NJRC NJU6048F High efficiency white led driver Datasheet

NJU6048
PRELIMINARY
High Efficiency White LED Driver
! PACKAGE OUTLINE
! GENERAL DESCRIPTION
The NJU6048 is a high-efficiency white LED driver. It
contains a high-efficiency step-up DC/DC converter and an
output driver. The IC can output max.18V and drive as many
as 4 white LEDs in series with a constant current, which
guarantees the LEDs with 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. The
NJU6048 also features low operating voltage of 1.7V and the
small package SOT-23 (MTP-5).
All of these benefits make the NJU6048 suitable for the
battery-powered portable applications such as cellular phones,
camcorders, PDAs, etc.
NJU6048F
! FEATURES
# Drives Up to 4White LEDs in Series
IOUT = 20mA(typical)
# Uses Small Inductor and Capacitors
# 1.7V to 6.5V Operating Voltage for Step-up Circuits (VDD)
# Low Switch RDS (ON)
VSW = 18V, RDS=0.8Ω (ISW=150mA)
# OVP Function
# CMOS Technology
# Package
: SOT-23 5 pin (MTP-5)
! PIN CONFIGURATION (TOP VIEW)
SW
1
VSS
2
FB
3
Ver.2005-06-09
5
VDD
4
OVP
-1-
NJU6048
! PIN DESCRIPTIONS
No.
SYMBOL
TYPE
DESCRIPTION
1
SW
Input
Switch Terminal
2
VSS
Power
Ground Terminal
3
FB
Input
Feedback Terminal
4
OVP
Input
Over Voltage protection Terminal
5
VDD
Power
Power Supply terminal
! BLOCK DIAGRAM
D1
L1
VIN
VDD
VOUT
SW
OVP
C2
C1
OVP
Bias
DC/DC
Control
+
VREF =
0.25V
FB
RLED
ILED
VSS
-2-
Ver.2005-06-09
NJU6048
! FUNCTIONAL DESCRIPTONS
(1) LED Current Control and Resistor RLED Selection
The NJU6048 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. Typically, the reference voltage
VREF is internally regulated to 0.25V and is used as 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=0.25 (typical)
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 250mA, 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 250mA. This switching cycle continues until the ILED reaches the level programmed by the
RLED, then the ILED current is maintained constant.
(2) Over Voltage Protection
OVP is designed to prevent the damage of internal NMOS switch in case the increased impedance of the
LED load (including the LED opened). Once the device detects over voltage at the output, the internal NMOS
switch is kept off until the output voltage drops below 14V.
(3) Inductor Selection
A 10uH inductor is recommended for most application. The selected inductor must have a saturation current
that meets the maximum peak current of the converter. Another important inductor parameter is the DC resistance.
The lower DC resistance the device has higher efficiency.
(4) 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.
(5) 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 NJU6048 application because of not
only the low ESR but also small package. Application requires good line regulation ±1%(typ) should use output
capacitor larger than 1uF. A ceramic capacitor is also recommended for the input decoupling-capacitor C1, and
should be placed as close to the NJU6048 as possible. A 4.7uF is sufficient for most applications.
Ver.2005-06-09
-3-
NJU6048
! ABSOLUTE MAXIMUMN RATINGS
Ta=25°C
PARAMETERS
VDD Power Supply
OVP Terminal to GND
SW Terminal Voltage
FB Terminal Voltage
Power Dissipation
Operating Temperature
Storage Temperature
Note1)
Note2)
SYMBOL
VDD
VOVP
VSW
VFB
PD
Topr
Tstg
CONDITIONS
SW terminal
FB terminal
MTP-5
RATINGS
UNIT
-0.3 to +7.0
-0.3 to 18.0V
-0.3 to +18.0
-0.3 to VDD
200
-40 to +85
-65 to +150
V
V
V
mW
°C
°C
All voltages are relative to VSS = 0V reference.
Do not exceed the absolute maximum 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 impact on the reliability.
! DC ELECTRICAL CHARACTERISTICS
(VDD=3.6V, VSS=0V, Ta=25°C)
PARAMETERS
VDD Power Supply
SYMBOL
CONDITIONS
VDD
OVP Threshold
VOVPTH
OVP Pin Input Current
Quiescent Current
FB Comparator Trip point
IOVPIC
ISTBY1
VFBP
Trigger
Release
VOVP=16V
VFB=0.3V
TYP.
1.7
15
16
10
242
Switch Off Time
tOFF
VFB =0V
Switch RDS(ON)
Switch Current Limit
Switch Leakage Current
RDS
ICL
IL
ISW=150mA
-4-
MIN.
