AIC1550 Low-Noise Synchronous PWM Step-Down DC/DC Converter DESCRIPTION FEATURES 95% Efficiency or up 800mA Guaranteed Output Current. Adjustable Output Voltage from 0.75V to VIN of a range from +2.5V to 6.5V. Very Low Quiescent Current: 35µA (Typ.). Fixed- 500KHz or Adjustable Frequency Synchronous PWM Operation. Synchronizable external Switching Frequency up to 1MHz. Accurate Reference: 0.75V (±2%). 100% Duty Cycle in Dropout. Low Profile 8-Pin MSOP Package. APPLICATIONS The AIC1550 is a low-noise pulse-widthmodulated (PWM) DC-DC step-down converter. It powers logic circuits in PDAs and small wireless systems such as cellular phones, handy-terminals. The device features an internal synchronous rectifier for high conversion efficiency. Excellent noise characteristics and fixed-frequency operation provide easy post-filtering. The AIC1550 is ideally suited for Li-ion battery applications. It is also suitable for +3V or +5V fixed input applications. The device can operate in either one of the following four modes. PDAs. Digital Still Cameras. Handy-Terminals. (1) Forced PWM mode operates at a fixed frequency regardless of the load. (2) Synchronizable PWM mode allows the synchronization by using an external switching frequency with a minimum harmonics. (3) PWM/PFM Mode extends battery life by switching to a PFM pulseskipping mode under light loads. (4) Shutdown mode sets device to standby, reducing supply current to 0.1µA or under. Cellular Phones. CPU I/O Supplies. Cordless Phones. Notebook Chipset Supplies. Battery-Operated Devices (4 NiMH/ NiCd or 1 Li-ion Cells). The AIC1550 can deliver over 800mA output current. The output voltage can be adjusted from 0.75V to VIN ranging from +2.5V to +6.5V. Other features of the AIC1550 include low quiescent current, low dropout voltage, and a 0.75V reference of ±2% accuracy. It is available in a space-saving 8-pin MSOP package. Analog Integrations Corporation Si-Soft Research Center DS-1550P-04 010405 3A1, No.1, Li-Hsin Rd. I , Science Park , Hsinchu 300, Taiwan , R.O.C. TEL: 886-3-5772500 FAX: 886-3-5772510 www.analog.com.tw 1 AIC1550 TYPICAL APPLICATION CIRCUIT VIN= 2.5V to 6.5V 1 BP CIN 22µF CBP 0.1µF LX VIN 2 BP 3 SHDN 4 FB GND 7 SYNC/ 6 MODE RT 5 VOUT = 1.8V L1 8 * 6.8µH D1 SS12 Optional CF R1 820K AIC1550 12P CO 22µF R2 560K CIN: TAIYO YUDEN LMK316F226ZL-T Ceramic capacitor CO1: TAIYO YUDEN LMK316F226ZL-T Ceramic capacitor L1: TDK SLF6025-6R8M1R3 D1: GS SS12 * Note: Efficiency can boost 2% to 4% if D1 is connected. ORDERING INFORMATION AIC1550XXXX PACKING TYPE TR: TAPE & REEL TB: TUBE PACKAGING TYPE O:MSOP8 PIN CONFIGURATION TOP VIEW VIN 1 BP 2 SHDN 3 FB 4 8 LX 7 GND 6 SYNC/MODE 5 RT C: Commercial Degree P: Lead Free Example: AIC1550COTR In MSOP Package & Taping & Reel Packing Type AIC1550POTR In MSOP Lead Free Package & Taping & Reel Packing Type 2 AIC1550 ABSOLUTE MAXIMUM RATINGS VIN, BP, SHDN, SYNC/MODE, RT to GND BP to VIN -0.3 to +7V .-0.3 to 0.3V LX to GND -0.3 ~ (VIN+0.3V) FB to GND -0.3 ~ (VBP+0.3V) Operating Temperature Range Junction Temperatrue Storage Temperature Range Lead Temperature (Soldering. 10 sec) -40°C ~ 85°C 125°C - 65°C ~ 150°C 260°C Absolute Maximum Ratings are those values beyond which the life of a device may be Impaired. TEST CIRCUIT Refer to Typical Application Circuit. 