LM3432BSQ National Semiconductor, LM3432BSQ Datasheet - Page 11

• 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

than 0.5 µs, the duty cycle will be rounded down to 0% and
for a control pulse width less than 0.5 µs off time, the duty
cycle will be rounded up to 100%. Therefore, 0.5µs becomes
LED SHORT FAULT DETECT
With DHC
If the Dynamic Headroom Control (DHC) feature is used, the
lowest voltage between the IOUT pins and ground among the
strings will be regulated to 0.625V typical (I
lowering the LED supply rail voltage, V
fault condition occurs and causes the voltage between any of
the IOUT pins and ground to exceed the typical short fault
threshold of 7.9V for more than 150 µs, the affected channel
(s) will be latched off and the FAULTb pin will be pulled to
ground. The affected channel(s) will remain latched off until
recycling power or toggling the EN pin. All of the other chan-
nels that are not affected will continue to function normally.
Without DHC
In applications where the DHC function is not used, the IOUT
pin voltage on each string will be the voltage difference be-
tween the LED supply rail voltage, V
across the entire LED string. If the voltage between any of the
IOUT pins and ground is less than 2V typical, the short fault
LED
, and the voltage drop
LED
FIGURE 2. PWM Dimming Switching Timing
. If an LED short
LED
= 20 mA) by
11
the finest pulse width resolution that can be realized. The
PWM switching timing for all six channels is shown in Figure
2.
detect feature will be active for all channels. In the event an
LED short fault condition occurs and causes the voltage be-
tween any of the IOUT pin and ground to exceed the typical
short fault threshold of 7.9V for more than 150 μs, the affected
channel(s) will be latched off and the FAULTb pin will be
pulled to ground. The affected channel(s) will remain latched
off until recycling power or toggling the EN pin. All of the other
channels that are not affected will continue to function nor-
mally. If the voltages between all IOUT pins and ground are
greater than 2V typical, the Short Fault Detect feature will be
disabled to prevent false triggering of the short fault detect
function.
LED OPEN FAULT DETECT (LM3432 ONLY)
For the LM3432, if an open fault should occur and the affected
channel sinks no current for greater than 50 µs, it will be
latched off (until recycling power or toggling EN pin). The
FAULTb pin’s output will be pulled to ground while the other
channels keep functioning normally. The open fault detection
and FAULTb indication features are inactive in the LM3432B.
30006420
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