AN30180A

12

Ver. AEB

OPERATION (Continued)

1. Power ON / OFF sequence

UVLO

VOUT

BGR

(1)(2) (3)

(5)

DCDC_ON

EN

SS

(4)

25

μs

the BGR start-up.

(2) When the BGR exceeds its threshold value, the

UVLO is released and the SS(SOFT START)

sequence is enabled.

During soft start the current limit of DC-DC Step

Down Regulator is set to be lower than Normal

current limit

for preventing rush current.

Internal circuit power supply is turned on and wait for

the time determined by internal timer.

(3) DCDC_ON is turned on then DC-DC Step Down

Regulator is enabled. VOUT is risen up to reaches

the set voltage.

(4) After a Soft start timer current limit is set to be

Normal current limit.

(5) When the EN pin is set to “Low”, the BGR and UVLO

stop operation. The VOUT pin voltage starts to drop

by output discharge resister and load resistance.

2. Protection

Output Over-Current Protection (OCP) function and

Short-Circuit Protection (OSP) function

(1) The Over-Current Protection is activated at about

1.8 A (Typ.).

During the OCP, the output voltage continues to

drop at the specified current.

(2) The Short-Circuit Protection function is

implemented when the output voltage decreases

and the VFB pin reaches to about 70 % of the

output voltage setting.

(3) The OSP operates intermittently at 2ms-ON,

16ms-OFF intervals.

Figure : OCP and OSP Operation

Output current [A]

Pendency

characteristics

(Ground short

protection detection

- about 70 % of Vout )

Intermittent

operation area

Over Current Protection (typ:1.8 A)

about 150 mA

(1)

(2)

(3)

VOUT

DCDC_ON

OSP

(3)

IOUT

(1)

(2)

16 ms

2 ms

16 ms

2 ms

SS

(2)

1.3 to 2.3 A

Note) The characteristics listed below are reference values derived from the design of the IC and are not guaranteed.