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PDF NJU6052 Data sheet ( Hoja de datos )
| Número de pieza | NJU6052 | |
| Descripción | White LED Driver / QFN28-N1 / SSOP20 | |
| Fabricantes | JRC | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de NJU6052 (archivo pdf) en la parte inferior de esta página. Total 23 Páginas | ||
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www.DataSheet4U.com
NJU6052
PRELIMINARY
White LED Driver with Automatic Dimming Control
! GENERAL DESCRIPTION
The NJU6052 is a white LED driver with an automatic
dimming control. It contains an output driver, a PWM
controller, a luminance sensor control (power supply for
sensor & A/D converter), a step-up DC/DC converter, a serial
interface, etc.
The output driver ensures a 60mA maximum capability
which allows the connection of 12 white LEDs (4 series x 3
parallels). Depending on the ambient light sensed with an
external luminance sensor, the PWM controller controls
PWM duty in 8 steps preselected out of 64 steps. In addition,
the frequency of the DC/DC converter is high so that it
permits the use of small, low-profile inductors and capacitors
to minimize the footprint in space-conscious applications.
All of these benefits make the NJU6052 suitable for the
battery-powered portable applications such as a cellular
phone, a camcorder, PDA, etc.
! PACKAGE OUTLINE
NJU6052KN1
NJU6052V
! FEATURES
# Drives up to 12 white LEDs (4 series x 3 parallels)
VSW = 18.0V(Max.), IOUT = 60mA
# Built-in PWM Dimming Control
(Selectable 8 out of 64 steps)
# Built-in Luminance Sensor Control (Power Supply for Sensor & A/D converter)
(No MPU-access required after initial setting)
# Built-in Temperature Compensation Circuit to Suppress the Characteristic Degradation of LEDs
# Uses Small Inductor and Capacitors
# 1.8V to 3.6V Operating Voltage for Logic Circuits (VDDL)
# 3.0V to 5.5V Operating Voltage for Step-up Circuits (VDD)
# CMOS Technology
# Package
: QFN28 / SSOP20
Ver.2004-02-26
-1-
1 page  
www.DataSheet4U.com
! FUNCTIONAL DESCRIPTONS
NJU6052
(1) LED CURRENT CONTROL
The NJU6052 incorporates the LED current control circuit to regulate the LED current (ILED), which is
programmed by the feedback resistor (RLED) connected between the FB and VSS terminals. The reference voltage
VREF is internally regulated to 0.6V typical and connected to the positive input of the built-in comparator A1.
Formula (1) is used to choose the value of the RLED, as shown below.
RLED
= VREF
I LED
--- Formula (1)
VREF=0.6V (TYP.)
Referring to the block diagram is recommended for understanding the operation of the LED current control.
The ILED is the constant current programmed by the RLED. When the feedback voltage on the FB terminal reaches
above the reference voltage VREF on the REF terminal (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 RLED), the comparator A1 detects it and turns on the internal MOS switch,
then the current of the inductor L1 begins increasing. When this switch current reaches 720mA and the
comparator A2 detects it, or when the predetermined switch-on-period expires, the MOS switch is turned off.
The L1 then 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 720mA. This switching cycle continues until the
ILED reaches the level programmed by the RLED, then the ILED is maintained constant.
When the feedback voltage is less than 1/2*VREF, the current limit of the MOS switch is reduced to 500mA
typical. This action reduces the average inductor-current, minimizes the power dissipation and protects the IC
against high current at start-up.
The total forward-voltage of the LEDs must be greater than the power supply voltage VDD, otherwise the
LEDs remain lighting up, being out of control.
(2) OSCILLATOR
The built-in oscillator incorporates a reference power supply, so its frequency is independent from the VDD.
The frequency is varied by the external capacitor CX, as shown in Figure 7.
(3) LUMINANCE SENSOR CONTROL
The luminance sensor control circuits consist of the power supply for sensor and the A/D converter. The A/D
converter senses the voltage on the SENS terminal and selects 1 out of 8 registers (PWM REGISTER 0–7). And
the data in the selected register is reflected to the PWM duty (PWM dimming control). The contents of the
registers can be programmed through the serial interface, in other words, the dimming control is user-settable.
The voltage sense and the register selection are updated at regular intervals, and the interval period is set by
the “DIVIDE” bits. The selected register is held by setting “1” at the “HOLD” bit of the command data.
Ver.2004-02-26
-5-
5 Page 
www.DataSheet4U.com
NJU6052
(9) APPLICATIONS INFORMATION
(9-1) PWM DUTY and LED CURRENT
The average LED current is programmed with the single resistor RLED and the PWM duty, as shown in
Formula (4).
I LED(avg)
=
I LED(max)
⋅
DUTY
100
I LED(max)
=
VREF
RLED
--- Formula (4)
(9-2) INDUCTOR SELECTION
Formula (5) is used to choose an optimum inductor, as shown below:
L
=
2
VOUT
η
− VIN ⋅
I2
LIMIT
⋅
f OSC
I LED
--- Formula (5)
η : Power conversion efficiency (= 0.7 to 0.8)
The power supply voltage VIN may fluctuate in battery-powered applications. For this reason, the minimum
voltage should be applied to the VIN in Formula (5).
The NJU6052 has about 200ns of delay time (TDELAY), which is defined as the period from the reach of the
current limit 720mA to the MOS-switch-off. The TDELAY may cause an overshoot-inductor-current, which is called
the peak current IL,PEAK, and calculated by Formula (6). Therefore, it is recommended that an inductor with a
rating twice of the IL,PEAK and a low DCR (DC resistance) be used for high efficiency.
I L,PEAK
=
I LIMIT
+
VIN(max)
L
−
VDS
⋅ TDELAY
--- Formula (6)
VDS
: Drain-Source voltage of the MOS switch (=ILIMIT*RON)
VIN(MAX) : Maximum of VIN Voltage
(9-3) DIODE SELECTION
A Schottky diode with a low forward-voltage-drop and a fast switching-speed is ideal. And the diode must
have a rating greater than the output voltage and the output current in the system.
(9-4) CAPACITOR SELECTION
A low ESR (Equivalent Series Resistance) capacitor should be used at the output to minimize output ripples. A
multi-layer ceramic capacitor is the best selection for the NJU6052 application because of not only the low ESR
but its small package. A ceramic capacitor as the input decoupling-capacitor is also recommended and should be
placed as close to the NJU6052 as possible.
Ver.2004-02-26
- 11 -
11 Page | ||
| Páginas | Total 23 Páginas | |
| PDF Descargar | [ Datasheet NJU6052.PDF ] | |
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