LDS8711008-T2-300 IXYS [IXYS Corporation], LDS8711008-T2-300 Datasheet - Page 8

• Manufacturer Part Number: LDS8711008-T2-300
• Description: High Efficiency 10 LED Driver with No External Schottky
• Manufacturer: IXYS [IXYS Corporation]

LDS8711
state equal t
pulse will be recognized as PWM pulse, and
maximum LED current will be set equal factory preset
value. If PWM frequency is above 5 kHz and duty
cycle is less than 50%, device will start in PWM mode
automatically; however, at lower frequencies or 100%
duty cycle, start procedure requires.
To start LDS8711 in Smart OneWire™ Interface
Mode, the first positive pulse applied to EN/PWM pin
after power-up should be equal t
by 16 command pulses in respect to Smart
OneWire™ interface command shown in the Table 1.
Every Smart OneWire™
program LED current may be represented in binary
code as 0000 0100 XXXX XXXX (MSB to LSB),
where X is a bit value in respect with desired current
value.
Example:
If desired LED current value is 22 mA, binary code is
equal 22 mA/0.125 mA – 1 = 43 (Dec) = 1010 1111
(Bin) and Smart OneWire™ interface command to set
this current is: 0000 0100 1010 1111 (MSB to LSB).
This command should be send (MSB first) through
EN/PWM pin as sequence of 16 pulses, each of
which represents bit zero or bit one depend on pulse
length that should be equal t
Smart OneWire™TIMING SPECIFICATION).
After 16
time to confirm end of the command and transfer to
PWM mode. Every next incoming pulse will be
recognized as PWM pulse, and it will turn LEDs on
(see Figure 2).
If LDS8711 is not able recognize command due
some error in programming or transmit, it will go in
shutdown mode after 10 ms timeout
Once in PWM mode, LDS8711 is not able recognize
Smart OneWire™ Interface commands and requires
restart to reprogram LED current.
Protection Mode
The output voltage V
maximum. This is to prevent the output pin from
exceeding its absolute maximum rating if LED string
is disconnected or any LED.in string burns out
creating open circuitry.
If the die temperature exceeds +150°C, the driver will
enter a thermal protection shutdown mode. When the
device temperature drops by about 20°C, the device
will resume normal operation.
© 2010 IXYS Corp.
Characteristics subject to change without notice
th
pulse, EN/PWM pin should be LOW for t
LO
(see Figure 1). Every next incoming
OUT
is limited at about 38 V
BO
interface command to
or t
SETUP2
B1
respectively (see
and followed
LO1
8
LED Selection
LEDs with forward voltages (V
5.0 V may be used. However, number of the LEDs in
string is limited by maximum output voltage that
cannot exceed over-voltage protection level. We
recommend using not more than 10 LEDs with V
3.6 V in string if V
more that eight LEDs if V
External Components
The LDS8711 requires four external components
only. The recommended input capacitor value is
between 1 and 10 µF, while the output capacitor
selection is function of desired output ripple, loop
stability, and inrush current.
The inductor should have minimum Rdc resistance to
increase driver’s efficiency. Recommended inductor
values are from 10 to 33 µH. The inductor ripple
current I
inductor value, and duty cycle and is determined by
the following equation:
where
V
Vd - is a current regulator voltage drop,
V
V
L is - inductance, and
f - is a switching frequency, 700 kHz.
Then, the switch cycle-by-cycle current limit is
equal:
where is expected efficiency.
The selected inductor should allow around 20%
higher peak current to avoid saturation.
The criterion for the output capacitor selection is:
For example:
If V
0.7 MHz, I
V, C
I
I
C
F
PM
IN
R
LIM
OUT
- is a LED forward voltage,

- is an input voltage,
IN
- is a voltage drop across PMOSFET,
OUT

= 2.7 V, N = 10, V
Lf

I
= 0.77 µF so 1.0 µF is a good choice.
(

 

R
OUT
NV
OUT
NV
is a function of switching frequency,
(
(
NV
F
NV
V
F
= 30 mA, and ripple voltage V

IN

F

V
F
V

IN
d

d
V

voltage is above 3.0 V and not
V
1

d
V
d
1
V
)
IN
V
)
IN
PM
F

R
)
may fall up to 2.7 V.
= 3.6 V, Vd = 0.25 V, f =
I
f

I
OUT
Doc. No. 8711DS, Rev. N1.0
2
R
F
V
) ranging from 1.3 V to
,
IN

V
1
IN

 

,
R
= 0.05
F
≤