LV52206XA Application Notes Rev-B Page No. Update Date 1 2013/11/1 2 2013/11/1 3 2013/11/1 4 2013/11/1 5 2013/11/1 6 2013/11/1 2013/11/1 Contents Overall composition Explanation of the terminal LED Currents setting and Select of control mode Start/Shut Down sequences Board layout External Part Selection Revision History 2013/11/1 < Overall composition > LV52206 is a Boost type DC-DC convertor for White LED drive. It integrated a MOSFET which can tolerate 43V. The maximum LED current is set in the IC inside. The default value is 20mA. We can set 32 steps of current values by using 1-wire control. (Digital mode) We can adjust dimming for LED currents by PWM signal. Change of LED current do not synchronize the PWM signal. It is converted to DC current by LPF of FCAP PIN. Fig.1 Block Diagram 1 < Explanation of the terminal > PIN No. A1 B1 PIN Sign LEDO1 LEDO2 Equivalent circuit Explanations Sink Pin of the LED current ; This PIN connect to the cathodal of the LED and pulls a set current. The voltage is used for the feedback control of DC-DC converter. A2 FCAP Filter PIN for input PWM signals ; A capacitor to convert PWM signal into DC is connected to this PIN. A3 B2 Power supply PIN (2.7V-5.5V) Input PIN of 1-wire and PWM control signal ; VIN SWIRE This PIN is used for enabling and dimming of the LED. B3 OVP OVP detection PIN ; To detect OVP at the time of the LED opening, connect the DC-DC Boost output. C1, C2 C3 GND SW GND PIN Switching PIN ; SW is output PIN of DC-DC convertor. 2 < LED Current setting and Select of control mode > The LED current is set in the IC inside. The default value is 20mA. LED Current setting Address=00 Table.1 Conversion list of LEDI Setting v.s. LED Current LEDI 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 A1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 A0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 D4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 D3 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 D2 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 Fig.2 shows the control curve by the digital mode. D1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 D0 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 LED Current(mA) 0 0.5 1 1.5 2 2.5 3 3.5 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 ; Default Fig.3 shows the control curve by the PWM mode. By the PWM mode, the LED current is decided with input signal DUTY. Fig.2 Digital Mode Fig.3 PWM Mode 3 < Start/Shut Down sequences > 1.Please input "High" into SWIRE PIN during the period that is longer than Ton(20uSec) to start IC. 2.Then, please select a mode during mode select period(Tsel) . When you select Digital Mode, please input "Low" longer than Tw1 after "High" longer than Tw0(100uSec) within Tsel(1mSec) period. It becomes PWM mode if you fail to set Digital mode in specified timing period. In the case of PWM frequency is less than 6.6kHz, it may become Digital Mode when you input a narrow pulse of Duty. To evade it, input "High" that is longer than Tsel(2.2mSec), and, please input PWM pulse afterwards. 3.IC shut down when you make SWIRE PIN Low longer than Toff(8.9ms) period. The Data register is stored at this point. The reset of the power supply is necessary to clear it. In addition, the mode is initialized when you shut down IC. Please make mode select each time you reboot. Digital Mode PWM Mode Fig.4 SWIRE Timing Diagram Start Up Shutdown VIN=3.6V, L=22uH, 6LED*2para Cfcap=22nF LEDI=20mAVIN=3.6V, L=22uH, 6LED*2para Cfcap=22nF LEDI=20mA S WIRE 5v/div S WIRE 5v/div VOUT 10v/div VOUT 10v/div IL 500m/div IL 500m/div Table.2 BITMAP of the LED Control adress A0 A1 R/W DATA D2 D1 D0 LEDI[4:0] 1 1 0 0 0 OVP 0 0 0 0 0 LED2OFFLED1OFF 0 0 0 0 0 Upper column : Register name Lower column : Default value D4 0 0 W 0 1 W 1 0 W D3 4 < Board Layout > The traces that carry the high-frequency switching current have to be carefully designed on the borad in order to minimize EMI, ripple and noise in general. The loop shown on Fig.5 corresponds to the current path when LV52206 internal switch is closed. The thicker lines show the switching current path. All these traces have to be short and wide enough to minimize parasitic inductance and resistance. Fig.6 shows the current loop, when LV52206 switch is open. Both loop areas should be as small as possible. Capacitor C1(VBAT-GND) has to be placed as close as possible to the VBAT pin and GND pin. The connection between SW pin to the inductor and schottky diode should be kept as short and wide as possible. The trace between schottky diode and the output capacitor C2 should also be as short and wide as possible. Capacitor C2(VOUT-GND) has to be placed as close as possible to the GND pin. Capacitor C3(FCAP-GND) has to be placed as close as possible to the FCAP pin. Fig5. Closed-switch Current Loop Fig.6 Open-switch Current Loop 5 < External Part Selection > < Capacitor > The ceramic capacitor from 1uF to 4.7uF is recommended as input capacitor C1. A ceramic capacitor requires attention which capacitance value decreases to by applying rating DC voltage. The ceramic capacitor from 1uF to 2.2uF is recommended as output capacitor C2. When LED become OPEN, because the OVP voltage is applied to each parts, please use parts which can endure 50V. < Schottky diode > To get the optimum efficiency, LV52204 demands a low forward voltage, high-speed and low capacitance schottky diode . Ensure that the diode average and peak current rating exceeds the average output current and peak inductor current. In addition, the diode’s reverse breakdown voltage must exceed the open LED protection voltage. < Inductor > Three different electrical parameters need to be considered when selecting an inductor, the value of the inductor, the saturation current and the DCR. Calculation formula of the peak current Ipeak_p = Iout / (n x ( 1- D )) + ( VIN x D ) / 2 x L1 x Fosc VIN:battery voltage, IOUT:load current, L:inductor value, Fosc: OSC frequency, D:duty cycle, n:converter efficiency varies with load current. D = ((Vout + Vf ) - VIN ) / ( Vout + Vf ) Vout:output voltage, Vf:forward voltage of Schottky diode. It is important to ensure that the inductor current rating is high enough such that it not saturate. As the inductor size is reduced, the peak current for a given set of conditions increases along with higher current ripple so it is not possible to deliver maximum output power at lower inductor values. DCR should be small to make efficiency better. The inductor value from 10uH to 22uH is recommended. 6 < Revision History > Revision O A B Date 2013/8/8 2013/9/4 2013/11/1 Discription of Revision & Writer Initial release requested by Tsutomu Tanaka Addition of External Part selection as Page.6 Correction of the character font Revision Change Originator Nobuyuki Otaka Nobuyuki Otaka Tsutomu Tanaka