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CAT4106HV4-GT2

P1-P3P4-P6P7-P9P10-P12P13-P15
CAT4106
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10
Device Operation
In a typical application, the CAT4106 drives an LED array
consisting of up to four separate strings. A single external
resistor value is used to select the drive level in all output
channels. Each channel provides a very well regulated and
tightly matched bias current on all LED strings.
An integrated DC/DC boost converter is used to generate
the high voltage output required to power the LED strings.
Up to a maximum of 6 W of LED power can be delivered
when powered from a 12 V supply.
To offer improved performance, the device also allows the
user to set the operating voltage level on the output drive
channels. A pair of external resistors is used to control the
nominal channel voltage, during normal operation. The
resulting output voltage (LED anodes) will be equal to the
sum of the adjusted channel voltage plus the maximum
forward voltage present on any string.
The CAT4106 provides four tightly matched current sinks
to accurately regulate LED current in each channel. Up to
175 mA per channel can be programmed by selecting a
suitable value for the external R1 resistor (connected
between RSET and GND pins).
LED Current Setting
The CAT4106 provides four tightly matched current sinks
to accurately regulate LED current in each channel. The
LED current is set by the external resistor R1 connected
between the RSET pin and ground. The following formula
gives the relationship between the resistor value and the
LED current per channel.
R1 [ 103
1.2 V
LED current per channel
Table 6. RESISTOR R1 AND LED CURRENT
LED Current per Channel (mA)
R1 (W)
10 12.4 k
20 6.19 k
30 4.12 k
50 2.49 k
100 1.24 k
150 820
Setting the Channel Voltage
Each LED channel typically requires less than 0.5 V of
headroom for full load operation. The lowest channel
operating voltage can be controlled and programmed via the
external resistor network connected between, CTRL, FB
and GND as shown in Figure 24.
Lowest LED pin voltage + V
FB
R2 ) R3
R3
For most applications, a gain of 2x (R2 equals R3) is
recommended. The CTRL output pin has optimal
performance when loaded with around 15 mA, which
equates to an R3 resistor value of 20 kW.
LED Detection
The CAT4106 detects failure conditions related to the
LED load, such as if one of the LED strings has been
disconnected (Open−LED) or if one LED string has a lower
LED pin voltage than expected (Short−LED). Either
condition is flagged by turning on the open−drain output on
the FAULT pin. The Open−LED detection is active in
normal operation. The Short−LED detection is only active
during power−up, just after the EN/PWM input goes from
low to high. If in normal operation (LEDs are in regulation)
a short−LED condition occurs, it will not be detected.
Figure 25. Cold Power−Up Short−LED Detection
Figure 26. Normal Operation Open−LED Detection
The test condition in Figure 25 is with one LED pin
shorted to the output (top LED anode). The test condition in
Figure 26 is with one LED pin floating or disconnected. In
both cases, the CAT4106 is set to drive 50 mA per channel.
Setting VFMIN Level (Short−LED)
The VFMIN level represents the minimum level expected
for the LED string voltage “window of operation”. This
voltage setting is based on the number of series LEDs being
used and the expected minimum forward voltage V
F
during
normal operation.
Example:
Consider a string of 6 LEDs in series, with each
LED having a V
F
range of 3.5 V ± 0.5 V. Since the
minimum V
F
of each LED is 3.0 V the overall lowest
expected string voltage would be 18 V. Any string voltage
of less than 18 V is considered as a short−circuit fault in one
or more of the series LEDs.
CAT4106
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The external resistor R6 value needed to set a VFMIN
level of 18 V is calculated as follows:
R6 + R7
ǒ
18 V
1.2 V
* 1
Ǔ
For R7 = 20 kW, R6 = 280 kW.
Setting VFMAX Level (Open−LED)
The VFMAX level represents the maximum level expected
for the LED string voltage “window of operation”. This
voltage setting is based on the number of series LEDs being
used and the expected maximum V
F
during normal operation.
Example:
Consider a string of 6 LEDs in series, with each
LED having a V
F
