SC1112STRT datasheet(17/23 Pages) SEMTECH

17 / 23 page

 2006 Semtech Corp.

www.semtech.com

POWER MANAGEMENT

SC1112

Adjustable Output Voltage Option

The adjustable output voltage option does not have an

internal resistor divider. The adjust pin connects directly to

the inverting input of the error amplifier, and the

output voltage is set using external resistors (please

refer to Figure 2). In this case, the adjust pin sources a

nominal 0.5µA, so the resistor values should be selected

to allow 50µA to flow through the divider. Again, a target

value

for

(maximum)

can

calculated:

Ω

≤

200

The output voltage can be calculated as follows:

200

VOUT

•

−











 +

•

The maximum output voltage that can be obtained from

the adjustable option is determined by the input supply

voltage and the R

DS(ON) and gate threshold voltage of the

external MOSFET. Assuming that the MOSFET gate

threshold voltage is sufficiently low for the output

voltage chosen and a worst-case drive voltage of 9V, V

OUT(MAX)

is given by:

)

MAX

)(

(

)

MAX

(

OUT

)

MIN

(

)

MAX

(

OUT

VTTIN

•

−

Applications Infomation (Cont.)

Figure 1: Adjusting The Output Voltage of VTT or AGP

SC1112

PWRGD

DELAY

5VSTBY

VTTSEL

AGPSEL

GND

CAP+

CAP-

VTTGATE

VTTSEN

AGPGATE

AGPSEN

ADJGATE

ADJSEN

VTTIN

C14

330u

AGP SELECT Signal

330u

AGP

C17

0.1u

C16

330u

0.1u

10u

C18

330u

VTT SELECT Signal

+3.3V

+5V STBY

0.1u

VTT

C19

330u

SC11

PWRGD

DELAY

5VSTBY

CAP+

CAP-

ADJGATE

ADJSEN

C12

330u

POWER GOOD

22n

C10

C13

0.1u

C11

0.1u

330u

VTT

Figure 2

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