cat4104 ON Semiconductor, cat4104 Datasheet - Page 9

• Manufacturer Part Number: cat4104
• Description: 700 Ma Quad Channel Constant Current Led Driver
• Manufacturer: ON Semiconductor

12 V
5 V
1 µF
APPLICATION INFORMATION
SINGLE 12 V SUPPLY
The circuit shown in Figure 3 shows how to power the
LEDs from a single 12 V supply using the CAT4104.
Three external components are needed to create a
lower voltage necessary for the VIN pin (below 5.5 V).
The resistor R2 and zener diode Z provide a
regulated voltage while the quiescent current runs
through
recommended
MM3Z6V2 zener diode (in SOD-323 package), and
2N7002L N-Channel transistor (in SOT23).
DAYLIGHT DETECTION
The circuit in Figure 4 shows how to use CAT4104 in
an automatic light sensor application. The light sensor
allows the CAT4104 to be enabled during the day and
disabled during the night. Two external components
are required to configure the part for ambient light
detection and conserve power. Resistor R1 sets the
bias for the light sensor. The recommended part is
Microsemi LX1972 light sensor.
© 2009 SCILLC. All rights reserved.
Characteristics subject to change without notice
C2
1 µF
C2
Figure 3. Single Supply Driving 12 LEDs
Sensor
Light
VDD
VSS
6.2 V
5 kΩ
R2
the
Z
R1
100 kΩ
Figure 4. Daylight Detection
OFF
0.1 µF
768 Ω
0.1 µF
C1
768 Ω
ON
R1
C1
OFF
N-Channel
parts
R1
ON
M
RSET
VIN
EN/PWM
RSET
VIN
EN/PWM
are
CAT4104
CAT4104
GND
GND
transistor
LED1
LED2
LED3
LED4
ON
LED1
LED2
LED3
LED4
Semiconductor
M.
The
175 mA
175 mA
9
NIGHT LIGHT
The circuit shown in Figure 5 illustrates how to use
the CAT4104 in an automatic night light application.
The light sensor allows the CAT4104 to be disabled
during the day and enabled during the night. Five
external
configure the part for night detection. Resistor R3
limits the quiescent current through the N-Channel
transistor M. Resistors R1 and R2 act as a voltage
divider to create the required voltage to turn on
transistor M, which disables the CAT4104. The
recommended parts are ON Semiconductor 2N7002L
N-Channel transistor (in SOT23) and the Microsemi
LX1972 light sensor.
LED CURRENT DERATING
The circuit shown in Figure 6 provides LED
rature derating to avoid over-driving the LED under
high ambient temperatures, by reducing
current to protect the LED from over-heating. The
positive thermo coefficient (PTC) thermistor RPTC is
used for temperature sensing and should be located
near the LED. As the temperature of RPTC increases,
the gate voltage of the MOSFET M1 decreases. This
causes the transistor M1 on-resistance to increase
which results in a reduction of the LED current. The
circuit is powered from a single VCC voltage of 5 V.
The recommended parts are Vishay 70ºC thermistor
PTCSS12T071DTE and ON Semiconductor 2N7002L
N-Channel transistor (in SOT23).
The PCB and heatsink for the LED should be designed
such that the LED current is constant within the normal
temperature range. But as soon as the ambient
temperature exceeds a max threshold, the LED current
drops to protect the LEDs from overheating.
5 V
1 µF
C2
1 MΩ
R2
Sensor
Light
VDD
VSS
components
R1
100 kΩ
Figure 5. Night Detection
0.1 µF
M
R3
100 kΩ
768 Ω
OFF
C1
R4
ON
are
RSET
VIN
EN/PWM
CAT4104
needed
GND
LED1
LED2
LED3
LED4
Doc. No. MD-4051 Rev. A
to
CAT4104
the LED
properly
tempe-
175 mA