ZXSC310_04 Datasheet, PDF (11/16 Pages) Zetex Semiconductors – LED DRIVER SOLUTION FOR LCD BACKLIGHTING

ZXSC310
Output Power Calculation
By making the above assumptions for inductance and
peak current the output power can be determined by:
TOFF
POUT = (VOUT − VIN) × IAV × _{TON + TOFF}
Note:VOUT=output voltage + Schottky rectifier voltage
drop.
Where
Capacitor selection
For pulsed operation, as in the maximum battery life
solution, no capacitors are required at the output to the
LED. For rectified operation, as in the maximum
brightness solution, a small value ceramic capacitor is
required, typically 2.2uF.
Generally an input capacitor is not required, but a small
ceramic capacitor may be added to aid EMC, typically
470nF to 1uF.
(notes)
TOFF ≅1.7us (internally set by ZXSC310)
and
TOFF⁽VOUT − VIN⁾
TON =
VIN
and
IPK + IMIN
IAV = ₂
Where
(_{VOUT − VIN}) _{× TOFF}
IMIN = IPK −
L
Operating frequency can be derived by:
1
F = _{(TON + TOFF)}
ISSUE 2 - MARCH 2004
11
SEMICONDUCTORS