LM3503SQX-25/NOPB National Semiconductor, LM3503SQX-25/NOPB Datasheet - Page 14
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LM3503SQX-25/NOPB
Manufacturer Part Number
LM3503SQX-25/NOPB
Description
IC LED DRIVER WHTE BCKLGT 16-LLP
Manufacturer
National Semiconductor
Series
PowerWise®r
Type
Backlight, White LEDr
Datasheet
1.LM3503SQ-16NOPB.pdf
(20 pages)
Specifications of LM3503SQX-25/NOPB
Constant Current
Yes
Topology
PWM, Step-Up (Boost)
Number Of Outputs
2
Internal Driver
Yes
Type - Primary
Backlight
Type - Secondary
White LED
Frequency
800kHz ~ 1.2MHz
Voltage - Supply
2.5 V ~ 5.5 V
Voltage - Output
23 V ~ 24 V
Mounting Type
Surface Mount
Package / Case
16-LLP
Operating Temperature
-40°C ~ 85°C
Current - Output / Channel
600mA
Internal Switch(s)
Yes
Efficiency
80%
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Other names
LM3503SQX-25
Available stocks
Company
Part Number
Manufacturer
Quantity
Price
Company:
Part Number:
LM3503SQX-25/NOPB
Manufacturer:
SANYO
Quantity:
6 218
www.national.com
Application Information
WHITE LED CURRENT SETTING
The white LED current is controlled by a DC voltage at the
Cntrl pin.
The relationship between the Cntrl pin voltage and Fb pin
voltage can be computed with the following:
V
V
Aside from varying the DC voltage at the Cntrl pin, white LED
dimming can be accomplished through the RC filtering of a
PWM signal. The PWM signal frequency should be at least a
decade greater than the RC filter bandwidth. Figure 3 is how
the LM3503 should be wired for PWM filtered white LED
dimming functionality. When using PWM dimming, it is rec-
ommended to add 1-2ms delay between the Cntrl signal and
the main Enable sginal (En1) to allow time for the output to
discharge. This will prevent potential flickering especially if
the Sub display is compose of 2 LEDs or less.
The equations below are guidelines for choosing the correct
RC filter values in relation to the PWM signal frequency.
Equation #1:
Cntrl
Fb
:
: Cntrl Pin Voltage. Voltage Range: 0.2V ≤ V
3.5V.
Feedback Pin Voltage.
FIGURE 3. If V
OUT2
WHITE LED DIMMING
Cntrl
is not used, En2 must be grounded
≤
14
LED CURRENT
The LED current is set using the following equation:
To determine the maximum output current capability of the
device, it is best to estimate using equations on page 16 and
the minimum peak current limit of the device (see electrical
table). Note the current capability will be higher with less
LEDs in the application.
Equation #2:
F
F
R:
C:
For example, using the above equations to determine the
proper RC values. Assume the following condition:V
C=0.01µF and F
equation 2. By rearranging equation 1 to solve for R; R =
318.5K ohms (standard value, R = 316K).
RC
PWM
:
: PWM Signal Frequency.
RC Filter Bandwidth Cutoff Frequency.
Chosen Filter Resistor.
Chosen Filter Capacitor.
PWM
= 500Hz, then F
20128634
RC
= 50Hz by relation to
IN
= 3.6V,