R1218X Datasheet, PDF (1/14 Pages) RICOH electronics devices division – Step-up DC/DC converter for Whilte LED Backlight

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, 1.5Ω, 20V Nch MOSFET (R1218XXX1A)
• Built-in 400mA, 1.5Ω, 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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