FAN53611(2012) データシートの表示（PDF） - Fairchild Semiconductor

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FAN53611
(Rev.:2012)

6 MHz 600 mA / 1 A Synchronous Buck Regulator

Fairchild Semiconductor 

Under-Voltage Lockout (UVLO)

The calculation for switching frequency is given by:

When EN is HIGH, the under-voltage lockout keeps the part

from operating until the input supply voltage rises high

enough to properly operate. This ensures no misbehavior of

fSW



min





tSW

1

( MAX

)

,

6MHz





(3)

the regulator during startup or shutdown.

where:

Thermal Shutdown (TSD)

When the die temperature increases, due to a high load

tSW (MAX )



40ns



1



VOUT 

VIN  IOUT

IOUT  ROFF

 RON  VOUT



(4)

condition and/or a high ambient temperature; the output

switching is disabled until the die temperature falls sufficiently.

where:

The junction temperature at which the thermal shutdown

activates is nominally 150°C with a 15°C hysteresis.

ROFF = RDSON _ N  DCRL

Minimum Off-Time Effect on Switching

Frequency

RON = RDSON _ P  DCRL

tOFF(MIN) is 40 ns. This imposes constraints on the maximum

VOUT that the FAN53601/11 can provide or the maximum

VIN

output voltage it can provide at low VIN while maintaining a

fixed switching frequency in PWM Mode.

When VIN is LOW, fixed switching is maintained as long as:

VOUT

VIN

 1 tOFF(MIN )  fSW

 0.7 .

The switching frequency drops when the regulator cannot

provide sufficient duty cycle at 6 MHz to maintain regulation.

This occurs when VOUT is 1.82 V and VIN is below 2.7 V at

high load currents (see Figure 32).

7,500

6,000

4,500

3,000

2.7VIN, AUTO

2.3VIN, AUTO

2.7VIN, PWM

2.3VIN, PWM

1,500

0

0

200

400

600

800

1000

Load Current (mA)

Figure 32. Frequency vs. Load Current to Demonstrate

tOFFMIN Effect, VIN=2.3 V and 2.7 V, VOUT=1.82 V,

Auto Mode, FPWM Dotted

© 2010 Fairchild Semiconductor Corporation

FAN53601 / FAN53611 • Rev. 1.0.1

10

www.fairchildsemi.com

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