L6920 1V HIGH EFFICIENCY SYNCRONOUS STEP UP CONVERTER ■ ■ ■ ■ ■ ■ ■ ■ 0.6 TO 5.5V OPERATING INPUT VOLTAGE 1V START UP INPUT VOLTAGE INTERNAL SYNCHRONOUS RECTIFIER ZERO SHUT DOWN CURRENT 3.3V AND 5V FIXED OR ADJUSTABLE OUTPUT VOLTAGE (2V UP TO 5.2V) 120mΩ INTERNAL ACTIVE SWITCH LOW BATTERY VOLTAGE DETECTION REVERSE BATTERY PROTECTION TSSOP8 ORDERING NUMBER: L6920D DESCRIPTION Applications ■ ONE TO THREE CELL BATTERY DEVICES ■ PDA AND HAND HELD INSTRUMENTS ■ CELLULAR PHONES - DIGITAL CORDLESS PHONE ■ PAGERS ■ GPS ■ DIGITAL CAMERAS The L6920 is a high efficiency step-up controller requiring only three external components to realize the conversion from the battery voltage to the selected output voltage. The start up is guaranteed at 1V and the device is operating down to 0.6V. Internal synchronous rectifier is implemented with a 120mΩ P-channel MOSFET and, in order to improve the efficiency, a variable frequency control is implemented. APPLICATION CIRCUIT L1 VCC 2.5V LX 8 7 C2 1 SHDN 5 LBI 2 3 REF 4 6 L6920 OUT VOUT 3.3V 500mA FB C3 C1 LBO GND D00IN1136C May 2003 1/12 L6920 PIN DESCRIPTION Pin Name Function 1 FB Output voltage selector. Connect FB to GND for Vout=5V or to OUT for Vout=3.3V. Connect FB to an external resistor divider for adjustable output voltage (from 2V to 5.2V) [see R4 and R5, fig. 7]. 2 LBI Battery low voltage detector input. The internal threshold is set to 1.23V. A resistor divider is needed to adjust the desired low battery threshold: R1 V LBI = 1.23V ⋅ 1 + -------- [see R1 and R2, fig. 7] R2 3 LBO Battery low voltage detector output. If the voltage at the LBI pin drops below the internal threshold typ. 1.23V, LBO goes low. The LBO is an open drain output and so a pull-up resistor (about 200KΩ) has to be added for correct output setting [see R3, fig. 7]. 4 REF 1.23V reference voltage. Bypass this output to GND with a 100nF capacitor for filtering high frequency noise. No capacitor is required for stability 5 SHDN Shutdown pin. When pin 5 is below 0.2V the device is in shutdown, when pin 5 is above 0.6V the device is operating. 6 GND 7 LX 8 OUT Ground pin Step-up inductor connection Power OUTPUT pin PIN CONNECTION (Top view) FB 1 8 OUT LBI 2 7 LX LBO 3 6 GND 4 5 SHDN REF TSSOP8 ABSOLUTE MAXIMUM RATINGS Symbol Vccmax Vout max Parameter Value Unit Vcc to GND 6 V LBI, SHDN, FB to GND 6 V Vout to GND 6 V Value Unit Thermal Resistance Junction to Ambient 250 °C/W Maximum Junction Temperature 150 °C THERMAL DATA Symbol Rth j-amb Tj 2/12 Parameter L6920 ELECTRICAL CHARACTERISTCS (Vin = 2V, FB = GND, Tamb = -40°C to 85°C and Tj < 125°C unless otherwise specified)) Symbol Parameter Test Condition Min. Typ. Max. Unit VCC SECTION Vin Minimum operating Input Voltage Vin Minimum Start Up Input Voltage Iq Quiescent Current 0.6 V 1 V Il =0 mA, FB = 1.4V, Vout = 3.3V LBI = SHDN = 2V, Tj = Tamb 9 15 µA Il =0 mA, FB = 1.4V, Vout = 5V LBI = SHDN = 2V, Tj = Tamb 11 18 µA Isd Shut Down Current Vin = 5V, Il =0 mA 0.1 5 µA Irev Reverse battery current Vin = -4V, Tj = Tamb 0.1 2 µA POWER SECTION Ron-N Active switch ON resistance 120 250 mΩ Ron-P Synchronous switch ON resistance 120 250 mΩ CONTROL SECTION Vout Output voltage Output voltage range VLBI FB = OUT, Il =0 mA 3.2 3.3 3.4 V FB = GND, Il =0 mA 4.9 5 5.1 V 5.2 V External divider LBI threshold 0°C < Tj < 70°C VLBO Ilim LBO logic LOW 2 1.18 1.23 1.27 V 1.205 1.23 1.255 V 0.2 0.4 V 0.8 1 1.2 A Isink < 250µA LX switch current limit Tonmax Maximum on time Vout = 2V to 5.3V 3.75 5 6.25 µs Toffmin Minimum off time Vout = 2V to 5.3V 0.75 1 1.25 µs SHDN SHDN logic LOW 0.2 V Vref SHDN logic HIGH 0.6 Reference Voltage 1.18 V 1.23 1.27 V 3/12 L6920 Figure 1. Efficiency vs. Output Current Figure 3. Startup Voltage vs Output Current 1.4 100 Vin = 2.4V 90 1.2 80 Vin = 1.2V 1 Startup voltage (V) EFFICIENCY η [%] 70 60 50 40 30 Vout = 3.3V L = 47µH C = 100µF 20 0.8 0.6 0.4 10 L = 47µH C = 22µF 0.2 0 0.01 0.1 1 10 100 1000 LOAD CURRENT [mA] 0 30 100 Vin = 3.6V 90 Vin = 2.4V 80 Vin = 1.2V EFFICIENCY η [%] 70 60 50 f Vout = 5V L = 47µH C = 100µF 40 30 20 10 0 0.01 0.1 1 10 LOAD CURRENT [mA] 4/12 100 60 90 120 Output current (mA) Figure 2. Efficiency vs. Output Current 1000 150 180 L6920 DETAILED DESCRIPTION The L6920 is a high efficiency, low voltage step-up DC/DC converter particularly suitable for 1 to 3 cells (Li-Ion/ polymer, NiMH respectively) battery up conversion. These performances are achieved via a strong reduction of quiescent current (10µA only) and adopting a synchronous rectification, that implies also a reduced cost in the application (no external diode required). Operation is based on maximum ON time - minimum OFF time control, tailored by a current limit set to 1A. A simplified block diagram is shown here below. Figure 4. Simplified Block Diagram VOUT OUT ZERO CROSSING - VREF + + -+ VBG SHDN A FB Y VOUT GND R1,R2 A B C Y B - VOUT LX OPAMP (CR) + C VBG - Q Toff min 1µsec S + GND + R CURRENT LIMIT LBO VIN FB Ton max 5µsec VBG LBI D99IN1041 PRINCIPLE OF OPERATION In L6920 the control is based on a comparator that continuously checks the status of output voltage. If the output voltage is lower than the expected value, the control function of the L6920 directs the energy stored in the inductor to be transferred to the load. This is accomplished by alternating between two basic steps: - TON phase: the energy is transferred from the battery to the inductor by shorting LX node to ground via the Nchannel power switch. The switch is turned off if the current flowing in the inductor reaches 1A or after a maximum on time set to 5µs. - TOFF phase: the energy stored in the inductor is transferred to the load through the synchronous switch for at least a minimum off time equal to 1µs. After this, the synchronous switch is turned off as soon as the output voltage goes lower than the regulated voltage or the current flowing in the inductor goes down to zero. So, in case of light load, the device works in PFM mode, as shown in figure 5. 5/12 L6920 Figure 5.1. PFM mode Condition: Vout = 5V; Vin =1.5V. Trace1: Vout (50mV~/div) Trace 4: IL (100mA/div) Time div.: 5µs/div Figure 5.3. Heavy load - Inductor current ripples below Ilim Trace1: Vout (100mV~/div) Trace 4: IL (200mA/div) Time div.: 20 µs/div Figure 5.2. Heavier load - Train pulses overlapping. Trace1: Vout (100mV~/div) Trace 4: IL (200mA/div) Time div.: 10 µs/div Figure 5.4. Heavy load and High ESR. Regulation falls in continuous mode of operation. Trace1: Vout (100mV~/div) Trace 4: IL (200mA/div). Time div.: 5 µs/div When Iload is heavier, the pulse trains are overlapped. Figures 5.2 - 5.4 show some possible behaviors. Considering that current in the inductor is limited to 1A, the maximum load current is defined by the following relationship: V in V out – V in I lo ad_lim = ----------- ⋅ I lim – T off min ⋅ -------------------------- ⋅ η eq. (1) V out 2⋅L Where η is the efficiency and Ilim =1A. Of course, if Iload is greater than Iload_lim the regulation is lost (figure 6). 