cat4106 ON Semiconductor, cat4106 Datasheet - Page 12

• Manufacturer Part Number: cat4106
• Description: 6w Quad Channel Dc/dc Led Driver With Diagnostics
• Manufacturer: ON Semiconductor

CAT4106
normal. If a disconnected LED string is reconnected,
the FAULT flag remains on and the channel disabled
until the device has been re-enabled with the EN pin
going from low to high.
If all LED channels are detected as being open-circuit,
then the boost converter will limit the output voltage to
the VFMAX setting. This eliminates the need for an
external protection zener.
ENABLE AND PWM DIMMING CONTROL
EN/PWM input signal provides two independent
functions. The first function is to enable and disable
the entire device. The second function is to apply
PWM dimming on the output channels while the chip
remains fully enabled. Applying logic high on the
EN/PWM input will power up the device. The device
will continue to remain powered up, even in the
presence of PWM signals being applied. To disable
the device into complete system shutdown mode, a
logic low must be applied to the EN/PWM input for
typically 5 ms.
The duty cycle applied at the EN/PWM is directly
applied to all the output channels. Each time the input
is taken low, all output channels will immediately be
switched off and the channels will resume normal
operation when the PWM is taken back high. The
response time of the channels when switching ON or
OFF is typically 0.2 µs.
During PWM dimming, the recommended minimum
pulse width interval (either High or Low) is 0.2 µs. The
recommended maximum pulse width during PWM
dimming is 2.5 ms, however this only applies to the
Low pulse interval. Pulse durations extending past
2.5 ms may cause the device to enter full shutdown
mode. The LED channel response time is much
longer if the device has been in shutdown mode.
For most applications, a maximum dimming resolution
can be achieved with PWM clock frequencies in the
range of 100 Hz to 2 kHz. Pulse width intervals of
1 μs, allows up to 1000:1 dimming ratio at 1 kHz PWM
frequency.
Doc. No. MD-5037, Rev. A
12
V
V
OFF...
ONE OR TWO LED STRING APPLICATIONS
The CAT4106 can be used to drive one or two strings
of LEDs by connecting together some LED pins. Also
for applications requiring LED current greater than
175 mA, LED channels can be tied together,
assuming the supply is suitable to drive the load.
Figure 7 shows a typical application for driving a
single string of LEDs. The LED current is equal to four
times the channel current.
Figure 8 shows a typical application for driving two
strings of LEDs. The LED current is equal to two times
the channel current.
V
V
OFF...
L
IN
Figure 8. Application Circuit for Two LED Strings
L
IN
Figure 7. Application Circuit for One LED String
R1
R1
ON... DIM...
ON... DIM...
C2
C1
C2
C1
R3
R3
R2
R2
VIN
EN/PWM
RSET
VCTRL
FB
VIN
EN/PWM
RSET
VCTRL
FB
L
L
GND
GND
CAT4106
CAT4106
SW
SW
PGND
PGND
Characteristics subject to change without notice
D
D
VFMAX
VFMAX
VFMIN
FAULT
VFMIN
FAULT
LED1
LED2
LED3
LED4
LED1
LED2
LED3
LED4
C3
C3
© 2009 SCILLC. All rights reserved.
LED Fault Detection
(open drain pull-down)
LED Fault Detection
(open drain pull-down)
R8
R4
R5
R8
R4
R5
R6
R7
R6
R7
V
V
IN
IN