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LB1940U Datasheet(PDF) 6 Page - Sanyo Semicon Device |
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LB1940U Datasheet(HTML) 6 Page - Sanyo Semicon Device |
6 / 8 page LB1940T/1940U No.7232-6/8 Application Circuit Diagram At constant-current control: The OUT current is controlled so that the RFG pin voltage is equal to the VC input pin voltage. For example, IOUT = 200mA (= 0.2V/1Ω) when VC = 0.2V and RFB = 1Ω. *: There is no priority relationship between respective input voltages (ENA, IN) and respective supply voltages (VDD, VS). For example, operation with VIN = 5V, VDD = 3V, VS = 2V is possible. Note: The input voltage range to the reference voltage input pin VC for constant-current setting is from 0.19V to 1.0V. Constant current setting The composition of the constant-control circuit of this IC is as shown in the figure below. The voltage entered in the VC pin is entered as a reference to the “+” side input of the constant-current control amplifier. The “-” side of this constant-current control amplifier is connected to the RFG pin via the wire bonded resistor Rb (= 0.1 Ω). The constant-current control circuit consists of comparison of the voltage generated at the external current detection resistor with the above reference voltage. In addition, since the bias current Ib (= 1.5µA) flows out of the positive (+) input of the constant current control amplifier during the constant current control, if the voltage is input to the VC pin by dividing the VREF voltage by 4.5 according to the dividing resistance (70k Ω and 20kΩ) as shown in the figure, the formula for calculating the VC voltage is as follows : VC = VREF/4.5+Ib ×20kΩ = VREF/4.5+0.03 Therefore, the theoretical equation to set the constant current IOUT is as follows: IOUT = VC/(RFB+Rb) = (VREF/4.5+0.03)/(RFB+Rb) ENA1 ENA2 IN1 IN2 S-GND SVDD Vref VC1 VC2 RFG1 RFG2 OUT1 OUT2 VDD VS2 VS1 OUT3 OUT4 CPU FC1 FC2 RfB RfB Ra Rb LB1940T LB1940U |
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