CAT3616 Datasheet, PDF (10/14 Pages) Catalyst Semiconductor – 6-Channel Charge Pump LED Driver with EZDimTM

CAT3616
LED CURRENT SETTING
The LED current is controlled by toggling the input
signals E¯N¯M¯ and E¯N¯¯S. E¯N¯M¯ controls the four LED
channels MAIN1 to MAIN4. E¯N¯¯S controls the two LED
lines SUB1 and SUB2. E¯N¯M¯ and E¯N¯¯S work the same
way. The chip must first be enabled by setting the
enable input EN high. On the first E¯N¯M¯ or E¯N¯¯S
transition from high to low, the LED current in the
associated LEDs is set to the full scale 31mA. On
each consecutive falling edge of E¯N¯M¯ or E¯N¯¯S, the
LED current is decreased by 1mA. On the 32^nd pulse,
the LED channel is turned off and the current drops to
0mA. One additional E¯N¯M¯ or E¯N¯¯S pulse resets the full
current to 31mA, as shown on Figure 1.
Consecutive pulses should be separated by 300ns or
more. Pulsing frequencies from 5kHz up to 1MHz are
supported during dimming operations. When the EN is
held low for 1.5ms or more, the CAT3616 enters the
shutdown mode and draws “zero” current. When the
enable EN input is low, toggling E¯N¯M¯ or E¯N¯¯S has no
effect.
Unused LED channels can be disabled independently
by connecting the corresponding main or sub LED pin
to VOUT.
Protection Mode
If an LED becomes open-circuit, the output voltage
VOUT is internally limited to about 5.5V. This is to
prevent the output pin from exceeding its absolute
maximum rating.
The driver enters a thermal shutdown mode as soon as
the die temperature exceeds about +165ºC. When the
device temperature drops down by about 20ºC, the device
resumes normal operation.
External Components
The driver requires a total of four external 1µF
ceramic capacitors: two for decoupling input and
output, and two for the charge pump. Both capacitor
types X5R and X7R are recommended for the LED
driver application. In the 1.5x charge pump mode, the
input current ripple is kept very low by design, and an
input bypass capacitor of 1µF is sufficient. In 1x mode,
the device operating in linear mode does not introduce
switching noise back onto the supply.
Recommended Layout
In 1.5x charge pump mode, the driver switches
internally at a high frequency of 1MHz. 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 TDFN exposed pad
(GND) must be connected to the ground plane
underneath. The use of multiple via improves the
package heat dissipation.
Doc. No. 5018 Rev. A
10
© 2006 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice