FAN53541 データシートの表示（PDF） - Fairchild Semiconductor

部品番号

コンポーネント説明

一致するリスト

FAN53541

2.4 MHz, 5 A TinyBuck™ Synchronous Buck Regulator

Fairchild Semiconductor 

PGOOD Pin

The PGOOD pin is an open-drain that indicates that the IC is

in regulation when its state is open. PGOOD pulls LOW

under the following conditions:

 The IC has operated in cycle-by-cycle current limit for

eight consecutive PWM cycles;

 The circuit is disabled, either after a fault occurs or when

EN is LOW; or

 The IC is performing a soft-start.

Thermal Shutdown

When the die temperature increases, due to a high load

condition and/or a high ambient temperature, the output

switching is disabled until the temperature on the die has

fallen sufficiently. The junction temperature at which the

thermal shutdown activates is nominally 155°C with a

20°C hysteresis.

Minimum Off-Time Effect on Switching

Frequency

tOFF(MIN) is 45 ns, which constrains the maximum VOUT/VIN

that the FAN53541 can provide, while still maintaining a fixed

switching frequency in PWM Mode. Regulation is maintained

even though the regulator is unable to provide sufficient

duty-cycle and operate at 2.4 MHz.

Switching frequency is the lower of 2.4 MHz or:

fSW (MHz)  22.2  1

VOUT  IOUT  ROFF

VIN  IOUT  (ROFF  RON )



(4)

where:

IOUT = load current, in A;

RON = RDS(ON)_P + DCRL, in Ohms; and

ROFF = RDS(ON)_N + DCRL, in Ohms.

A result of <0 MHz indicates 100% duty cycle operation.

Application Information

Selecting the Inductor

The output inductor must meet both the required inductance

and the energy handling capability of the application. The

inductor value affects the average current limit, output

voltage ripple, transient response, and efficiency.

The ripple current (∆I) of the regulator is:

I 

VOUT

VIN





VIN

L

 VOUT

 fSW



(5)

The maximum average load current, IMAX(LOAD), is related to

the peak current limit, ILIM(PK), by the ripple current as:

IMAX(LOAD)



ILIM(PK)



I

2

(6)

The FAN53541 is optimized for operation with L=470 nH, but

is stable with inductances up to 1.2 H (nominal). The

inductor should be rated to maintain at least 80% of its value

at ILIM(PK). Failure to do so lowers the amount of DC current

the IC can deliver.

Efficiency is affected by the inductor DCR and inductance

value. Decreasing the inductor value for a given physical

size typically decreases the DCR; but since ∆I increases, the

RMS current increases, as do core and skin-effect losses.

IRMS 

IOUT(DC)2



I2

12

(7)

The increased RMS current produces higher losses through

the RDS(ON) of the IC MOSFETs as well as the inductor ESR.

Increasing the inductor value produces lower RMS currents,

but degrades transient response. For a given physical

inductor size, increased inductance usually results in an

inductor with lower saturation current.

Table 3 shows the effects on regulator performance of higher

inductance than the recommended 470 nH.

Table 3. Inductor Value and Regulator

Performance

IMAX(LOAD)

Increase

∆VOUT (Eq.(8))

Decrease

Transient Response

Degraded

Inductor Current Rating

The FAN53541’s current-limit circuit can allow a peak current

of about 8.8 A to flow through L1 under worst-case

conditions. If it is possible for the load to draw that much

continuous current, the inductor should be capable of

sustaining that current or failing in a safe manner.

For space-constrained applications, a lower current rating for

L1 can be used. The FAN53541 may still protect these

inductors in the event of a short circuit, but may not be able

to protect the inductor from failure if the load is able to draw

higher currents than the DC rating of the inductor.

© 2013 Fairchild Semiconductor Corporation

FAN53541 • Rev. 1.0.2

11

www.fairchildsemi.com

Share Link: