LDS8869 IXYS Corporation, LDS8869 Datasheet - Page 11

• Manufacturer Part Number: LDS8869
• Description: Lds8869 6-channel Ultra Low Dropout Led Driver
• Manufacturer: IXYS Corporation

LDS8869
recognizes this condition as “LED Short” and disables
this channel. If LED pin voltage is less than (Vout –
1.5V), LDS8869 restores LED current at this
particular channel to programmed value.
2. V
The charge pump’ output voltage V
limits at about 6.2 V maximum. This is to prevent the
output pin from exceeding its absolute maximum
rating.
3. V
If V
enabled, input current may increase up to 200 – 300
mA within 20 µs after enable and is limited to 35 – 40
mA after that.
4. Over-Temperature Protection
If the die temperature exceeds +150°C, the driver will
enter shutdown mode. The LDS8869 requires restart
after die temperature falls below 130°C.
5. Input Voltage Under-Voltage Lockout
If V
enters shutdown mode and all registers data are
cleared. Device requires restart when input voltage
rises above 2.3 V. To restart device, set EN/SET pin
logic low, turn V
and program I
6. Low V
If, in 2x mode, V
LED current for given LED V
open circuit, or if any LED at active channels is
disconnected,
changing modes (2x – 1x – 1.33x -1.5x – 2x -…) in
an attempt to compensate insufficient voltage. As a
result, average current at all other channels that are
ON may fall below regulated level.
LED Selection
LEDs with forward voltages (V
3.6 V may be used. Charge pumps operate in highest
efficiency when V
multiplied by switching mode, i.e. V
and so on. If the power source is a Li-ion battery,
LEDs with VF = 2.7V - 3.3V are recommended to
achieve highest efficiency performance and extended
operation on a single battery charge.
External Components
The driver requires two external 1 µF ceramic capa-
citors (C
citors (C1 and C2) X5R or X7R type. Capacitors C1
and C2 may be increased up to 1 µF to improve
charge pump efficiency by 3%. In all charge pump
© 2009 IXIS Corp.
Characteristics subject to change without notice
OUT
OUT
OUT
IN
falls below 2.2 V (typical value), LDS8869
Over-Voltage Protection
Short Circuit Protection
IN
is shorted to ground before LDS8869 is
IN
and C
or High LED V
LED
IN
OUT
using 1-wire interface.
LDS8869
IN
F
off/on, set EN/SET pin logic high,
) and two 0.22 µF ceramic capa-
is too low to maintain regulated
voltage is close to V
F
Voltage Detection
F
F
starts
, or LED becomes an
) ranging from 1.6 V to
IN
OUT
x 1, V
subsequently
automatically
IN
IN
voltage
x 1.33,
11
modes, the input current ripple is very low, and an
input bypass capacitor of 1µF is sufficient.
In 1x mode, the device operates in linear mode and
does not introduce switching noise back onto the
supply.
Recommended Layout
In charge pump mode, the driver switches internally
at a high frequency. It is recommended to minimize
trace length to all four capacitors. A ground plane
should cover the area under the driver IC as well as
the bypass capacitors. Short connection to ground on
capacitors C
use of multiple via. A copper area matching the
TQFN exposed pad (TAB) must be connected to the
ground plane underneath. The use of multiple via
improves the package heat dissipation.
Figure 4. Recommended layout
IN
and C
OUT
can be implemented with the
Doc. No. 8869_DS, Rev. N2.1