3 AIC1550 ELECTRICAL CHARACTERISTICS (VIN=+3.6V, TA=+25°C, SYNC/MODE =GND, SHDN =IN, unless otherwise specified.) (Note1) PARAMETER Input Voltage Range Output Adjustment Range Feedback Voltage SYMBOL CONDITIONS V VOUT VREF VIN V VFB 0.735 0.765 V IFB P-Channel Current-Limit +1 % IOUT = 0 to 800mA -1.3 % VFB = 1.4V, -50 0.01 50 VIN = 3.6V 0.32 0.65 VIN = 2.5V 0.38 VIN = 3.6V 0.32 VIN = 2.5V 0.38 (Note 2) Threshold fOSC SYNC Capture Range UVLO VIN rising, typical hysteresis is 85mV VIH SHDN , SYNC/MODE, LIM Logic Input Low VIL SHDN , SYNC/MODE, LIM SYNC/MODE Minimum Pulse Width 70 µA 0.1 1 µA -20 0.1 20 µA 400 500 600 KHz 1000 KHz 100 Logic Input High Logic Input Current 35 500 dutyMAX SHDN , SYNC/MODE, LIM High or low Ω A leakage current VIN = 5.5V, VLX = 0 or 5.5V Ω 2.1 SHDN = LX = GND, includes LX LX Leakage Current 0.65 nA 1.5 VFB = 1.4V, LX unconnected Shutdown Supply Current Threshold 1 SYNC/MODE = GND, Quiescent Current 0.75 Duty Cycle = 100% to 23% N-Channel On-Resistance NRDS(ON) ILX = 100mA Undervoltage Lockout UNITS 6.5 P-Channel On-Resistance PRDS(ON) ILX = 100mA Maximum Duty Cycle MAX 2.5 Load Regulation Oscillator Frequency TYP VIN Line Regulation FB Input Current MIN 1.9 % 2.0 2.1 2 -1 500 V V 0.1 0.4 V 1 µA nS Note 1: Specifications are production tested at TA=25°C. Specifications over the -40°C to 85°C operating temperature range are assured by design, characterization and correlation with Statistical Quality Controls (SQC). Note 2: Maximum specification is guaranteed by design, not production tested. 4 AIC1550 TYPICAL PERFORMANCE CHARACTERISTICS (TA=25oC, VIN=3.6V, SYNC/MODE=GND, with Schottky diode D1, unless otherwise noted.) 100 100 VIN=2.1V 80 70 VIN=5.0V 60 VIN=6.5V VIN=2.3V 80 70 VIN=3.3V VOUT=1.2V VOUT=1.5V 40 0.1 1 10 100 0.1 1000 1 Load Current (mA) (R f 100 1000 t t i l li ti i it) 100 VIN=3.3V VIN=2.1V 90 90 80 70 Efficiency (%) Efficiency (%) 100 (Refer to typical application circuit) (Refer to typical application circuit) VIN=6.5V VIN=5.0V 60 50 0.1 80 70 VIN=6.5V VIN=5.0V 60 50 VOUT=1.8V VIN=3.3V VOUT=2.5V 40 1 10 100 40 1000 0.1 1 Load Current (mA) Fig. 3 Load Current vs. Efficiency (VOUT=1.8V) Fig. 4 (Refer to typical application circuit) 100 1000 Load Current (mA) Load Current vs. Efficiency (VOUT=2.5V) 100 VIN=3.6V VIN=3.6V 90 80 80 Efficiency (%) 90 VIN=4.2V 70 60 50 1 10 100 VIN=6.5V 70 VIN=5.0V 60 VIN=4.2V 50 VOUT=3.0V 0.1 10 (Refer to typical application circuit) 100 Efficiency (%) 10 Load Current (mA) Fig. 2 Load Current vs. Efficiency (VOUT=1.5V) Fig. 1 Load Current vs. Efficiency (VOUT=1.2V) 40 VIN=6.5V VIN=5.0V 60 50 50 40 VIN=2.1V 90 Efficiency (%) Efficiency (%) 90 1000 40 0.1 1 10 VOUT=3.3V 100 1000 Load Current (mA) Load Current (mA) Fig. 5 Load Current vs. Efficiency (VOUT=3.0V) Fig. 6 Load Current vs. Efficiency (VOUT=3.3V) (Refer to typical application circuit) (Refer to typical application circuit) 5 AIC1550 TYPICAL PERFORMANCE CHARACTERISTICS (continued) 0.765 100 W/ Schottky Diode 90 Reference Voltage (V) Efficiency (%) 80 Wo/ Schottky Diode 70 60 SYNC= VIN 50 40 VOUT=3.0V 30 0.1 1 10 Load Current (mA) VIN=3.6V 0.760 SYNC= GND 100 0.755 0.750 0.745 0.740 0.735 0.730 0.725 -50 1000 -25 550 50 75 100 125 550 540 VIN=3.6V 530 530 520 Frequency (KHz) Frequency (KHz) 25 Temperature (°C) Fig. 8 Reference Voltage vs. Temperature Fig. 7 Load Current vs. Efficiency (W/ or W/O Schottky Diode) 540 0 510 500 490 480 520 510 500 490 480 470 470 460 460 450 -40 -20 0 20 40 60 80 100 450 120 2.0 Temperature (°C) 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 Supply Voltage (V) Fig. 10 Frequency vs. Input Voltage Fig. 9 