WHITE E STEP-UP CONVERTER FEATURES Inherently Matched E Current High Efficiency: 84% Typical rives Up to Four Es from a 3.2V Supply rives Up to Six Es from a 5V Supply 36V Rugged Bipolar Switch Fast 1.2MHz Switching Frequency Uses Tiny 1mm Tall Inductors Requires Only Output Capacitor APPICATIONS Cellular Phones PAs, Handheld Computers igital Cameras MP3 Players GPS Receivers ESCRIPTION The is a step-up C/C converter specifically designed to drive white Es with a constant current. The device can drive two, three or four Es in series from a i-ion cell. Series connection of the Es provides identical E currents resulting in uniform brightness and eliminating the need for ballast resistors. The output capacitor can be as small as, saving space versus alternative solutions. A low 95mV feedback voltage minimizes power loss for better efficiency. TYPICA APPICATION OFF ON C1 1 F 1 Figure 1. i-ion Powered river for Three White Es 1 E 1 E 2 E 3 C1, C2: X5R OR X7R IEECTRIC 1: CENTRA SEMICONUCTOR CMSH-3 1: MURATA QH3C-22 OR EQUIVAENT 6.3 15mA C2 1937 F1a 9 Conversion Efficiency =3V =3.6V 6 5 1 15 2 E CURRENT (ma) PIN FUNCTIONS TOP VIEW 3 2 1 ORER PART NUMBER CM5 4 5 SOT-23-5 PIN PIN NAME PIN ESCRIPTION 1 Switch Pin. (Minimize trace area at this pin to reduce EMI.) 2 Ground Pin. Connect directly to local ground plane. 3 Feedback Pin. Reference voltage is 95 mv. (Calculate resistor value according to the formula: R =95 mv / I E.) 4 Shutdown Pin. (Connect to 1.5 V or higher to enable device;.4 V or less to disable device.) 5 Input Supply Pin. (Must be locally bypassed.) 1
EECTRICA CHARACTERISTICS T A = 25 C, = 3V, V = 3V, unless otherwise noted. PARAMETER CONITIONS MIN. TYP. MAX. UNIT Minimum Operating Voltage 2.5 V Maximum Operating Voltage 1 V Feedback Voltage I = 1mA, uty Cycle = 66% 86 95 14 mv Pin Bias Current 1 45 1 na 1.9 2.5 ma Supply Current = V.1 1. μa Switching Frequency.8 1.2 1.6 MHz Maximum uty Cycle 9 % Switch Current imit 32 ma Switch V CESAT I = 25mA 35 mv Switch eakage Current V = 5V.1 5 μa Voltage High 1.5 V Voltage ow.4 V Pin Bias Current μa ABSOUTE MAXIMUM RATINGS (Note 1) Input Voltage ( ) 1V Operating Temperature Range C to C Voltage 36V Maximum Junction Temperature 125 C Voltage 1V Storage Temperature Range C to 15 C Voltage 1V ead Temperature (Soldering, 1 sec) 3 C Note 1: Absolute Maximum Ratings are those values beyond which the life of the device may be impaired. Figure 2. BOCK IAGRAM 5 3 V REF 1.25V 95mV + A1 R C COMPARATOR A2 R S Q RIVER 1 Q1 C C + + Switch Pin. 4 SHUTOWN Σ RAMP GENERATOR.2Ω 2 1.2MHz OSCIATOR 1937 B1 2
OPERATION The uses a constant frequency, current mode control scheme to provide excellent line and load regulation. Operation can be best understood by referring to the block diagram in Figure 2. At the start of each oscillator cycle, the SR latch is set, which turns on the power switch Q1. A voltage proportional to the switch current is added to a stabilizing ramp and the resulting sum is fed into the positive terminal of the PWM comparator A2. When this voltage exceeds the level at the negative input of A2, the SR latch is reset turning off the power switch. The level at the negative input of A2 is set by the error amplifier A1, and is simply an amplified version of the difference between the feedback voltage and the reference voltage of 95mV. In this manner, the error amplifier sets the correct peak current level to keep the output in regulation. If the error amplifier s output increases, more current is delivered to the output; if it decreases, less current is delivered. Minimum Output Current The can regulate three series Es connected at low output currents, down to approximately 4mA from a 4.2V supply, without pulse skipping, using the same external components as specified for 15mA operation. As current is further reduced, the device will begin skipping pulses. This will result in some low frequency ripple, although the E current remains regulated on an average basis down to zero. APPICATIONS INFORMATION Inductor Selection A 22mH inductor is recommended for most applications. Although small size and high efficiency are major concerns, the inductor should have low core losses at 1.2MHz and low CR (copper wire resistance). Some inductors in this category with small size are listed in Table 1. Capacitor Selection The small size of ceramic capacitors makes them ideal for applications. X5R and X7R types are recommended because they retain their capacitance over wider voltage and temperature ranges than other types such as Y5V or Z5U. A input capacitor and a output capacitor are sufficient for most applications. Recommended Ceramic Capacitor Manufacturers: Taiyo Yuden, AVX, Murata, Kemet. iode Selection Schottky diodes, with their low forward voltage drop and fast reverse recovery, are the ideal choices for applications. The forward voltage drop of a Schottky diode represents the conduction losses in the diode, while the diode capacitance (C T or C ) represents the switching losses. For diode selection, both forward voltage drop and diode capacitance need to be considered. Schottky diodes with higher current ratings usually have lower forward voltage drop and larger diode capacitance, which can cause significant switching losses at the 1.2MHz switching frequency of the. A Schottky diode rated at 1mA to 2mA is sufficient for most applications. Some recommended Schottky diodes are listed in Table 2. Table 2. Recommended Schottky iodes PART NUMBER FORWAR CURRENT (ma) CMSH-3 1 CMSH2-3 1 BAT54 2 VOTAGE ROP (V).58 at 1mA.49 at 2mA.53 at 1mA IOE CAPACITANCE (pf) 7. at 1V 15 at 1V 1 at 25V MANUFACTURER Central Central Zetex Table 1. Recommended Inductors PART NUMBER CR ( ) CURRENT RATING (ma) MANUFACTURER QH3C22.71 25 Murata EJPC22KF 4. 16 Panasonic CRH316-22.53 35 Sumida B212B22M 1.7 Taiyo Yuden EM252-22 5.5 125 Taiyo Yuden 3
E Current Control The E current is controlled by the feedback resistor ( in Figure 1). The feedback reference is 95mV. The E current is 95mV/. In order to have accurate E current, precision resistors are preferred (1% is recommended). The formula and table 3 for selection are shown below. = 95mV/I E Table 3. Resistor Value Selection I E (ma) ( ) 5 19.1 1 9.53 12 7.87 15 6.34 2 4. Open-Circuit Protection In the cases of output open circuit, when the Es are disconnected from the circuit or the Es fail, the feedback voltage will be zero. The will then switch at a high duty cycle resulting in a high output voltage, which may cause the pin voltage to exceed its maximum 36V rating. A zener diode can be used at the output to limit the voltage on the pin (Figure 3). The zener voltage should be larger than the maximum forward voltage of the E string. The current rating of the zener should be larger than.1ma. 2. Using a C Voltage For some applications, the preferred method of brightness control is a variable C voltage to adjust the E current. The dimming control using a C voltage is shown in Figure 4. As the C voltage increases, the voltage drop on R2 increases and the voltage drop on decreases. Thus, the E current decreases. The selection of R2 and R3 will make the current from the variable C source much smaller than the E current and much larger than the pin bias current. For V C range from V to 2V, the selection of resistors in Figure 4 gives dimming control of E current from ma to 15mA. 3. Using a Filtered PWM Signal The filtered PWM signal can be considered as an adjustable C voltage. It can be used to replace the variable C voltage source in dimming control. The circuit is shown in Figure 5. 1 R2 1k V C R3 R2 6.3Ω 1937 F7 Figure 4. imming Control Using a C Voltage 6.3 1937 F5 Figure 3. E river with Open-Circuit Protection imming Control There are some different types of dimming control circuits: PWM 1k R3. R2 6.3Ω 1937 F8 1. Using a PWM Signal to Pin Figure 5. imming Control Using a Filtered PWM Signal With the PWM signal applied to the pin, the is turned on or off by the PWM signal. The Es operate at either zero or full current. The average E current increases proportionally with the duty cycle of the PWM signal. A % duty cycle will turn off the and corresponds to zero E current. A 1% duty cycle corresponds to full current. The typical frequency range of the PWM signal is 1kHz to 1kHz. The magnitude of the PWM signal should be higher than the minimum voltage high. 4
TYPICA APPICATIONS V C IMMING 2Ω 86 84 82 78 76 74 72 = 3.6V = 3V : TAIYO YUEN JMK17BJ15 : AVX 63Z15 : CENTRA CMSH2-3 : MURATA QH3C22 1937 TA5a 1 2 3 E CURRENT (ma) i-ion to Two White Es Two E Efficiency V C IMMING TYPICA APPICATIO 9 = 3V = 3.6V U 4 1937 TA5a i-ion to Four W : TAIYO YUEN JMK17BJ15 : AVX 63Y224 : CENTRA CMSH-3 : MURATA QH3C22 i-ion to Three White Es 1937 TA1a 6 5 1 15 2 E CURRENT (ma) Three E Efficiency 1937 TA1b V C IMMING = 3V Four E Efficiency = 3.6V : TAIYO YUEN JMK17BJ15 : AVX 63Y224 : CENTRA CMSH-3 : MURATA QH3C22 1937 TA2a 6 5 1 15 2 OA CURRENT (ma) i-ion to Four White Es Four E Efficiency 1937 TA2b REATE PARTS 5
TYPICA APPICATIONS V C IMMING = 3V = 3.6V : TAIYO YUEN JMK17BJ15 : TAIYO YUEN GMK212BJ224 : CENTRA CMSH-3 : MURATA QH3C22 1937 TA3a 2 4 6 8 OA CURRENT (ma) 1 12 1937 TA3b i-ion to Five White Es Five E Efficiency 5V V C IMMING : TAIYO YUEN JMK17BJ15 : TAIYO YUEN GMK212BJ224 : CENTRA CMSH-3 : MURATA QH3C22 1937 TA4a 5 1 OA CURRENT (ma) 1937 TA4b 15 5V to Seven White Es Seven E Efficiency PACKAGE SOT-23-5.62 MAX.95 REF 2.9 BSC (NOTE 4) 1.22 REF 3. MAX 2.62 REF 1.4 MIN 2. BSC 1.5 1. (NOTE 4) PIN ONE RECOMMENE SOER PA AYOUT PER IPC CACUATOR.95 BSC.3.45 TYP 5 PCS (NOTE 3)..9.2 BSC ATUM A 1. MAX.1.1.3.5 REF.9.2 1.9 BSC NOTE: (NOTE 3) S5 TSOT-23 32 1. IMENSIONS ARE IN MIIMETERS 2. RAWING NOT TO SCAE 3. IMENSIONS ARE INCUSIVE OF PATING 4. IMENSIONS ARE EXCUSIVE OF MO FASH AN META BURR 5. MO FASH SHA NOT EXCEE.254mm 6. JEEC PACKAGE REFERENCE IS MO-193 6