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NJU6050
Ver.2003-12-26
High Efficienc y White LED Dri ver
! GENERAL DESCRIPTION
The NJU6050 is a high-efficiency white LED driver. It
contains a high-efficiency step-up DC/DC converter and an
output driver. The IC ensures a 28V maximum capacity
which allows series connection of 8 white LEDs with a
constant current so that the LED currents are identical for
uniform brightness.
The high frequency of the step-up converter permits the
use of small, low-profile inductors and capacitors to
minimize the footprint in space-conscious applications. And
additional features are a low operating voltage of 2.5V and
the small package SOT-23 (MTP-5).
All of these benefits make the NJU6050 suitable for the
battery-powered portable applications such as a cellular
phone, a camcorder, PDA, etc.
! FEATURES
#
Drives Up to 8 White LEDs in Series
V
SW
= 28V, I
OUT
= 20mA
#
Uses Small Inductor and Capacitors
#
2.5V to 6.5V Operating Voltage for Step-up Circuits (V
DD
)
#
CMOS Techno logy
#
Package : SOT-23 5 pin (MTP-5)
! PIN CONFIG URATION ( TOP VIEW)
PRELIMINARY
!PACKAGE O UTLINE
SW
V
SS
FB
1
2
3 4
5V
DD
SHDNb
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NJU6050
Ver.2003-12-26
! PIN DESCRIPTIO NS
No. SYMBOL TYPE DESCRIPTION
1 SW Input Switch Terminal
2 V
SS
Power Ground Terminal
3 FB Input Feedback Terminal
4 SHDNb Input Shutdow n Terminal Active “L”
“L” : Shutdown
“H” : Normal Operation
5 V
DD
Power Power Supply terminal
! BLOCK DIAGR AM
! FUNCTIONAL DESCRIPTONS
(1) LED Current Cont rol and Resistor R
LED
Selection
The NJU6050 incorporates the LED current cont rol to regulate the LED current (I
LED
), which is programmed
by the feedback resistor (R
LED
) connected between the FB and the V
SS
terminals. The reference voltage V
REF
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 R
LED
, as shown below.
V
REF
=1.2V (typ.)
The I
LED
is the constant current programmed by the R
LED
. When the feedback voltage on the FB terminal
reaches above the reference voltage V
REF
(i.e., I
LED
is above the level programme d by R
LED
), the output capacitor
C2 delivers the I
LED
. Once the feedback voltage drops below the reference voltage (i.e., I
LED
drops below the level
programmed by the R
LED
), 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 I
LED
reaches the level programmed by the
R
LED
, then the I
LED
current is maintained constant.
LED
REF
LED
I
V
R=
--- Formula (1)
FB C2
SHDNb
D1
C1
Shutdown
circuit
V
DD
V
SS
DC/DC
Control
V
REF
SW
-
+
V
IN
V
OU
T
L1
R
L
E
D
1.2V
Bias
I
LED
D2
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NJU6050
Ver.2003-12-26
(2) Inductor Selection
The following equation gives the optimum inductor value:
L = t
OFF
Formula (2)
VD : Schottky diode Voltage
I
CL
:Switch current limit
The power supply voltage V
IN
may fluctuate in battery-powered applications. For this reason, the minimum
voltage should be applied to the V
IN
in Formula (2).
The NJU6050 has about 100ns of delay time (T
DELAY
), which is defined as the period from the reach of the
current limit 350mA to the MOS-switch-off. The T
DELAY
may cause an overshoot-inductor-current, which is called
the peak current I
L,PEAK
, and calculated by Formula (3). Therefore, it is recommended that an inductor with a
rating twice of the I
L,PEAK
and a low DCR (DC resistance) be used for high efficiency.
I
L,PEAK
= I
CL
+ t
DELAY
Formula (3)
V
DS
: Drain-Source voltage of MOS switch (=I
LIMIT
*R
ON
)
V
IN(MAX)
: Maximum of V
IN
Voltage
(3) Diode Selection
A schottky diode with a low forward-voltage-drop and a fast switching-speed is ideal for the D1. And the D1
must have a rating greater than the output voltage and output current in the system.
(4) Capacitor Selection
A low ESR (Equivalent Series Resistance) capacitor should be used as the output capacitor C2 to minimize
output ripples. A multi-layer ceramic capacitor is the best selection for the NJU6050 application because of not
only the low ESR but its small package. A ceramic capacitor is also recommended for the input
decoupling-capacitor C1, and should be placed as close to the NJU6050 as possible.
(5) Open-circuit Protection
The zener diode D2 works as an open-circuit protection. When the LED is disconnected from the circuit, the
feedback voltage on the FB terminal is pulled down to 0V, which makes the switching frequency maximum.
Without the diode D2, the SW voltage exceeds the absolute maximu m rating, and this voltage stress may cause a
permanent damage to the IC.
The zener voltage must be greater than the maximum forward-voltage of the LED string.
