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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

V

In PSAVE mode, V

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

been reached, the switching is stopped and the quiescent

current is reduced. V

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

mode, the load must be increased, causing V

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

at +1.5% above V

V

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,

V

OUT

= Output voltage

V

IN

= Input voltage

I

OUT

= Output current

R

DSP

= PMOS switch ON resistance

R

IND

= Series resistance of the inductor

)

R

(R

I

V

V

IND

DSP

OUT

IN

OUT

)

R

(R

I

V

V

IND

DSP

OUT

IN

OUT

Minimum V

2.7

2.75

2.8

2.85

2.9

2.95

3

0.05

0.1

0.15

0.2

0.25

0.3

Inductor DC R esistance

(

Ω

)

Power Save Operation

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