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R1218X Schematic ( PDF Datasheet ) - Ricoh Corporation

Teilenummer R1218X
Beschreibung Step Up DC/DC Converter
Hersteller Ricoh Corporation
Logo Ricoh Corporation Logo 




Gesamt 14 Seiten
R1218X Datasheet, Funktion
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R1218x SERIES
Step-up DC/DC converter for Whilte LED Backlight
NO.EA-006-1025
OUTLINE
The R1218X Series are PWM control type step-up DC/DC converter ICs with low supply current. The R1218X
is fully dedicated to drive White LED with constant current. Each of these ICs consists of an NMOS FET, an
oscillator, a PWM comparator, a voltage reference unit, an error amplifier, an under voltage lockout circuit
(UVLO), an over-voltage protection circuit (OVP), and so on. The R1218X can drive white LEDs with high
efficiency with low supply current. A diode is built-in the R1218XXX1A, therefore it is possible to drive up to
4LEDs without an external diode. The R1218XXX2A, an external diode is necessary, however, up to 6 serial
LEDs can be driven with the R1218XXX2A.
Constant current can be set with an external resistance value. Dimming control is possible by PWM signal for
CE pin. Feedback voltage is 0.2V, therefore power loss by current setting resistance is small and efficiency is
good. Maximum duty cycle is internally fixed, Typ. 91%. LEDs can be driven from low voltage. Protection circuits
are the current limit of Lx peak current, the over voltage limit of output, and the under voltage lockout function.
Packages are standard SOT23-6 and very tiny PLP1820-6.
FEATURES
Operating voltage ............................................. 1.8V to 5.5V
Built-in 400mA, 1.5, 20V Nch MOSFET (R1218XXX1A)
Built-in 400mA, 1.5, 29V Nch MOSFET (R1218XXX2A)
High Frequency PWM control .......................... Oscillator Frequency 1.2MHz
Maximum Duty Cycle ....................................... Typ. 91%
Low Feedback Voltage ..................................... Typ. 0.2V
UVLO Threshold Voltage.................................. Typ. 1.6V (Hysteresis Typ. 0.1V)
Lx Current limit Protection ................................ Typ. 700mA
Over Voltage Protection (OVP) Threshold ....... Typ. 9.5V(R1218X02XA)
.......................................................................... Typ. 14.0V(R1218X03XA)
.......................................................................... Typ. 18.5V(R1218X04XA)
.......................................................................... Typ. 23.0V(R1218X052A)
.......................................................................... Typ. 27.5V(R1218X062A)
LED dimming control .....................................by external PWM signal (Frequency 500Hz to 5kHz) to CE pin
.......................................................................by feedback voltage and filtered PWM signal (high frequency)
Packages.......................................................... SOT23-6 or PLP1820-6
APPLICATION
White LED Backlight for portable equipment
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R1218X Datasheet, Funktion
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R1218X
VFB Voltage, Oscillator Frequency, Maximum Duty OVP Detector Threshold, OVP Released Voltage
Test Circuit
Test Circuit
VIN LX
VIN LX
CE
GND
V FB
CE
GND
V OUT
V FB
TYPICAL APPLICATIONS
R1218X041A
L1
22uH
C1
1uF
VIN LX
CE V
OUT
R1218X062A
L1
22uH
C2
0.22uF
C1
1uF
VIN
CE
LX
VOUT
GND VFB
R1
10
GND VFB
C2
0.22uF
R1
10
LED Current setting
LED current can be set with feedback resister(R1)
ILED=VFB/R1
LED Dimming Control, Softstart
(1) LED dimming control by PWM signal to CE pin
LED dimming control is possible by forcing PWM signal to CE pin. When the power-on or start up with CE pin,
softstart function works, however, after that, if the CE pin is set as "L" and set CE pin "H" again during the shutdown
delay time, softstart function is disabled and starts up fast to normal mode, therefore 200Hz to 5kHz PWM signal is
standard. By the CE pin input, LED turns on and off. Average LED current varies depending on the duty cycle of CE input.
Too high frequency PWM signal is not effective because of its delay.
(2)Dimming control by DC voltage
LED dimming control is also possible by using the DC voltage to VFB pin. LED current is adjustable by DC voltage and
resisters, R1 and R2 in the figure 4.
ILED=(DC-0.2)/R2-0.2/R1
(3)Dimming control by feedback voltage and filtered PWM signal
LED dimming control is also possible by using the feedback voltage and filtered PWM signal. LED current is adjustable
according to the "H" level (VH) and "L" level(VL) of PWM signal and resisters, R1, R2, R3, and R4 in the figure5.Duty
6
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R1218X pdf, datenblatt
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R1218X
7. PWM Dimming Control (6 LED) VIN=3.6V,R1=10
7-1. Duty vs. LED Current (Topt=25°C)
25
22.5
20
17.5
15
12.5
10
7.5
5
2.5
0
0
R1218X062A
5kHz
1kHz
200Hz
20 40 60 80 100
DUTY (%)
7-2. Output Voltage Waveform (Topt=25°C)
50 R1218X062A
Fosc=200Hz
10
CE Input Voltage
40
5
30
Output Voltage
20
0
10
0
R1218X062A
50
40 CE Input Voltage
30
20
10 Output Voltage
0
Fosc=5kHz
10
5
0
0 0.8 1.6 2.4 3.2 4
Time (ms)
0 0.04 0.08 0.12 0.16 0.2
Time (ms)
8. VFB Voltage vs. Temperature
0.215
R1218x041A
VIN=3.6V
0.21
0.205
0.2
0.195
0.19
0.185
-50
-25 0
25 50 75
Temperature Topt (°C)
100
9. UVLO Detector Threshold/Released Voltage vs. Temperature
R1218x041A
VIN=3.6V
1.7
1.66
UVLO Released
1.62
1.58
UVLO Detector
1.54
1.5
-50
-25 0 25 50 75
Temperature Topt (°C)
100
12
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