LDS8620 IXYS Corporation, LDS8620 Datasheet - Page 9

• Manufacturer Part Number: LDS8620
• Description: Lds8620 200 Ma, Dual Output Led Flash/lamp Driver
• Manufacturer: IXYS Corporation

LDS8620
5. Input Voltage Under-Voltage Lockout
If V
enters shutdown mode. Device requires restart when
input voltage rises above 2.2 V.
6. Low V
If, in 2-x mode, V
LED current for given LED V
open circuit, or if any LED at active channels is
disconnected,
changing modes (2-x – 1-x – 1.5-x – 2-x -…) in an
attempt to compensate insufficient voltage. As a
result, average current at all other channels that are
ON may be below regulated level.
LED Selection
LEDs with forward voltages (V
4.5 V may be used. Charge pumps operate in the
highest efficiency mode when V
Vin voltage multiplied by switching mode, i.e. Vin x 1,
Vin x 1.5 and so on. If the voltage source is a Li-ion
battery, we recommend selecting LED with V
3.6 V to extend the battery life and achieve highest
efficiency.
External Components
The LDS8620 requires two external 1 µF ceramic
capacitors (X5R or X7R type) for decoupling input,
output, and two 0.22 µF capacitors (X5R or X7R
type)
modes, the input current ripple is very low, and an
input bypass capacitor of 1 µF is sufficient.
In 1-x mode, the device operates in linear mode and
does not introduce switching noise back onto the
supply.
© 2009 IXYS Corp.
Characteristics subject to change without notice
IN
falls below 2.1 V (typical value), LDS8620
for the charge pump. In all charge pump
IN
or High LED V
LDS8620
IN
is too low to maintain regulated
F
Voltage Detection
F
F
starts
, or LED becomes an
) ranging from 1.6 V to
F
voltage is close to
subsequently
F
= 2.7 –
9
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 Cin and Cout can be implemented with the
use of multiple via. A copper area matching the
TQFN exposed pad (PAD) must be connected to the
ground plane underneath. The use of multiple via
improves the package heat dissipation.
Figure 3. Recommended layout
Doc. No. 8620DS, Rev. N1.1