SC604A datasheet(4/18 Pages) SEMTECH

4 / 18 page

 2005 Semtech Corp.

www.semtech.com

SC604A

POWER MANAGEMENT

Definitions

LED Accuracy

The LED current is determined by the R

SET resistor (ILED

vs. R

SET data is found on pages 9 and 10).

This term

does not include the tolerance of the resistor R

SET.

maximum accuracy is required, a precision resistor is

needed. To calculate the error I

LED-ERR[%], use the formula

LED-ERR [%] = ±

Current Matching

Current Matching refers to the difference in current from

one LED to the next. The

∆I between any two LEDs will

meet this requirement. To calculate the error I

LED-LED-ERR ,

first identify the highest and lowest value of the 4 LED

currents, and use the formula:

LED-LED-ERR [%] =

which reduces to ±

1x Mode, 1.5x Mode and 2x Mode

1x Mode, 1.5x Mode and 2x Mode all refer to the charge

pump configuration. These modes boost the battery input

voltage and ensure there is enough voltage at V

OUT so

that the regulated current will flow through the LEDs and

return via the I

LED pins.

LED

()

MEASURED

I LED

100

IMAX

IMAX + IMIN

-1

100%

IMIN

IMAX + IMIN

-1

100%

IMIN

100%

IMAX

IMIN

IMAX +

Input Current

The total input current of the SC604A is a function of

the sum of the LED currents, the charge pump mode

and the quiescent current. The quiescent current trend

is charted on page 12 and used to calculate I

IN in the

following examples.

IN = IOUT

Mode + I

Q =

LED1+ILED2+ILED3+ILED4 )

Mode + I

Example 1:

Mode = 1x, I

Q = 2.4mA,

LED1+ILED2+ILED3+ILED4 = 4

15mA = 60mA

Answer 1:

IN = IOUT

Mode + I

Q = 60mA

1 + 2.4mA =

62.4mA

Example 2:

Mode = 1.5x, I

Q = 2.4mA,

LED1+ILED2+ILED3+ILED4 = 4

15mA = 60mA

Answer 2:

IN = IOUT

Mode + I

Q = 60mA

1.5 + 2.4mA =

92.4mA

Mode Transition Voltage

Mode transition voltage refers to the input voltage at

the point just before the charge pump changes from a

weaker mode to a stronger mode. V

TRANS1X is the

transition from 1x to 1.5x mode, and V

TRANS1.5X is the

transition from 1.5x to 2x mode. Equations for V

TRANS1X

and V

TRANS1.5X are given on page 7.

SC604A Datasheet(PDF) 4 Page - Semtech Corporation

SC604A Datasheet(HTML) 4 Page - Semtech Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Datasheet Download

Link URL