[AP3440]

016008997-E-00

2016/10

- 9 -

11. Functional Descriptions

11.1 Normal Operation

The AP3440 operates by PWM control in current mode. It integrates feedback resistances and the

output voltage is 1.227V typ. A potential difference of the feedback output voltage of the VO1/2 pin and

internal reference voltage is amplified by the error amplifier to set a target value of the coil current. An

internal current sense circuit detects the coil current. Synchronous rectification is executed as the

internal high-side P-channel MOSFET is turned off and low-side N-channel MOSFET is turned on when

the coil current reaches a target value after internal high-side P-channel MOSFET is turned on.

11.2 External Synchronous Function

The AP3440 synchronizes the driving frequency to a falling edge (“H”

→ “L”) of input clock to the FSIN

pin. Frequency of the input clock must be in a range from 1800kHz to 2250kHz and the “L” period should

be in a range from 100ns to 384ns. When using an internal oscillation frequency, the FSIN pin should be

open or connected to the SGND and PGND pins. Note that switching operation is stopped if the FSIN pin

is fixed to “H” level since a falling edge of the internal clock is not generated.

Figure 7. External Synchronous Timing Chart

11.3 Extrenal Synchronous Clock Output

An inverted clock of the driving frequency generated internally is output from the FSO pin. The AP3440

outputs an inverted clock of the external synchronous clock when inputting an external synchronous

clock.

11.4 Power Good Function

The AP3440 has a power good function that indicates the output voltage status by the PG pin. The PG

pin must be pulled up by a resistor connected to the VIN pin since the PG pin is an open drain output of

N-channel MOSFET (hereinafter PG_MOS). The PG-MOS is turned off when the output voltage is in a

range of PWGDH and PWGDL for 10ms. The PG-MOS is turned on when the output voltage is out of the

power-good range for more than 2us continuously. The PG-MOS is always ON during power-off status

and soft start operation. Refer to the section “9. Electrical Characteristics” about PWGDH and PWGDL.