[AP3603]

015000004-E-02

2015/07

- 9 -

10.8

CC1 and CC2 Pin Voltage (Error Amplifier output) Clamping Function

The voltage of CC pin (CC1 and CC2) which is the output of error amplifier stays around 1.2V (SS pin

voltage) under the condition of normal PWM operation. The feedback response goes worse in case the

voltage difference between CC pin (CC1 and CC2) and 1.2V becomes large under the abnormal condition

like the output voltage beyond setting voltage. It causes the over shoot or under shoot. The AP3603 clamps

the voltage of CC pin (CC1 and CC2) as below to prevent CC pin (CC1 and CC2) voltage from going out of

a normal operating condition

Detect condition

Release condition

Operation

CCx pin voltage≦0.9V

or

FBx pin voltage≦3.6V×75%

Switching command has requested

or

FBx pin voltage≧3.6V×85%

CCx pin connects to SS pin and

Error Amplifier output

disconnect to CCx pin

10.9

External Synchronous Operation

External synchronization is available by an input timing signal to the FSYN pin. The AP3603 enters external

synchronous operation mode when edge of FSYN turns off the external MOSFET connected to DRV2. If the

high level input of FSYN continues more than 1 cycle of internal CLK, the AP3603 change the

synchronization from external clock to internal oscillator. The input signal to the FSYN pin for

synchronization must be 50% duty. FSYN pin must be open in case of no use of external synchronous

operation. The AP3603 does not operate if FSYN pin connect to GND because internal OSC does not

generate the clock signal. At the case of using an external synchronous operation, FSYN pin must be open

before and during startup. And input the external clock to FSYN pin after V8 voltage reach the target (8V

) approximately.

Hi入力時は内部CLK優先

固定オフ時間

外部同期可能

外部同期可能

外部同期開始

外部同期解除

内部発振

50%

内部CLK

内部発振

50%

50%

50%

外部同期

FSYN(外部CLK)

DRV1

DRV2

Figure 2. External Synchronous Timing Chart

Internal OSC

Internal OSC

External SYNC

Precede internal clock in input High

Fixed OFF time

Available

external

Sync

Available

external

Sync

Enter

external

Sync

Exit

external

Sync

FSYN

(External CLK)

Internal CLK

DRV1

DRV2