NJU6050 Просмотр технического описания (PDF) - Japan Radio Corporation
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NJU6050 Datasheet PDF : 8 Pages
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NJU6050
PIN DESCRIPTIONS
No.
SYMBOL
1
SW
2
VSS
3
FB
4
SHDNb
5
VDD
TYPE
Input
Power
Input
Input
Power
DESCRIPTION
Switch Terminal
Ground Terminal
Feedback Terminal
Shutdown Terminal Active “L”
“L” : Shutdown
“H” : Normal Operation
Power Supply terminal
BLOCK DIAGRAM
VIN
C1
L1
VDD
SW
Bias
SHDNb
Shutdown
circuit
VSS
D1
VOUT
DC/DC
Control
-
+
VREF
1.2V
FB
D2
RLED
C2
ILED
FUNCTIONAL DESCRIPTONS
(1) LED Current Control and Resistor RLED Selection
The NJU6050 incorporates the LED current control to regulate the LED current (ILED), which is programmed
by the feedback resistor (RLED) connected between the FB and the VSS terminals. The reference voltage VREF is
internally regulated to 1.2V typical and connected to the positive input of the built-in comparator. Formula (1) is
used to choose the value of the RLED, as shown below.
RLED
= VREF
I LED
--- Formula (1)
VREF=1.2V (typ.)
The ILED is the constant current programmed by the RLED. When the feedback voltage on the FB terminal
reaches above the reference voltage VREF (i.e., ILED is above the level programmed by RLED), the output capacitor
C2 delivers the ILED. Once the feedback voltage drops below the reference voltage (i.e., ILED drops below the level
programmed by the RLED), the MOS switch is turned on, then the current of the inductor L1 begins increasing.
When the switch current reaches 350mA, the MOS switch is turned off, then the L1 delivers current to the output
through the diode D1 as the inductor current drops. After that, the MOS switch is turned on again and the switch
current increases up to 350mA. This switching cycle continues until the ILED reaches the level programmed by the
RLED, then the ILED current is maintained constant.
-2-
Ver.2004-02-25
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