PWM/VFM, Dual-channel Step-up/Inverting DC/DC Converter with Synchronous Rectifier for LCD
The R1287x is a CMOS-based PWM/ VFM dual-channel step-up/ inverting DC/DC converter with synchronous rectifier for LCD. The step-up DC/DC converter (CH1) generates a 4.5V to 5.8V boosted output voltage and the inverting DC/DC converter (CH2) generates a −4.5V to −6.0V inverting output voltage.
Internally, the R1287x consists of an oscillator circuit, PWM control circuits, a reference voltage unit, error amplifiers, soft-start circuits, a LX peak current limit circuit, short protection circuits, thermal shutdown circuit, an under voltage lockout circuit (UVLO), a NMOS transistor driver and a synchronous PMOS transistor driver for CH1, and a PMOS transistor driver and a synchronous NMOS transistor driver for CH2.
The R1287x is employing synchronous rectification for improving the efficiency of rectification by replacing diodes with built-in switching transistors. Using synchronous rectification not only increases circuit performance but also allows a design to reduce parts count.
The R1287x provides the normal PWM control or the PWM/VFM auto switching control. The PWM normal control switches at fixed frequency rate in low output current in order to reduce noise. Likewise, the PWM/VFM auto switching control automatically switches from PWM mode to VFM mode in low output current in order to achieve high efficiency. RICOH’s unique control method can suppress a ripple voltage in the VFM mode, thus the R1287x can achieve both low ripple voltage at light load and high efficiency.
Both CH1 and CH2 can independently control the ON/OFF control and freely set the starting sequence and shutdown sequence.
Both CH1 and CH2 own an auto-discharge function which actively discharges the output voltage to ground when the device is placed in shutdown mode.
The R1287x is offered in a 12-pin WLCSP-12-P1 package and a 12-pin DFN3030-12 package.
||2.5V to 5.5V|
|Selectable Step-up Output Voltage (VOUTP)||R1287xxxxy:||4.5V to 5.8V (0.1V Step)|
|Step-up Output Voltage (Externally adjustable)||R1287x001y:||4.5V to 5.8V|
|Maximum Output Current (Dependent on inductance)||R1287xxxxB/D:||200mA|
|Selectable Step-up Output Voltage (VOUTN)||R1287xxxxy:||−4.5V to −5.8V (0.1V Step)|
|Inverting Output Voltage (externally adjustable)||R1287x001y:||−4.5V to −6.0 V|
|Maximum Output Current (dependent on inductance)||R1287xxxxB/D:||200mA|
|ON/OFF Control: Operates CH1/CH2 separately by the EN1/EN2 pin.|
|Auto-discharge Function: Discharges the output voltage to GND within a short time in shutdown mode.|
|Latch-type Short Circuit Protection: Short-circuiting of either one of CH1 or CH2 activates this circuit.|
- ・Power source for hand-held equipment
- ・Power source for LCD
|Data Sheet||Flyer||Design Guide||Package Info.||Quality Assurance Data|
|R1287x Series||WLCSP-12-P1||to be prepared|
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