11

NN30312A

Ver. CEB

OPERATION

1. Protection

(1).Output Over-Current Protection (OCP) function

And Short-Circuit Protection (SCP) function

1) The Over Current Protection is activated at about 15

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 60 % of the set voltage of 0.6 V.

3) The SCP operates intermittently at 2 ms-ON, 16 ms

OFF intervals.

FCCM

High

Skip

Low

Mode

MODE pin

(2).Switching Frequency Setting

The IC can operate at three different frequency : 1250

kHz, 750 kHz and 250 kHz.

The Switching Frequency can be set by FSEL pin as

follows.

750

Open

High

Low

FSEL pin

1250

250

Frequency [kHz]

2. Pin Setting

(1).Operating Mode Setting

The IC can operate at two different modes : Skip mode

and Forced Continuous Conduction mode (FCCM).

In Skip mode, the IC is working under pulse skipping

mechanism to improve efficiency at light load condition.

In FCCM mode, the IC is working at fixed frequency to

avoid EMI issues.

The Operating Mode can be set by MODE pin as follows.

(3).Thermal Shut Down (TSD)

When the IC internal temperature becomes more than

about 130

°C, TSD operates and DCDC turns off.

(2).Over Voltage Detection (OVD) and Under Voltage

Detection (UVD)

1).The NMOS connected to the PGOOD pin turns ON

when the output voltage rises and the VFB pin voltage

reaches 115 % of its set voltage (0.6 V).

2).After (1) above, the NMOS connected to the PGOOD

pin is turned OFF after 1 ms when the output voltage

drops and the VFB pin voltage reaches 110 % of its set

voltage (0.6 V).

3).The NMOS connected to the PGOOD pin turns ON

when the output voltage drops and the VFB pin

voltage reaches 85 % of its set voltage (0.6 V).

4).After (3) above, the NMOS connected to the PGOOD

pin is turned OFF after 1 ms when the output voltage

drops and the VFB pin voltage reaches 90 % of its set

voltage (0.6 V).

Figure : OCP and SCP Operation

Output current [A]

Pendency

characteristics

(Ground short

protection Detection

about 60% of Vout )

Intermittent

operation area

Over Current Protection ( typ : 15 A )

about 2 A

1)

2)

3)

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

Figure : OVD and UVD Operation

115 %

110 %

90 %

85 %

0.6 V

0.6 V

VFB

PGOOD

1 ms

1 ms

Note: PGOOD Pin is pulled up to VREG pin

1)

2)

3)

4)

10.5 A to 20.5 A