Oscillator Frequency vs. Temperature 1.82 0.44 0.42 Output Voltage (V) RDSON (mΩ) 1.80 Main Switch 0.40 0.38 0.36 0.34 0.32 VIN=3.6V 1.78 1.76 0.30 0.28 1.74 Synchronous Switch 0.26 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Supply Voltage (V) Fig. 11 RDSON vs. Supply Voltage 5.5 6.0 1.72 1 10 100 1000 Load Current (mA) Fig. 12 Output Voltage vs. Load Current 6 AIC1550 TYPICAL PERFORMANCE CHARACTERISTICS (continued) 300 100 VOUT=1.8V PWM/PFM 90 80 200 Efficiency (%) DC Supply Current (μA) 250 SYNC/PWM=IN 150 100 70 PWM 60 50 40 SYNC/PWM=GND 30 VIN=3.6V VOUT=1.8V 50 20 0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 Supply Voltage (V) Fig. 13 DC Supply Current vs. Supply Voltage 10 0.1 1 10 Fig. 14 100 1000 Load current (mA) Efficiency vs. Load current Operation Frequency (KHz) 1000 900 800 700 600 500 2250 2000 Fig. 15 1500 1250 1000 750 Tuning Resistor RT (kΩ) 1750 500 Operation Frequency vs. Tuning Resistor VOUT=1.8V; ILOAD=50mA to 500mA; SYNC/MODE=IN Fig. 17 Load Transient Response 250 Fig. 16 Start-up from Shutdown, RLOAD=3Ω VOUT=1.8V; ILOAD=50mA to 500mA; SYNC/MODE=GND Fig. 18 Load Transient Response 7 AIC1550 TYPICAL PERFORMANCE CHARACTERISTICS (continued) VIN=3.3V to 5V, IOUT=1.8V; ILOAD=200mA to 500mA; SYNC/MODE=IN Fig. 19 Line Transient Response Fig. 20 Short Circuits Protection VIN=3.6V, VOUT=1.8V, ILOAD=800mA VOUT VIN=3.6V; VOUT=1.8V; ILOAD=500mA VLX SYNC/MODE=IN Fig. 21 Switching Waveform Fig. 22 Output Ripple voltage 8 AIC1550 BLOCK DIAGRAM BP C hip S upply 10 0.75V REF C urrent A MP . SHDN V IN V IN + X5 - 5 S lope RT 500K H z O scillator Frequency S YN C + S election P hase C om pensation FB FB REF Q1 x1 C urrent Lim it C om parator C om pensation - E rror A MP . Q2 X20 REF - PW M C om parator + LX A ntiS hootT hrough C ontrol Logic + Q3 P W M/P FM C ontrol Zero C ross C om parator - REF + + GND P FM C om parator PIN DESCRIPTIONS PIN 1: VIN- PIN 2: BP- Supply Voltage Input ranging from +2.5V to +6.5V. Bypass with a 22µF capacitor. Supply Bypass Pin internally connecting to VIN. Bypass with a 0.1µF capacitor. Shutdown-Control PIN 3: SHDN - Active-Low, Input reducing supply current to 0.1µA in shutdown mode. PIN 4: FBFeedback Input. PIN 5: RTFrequency Adjustable Pin connecting to GND through a resistor to increase frequency. (Refer to Fig. 15) PIN 6: SYNC/MODEOscillator Sync and Low-Noise, Mode-Control Input. SYNC/MODE = VIN (Forced PWM Mode) SYNC/MODE = GND (PWM/PFM Mode) An external clock signal connecting to this pin allows LX switching synchronization. PIN 7: GND- Ground. PIN 8: LX- Inductor connecting to the Drains of the Internal Power MOSFETs 9 AIC1550 APPLICATION INFORMATION Introduction AIC1550 is a low-noise, pulse-width-modulated (PWM), DC-DC step-down converter. It features an internal synchronous rectifier, which eliminates external Schottky diode. AIC1550 is suitable for Li-lon battery applications, or can be used at 3V or 5V fixed input voltage. It operates in one of following four modes. (1) Forced PWM mode operates at a fixed frequency regardless of the load. (2) Synchronizable PWM mode allows the synchronization by using an external switching frequency with a minimum harmonics. (3) PWM/PFM Mode extends battery life by switching to a PFM pulseskipping mode under light loads. (4) Shutdown mode sets device to standby, reducing supply current to 0.1µA or under. Continuous output current of AIC1550 can be upward to 800mA and output voltage can be adjusted from 0.75V