Unit
6.5
17
14
15
80
258
V
V
V
µA
µA
mV
400
200
Switch Off, VSW=18V
250
MAX.
0.8
250
0.1
ns
1.2
300
5.0
Ω
mA
µA
Ver.2005-06-09
NJU6048
•
TEST CIRCUITS
OVP Threshold Voltage
VIN
A
VDD
SW
OVP
A
NJU6048
FB
V
4.7uF
VSS
GND
Quiescent Current
5V
15Ω
VIN
A
VDD
SW
OVP
NJU6048
FB
4.7uF
VSS
0.3V
GND
Ver.2005-06-09
-5-
NJU6048
FB Comparator Trip point
In stepping down VFB from 300mV, VFBP is the threshold voltage to begin switching operation.
A
VIN
VDD
SW
OVP
NJU6048
FB
4.7uF
VSS
V
VFB=300mV
→200mV
GND
Switch Off Time
10uH
VIN
VDD
SW
OVP
NJU6048
1uF
FB
4.7uF
VSS
12Ω
GND
-6-
Ver.2005-06-09
NJU6048
Switch Current Limit / Switch RDS(ON)
V
A
VIN
VDD
SW
OVP
NJU6048
FB
4.7uF
VSS
GND
Switch Leakage Current
18V
A
VIN
VDD
SW
OVP
NJU6048
FB
4.7uF
VSS
GND
Ver.2005-06-09
-7-
NJU6048
! TYPICAL PERFORMANCE
(VDD=3.6V, VSS=0V, L=10µH, Ta=25°C)
Efficiency vs. Output Current
Efficiency vs. Input Voltage
SW RDS_on vs. Input Voltage
SW RDS_on vs. Temperature
Current Limit vs. Input Voltage
-8-
Current Limit vs. Temperature
Ver.2005-06-09
NJU6048
(VDD=3.6V, VSS=0V, L=10µH, Ta=25°C)
OVP Trigger Threshold vs. Input Voltage
OVP Trigger Threshold vs. Temperature
OVP Release Threshold vs. Input Voltage
OVP Release Threshold vs. Temperature
LED Current vs. Input Voltage
Ver.2005-06-09
LED Current vs. Duty Cycle
-9-
NJU6048
(VDD=3.6V, VSS=0V, L=10µH, Ta=25°C)
PWM Dimming
OVP Waveform
Inrush Current Waveform
- 10 -
Ver.2005-06-09
NJU6048
! TYPICAL APPLICATION CIRCUITS
(1) 4 white LEDs
L1
D1
VOUT
VIN
C2
C1
VDD
VSS
SW
OVP
FB
RLED1
Referential List of External Components
IC1
L1
D1
C1
C2
RLED1
LED1 to 4
Ver.2005-06-09
Component
LED Driver IC
Inductor
Schottky Diode
Ceramic Capacitor
Ceramic Capacitor
Chip Resistor
White LED
Supplier / Parts Number
NJRC / NJU6048
Murata / LQH32CN100K23
On Semiconductor / MBR0530
Murata / GRM21BF11A475Z
Taiyo Yuden / TMK325BJ105MD
Standard
Nichia / NSCW215T
Qty
1
1
1
1
1
1
4
Value
10uH
4.7uF/10V
1uF/25V
12Ω
-
- 11 -
NJU6048
(2) 4 white LEDs & Dimming control by external PWM signal
L1
D1
VOUT
VIN
C2
C1
VDD
SW
VSS
OVP
FB
R2
R3
3V(VBIAS)
PWM Input
RLED2
R4
Referential List of External Components
IC1
L1
D1
C1
C2
RLED2
R2
R3
R4
LED1 to 4
- 12 -
Component
LED Driver IC
Inductor
Schottky Diode
Ceramic Capacitor
Ceramic Capacitor
Chip Resistor
Chip Resistor
Chip Resistor
Chip Resistor
White LED
Supplier / Parts Number
NJRC / NJU6048
Murata / LQH32CN100K23
On Semiconductor / MBR0530
Murata / GRM21BF11A475Z
Taiyo Yuden / TMK325BJ105MD
Standard
Standard
Standard
Standard
Nichia / NSCW215T
Qty
1
1
1
1
1
1
1
1
1
4
Value
10uH
4.7uF/10V
1uF/25V
5.1Ω
15KΩ
300KΩ
430KΩ
-
Ver.2005-06-09
NJU6048
MEMO
[CAUTION]
The specifications on this databook are only
given for information , without any guarantee
as regards either mistakes 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.
Ver.2005-06-09
- 13 -
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