6/12 L6920 Figure 6. No regulation. Iload > Iload_lim Trace1: Vout (100mV~/div) Trace 4: IL (200mA/div). Time div.: 5 µs/div The synchronous switch body diode causes a parasitic path between power supply and output that can't be avoided also in shutdown. Low battery detection The L6920 includes a low battery detector comparator. Threshold is VREF voltage and a 1.3% hysteresis is added to avoid oscillations when input crosses the threshold slowly. The LBO is an open drain output so a pull up resistor is required for a proper use. Reverse polarity A protection circuit has been implemented to avoid that L6920 and the battery are destroyed in case of wrong battery insertion. Start-up In addition, this circuit has been designed so that the current required by the battery is zero also in reverse polarity. One of the key features of L6920 is the startup at supply voltage down to 1V (please see the diagram in Figure 3. in case of heavy load). APPLICATION INFORMATION The device leaves the startup mode of operation as soon as VOUT goes over 1.4V. During startup, the synchronous switch is off and the energy is transferred to the load through its intrinsic body diode. Output voltage must be selected acting on FB pin. Three choices are available: fixed 3.3V, 5V or adjustable output set via an external resistor divider. The N-channel switches with a very low RDSon thanks to an internal charge pump used to bias the power mos gate. Because of this modified behavior, TON/TOFF times are lengthened. Current limit and zero crossing detection are still available. Shutdown In shutdown mode (SHDN pulled low) all internal circuitries are turned off, minimizing the current provided by the battery (ISHDN < 100 nA, in typical case). Both switches are turned off, and the low battery comparator output is forced in high impedance state. Output voltage selection OUTPUT VOLTAGE SELECTION VOUT = 3.3V FB pin connected to OUT (see application circuit) VOUT = 5V FB pin connected to GND 2V ≤ VOUT ≤ 5.2V FB pin connected to a resistive divider VOUT = 1.23V 1 + R4 -------- R5 7/12 L6920 Figure 7. Demoboard Circuit Panasonic ELL6RH100M +VBATT VBATT R1 N.C. LBI 7 GND 8 C4 100nF 4 VOUT 6 1 VOUT 5 C1 47µF C3 N.C. R3 N.C. L6920 3 GND Panasonic EEFCDJ470R GND LBO LBO SHDN J1 1 2 3 SHDN 1 F.B. R4 N.C. 2 J2 3 R5 N.C. not mounted components Jumper Panasonic EEFCDJ470R C2 47µF 2 R2 N.C. VREF +VBATT L1 10µH Position D01IN1310 Function 1-2 Device enabled 2-3 Device disabled J1 None J2 Adjustable using R4 and R5 [not mounted] 1-2 3.3V output voltage 2-3 5V output voltage R4, R5 should be selected in the range of 100kΩ - 10MΩ to minimize consumption and error due to current sunk by FB pin (few nA). Output capacitor selection The output capacitor affects both efficiency and output ripple so its choice has to be considered with particular care. The capacitance value should be in the range of about 10µF-100µF. An additional, smaller, low ESR capacitor can be in parallel for high frequency filtering. A typical value can be around 1µF. If very high performances, in terms of efficiency and output voltage ripple, are required, a very low ESR capacitor has to be chosen. Ceramic capacitors are the lowest ESR but they are very expensive. Other possibilities are low-ESR tantalum capacitors, available from KEMET, AVX and other sources. POSCAP capacitors from SANYO and polymeric capacitors from PANASONIC are also good. Below there is a list of some capacitors suppliers. The cap values and rated voltages are only a suggested possibility 8/12 L6920 Table 1. Capacitors distributors main list Manufacturer Series