to VIN with an input range from 2.5V to 6.5V by a voltage divider. AIC1550 also features high efficiency, low dropout voltage, and a 0.75V reference with ±2% accuracy. It is available in a space-saving 8-pin MSOP package. Operation When power on, control logic block detects SYNC/MODE pin connecting to VIN or GND to determine operation function and gives a signal to PWM/PFM control block to determine the proper comparator (ref. Block Diagram). AIC1550 works with an internal synchronous rectifier － Q3, to increase efficiency. When control logic block turns Q2 on, Q3 will turn off through anti-short-through block. Similarly, when Q3 is on, Q2 will turn off. AIC1550 provides current limit function by using a 5Ω resistor. When Q1 turns on, current follows through the 5Ω resistor. And current amplifier senses the voltage, which crosses the resistor, and amplifies it. When the sensed voltage gets bigger than reference voltage, control logic shuts the device off. PWM/PFM Function When connecting SYNC/MODE pin to VIN, the device is forced into PWM (Pulse-WidthModulated) mode with constant frequency. Advantage of constant frequency is easily reducing noise without complex post-filter. But its disadvantage is low efficiency at light loading. Therefore, AIC1550 provides a function to solve this problem. When connecting SYNC/MODE pin to GND, device is able to get into PWM/PFM (Pulse-Frequency-Modulated) modes. Under a light loading condition, the device turns to PFM mode, which results in a higher efficiency. PWM mode is on when heavy loading applies and the noise is reduced. Frequency Synchronization Connecting an external clock signal to SNYC/MODE pin can control switching frequency. The acceptable range is from 500kHz to 1MHz. This mode exhibits low output ripple as well as low audio noise and reduces RF interference while providing reasonable low current efficiency. 10 AIC1550 100% Duty Cycle Operation When the input voltage approaches the output voltage, the converter continuously turns Q2 on. In this mode, the output voltage is equal to the input voltage minus the voltage, which is the drop across Q2. If input voltage is very close to output voltage, the switching mode goes from pure PWM mode to 100% duty cycle operation. During this transient state mentioned above, large output ripple voltage will appear on output terminal. Components Selection Inductor The inductor selection depends on the operating frequency of AIC1550. The internal switching frequency is 500KHz, and the external synchronized frequency ranges from 500KHz to 1MHz. A higher frequency allows the uses of smaller inductor and capacitor values. But, higher frequency results lower efficiency due to the internal switching loss. The ripple current ∆IL interrelates with the inductor value. A lower inductor value gets a higher ripple current. Besides, a higher VIN or VOUT can also get the same result. The inductor value can be calculated as the following formula. V 1 (1) L= VOUT 1 − OUT (f )(∆IL ) VIN Users can define the acceptable ∆IL to gain a suitable inductor value. Since AIC1550 can be used in ceramic capacitor application, the component selection will be different from the one for the application above. AIC1550 has a built-in slope compensation, which acitvates when duty cycle is larger than 0.45. The slope Ma, 0.27V/μs, has to be larger than half of M2. M2 is equal to output voltage divided by L1. The formula of inductor is shown as below: V