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R1218x Series

Step-up DC/DC converter for White LED Backlight

Data Sheet / Flyer

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, a current limit circuit, an under voltage lockout circuit (UVLO), an over-voltage protection circuit (OVP).

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 7 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 resistor is small and efficiency is good. Maximum duty cycle is internally fixed, Typ. 91% to 92%. 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 SOT-23-6 and very tiny DFN(PLP)1820-6.

Input voltage	1.8V to 5.5V
Built-in 400mA, 1.5Ω, 20V Nch MOSFET and diode (R1218xxx1A)
Built-in 400mA, 1.5Ω, 33V Nch MOSFET (R1218xxx2A)
Oscillator Frequency(PWM control)	1.2MHz
Maximum Duty Cycle	Typ. 91% to 92%
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 (R1218x021xA) Typ. 14.0V (R1218x031A) Typ. 18.5V (R1218x041A) Typ. 23.0V (R1218x052A) Typ. 27.5V (R1218x062A) Typ. 31.5V (R1218x072A)
LED dimming control	by external PWM signal (Frequency 200Hz to 5kHz) to CE pin by feedback voltage and filtered PWM signal (high frequency)
Packages	DFN(PLP)1820-6, SOT-23-6