V
OUT
-V
IN(MIN)
+V
D
I
CL
V
IN(MAX)
+V
DS
L
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NJU6050
Ver.2003-12-26
! ABSOLUTE MAXIMUMN RATI NGS
Ta=25
°C
PARAMETERS SYMBOL CONDITIONS RATINGS UNIT
VDD Power Supply V
DD
-0.3 to +7.0 V
SHDNb Terminal Voltage V
SHDNb
SHDNb terminal -0.3 to +7.0 V
S W Terminal Volt age V
SW
SW terminal -0.3 to +30.0 V
FB Terminal Volt age V
FB
FB terminal -0.3 to V
DD
V
Power Dissipation PD MTP-5 200 mW
Operating Temperature T
opr
-40 to +85 °C
Storage Temperature T
stg
-65 to +150 °C
Note1) All voltages are relative to V
SS
= 0V reference.
Note2) Do not exceed the absolute maxi mum ratings, otherwise the stress may cause a permanent damage to the IC. It is
also recommended that the IC be used in the range specified in the DC electrical characteristics, or the electrical
stress may cause mulfunctions and im pact on the reliability.
! DC ELECTRICAL CHARACTERISTICS
(V
DD
=3.6V, V
SHDNb
=3.6 V, V
SS
=0V, Ta=25°C)
PARAMETERS SYMBOL CONDITIONS MIN. TYP. MAX. Unit
V
DD
Power Supply V
DD
2.5 6.5 V
I
STBY1
No switching 20 30
Quiescent Current I
STBY2
V
SHDNb
=0V 0.1 1
µA
FB Comparator Trip point V
FBP
1.18 1.2 1.22 V
Output Voltage Line Regulation V
K
2.5V<V
IN
<6.5V -0.05 %/V
FB Terminal Bias Current I
FB
V
FB
= 1.2V 30.0 80.0 nA
V
FB
> 1.0V 500 ns
Switch Off Time t
OFF
V
FB
< 0.6V 1.6
µs
Switch VDS(ON) V
DS
I
SW
=300mA 250 350 mV
Switch Current Limit I
CL
300 350 400 mA
SHDNb Terminal Current I
SHDNb
0.1 1.0
µA
SHDNb Input Voltage High V
SHDNH
0.9 V
SHDNb Input Voltage Low V
SHDNL
0.25 V
Switch Leakage Current I
L
Switch Off, V
SW
=28V 0.01 5.0
µA
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NJU6050
Ver.2003-12-26
! TYPICAL PERFORMANCE
(V
DD
=3.6V, V
SHDNb
=3.6 V, V
SS
=0V, L=10µH, Ta=25°C)
Output Voltage vs. Input Voltage Output Voltage vs. Load Current
Efficiency vs. Load Current Quiescent Current vs. Temperature
V
DS(ON)
vs. Temperature Feedback Voltage vs. Temperature
- 6 -
NJU6050
Ver.2003-12-26
(V
DD
=3.6V, V
SHDNb
=3.6 V, V
SS
=0V, L=10µH, Ta=25°C)
FB Bias Current vs. Temperature Switch Current Limit vs. Temperature
Line Transient Load Transient
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NJU6050
Ver.2003-12-26
! TYPICAL APP LIC ATION CIRCUITS
(1) 8 white LEDs
(2) 8 white LEDs & Dimming control by external PWM signal
Referential List of External Components
Component Supplier / Parts Number Qty Value
IC1 LED Driver IC NJ RC / NJU6050F 1
L1 Inductor MURATA / LQH32CN100K11 1 10µH
D1 Schottky Diode On semiconductor / MBR0530 1
D2 Zener Diode ROHM / UDZS27B 1 27V
C1 Ceramic Capacitor TAIYO YUDEN / CE JMK212BJ475 1 4.7µF 6.3V
C2 Ceramic Capacitor TAIYO YUDEN / CE GMK316BJ105 1 1µF 35V
R
LED
(R1) Chip Resisto r Standard 1
30Ω
R2 Chip Resisto r Standard 1
120kΩ
R3 Chip Resisto r Standard 1
240kΩ
R4 Chip Resisto r Standard 1
620kΩ
LED1 to 8 White LED NICHIA / NSCW 215T 8
D1
L1
C2
SHDNb
C1 V
DD
V
SS
SW
V
IN
V
OUT
R
LED
(30Ω)
FB R2
R3
R4
3V
(
V
BI
A
S
)
PWM Input
D2
D1
L1
C2
SHDNb
C1 V
DD
V
SS
SW
V
IN
V
OU
T
R
LED
(60Ω)
FB
D2
R2
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NJU6050
Ver.2003-12-26
MEMO
[CAUTION]
The specifications on this databook are only
given for information , without any guarantee
as regards either mi stakes or omissions. The
application circuits in this databook are
described only to show representative usages
of the product and not intended for the
guarantee or permission of any right including
the industrial rights.
