SC196AEVB datasheet(8/17 Pages) SEMTECH

8 / 17 page

www.semtech.com

SC196A

PRELIMINARY

POWER MANAGEMENT

Applications Information (Cont.)

Power Save Mode Operation

The PSAVE mode may be selected by tying the SYNC/

PWM pin to GND. Selecting PSAVE mode will enable the

SC196A to automatically activate/deactivate operation

at light loads, maximizing efﬁciency across the full load

range. The SC196A automatically detects the load current

at which it should enter PSAVE mode. The SC196A is

optimized to track maximum efﬁciency with respect to

IN.

In PSAVE mode, V

OUT is driven from a lower level to an

upper level by a switching burst. Once the upper level has

been reached, the switching is stopped and the quiescent

current is reduced. V

OUT falls from the upper to lower levels

in this low current state as the load current discharges

the output capacitor. The burst-to-off period in PSAVE will

decrease as the load current reduces.

The PSAVE switching burst frequency is controlled so that

the inductor current ripple is similar to that in PWM mode.

The minimum switching frequency during this period is

limited to 650kHz.

The SC196A automatically detects when to exit PSAVE

mode by monitoring V

OUT . For the SC196A to exit PSAVE

mode, the load must be increased, causing V

OUT to

decrease until the power save exit threshold is reached.

PSAVE levels are set high to minimize the undershoot

when exiting PSAVE. The lower PSAVE comparator level

is set +0.7% above V

OUT, and the upper comparator level

at +1.5% above V

OUT with the exit threshold at -2% below

OUT.

If PSAVE operation is required, then a 22μF output

capacitor must be used.

100% Duty Cycle Operation

The 100% duty cycle mode may be selected by connecting

the MODE pin high. This will allow the SC196A to maintain

output regulation under low input voltage/high output

voltage conditions.

In 100% duty cycle operation, as the input supply drops

toward the output voltage, the PMOS on-time increases

linearly above the maximum value in ﬁxed-frequency

operation until the PMOS is active continuously. Once

the PMOS is switched on continuously, the output voltage

tracks the input voltage minus the voltage drop across

the PMOS power device and inductor according to the

following relationship:

where,

OUT

= Output voltage

= Input voltage

OUT

= Output current

DSP

= PMOS switch ON resistance

IND

= Series resistance of the inductor

)

IND

DSP

OUT

)

IND

DSP

OUT

Minimum V

IN for Fixed Frequency Operation Vs. RIND

2.7

2.75

2.8

2.85

2.9

2.95

0.05

0.1

0.15

0.2

0.25

0.3

Inductor DC R esistance

(

)

VOUT = 1.8V

IOUT =1A

Power Save Operation

VOUT

0.7%

1.5%

PSAVE Mode at Light Load

PWM Mode at Medium/

High Load

-2%

BURST

OFF

Higher Load

Applied

0 A

Inductor Current

Time

SC196AEVB датащи(PDF) 8 Page - Semtech Corporation

SC196AEVB датащи(HTML) 8 Page - Semtech Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

датащи скачать

ссылки URL