cat4104 ON Semiconductor, cat4104 Datasheet - Page 8

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

CAT4104
BLOCK DIAGRAM
BASIC OPERATION
The CAT4104 has four tightly matched current sinks
to regulate LED current in each channel. The LED
current in the four channels is mirrored from the
current flowing through the RSET pin according to the
following formula:
Table 1 shows standard resistor values for RSET and
the corresponding LED current.
Table 1. RSET Resistor Settings
Doc. No. MD-4051 Rev. A
LED Current [mA]
100
175
20
60
VIN
I
LED
EN/PWM
≅
RSET
100
RSET [kΩ]
VIN
0.768
×
6.34
2.10
1.27
1.2
R
SET
Figure 2. CAT4104 Functional Block Diagram
V
1.2 V Reference
Current Setting
8
LED1
Tight current regulation for all channels is possible
over a wide range of input voltages and LED voltages
due to independent current sensing circuitry on each
channel.
Each LED channel needs a minimum of 400 mV
headroom to sink constant regulated current up to
175 mA. If the input supply falls below 2 V, the under-
voltage lockout circuit disables all LED channels. Any
unused LED channels should be left open.
For applications requiring more than 175 mA current,
LED channels can be tied together to sink up to a
total of 700 mA from the one device.
The LED channels can withstand voltages up to 25 V.
This makes the device ideal for driving long strings of
high power LEDs from a high voltage source.
LED2
GND
LED3
LED4
4 Current Sink
Regulators
Characteristics subject to change without notice
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