AIC1553CVTR

AIC1553 Compact 500KHz PWM/PFM, Step-Down DC/DC Converters FEATURES Tiny 5-Lead SOT-23 package Uses Tiny Capacitors and Inductor High Frequency Operation: 500KHz High Output Current: 500mA Low RDS(ON) Internal Switch: 0.6Ω High Efficiency: Up to 90% Current Mode Operation for Excellent Line and Load Transient Response Short-Circuit Protected Low Quiescent Current: 22µA Low Dropout Operation: 100% Duty Cycle Ultralow Shutdown Current: IQ < 1µA Peak Inductor Current Independent of Inductor Value Low Output Voltages: Down to 0.75V DESCRIPTION The AIC1553 is a step-down, current mode, DC/DC converter. It operates from 2.5V to 5.5V input voltage range and switches at 500KHz, allowing the use of tiny, low cost capacitors and inductors. The output voltage is adjustable from 0.75V to 5V. A built-in 0.6Ω switch allows up to 0.5A of output current at high efficiency. The AIC1553 operates continuously to very low load currents to provide low ripple at the expense of light load efficiency. With no load, the AIC1553 draws only 22µA. In shutdown mode, it draws less than 1µA, making it ideal for current sensitive applications. The tiny 5-lead SOT-23 package makes it easy to save the layout area. APPLICATIONS Cellular Phones. PDAs and Handy-Terminals. CPU I/O Supplies. Cordless Phones. Notebook Chipset Supplies. Handheld Equipment TYPICAL APPLICATION CIRCUIT U1 VIN 2.5V~5.5V 5 + C1 10µF VIN SW 1 L1 6.8µH C3 22pF R2 560K R1 240K C2 47µF VOUT 2.5V D1 SS12 3 C4 4.7µF GND 2 4 SD VFB ON/OFF AIC1553 2.5V/500mA Step-Down Converter Analog Integrations Corporation 4F, 9 Industry E. 9th Rd, Science-Based Industrial Park, Hsinchu, Taiwan TEL: 886-3-5772500 FAX: 886-3-5772510 www.analog.com.tw DS-1553-P2 061402 1 AIC1553 ORDERING INFORMATION AIC1553CXXX XX PACKING TYPE TR: TAPE & REEL BG: BAG PACKING TYPE TR: TAPE & REEL BG: BAG 1 2 3 PIN CONFIGURATION FRONT VIEW VIN 5 SD 4 PACKAGE TYPE V: SOT-23-5 Example: AIC1553CVTR In SOT-23-5 Package & Tape & Reel Packing Type SW GND VFB SOT-23-5 MARKING Part No. Marking AIC1553CV EP01 ABSOLUTE MAXIMUM RATINGS (Voltage Referred to GND Pin) VIN Pin Voltage SD Voltage (Pin 4) VFB Voltage (Pin 3) VIN – SW (Max Switch Voltage) Operating Temperature Range Junction Temperature Range Storage Temperature Range - 0.3 to + 6V - 0.3 to + 6V - 0.3 to + 6V 7.0V to - 0.3V -40°C ~ 85°C 125°C - 65°C ~ 150°C TEST CIRCUIT Refer to TYPICAL APPLICATION CIRCUIT. 2 AIC1553 ELECTRICAL CHARACTERISTICS (VIN=3.6V, TA=25°C, unless otherwise specified.) PARAMETER Operating Voltage Range Feedback Pin Input Current Feedback Voltage Reference Voltage Line Regulation Output Voltage Load Regulation Quiescent Current Shutdown Mode Input DC Supply Current Shutdown Threshold High Shutdown Threshold Low Peak Switch Current Threshold Switch ON Resistance VSD ISW(PEAK) VFB = 0V RDS(ON) VIN = 3.3V, VFB = 0V 0.3 0.7 SYMBOL VIN IFB VFB ΔVLINE REG VIN=2.5V to 5V, ILOAD=200mA ΔVLOAD REG ILOAD=100mA to 500mA IQ 0.75 5 5 22 0.25 1.4 0.6 1.1 0.6 1 1.6 15 20 TEST CONDITIONS MIN 2.5 TYP MAX 5.5 ±0.1 UNIT V µA V mV mV µA µA V A Ω 3 AIC1553 TYPICAL PERFORMANCE CHARACTERISTICS 0.770 0.765 600 575 Reference Voltage (V) VIN=3.6V Frequency (KHz) 0.760 0.755 0.750 0.745 0.740 0.735 0.730 VIN=3.6V 550 525 500 475 450 425 400 -50 Temperature (°C) 0 50 100 150 -50 0 50 100 150 Temperature (°C) Fig. 2 Frequency vs. Temperature Fig. 2 Reference Voltage vs. Temperature 650 ON Resistance (mΩ) 600 550 500 450 400 2 3 4 5 6 Supply Voltage (V) Fig. 3 Switch Resistance vs. Supply Voltage 100 95 90 100 VOUT=1.5V Efficiency (%) 95 90 85 80 75 70 65 VOUT=2.5V VIN=3.3V VIN=3.3V Efficiency (%) 85 80 75 70 65 60 55 50 45 40 1 10 100 1000 VIN=2.5V VIN=3.3V VIN=5V VIN=5V 1 10 100 1000 Load Current (mA) Fig. 4 Efficiency