V OUT = OUT (2) 2 × Ma 2 × 0.27 Note that output voltage can be defined according L1 > to user’s requirement to get a suitable inductor value. Output Capacitor The selection of output capacitor depends on the suitable ripple voltage. Lower ripple voltage corresponds to lower ESR (Equivalent Series Resistor) of output capacitor. Typically, once the ESR is satisfied with the ripple voltage, the value of capacitor is adequate for filtering. The formula of ripple voltage is as below: 1 (3) ∆VOUT = ∆IL ESR + 8 fC OUT Besides, in buck converter architecture frequency stands at 1/√(LC) when a double pole formed by the inductor and output capcitor occurs. This will reduce phase margin of circuit so that the stability gets weakened. Therefore, a feedforward capacitor that is parallel with R1 can be added to reduce output ripple voltage and increase circuit stability. The output capacitor can be calculated as the following formula. 1 L1 × C ≅ O 1 R1 × CF (4) For more reduction in the ripple voltage, a 12pF ceramic capacitor, which is parallel with output capacitor, is used. External Schottky Diode AIC1550 has an internal synchronous rectifier, instead of Schottky diode in buck converter. However, a blank time, which is an interval when both of main switch, Q2, and synchronous rectifier, Q3, are off; occurs at each switching cycle. At the moment, AIC1550 has a decreasing efficiency. Therefore, an external Schottky diode is needed to reinforce the efficiency. 11 AIC1550 Since the diode conducts during the off time, the peak current and voltage of converter is not allowed to exceed the diode ratings. The ratings of diode can be calculated by the following formulas: VD,MAX( OFF ) = VIN ID,MAX( ON) = IOUT,MAX + ID,AVG( ON) (5) ∆IL 2 (6) = IOUT − IIN = IOUT − D × IOUT = (1 − D) × IOUT (7) Adjustable Output Voltage AIC1550 appears a 0.75V reference voltage at FB pin. Output voltage, ranging from 0.75V to VIN, can be set by connecting two external resistors, R1 and R2. VOUT can be calculated as: R1 (8) ) VOUT = 0.75 V × (1 + R2 Applying a 12pF capacitor parallel with R1 can prevent stray pickup. They should sit as close to AIC1550 as possible. But load transient response is degraded by this capacitor. Layout Consideration To ensure a proper operation of AIC1550, the following points should be given attention to: 1. Input capacitor and Vin should be placed as close as possible to each other to reduce the input ripple voltage. 2. The output loop, which is consisted of inductor, Schottky diode and output capacitor, should be kept as small as possible. 3. The routes with large current should be kept short and wide. 4. Logically the large current on the converter, when AIC1550 is on or off, should flow at the same direction. 5. The FB pin should connect to feedback resistors directly. And the route should be away from the noise source, such as inductor of LX line. 6. Grounding all components at the same point may effectively reduce the occurrence of loop. A stability ground plane is very important for gaining higher efficiency. When a ground plane is cut apart, it may cause disturbed signal and noise. If possible, two or three through-holes can ensure the stability of grounding. Fig.24 to 27 show the layout diagrams of AIC1550. Example Here are two examples to prove the components selector guide above. 