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CAT3643HV3-GT2

P1-P3P4-P6P7-P9P10-P12P13-P14
CAT3643
http://onsemi.com
10
Block Diagram
Figure 28. CAT3643 Functional Block Diagram
Mode Control
1, 1.3 MHz
Oscillator
1x mode (LDO)
1.33x, 1.5x, 2x Charge Pump
GND
LED1
LED2
LED3
LED Channel
Current Regulators
Current
Setting DAC
Serial
Interface
Registers
Reference
Voltage
EN/DIM
RSET
100 kΩ
V
OUT
V
IN
C
1−
C
1+
C
2−
C
2+
Basic Operation
At power−up, the CAT3643 starts operating in 1x mode
where the output will be approximately equal to the input
supply voltage (less any internal voltage losses). If the
output voltage is sufficient to regulate all LED currents, the
device remains in 1x operating mode.
If the input voltage is insufficient or falls to a level where
the regulated currents cannot be maintained, the device
automatically switches into 1.33x mode (after a fixed delay
time of about 400 ms). In 1.33x mode, the output voltage is
approximately equal to 1.33 times the input supply voltage
(less any internal voltage losses).
The above sequence repeats in the 1.33x and 1.5x mode
until the driver enters the 2x mode. In 1.5x mode, the output
voltage is approximately equal to 1.5 times the input supply
voltage. While in 2x mode, the output is approximately
equal to 2 times the input supply voltage.
If the device detects a sufficient input voltage is present to
drive all LED currents in 1x mode, it will change
automatically back to 1x mode. This only applies for
changing back to the 1x mode. The difference between the
input voltage when exiting 1x mode and returning to 1x
mode is called the 1x mode transition hysteresis (V
HYS
) and
is about 500 mV.
CAT3643
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11
LED Current Selection
At power−up, the initial LED current is set to full scale
(100% brightness) by the external resistor R
SET
as follows:
LED current + 132
0.6 V
R
SET
The EN/DIM pin has two primary functions. One function
enables and disables the device. The other function is LED
current dimming with six different levels by pulsing the
input signal, as shown on Figure 29. On each consecutive
pulse rising edge, the LED current is divided by half to 50%,
then 25%, 12.5%, 6.25% and 3.125% dimming levels.
Pulses faster than the minimum T
LO
may be ignored and
filtered by the device. Pulses longer than the maximum T
LO
may shutdown the device.
The LED driver enters a “zero current” shutdown mode if
EN/DIM is held low for 1.5 ms or more.
Figure 29. EN/DIM Digital Dimming Timing Diagram
EN/DIM
LED
Current
Shutdown
Shutdown
100%
50%
25%
12.5%
6.25%
3.12%
100%
T
LED
T
SETUP
T
LO
T
HI
T
PWRDWN
Table 7. LED CURRENT DIMMING LEVELS
EN/DIM # of Pulses * R
SET
Gain LED Current
EN = High 132 132 x 0.6 V / R
SET
1
st
66 66 x 0.6 V / R
SET
2
nd
33 33 x 0.6 V / R
SET
3
rd
16.5 16.5 x 0.6 V / R
SET
4
th
8.25 8.25 x 0.6 V / R
SET
5
th
4.125 4.125 x 0.6 V / R
SET
6
th
132 132 x 0.6 V / R
SET
x
th
Device cycling through gain selection GAIN x 0.6 V / R
SET
* The gain is changed on the rising edges of the EN/DIM input.
CAT3643
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12
Unused LED Channels
For applications not requiring all the channels, it is
recommended the unused LED pins be tied directly to V
OUT
(see Figure 30).
Figure 30. Application with 2 LEDs
GND
LED1
LED2
LED3
RSET
EN/DIM
CAT3643
1 mF
1 mF
C1−C1+ C2−C2+
1 mF
1 mF
ENABLE
DIMMING
C
OUT
V
OUT
R
SET
V
IN
V
IN
C
IN
Protection Mode
If an LED is disconnected, the driver senses that and
automatically ignores that channel. When all LEDs are
disconnected, the driver goes to 1x mode where the output
is equal to the input voltage.
As soon as the output exceeds about 6 V, the driver resets
itself and reevaluate the mode.
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 1.3 V to
4.3 V may be used. 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 3.3 V is selected
over one with V
F
of 3.5 V, the driver will stay in 1x mode for
lower supply voltage of 0.2 V. This helps improve the
efficiency and extends battery life.
External Components
The driver requires four external 1 mF 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 1 mF 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
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.
Figure 31. TDFN−12 Recommended Layout
C2
C1
VIN
GND
VOUT
GND
RSET
EN/DIM
Pin1
C
IN
C
OUT
P1-P3P4-P6P7-P9P10-P12P13-P14

CAT3643HV3-GT2

Mfr. #:
Buy CAT3643HV3-GT2
Manufacturer:
ON Semiconductor
Description:
LED Lighting Drivers LED Driver,Quad mode,3 ch
Lifecycle:
New from this manufacturer.
Delivery:
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