vs. Load Current Load Current (mA) Fig. 5 Efficiency vs. Load Current 4 AIC1553 TYPICAL PERFORMANCE CHARACTERISTICS 2.60 1.54 (Continued) VOUT=1.5V 2.58 VOUT=2.5V VIN=5V 1.52 VIN=3.3V Output Voltage (V) Output Voltage (V) 2.56 2.54 2.52 2.50 2.48 2.46 2.44 2.42 2.40 1.50 VIN=2.5V 1.48 VIN=3.3V 1.46 0 100 200 300 400 500 0 100 200 300 400 500 Load Current (mA) Fig. 6 Load Regulation 200 180 Load Current (mA) Fig. 7 Load Regulation Supply Current (µA) 160 140 120 100 80 60 40 20 2 VIN=2.5V VOUT=1.5V 3 4 5 6 Supply Voltage (V) Fig. 8 2.60 DC Supply Current 100 VOUT=2.5V 95 90 Output Voltage (V) VOUT=2.5V Efficiency (%) 2.55 ILOAD=200mA 85 80 75 70 65 ILOAD=100mA 2.50 ILOAD400mA 2.45 ILOAD=10mA 2.40 60 2 3 4 5 6 2 3 4 5 6 Supply Voltage (V) Fig. 9 Line Regulation Fig. 10 Supply Voltage (V) Efficiency vs. Input Voltage 5 AIC1553 TYPICAL PERFORMANCE CHARACTERISTICS (Continued) Fig. 11 Start-up ILOAD =400mA VIN =3.3V, VOUT=2.5V Fig. 12 Load Transient Response ILOAD=20mA to 400mA VIN=3.3V, VOUT=2.5V BLOCK DIAGRAM VIN 0.75V REF GND Current AMP. Current Limit Comparator + VIN VIN + X5 5Ω x20 Slope Compensation 500KHz Oscillator x1 LX Phase Compensation FB FB REF Error AMP. PWM Comparator + Control Logic Driver Shutdown SHDN + PWM/PFM Control REF + PFM Comparator 6 AIC1553 PIN DESCRIPTIONS PIN 1: SW - Switch Node. The Switch node connects to the inductor. This pin swings from VIN to a Schottky diode (external) voltage drop below ground. The cathode of the Schottky diode must be closely connected to this pin. - Ground Pin. Connect to the (-) terminal of COUT, the Schottky diode and (-) terminal of CIN. - Output Feedback Pin. Receives the feedback voltage from the external resistive divider across the output. Nominal voltage for this pin is 0.75V. PIN 4: SD - Shutdown Pin. Voltage at 1.6V or higher may enable the device. Connect this pin to Ground for shutdown. - Main Power Supply. Main supply pin and the (+) Input to the Current Comparator. Must be closely decoupled to ground. PIN 5: VIN PIN 2: GND PIN 3: VFB APPLICATION INFORMATION Overview AIC1553 is a step-down DC-DC converter using PWM current mode architecture. The 2.5V to 5.5V input voltage range ideally suited for single Li-ion or 3cell NiMH/NiCd batteries applications. 0.75V of feedback reference voltage allows low output tiny, voltages small down to and 0.75V. Switching Under frequency is set at 500kHz, allowing the use of capacitors inductor. morning load current AIC1553 operates in PWM mode with a fixed switching frequency of typical 500kHz. At light load current, the device automatically enters the PFM mode operation, the switching frequency is reducing to decrease gate charge losses. At the same time, the quiescent current is typically only 22µA to achieve the high efficiency. In shutdown mode, it draws less than 1µA, making it ideal for current sensitive applications. with input voltage feed forward. The fixed switching frequency of typical 500kHz allowing the use of tiny, small capacitors and inductor. The current mode operation achieves excellent line and load transient response. At the beginning of each cycle, the high side P-MOSFET turns on. The current flowed the inductor ramps up and is sensed through an internal circuitry. The high side P-MOSFET turns off until the sensed current causes the PWM comparator to trip or the inductor current reaches the peak switch current threshold 0.7A. The inductor current flows through the external Schottky diode to output terminal. After the period, the switch turns on and the next clock cycle starts again. When the output terminal is short to ground, the input peak current will be limit under the peak switch current threshold 0.7A. PWM Mode Operation During PWM mode