LDS8681 IXYS Corporation, LDS8681 Datasheet - Page 6

• Manufacturer Part Number: LDS8681
• Description: 800 Ma, Dual Output Led Flash/pwm Dimming Lamp Driver
• Manufacturer: IXYS Corporation

LDS8681
Unused LED Channels
For applications with only one LED, unused channel
can be connected to V
teed together to provide sum of the currents set at
each channel.
Protection Modes
The LDS8681 has follow protection modes:
1. LED short to V
If LED pin is shorted to V
becomes as short circuit, or LED pin voltage is within
from V
recognizes this condition as “LED Short” and disables
this channel. If LED pin voltage is less than (Vout –
1.5V), LDS8681 restores LED current at this
particular channel to programmed value.
2. V
The charge pump’ output voltage V
limits at about 5.9 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 1 A within
20 µs after enable and is limited to ~ 90 mA after
that.
4. Over-Temperature Protection
If the die temperature exceeds +160°C, the driver will
enter shutdown mode. Device restores normal
operation after die temperature falls below 135°C.
5. Input Voltage Under-Voltage Lockout
If V
LDS8681 will restart when input voltage rises above
2.3 V called lockout mode. If V
1.7 V, LDS8681 device will enter shutdown mode..
To restart device, set EN pin logic low for more than
50 ms and logic high after that..
6. Open LED Definition
When LED becomes an open circuit, device will enter
into 2-x mode unless this unused LED channel is
connected to V
LED Selection
If the power source is a Li-ion battery, LEDs with
lowest forward voltages are recommended to achieve
highest efficiency and extended operation on a single
battery charge.
© 2009 IXYS Corp.
Characteristics subject to change without notice
IN
OUT
OUT
OUT
falls below 2.3 V but above 1.7 V (typical value),
Over-Voltage Protection
Short Circuit Protection
OUT
is shorted to ground before LDS8681 is
to (V
OUT
OUT
directly.
OUT
protection
OUT
- 1.5V)
or both channels may be
OUT
IN
, LED burned out
continues fall below
range, LDS8681
OUT
automatically
6
LEDs with forward voltages (V
4 V may be used. Charge pump operates in highest
efficiency when V
multiplied by switching mode, i.e. V
External Components
The driver requires three external ceramic capacitors
(C1, C
pump mode, 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 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
TDFN exposed pad (PAD) must be connected to the
ground plane underneath. The use of multiple via
improves the package heat dissipation (see figure
below).
The ground plane on the top layer is connected to the
ground plane on the bottom layer through two vias to
imporove power dissipation.
IN
, and C
IN
and C
OUT
F
) X5R or X7R type. In 2-x charge
voltage is close to V
OUT
can be implemented with the
Doc. No. 8681_DS, Rev. N1.0
F
) ranging from 1.6 V to
IN
x 1 or V
IN
IN
voltage
x 2