CAT3637 Datasheet, PDF (11/14 Pages) Catalyst Semiconductor – 6-Channel Programmable High Efficiency Quad-Mode™ LED Driver

CAT3637
Unused LED Channels
External Components
For applications with 5 LEDs or less, unused LEDs
can be disabled by connecting the LED pin directly to
VOUT, as shown on Figure 4. If LED pin voltage is
within 1V of VOUT, then the channel is switched off
and a 200μA test current is placed in the channel to
sense when the channel moves below VOUT – 1V.
1µF
1µF
The driver requires two external 1μF ceramic
capacitors for decoupling input, output, and for the
charge pump. Both capacitors type X5R and X7R are
recommended for the LED driver application. In all
charge pump modes, the input current ripple is kept
very low by design and an input bypass capacitor of
1μF is sufficient.
V_IN
2.5V CIN
to
5.5V ^1µF
1-Wire
Programming
C1-
VIN
C1+ C2- C2+
VOUT
CAT3637
EN/SET
GND
LED1
LED2
LED3
LED4
LED5
LED6
Figure 5. Five LED Application
Protection Mode
In 1x mode, the device operates in linear mode and
V_OUT
does not introduce switching noise back onto the
supply.
C_OUT
1µF ^{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_IN and C_OUT can be implemented with the
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.
If an LED is disconnected, the output voltage VOUT
automatically limits at about 5.5V. This is to prevent
the output pin from exceeding its absolute maximum
rating.
If the die temperature exceeds +150°C the driver will
enter a thermal protection shutdown mode. When the
device temperature drops by about 20°C the device
will resume normal operation.
LED Selection
LEDs with forward voltages (V_F) ranging from 1.3V to
5.0V may be used with the CAT3637. Selecting LEDs
with lower V_F is recommended in order to improve the
efficiency by keeping the driver in 1x mode longer as
the battery voltage decreases.
For example, if a white LED with a V_F of 3.3V is
selected over one with V_F of 3.5V, the CAT3637 will
stay in 1x mode for lower supply voltage of 0.2V. This
helps improve the efficiency and extends battery life.
Figure 6. Recommended Layout
© Catalyst Semiconductor, Inc.
11
Characteristics subject to change without notice
Doc. No. MD-5033 Rev. A