AP4460 datasheet(8/18 Pages) AKM

8 / 18 page

[AP4460]

014012310-E-01

2015/04

- 8 -

10 . Functional Descriptions

10.1 Operation

The AP4460 is a synchronous step-up DC-DC converter that can be activated by a single solar cell. The IC

has a power management function which supplies power to an external system, charges super capacitors, or

controls the power path to supply power from the super capacitor to the external system.

The AP4460 can be

operated from 0.35V (typ) at the VIN pin. The start-up circuit is operated when VVIN voltage reaches VINSTUP.

Then, the internal charge pump circuit boosts VVIN voltage and charges the capacitor connected to the VCP

pin (CVCP). When the VCP voltage reaches enough level, the internal start-up circuit switches the N-channel

MOSFET transistor (S1) and charges the external capacitor connected to the VD pin (CVD). The start-up

circuit is stopped when the VD voltage reaches VPORH level, then the DC-DC converter starts the operation.

When the VD voltage drops to the level less than VPORL, the DC-DC converter stops and the start-up circuits

is operated again.

Figure 2. State transition of Start-up and DC-DC operation

The DC-DC converter activates the N-channel MOSFET transistor (N1) during TON period to charge the coil.

After TON period, the energy stored in the coil is charged to the CVD capacitor by a power switching of N1

transistor (becomes OFF) and the P1 transistor (becomes ON). The control circuits of the DC-DC sets the P1

transistor off when the SW voltage becomes less than the VD voltage, and then the N1 transistor turns on. The

operation of DC-DC converter is controlled by three reference voltages such as VDSET, MPPL and MPPH

voltages. The VDSET voltage controls the output voltage level (VVDTGT) of DC-DC converter. When the VD

voltage reaches VVDTGT level, the DC-DC converter stops the switching operation and enters 'Skip' state to save

current consumption. When the VD voltage becomes less than VVDTGT - VVDTGTHYS, the DC-DC converter goes to

'Switching' state and boosts the VD voltage. The inputs of the MPPH pin and the MPPL pin (VMPPH and VMPPL)

control the input voltage of the DC-DC converter (VVIN) for effective voltage level of a solar cell. When the VVIN

voltage becomes less than VMPPTL voltage, the DC-DC converter stops switching operation and goes to Skip state

until VVIN voltage reaches VMPPTH voltage. By adjusting input levels of the MPPH pin and the MPPL pin (VMPPH

and VMPPL), the maximum output solar power can be efficiently generated.

The DDCONB (N-channel MOSFET open drain) pin outputs “L” when VVIN voltage is in between VMPPL and

VMPPH. The DC-DC converter has the over voltage protection function for the VD pin. When the VD voltage

exceeds VOV level, the DC-DC converter transitions to Skip state to prevent further voltage increase. When the

VD voltage becomes lower than VOV-VOVHYS, the converter restarts switching operation.

Figure 3. State Transition of DC-DC Operation

AP4460 Datasheet(PDF) 8 Page - Asahi Kasei Microsystems