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NJU6052

REMOTE CONTROL COMMANDER IC

Japan Radio Corporation  

NJU6052

! FUNCTIONAL DESCRIPTONS

(1) LED CURRENT CONTROL

The NJU6052 incorporates the LED current control circuit to regulate the LED current (ILED), which is

programmed by the feedback resistor (RLED) connected between the FB and VSS terminals. The reference voltage

VREF is internally regulated to 0.6V typical and connected to the positive input of the built-in comparator A1.

Formula (1) is used to choose the value of the RLED, as shown below.

RLED

= VREF

I LED

--- Formula (1)

VREF=0.6V (TYP.)

Referring to the block diagram is recommended for understanding the operation of the LED current control.

The ILED is the constant current programmed by the RLED. When the feedback voltage on the FB terminal reaches

above the reference voltage VREF on the REF terminal (i.e., ILED is above the level programmed by RLED), the

output capacitor C2 delivers the ILED. Once the feedback voltage drops below the reference voltage (i.e., ILED

drops below the level programmed by RLED), the comparator A1 detects it and turns on the internal MOS switch,

then the current of the inductor L1 begins increasing. When this switch current reaches 720mA and the

comparator A2 detects it, or when the predetermined switch-on-period expires, the MOS switch is turned off.

The L1 then delivers current to the output through the diode D1 as the inductor current drops. After that, the MOS

switch is turned on again and the switch current increases up to 720mA. This switching cycle continues until the

ILED reaches the level programmed by the RLED, then the ILED is maintained constant.

When the feedback voltage is less than 1/2*VREF, the current limit of the MOS switch is reduced to 500mA

typical. This action reduces the average inductor-current, minimizes the power dissipation and protects the IC

against high current at start-up.

The total forward-voltage of the LEDs must be greater than the power supply voltage VDD, otherwise the

LEDs remain lighting up, being out of control.

(2) OSCILLATOR

The built-in oscillator incorporates a reference power supply, so its frequency is independent from the VDD.

The frequency is varied by the external capacitor CX, as shown in Figure 7.

(3) LUMINANCE SENSOR CONTROL

The luminance sensor control circuits consist of the power supply for sensor and the A/D converter. The A/D

converter senses the voltage on the SENS terminal and selects 1 out of 8 registers (PWM REGISTER 0–7). And

the data in the selected register is reflected to the PWM duty (PWM dimming control). The contents of the

registers can be programmed through the serial interface, in other words, the dimming control is user-settable.

The voltage sense and the register selection are updated at regular intervals, and the interval period is set by

the “DIVIDE” bits. The selected register is held by setting “1” at the “HOLD” bit of the command data.

Ver.2004-02-26

-5-

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