSEMI

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MICRO POWER STEP-UP DC-DC CONVERTER

AP3015/A

Aug. 2006 Rev. 1. 0

BCD Semiconductor Manufacturing Limited

Preliminary Datasheet

Figure 13. Efficiency

Typical Performance Characteristics (Continued)

Figure 12. Efficiency

Unless otherwise noted, VIN=1.2V

Application Information

Operating Principles

AP3015/A feature a constant off-time control scheme.

Refer to Figure 3，the bandgap voltage VREF (1.23V

typical) is used to control the output voltage.

When the voltage at the FB pin drops below the lower

hysteresis point of Feedback Comparator (typical

hysteresis is 8mV), the Feedback Comparator enables

the chip and the NPN power switch is turned on, the

current in the inductor begins to ramp up and store

energy in the coil while the load current is supplied by

the output capacitor. Once the current in the inductor

reaches

the

current

limit,

the

Current-Limit

Comparator resets the 400ns One-Shot which turns off

the NPN switch for 400ns. The SW voltage rises to the

output voltage plus a diode drop and the inductor

current begins to ramp down. During this time the

energy stored in the inductor is transferred to COUT

and the load. After the 400ns off-time, the NPN switch

is turned on and energy will be stored in the inductor

again.

This cycle will continue until the voltage at FB pin

reaches 1.23V, the Feedback Comparator disables the

chip and turns off the NPN switch. The load current is

then supplied solely by output capacitor and the output

voltage will decrease. When the FB pin voltage drops

below the lower hysteresis point of Feedback

Comparator, the Feedback Comparator enables the

device and repeats the cycle described previously.

Under not switching condition, the IQ of the device is

about 17

µA.

The AP3015/A contain additional circuitry to provide

protection during start-up or under short-circuit

conditions. When the FB pin voltage is lower than

approximately 0.6V, the switch off-time is increased

to 1.5

µs and the current limit is reduced to about

250mA (70mA for AP3015A). This reduces the

average inductor current and helps to minimize the

power dissipation in the AP3015/A power switch, in

the external inductor and in the diode.

The SHDN pin can be used to turn off the AP3015/A

and reduce the IQ to less than 1µA. In shutdown mode

the output voltage will be a diode drop below the input

voltage.

0.1

Load Current (mA)

AP3015

OUT

=20V, L=10µH, C

OUT

=1µF

Refer to Figure 14

=4.2V

=3.3V

=2.5V

0.1

Load Current (mA)

AP3015A

OUT

=3.3V, L=10µH, C

OUT

=20µF

Refer to Figure 15

=2.5V

=1.2V

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