FAN48632 datasheet(10/13 Pages) FAIRCHILD

部件名	FAN48632

功能描述	2.5 MHz, 2.0 A Pulsed-Load Synchronous TinyBoost

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制造商	FAIRCHILD [Fairchild Semiconductor]

网页	http://www.fairchildsemi.com

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FAN48632

• Rev. 1.0.3

10

Bypass Operation

In normal operation, the device automatically transitions from

Boost Mode to Bypass Mode, if VIN goes above target VOUT. In

Bypass Mode, the device fully enhances both Q1 and Q3 to

provide a very low impedance path from VIN to VOUT. Entry to

the Bypass Mode is triggered by condition where VIN > VOUT

and no switching has occurred during past 5 µs. To soften the

entry to Bypass Mode, Q3 is driven as a linear current source

for the first 5 µs. Bypass Mode exit is triggered when VOUT

reaches the target VOUT voltage. During Automatic Bypass

Mode, the device is short-circuit protected by voltage

comparator tracking the voltage drop from VIN to VOUT; if the

drop exceeds 200 mV, a FAULT is declared.

With sufficient load to enforce CCM operation, the Bypass

Mode to Boost Mode transition occurs at the target VOUT. The

corresponding input voltage at the transition point is:

BYP

ON

DS

P

ON

DS

L

LOAD

OUT

IN

R

DCR

I

V

)

(

)

(

||

)

(









EQ. 1

The Bypass Mode entry threshold has 25 mV hysteresis

imposed at VOUT to prevent cycling between modes. The

transition from Boost Mode to Bypass Mode occurs at the

target VOUT+25 mV. The corresponding input voltage is:

)

(

25

)

(

P

ON

DS

L

LOAD

OUT

IN

R

DCR

I

mV

V









EQ. 2

Forced Bypass

Entry to Forced Bypass Mode initiates with a current limit on

Q3 and then proceeds to a true bypass state. To prevent

reverse current to the battery, the device waits until output

discharges below VIN before entering Forced Bypass Mode.

Low-IQ Forced Bypass Mode is available for the FAN48632.

After the transition is complete, most of the internal circuitry is

disabled to minimize quiescent current draw. OCP, UVLO,

output OVP and over-temperature protections are inactive in

Forced Bypass Mode.

In Forced Bypass Mode, VOUT can follow VIN below VOUT(MIN).

VSEL

VSEL can be asserted in anticipation of a positive load

transient. Raising VSEL increases VOUT(MIN) by a fixed amount

and VOUT is stepped to the corresponding target output voltage

in 20 µs. The functionality can also be utilized to mitigate

undershoot during severe line transients, while minimizing

VOUT during more benign operating conditions to save power.

类似零件编号 - FAN48632

制造商	部件名	数据表	功能描述
ON Semiconductor	FAN48632	1Mb / 15P	Pulsed-Load Synchronous TinyBoost Regulator with Bypass Mode for GSM PA Supply April 2014 Rev. 1.0.3
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	FAN48632UC33X	1Mb / 15P	Pulsed-Load Synchronous TinyBoost Regulator with Bypass Mode for GSM PA Supply April 2014 Rev. 1.0.3
	FAN48632UC35X	1Mb / 15P	Pulsed-Load Synchronous TinyBoost Regulator with Bypass Mode for GSM PA Supply April 2014 Rev. 1.0.3

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