Cap Value (µF) Rated Voltage (V) ESR (mΩ) AVX TPS 15 to 470 6.3 50 to 1500 KEMET T510/T494/ T495 10 to 470 6 30 to 1000 PANASONIC EEFCD 22 to 47 6.3 50 to 700 SANYO POSCAP TPA/B/C 22 to 230 6.3 40 to 80 SPRAGUE 595D 100 to 390 6.3 160 to 700 Inductor selection Usually, inductors ranging between 5µH to 40µH satisfy most of the applications. Small value inductors have smaller physical size and guarantee a faster response to load transient but in steady state condition a bigger ripple on output voltage is generated. In fact the output ripple voltage is given by Ipeak multiplied by ESR. Furthermore, as shown in equation (1), inductor size affects also the maximum current deliverable to the load. Lastly, a low series resistance is suggested if very high efficiency values are needed. Anyway, the saturation current of the choke should be higher than the peak current limit of the device (1A). Good surface mounting inductors are available from COILCRAFTS, COILTRONICS, MURATA and other souces. In the following table are listed some suggested components. Table 2. Inductors distributors main list Manufacturer Coilcraft Series Inductor Value (uH) Saturation Current (A) DO1813HC 22 to 33 1 to 1.2 DO1608 4.7 to 15 0.9 to 1.5 UP1B 22 to 33 1 to 1.2 TP3 4.7 to 15 0.97 to 1.6 HM76-2 22 to 33 1 to 1.2 HM76-1 4.7 to 10 1 to 1.5 Murata LQN6C 10 to 22 1.2 to 1.7 Panasonic ELL6SH 10 to 22 0.9 to 1.5 ELL6RH 5.1 to10 11 to 1.55 CR43 4.7 to 10 0.84 to 1.15 Coiltronics BI Sumida Layout Guidelines The board layout is very important in order to minimize noise, high frequency resonance problems and electromagnetic interference. It is essential to keep as small as possible the high switching current circulating paths to reduce radiation and resonance problems. So, the output and input cap should be very close to the device. The external resistor dividers, if used, should be as close as possible to the pins of the device (FB and LBI) and as far as possible from the high current circulating paths, to avoid pick up noise. Large traces for high current paths and an extended groundplane, help to reduce the noise and increase the efficiency. For an example of recommended layout see the following evaluation board 9/12 L6920 Figure 8. Figure 8. Demoboard Components (Top side). 4.5cm 4cm Figure 9. Demoboard Layout (Top side). 4.5cm 4cm Figure 10. Demoboard Layout (Bottom side). 4.5cm 4cm 10/12 L6920 mm inch DIM. MIN. TYP. A MAX. MIN. TYP. 1.20 A1 0.050 A2 0.800 b MAX. 0.047 0.150 0.002 1.050 0.031 0.190 0.300 0.007 0.012 c 0.090 0.200 0.003 0.008 D (1) 2.900 3.000 3.100 0.114 0.118 0.122 E 6.200 6.400 6.650 0.244 0.252 0.260 E1 (1) 4.300 4.400 4.500 0.169 0.173 0.177 e L L1 k aaa Note: 1.000 0.650 0.450 0.600 OUTLINE AND MECHANICAL DATA 0.006 0.039 0.041 0.026 0.750 0.018 1.000 0.024 0.027 0.039 0˚ (min.) 8˚ (max.) 0.100 0.004 1. D and F does not include mold flash or protrusions. Mold flash or potrusions shall not exceed 0.15mm (.006inch) per side. TSSOP8 (Body 4.4mm) 0079397 (Jedec MO-153-AA) 11/12 L6920 Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specifications mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics. The ST logo is a registered trademark of STMicroelectronics © 2003 STMicroelectronics - All Rights Reserved STMicroelectronics GROUP OF COMPANIES Australia - Brazil - Canada - China - Finland - France - Germany - Hong Kong - India - Israel - Italy - Japan -Malaysia - Malta - Morocco Singapore - Spain - Sweden - Switzerland - United Kingdom - United States. http://www.st.com 12/12