range of 3.5 V ± 0.5 V. Since the
maximum V
F
of each LED is 4.0 V, the overall maximum
expected string voltage would be 24 V. Any string voltage
which appears greater than 24 V would be considered as
containing an open−circuit in one or more of the series
LEDs. The external resistor R4 value needed to set a
VFMAX level of 24 V is calculated as follows:
R4 + R5
ǒ
24 V
1.2 V
* 1
Ǔ
For R5 = 20 kW, R4 = 380 kW.
In normal operation, the LED string which has the largest
V
F
will be used to set the VCTRL/VFB voltage levels. If the
largest string voltage tries to exceed VFMAX setting, it will
no longer be allowed to control the voltage level of
VCTRL/VFB (i.e. it will be ignored) and subsequently the
next largest LED string voltage will then be used in the
control loop. All remaining functional LED channels will
continue to operate as 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 ms.
During PWM dimming, the recommended minimum
pulse width interval (either High or Low) is 0.2 ms. The
recommended maximum pulse width during PWM
dimming is 2.0 ms, however this only applies to the Low
pulse interval. Pulse durations extending past 2.0 ms may
cause the device to enter full shutdown mode. The LED
channel response time is 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 500 Hz to 2 kHz. Pulse width intervals of 1 ms, allows up
to 1000:1 dimming ratio at 1 kHz PWM frequency.
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 27 shows a typical
application for driving a single string of LEDs. Note:
VFMIN is disabled for one string.
Figure 27. Application Circuit for One LED String
GND
LED2
LED3
LED1
LED4
RSET
EN/PWM
CAT4106
VIN
VFMAX
VFMIN
C1
SW
R1
PGND
FB
VCTRL
R3
R5
R7
R8
LED Fault Detection
(open drain pull−down)
R4
R6
R2
C2
L
D
C3
V
IN
V
IN
V
L
FAULT
OFF... ON... DIM...
Figure 28 shows a typical application for driving two
strings of LEDs. The LED current is equal to two times the
channel current.
Figure 28. Application Circuit for Two LED Strings
GND
LED2
LED3
LED1
LED4
RSET
EN/PWM
CAT4106
VIN
VFMAX
VFMIN
C1
SW
R1
PGND
FB
VCTRL
R3
R5
R7
R8
LED Fault Detection
(open drain pull−down)
R4 R6
R2
C2
L
D
C3
OFF... ON... DIM...
FAULT
V
IN
V
IN
V
L
CAT4106
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12
Application Information
External Component Selection
Capacitors
The CAT4106 requires small ceramic capacitors of 1 mF
on the VIN pin (C1), 4.7 mF on the inductor input (C2), and
10 mF on the output (C3). Under normal condition, a 4.7 mF
input capacitor (C2) is sufficient. The voltage rating of each
capacitor should be compatible with the maximum voltage
applied. For the output, a 50 V rated capacitor (C3) is
recommended in case the LED becomes disconnected
(Open−LED condition). X5R and X7R capacitor types are
ideal due to their stability across temperature range.
Inductor
A 47 mH inductor is recommended for most applications.
In cases where the efficiency is critical, inductances with
lower series resistance are preferred. Inductors with current
rating of 1 A or higher are recommended for most
applications. Coiltronics DR73−470 inductor rated at 1.08 A
is recommended for most applications.
Schottky Diode
The current rating of the Schottky diode (D) must exceed
the peak current flowing through it. A 1 A rated Schottky
diode is recommended. The Schottky diode performance is
rated in terms of its forward voltage at a given current. In
order to achieve the best efficiency, this forward voltage
should be as low as possible. The response time is also
critical since the driver is operating at 1 MHz. NXP
PMEG6010CEJ (60 V / 1 A rated) Schottky barrier rectifier
is recommended for most applications.
Recommended Layout
The board layout should provide good thermal dissipation
through the PCB. Multiple via can be used to connect the tab
of the CAT4106 to a large ground plane underneath the
package.
Input capacitor C1 should be placed as close to the driver
IC as possible. The RSET resistor (R1) and channel voltage
setting resistor (R3) should have a Kelvin connection to the
GND pin of the CAT4106.
Figure 29. Recommended Layout for TQFN−16
P1-P3P4-P6P7-P9P10-P12P13-P15

CAT4106HV4-GT2

Mfr. #:
Buy CAT4106HV4-GT2
Manufacturer:
ON Semiconductor
Description:
LED Lighting Drivers LED DRVR BOOST 4CH/10LED
Lifecycle:
New from this manufacturer.
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