R1218XXX1A RICOH [RICOH electronics devices division], R1218XXX1A Datasheet

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R1218XXX1A

Manufacturer Part Number
R1218XXX1A
Description
Step-up DC/DC converter for Whilte LED Backlight
Manufacturer
RICOH [RICOH electronics devices division]
Datasheet
1.R1218XXX1A.pdf (14 pages)
OUTLINE
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.
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.
FEATURES
APPLICATION
Step-up DC/DC converter for Whilte LED Backlight
The R1218X Series are PWM control type step-up DC/DC converter ICs with low supply current. The R1218X
Constant current can be set with an external resistance value. Dimming control is possible by PWM signal for
Packages are standard SOT23-6 and very tiny PLP1820-6.
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
White LED Backlight for portable equipment
R1218x SERIES
NO.EA-006-1025
1

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R1218XXX1A Summary of contents

Page 1

... 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 serial LEDs can be driven with the R1218XXX2A ...

Page 2

... R1218X BLOCK DIAGRAMS R1218XXX1A Err. Amp PWM Comp + + – – ref ref ref ref Shu tdown delay R1218XXX2A Err. Amp PWM Comp + + – – Vref Vref Vref Vref Shutdown delay ...

Page 3

SELECTION GUIDE The OVP threshold voltage and the package for the ICs can be selected at the user's request. The selection can be available by designating the part number as shown below; R1218xxxxx- Code ...

Page 4

... Chip Enable Pin V Feedback Pin FB Lx Switching Pin (Open Drain Output) GND Ground Pin V Power Supply Input Pin IN V Output Voltage OUT Item R1218XXX1A R1218XXX2A R1218XXX1A R1218XXX2A R1218NXXXA suspended in air R1218KXXXA*Note1 Conditions V =5.5V, V =0V load =5.5V falling ...

Page 5

... GND GND GND GND Conditions V =3. =3.6V, -40 C Topt =5.5V, V = =3.6V, I =100mA IN SW R1218XXX1A V =20V LX R1218XXX2A V =29V LX V =3. =3.6V =0V IN OUT FB V =3.6V =0V IN OUT FB R1218X021A R1218X031A V =3.6V IN R1218X041A V rising OUT ...

Page 6

R1218X VFB Voltage, Oscillator Frequency, Maximum Duty Test Circuit GND GND GND GND TYPICAL APPLICATIONS ...

Page 7

PWM signal duty cycle can be used up to the maximum LED current and minimum LED current as in the next formulas. I =(0.2-R2*(VH-0.2)/(R3+R4))/R1 LEDMIN I =(0.2-R2*(VL-0.2)/(R3+R4))/R1 LEDMAX For example, supposed that the PWM signal level is ...

Page 8

R1218X TYPICAL CHARACTERISTICS 1) Efficiency vs 2LED) L:LQH32CN220 Topt=25 C LED R1218X021A 100 LED Current I R1218X021A 100 ...

Page 9

R1218X031A 100 LED 電流 I LED 3. Efficiency vs. ILED (4 LED ) L: LQH32CN220, Topt=25 C R1218X041A 100 ...

Page 10

R1218X 4. Efficiency vs. I (6LED) L: LQH32CN220, Diode: CRS02 LED R1218X062A 100 LED Current I R1218X062A 100 ...

Page 11

Output Voltage Waveform (Topt=25 C) R1218X021A 25 CE Input Voltage Output Voltage 0.8 1.6 2.4 Time (ms) 6. PWM Dimming Control (4 LED) 6-1. Duty vs. LED Current (Topt=25 C) R1218X041A 25 22.5 ...

Page 12

R1218X 7. PWM Dimming Control (6 LED) 7-1. Duty vs. LED Current (Topt=25 C) R1218X062A 25 22.5 20 17.5 15 12.5 10 7 DUTY (%) 7-2. Output Voltage Waveform (Topt=25 C) R1218X062A 50 CE ...

Page 13

Oscillator Frequency vs. Temperature R1218x041A 1400 1350 1300 1250 1200 1150 1100 1050 1000 -50 - Temperature Topt (°C) 12. OVP Detector Threshold/Released Voltage vs. Temperature R1218x041A 20.5 20 19.5 19 18.5 18 17.5 17 16.5 -50 ...

Page 14

R1218X 15. OVP Transient Response (Topt=25 C) R1218X021A 15 12.5 OVP Voltage 10 7 Time (ms) R1218X062A 35 OVP Voltage Time (ms) 16. Efficiency ...

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