operation the converter uses a fast response, current mode, controller circuitry PFM Mode Operation As the load is relatively light and the peak current doesn’t reach the power save mode threshold, 7 AIC1553 the AIC1553 automatically enters a pulse The RL =DC resistance of the inductor frequency modulation (PFM) mode. switching frequency depends on the loading condition and with a minimum quiescent current and maintains high efficiency. The high side PMOSFET operates intermittently. When output voltage drops, the error comparator enable the PFM controller and the output voltage rises until the error comparator trips. When the output voltage falls below until the error comparator trips again and the next cycle will be started. At no load connection, the quiescent current is typically only 22µA. Selecting the Output Voltage The output voltage can be set by a resistive divider. Use the following equation to calculate: VOUT=0.75V(1+R2/R1) The feedback reference voltage 0.75V allows low output voltages from 0.75V to input voltage. For stability of feedback compensation, it is required a small bypass capacitor 22pF in parallel to the upper feedback resistor. Shutdown The whole circuit is shutdown when SD pin is low level. In shutdown mode, the supply current is reduced to less 1µA. For proper operation, the SD pin must be connected and must not be left floating. Inductor Selecting The inductor value directly determines the inductor ripple current. The larger the inductor value, the small inductor ripple current and small output ripple voltage. But, the larger the inductor value causes a slower load transient response and larger conduction losses of the inductor. The ∆IL can be calculated as: VOUT  VOUT  1 −  f ×L  VIN  Low Dropout Operation The dropout voltage of buck converter depends on the maximum duty cycle and the voltage across the high site switch. AIC1553 offers a low input to output voltage difference, while it operates in the 100% duty cycle mode. The minimum input voltage to maintain regulation, depending on the loading current and output voltage. The minimum input voltage can be calculated as: VIN(MIN)≥VOUT +IOUT(MAX)(RDS(ON)+RL) Where: IOUT(MAX) = maximum output current RDS(ON) resistance = maximum P-MOSFET turn on ∆IL = To avoid saturation of the inductor, the rated current of the inductor should be less than the peak current of the inductor. IL(PEAK) =IOUT(MAX)+∆L/2 Input and Output Capacitor Selecting The input capacitor must be sufficient to filter the pulsating input current. A low ESR capacitor provides the small drop voltage to stabilize the input voltage during the transient loading. The input capacitor should be larger than 10µF and the ceramic capacitors and low ESR value of tantalum capacitors are recommend. 8 AIC1553 The selection of output capacitor dominates the ESR of the capacitor. The capacitance is adequate for filtering and the low ESR value shows a low ripple voltage. The output ripple voltage can be calculated as: ∆VO ≅  1 ∆IL    8COUT   + ESR     Layout Considerations Due to the high switching frequency and large transient current, the layout is recommended to have a ground plane and short connections to each component. Minimize the length and the sufficient traces for power- flow loop. Fig. 13 is recommended placement for components. Ceramic capacitor with low ESR value provides the low output ripple. For required, the ceramic capacitor parallel a tantalum capacitor is satisfied. Fig. 13 The Recommended Placement and Routing of AIC1553 PHYSICAL DIMENSIONS SOT-23-5 (unit: mm) D C L HE SYMBOL A A1 A2 b C MIN 1.00 — 0.70 0.35 0.10 2.70 1.40 2.60 0.37 1° MAX 1.30 0.10 0.90 0.50 0.25 3.10 1.80 3.00 — 9° e θ1 D E e A2 A A1 b 1.90 (TYP) H L θ1 9