1. Tantalum capacitors application: Assume AIC1550 is used for mobile phone application, which uses 1-cell Li-ion battery with 2.7V to 4.2V input voltage for power source. The required load current is 800mA, and the output voltage is 1.8V. Substituting VOUT=1.8V, VIN=4.2V, ∆I=250mA, and f=500KHz to equation (1) L= 1 .8 V 1.8 V 1 − = 8.23µH 4 .2 V 500KHz × 250mA Therefore, 10µH is proper for the inductor. And the inductor of series number SLF6025-100M1R0 from TDK with 57.3mΩ series resistor is recommended for the best efficiency. For output capacitor, the ESR is more important than its capacity. Assuming ripple voltage ∆V=100mV, then the ESR can be calculated as: ∆V 100mV ESR= = = 0.4Ω ∆I 250mA Therefore, a 33µH/10V capacitor, MCM series from NIPPON, is recommend. Schottky selection is calculated as following. VD,MAX( OFF ) = VIN = 4.2V 12 AIC1550 ∆IL 2 250mA = 800mA + 2 = 925mA VOUT is substituted by 1.8V in equation (2) as ID,MAX(ON) = IOUT,MAX + L1 > Let L1 = 6.8µH, and choose CF = 12pF, R1 = 820kΩ. ID,avg( ON) = (1 − D) × IOUT Co calculated by the following formula can improve circuit stability. 1 .8 ) × 800mA 4 .2 = 457 .14mA = (1 − 1 According the datas above, the Schottky diode, SS12, from GS is recommend. For feedback resistors, choose R2=390kΩ and R1 can be calculated as follow: 1 .8 V R1 = − 1 × 390kΩ = 546kΩ ; use 560kΩ 0 . 75 Fig. 22 shows the application circuit of AIC1550, and Fig. 23 to 26 show the layout diagrams of it. Of the same AIC1550 application above, except for ceramic capacitor used, Co, R1, and R2 can be calculated as following formulas. And the same values of load current and output voltage at 800mA and 1.8V respectively are used. 1 BP + CIN 10µF CBP 0.1µF LX VIN 2 BP 3 SHDN 4 FB L1 × C C O GND 7 RT 5 O 1 R1 × CF 2 2 ( ( R1 × CF ) 820k × 12pF) = = L1 6.8µ. = 12 µF Say, CO is 22µF. Then, R2 can be decided by equation (8) as R1 = VOUT 1.8 −1= − 1 = 1.4 Vref 0.75 So, R2 = 560kΩ. Note: Schottky diode, SS12 from GS, is still required in this application. VOUT = 1.8V L1 8 SYNC/ 6 MODE ≅ Therefore, R2 2. Ceramic capacitors application: VIN= 2.5V to 6.5V V OUT = 1.8 = 3.33 µH 0.54 0.54 10µF D1 SS12 ** Optional CF R1 560K AIC1550 R2 390K 10P + *CO1 33µF *CO2 4.7µF * Note: CO1 can be omitted if CO2 in 10µF Ceramic CIN: NIPPON 10µF/6V Tantalum capacitor ** Note: Efficiency can boost 2% to 4% if D1 is connected. CO1: NIPPON 33µF/6V Tantalum capacitor L: TDK SLF6025-100M1R0 D1: GS SS12 Fig. 23 AIC1550 Application Circuit (Tantalum capacitor application) 13 AIC1550 Fig. 24 Top Layer Fig. 25 Bottom Layer Fig. 26 Top Over Layer Fig. 27 Bottom Over Layer 14 AIC1550 PHYSICAL DIMENSIONS (unit: mm) MSOP 8 D S Y M B O L MSOP-8 MILLIMETERS MIN. MAX. E E1 A A A SEE VIEW B A1 0.05 0.15 A2 0.75 0.95 b 0.25 0.40 c 0.13 0.23 D 2.90 E A2 e 1.10 E1 2.90 A e L A1 θ 3.10 4.90 BSC 3.10 0.65 BSC 0.40 0.70 0° 6° b 0.25 c WITH PLATING BASE METAL SECTION A-A θ L VIEW B Note: Information provided by AIC is believed to be accurate and reliable. However, we cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an AIC product; nor for any infringement of patents or other rights of third parties that may result from its use. We reserve the right to change the circuitry and specifications without notice. Life Support Policy: AIC does not authorize any AIC product for use in life support devices and/or systems. Life support devices or systems are devices or systems which, (I) are intended for surgical implant into the body or (ii) support or sustain life, and whose failure to perform, when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. 15