LM3530UME-25A/NOPB National Semiconductor, LM3530UME-25A/NOPB Datasheet - Page 24

• Manufacturer Part Number: LM3530UME-25A/NOPB
• Description: IC LED DRVR PRGRAM I2C 10LED SMD
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM3530UME-25A/NOPB

• Topology: PWM, Step-Up (Boost)
• Number Of Outputs: 1
• Internal Driver: Yes
• Type - Primary: Backlight
• Type - Secondary: White LED
• Frequency: 500kHz
• Voltage - Supply: 2.7 V ~ 5.5 V
• Mounting Type: Surface Mount
• Package / Case: 12-XFBGA
• Operating Temperature: -40°C ~ 85°C
• Current - Output / Channel: Adjustable
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -
• Other names: LM3530UME-25A/NOPBTR

www.national.com
Referring to
Zone 0 so it takes 2 averaging periods for the LM3530 to
change to the new zone. After the ALS1 voltage remains at
437.5mV for two averaging periods (end of period #2) the
LM3530 sees a repeat of Zone 2 and signals the LED current
to begin ramping to Zone 2's target beginning at average pe-
riod #3. Since the ramp rate is set at 16.384ms/step the LED
current goes from 0 to 1.3mA in 76 × 16.384ms = 1.245s (ap-
proximately 5 average periods).
After the LED current has been at its steady state of 1.3mA
for a while, the ambient light suddenly steps to 900 LUX for
500ms and then steps back to 500 LUX. In this case the 900
LUX will place the ALS1 voltage at approximately 979mV cor-
responding to Zone 4 somewhere during average period #10
and fall back to 437.5mV somewhere during average period
#12. The averager output during period #10 goes to 3, and
Figure
14, initially the Averager is loaded with
FIGURE 14. ALS Averaging Example
24
then during period #11, goes to 4. Since there have been 2
increases in the average during #10 and #11, the beginning
of average period #12 shows a change in the brightness zone
to Zone 4. This results in the LED current ramping to the new
value of 22.5mA (Zone 4's target). During period #12 the am-
bient light steps back to 500 LUX and forces ALS1 to 437.5mV
(corresponding to Zone 2). After average periods #12 and #13
have shown that the averager transitioned lower two times,
the brightness zone changes to the new target at the begin-
ning of period #14. This signals the LED current to ramp down
to the zone 2 target of 1.3mA. Looking back at average peri-
ods #12 and #13, the LED current was only able to ramp up
to 7.38mA due to the ramp rate of 16.384ms/step (2 average
periods of 256ms each) before it was instructed to ramp back
to Zone 2's target at the start of period #14. This example
demonstrates not only the averaging feature, but how addi-
tional filtering of transient events on the ALS inputs can be
accomplished by using the LED current ramp rates.
30086684