LM3432BSQ National Semiconductor, LM3432BSQ Datasheet - Page 15

• Manufacturer Part Number: LM3432BSQ
• Description: LM3432/LM3432B 6-Channel Current Regulator for LED Backlight Application; Package: LLP; No of Pins: 24; Qty per Container: 1000; Container: Reel
• Manufacturer: National Semiconductor

Dynamic Headroom Control, DHC with LM3430
When the LM3432/LM3432B are powered with National
Semiconductor's Boost Controller for LED Backlighting,
LM3430, the Dynamic Headroom Control (DHC) feature
helps to provide the optimal system efficiency. By connecting
VDHC through a gain setting resistor to the DHC pin of the
LM3430 that is supplying the LED power rail, the LM3432/
LM3432B’s DHC function will regulate the minimum of the ON
voltage of the six channels to 0.625V typical (I
This is the minimum voltage headroom required at outputs to
keep the current regulator in its linear operating range. In or-
der not to interfere with the feedback loop response of the
upstream DC-DC converter, the DHC response time constant
FIGURE 5. Achieving Higher LED String Current by Grouping IOUT Ports
OUT
= 20 mA).
15
must be set to a large enough value by adding a capacitor
from CDHC pin to ground.
Figure 6 is an application schematic of a LED panel driver
using both the LM3430 and the LM3432/LM3432B with the
Dynamic Headroom Control function enabled. The LM3430
boosts a voltage from VIN to 50V nominal to supply the LED
strings. With the DHC function disabled, the LM3430 will keep
the LED string supply regulated at 50V. When the DHC is
enabled, this voltage will dynamically be regulated down to a
voltage that can just keep all LED string currents in regulation.
That is about 40V in the application shown in Figure 6. The
reduction in this rail voltage can significantly improve the
overall system efficiency.
www.national.com
30006427