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LDS8868 Datasheet(PDF) 9 Page - IXYS Corporation

Part No. LDS8868
Description  6-Channel Ultra Low Dropout LED Driver
Download  14 Pages
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Manufacturer  IXYS [IXYS Corporation]
Direct Link  http://www.ixys.com
Logo IXYS - IXYS Corporation

LDS8868 Datasheet(HTML) 9 Page - IXYS Corporation

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LDS8868
© 2009 IXYS Corp.
9
Doc. No. 8868_DS, Rev. N2.1
Characteristics subject to change without notice
BLOCK DIAGRAM
Figure 2. LDS8868 Functional Block Diagram
BASIC OPERATION
At power-up, EN pin should be logic LOW. During
power-up device performs internal circuits reset that
requires less than 10µs. To start device, EN pin
should be set logic HIGH at least 10µs after VIN
applied. Device starts operating at 1x mode at which
the VOUT is approximately equal to VIN (less any
internal voltage losses). If the output voltage is
sufficient to regulate all LED currents, the device
remains in 1x operating mode.
. The low dropout PowerLite
™ Current regulator
(PCR) performs well at input voltages up to 75 mV
above LED forward voltage VF significantly increasing
driver’s efficiency. The LDS8868 monitors voltage
drop Vd across PCR at every channel in ON state. If
this voltage falls below 75 mV (typical) at any one
channel, (channel with LED with highest forward
voltage), the Mode Control Block changes charge
pump mode to the next multiplication ratio.
Vd (LEDX1/2) = VIN x M – VF – Rcp x Iout, where Rcp
is a Charge Pump Output Resistance at given mode,
Iout is sum of all LED currents, and M is a charge
pump’ multiplication ratio.
If the input voltage is insufficient or falls to a level
where Vd
≤75 mV, and the regulated currents cannot
be maintained, the low dropout PowerLite
™ Current
Regulator switches the charge pump into 1.5x mode
(after a fixed delay time of about 800μs). In 1.5x
mode,
the
charge
pump’
output
voltage
is
approximately equal to 1.5 times the input supply
voltage (less any internal voltage losses).
This sequence repeats until driver enters the 2x
mode.
LED Current Setting
The current in each of the six LED channels is
programmed through the 1-wire EN/SET digital


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