CAT4106_14 Datasheet, PDF (9/15 Pages) ON Semiconductor – 6 W Quad Channel DC/DC LED Driver

CAT4106
power−up and works best when V_FMIN is set at least twice
the value of V_L. The VFMIN input circuitry consists of a
comparator referenced to 1.2 V. A typical value for resistor
R7 is around 20 kW. R6 can be calculated as follows:
ǒ Ǔ R6 + R7
V_FMIN
1.2 V
*
1
If this detection feature is not needed, the VFMIN pin
must be tied to ground.
VFMAX pin uses a pair of external resistors (R4 & R5) to
program the worst case, maximum LED string forward
voltage (V_FMAX) expected in the specific application. If any
LED string fails to become regulated before the
programmed voltage is reached, the string will be
considered to contain LEDs which are open−circuit and a
fault condition will be flagged. When an open−circuit is
flagged, the individual channel that causes the open−circuit
is internally flagged and subsequently ignored. In the event
that all channels are detected as being Open−LED, the
Output Voltage (top LED Anode) will stabilize at the
V_FMAX programmed voltage. The VFMAX input circuitry
consists of a comparator referenced to 1.2 V.
A typical value for resistor R5 is 20 kW. R4 can be
calculated as follows:
ǒ Ǔ R4 + R5
V_FMAX
1.2 V
*
1
If this detection feature is not needed, the VFMAX pin
must be tied to ground.
FAULT is an open−drain, active−low, logic signal which
becomes active during an LED short−circuit or open−circuit
condition. The pin must be connected to a pull−up resistor
of around 100 kW tied to VIN. The drive pull−down
resistance (when active) is typically less than 100 W. The
diagnostic sequence used to determine a fault condition is
initiated when the device is first enabled.
PGND pin is the source connection terminal of the high
voltage CMOS power switch in the DC/DC converter. The
inductor supply bypass capacitor should be connected in
close proximity to the PGND pin. The return current from
PGND should be connected to the PCB ground plane.
GND is the ground reference pin for the device. All analog
control voltages are referenced to this pin. In addition, all
LED drive currents are conducted through the GND pin.
TAB is the thermal pad connection of the package and
should be connected to PCB ground plane.
Block Diagram
V_L
L
300 mV
OVP
Controller
1 MHz PWM
Controller
D
R4 R6
R5
R7
SW _VFMAX
VFMIN
Ctrl/Fault
Detector
1A
1W
Supply
VIN
EN/DIM
System
Shutdown ^EN/SD
Delay
I1 I2
PWM_DIM
200 kW
Drive Control
IRSETx100
I3 I4
0 − 175 mA
C3
LED
Cluster
N_Series
M_Parallel
FAULT
mC Diagnostics
CTRL
R2
FB
LED1
LED2
LED3
LED4
R3
LEDn
LED1
RSET
R1
GND
PGND
Figure 24. CAT4106 Simplified Functional Block Diagram
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