PA5910_15 Datasheet, PDF (7/9 Pages) Protek Devices – SWITCHING TYPE LED DRIVER

ANALOG PRODUCTS DIVISION
PA5910
Switching Type LED Driver.
VDD
BANDGAP
PA5910
R_OFF
TOFF
OFF
C_OFF
TIME
SQ
R
DRV
EN
250mV
GND
CS
T_OFF can be reduced by adding R_OFF and increased by adding C_OFF
Operation Frequency can be calculated by the following formula F = ¹ = ^{1 − D}
T T_OFF
When T_OFF is connected to a 1000pF capacitor, T_OFF =51μS, D=0.1 the resultant frequency will be 20 KHz.
Inductor Design.
Inductor selection criteria are to ensure that current flow through inductor is less than the maximum value
specified.
Referring to the typical application in Fig.5 the value can be calculated from the desired peak-to-peak LED ripple
current in the Inductor. Typically the ripple current is selected to be 30% of the nominal LED current. In this
example the I_LED is 350mA
For example, when the string consists of 12 High Brightness LED’s and each diode has a forward drop of 3.3V at
nominal current, the total LED voltage V_LEDS is 39.6V
Knowing the rectified input voltage V_IN = 220V x 1.414 = 310V, the duty ratio can be determined as:
D = ^VLED = ^39.6 = 0.128
V_IN 310
Given the switching frequency (20KHz) the required on time of the MOSFET can be calculated by:
TON = ^D = 6.4µS
f_OSC
The required value of the inductor is given by:
( ) L =
V_IN − V_LED
× ^TON
0.3 × I_LED
= 16mH
7
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