LDS8710 IXYS, LDS8710 Datasheet - Page 7

• Manufacturer Part Number: LDS8710
• Description: LED Drivers HE 10 LED driver No Ext Schottky
• Manufacturer: IXYS

Specifications of LDS8710

• Operating Supply Voltage: 2.7 V to 5.5 V
• Maximum Supply Current: 3 mA
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Package / Case: TDFN-8
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

LDS8710
External Components Selection
The LDS8710 requires four external components
only. The recommended input capacitor value is
between 1.0 and 10 µF, while the output cap
selection is function of desired output ripple, loop
stability, and inrush current. We recommend C
1 µF.
The inductor should allow around 20% higher peak
current than LDS8710 Switch Current Limit I
table Electrical Operating Characteristics on page 2).
However, the maximum ripple current through
inductor I
V
N – is number of LEDs per string
Vd - is a current regulator voltage drop = 0.25 V,
V
We recommend continuous conduction mode for
inductor to achieve highest efficiency. That limits I
value as
Inductor value L is a function of switching frequency,
input and output voltage and is determined by
following equation:
V
(PMOSFET) = 1.5 ohms x I
L - is an inductance, H, and
f - is a switching frequency, 700 kHz.
Inductor should have minimum DC resistance to
avoid driver’s efficiency degradation.
.
© 2010 IXYS Corp.
Characteristics subject to change without notice
I
I
L
F
IN
PM
R
R

- is a LED forward voltage, V
- is an input voltage, V


- is a voltage drop across synchronous rectifier
I
2
2
R

 

I
f
I
LED
R

 

LIM
should not exceed
NV


NV

V
F
IN
I
F

LED
V

d
V

NV
V
d
1

1
IN

V

F
PM

LED
V

, (A),
d
V

IN

 

, where

V
1
IN

 

, where
LIM
OUT
(see
=
R
7
The equation for the output capacitor selection is:
V
For example:
If V
0.7 MHz, I
V, C
We recommend C
efficiency and driver’s stability.
Recommended Layout
In active mode, the driver switches internally at a high
frequency. We recommend minimize trace length to
all external capacitors and inductor. The input and
output ceramic capacitors (X5R or X7R type) should
located as close to the device’ pins as possible to
prevent from EMI distribution
A ground plane should cover the area under the
driver IC as well as the bypass capacitors. Short
connection to ground on capacitors C
be implemented with the use of multiple via. A copper
area matching the TDFN exposed pad (PAD) must
be connected to the ground plane underneath. The
use of multiple via improves the package heat
dissipation.
C
R
OUT
– is a ripple voltage at the output.
IN
OUT
= 2.7 V, N = 10, V

= 0.77 µF so 1 µF is a good choice.
(
NV
OUT
Figure 3. Recommended layout
(
NV
F
= 30 mA, and ripple voltage V

F
V

d
OUT
V

d
V
)
V
IN
= 1 µF to achieve better
F
R
)
= 3.6 V, Vd = 0.25 V, f =
I
f
OUT
Doc. No. 8710DS, Rev. N1.0
, where
IN
and C
R
OUT
= 0.05
can