AIC1553 Compact 500KHz PWM/PFM, Step-Down DC/DC Converters FEATURES DESCRIPTION Tiny 5-Lead SOT-23 package Uses Tiny Capacitors and Inductor High Frequency Operation: 500KHz High Output Current: 500mA 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 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 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 Low Quiescent Current: 22µA Low Dropout Operation: 100% Duty Cycle load currents to provide low ripple at the expense of light load efficiency. With no load, Ultralow Shutdown Current: IQ < 1µA Peak Inductor Current Independent of Inductor Value Low Output Voltages: Down to 0.75V 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 APPLICATIONS easy to save the layout area. 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 ON/OFF VFB VOUT 6.8µH 2.5V GND 2 4 SD L1 D1 SS12 C3 22pF 3 R2 560K R1 240K AIC1553 C2 47µF C4 4.7µF 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 PIN CONFIGURATION PACKING TYPE TR: TAPE & REEL BG: BAG FRONT VIEW VIN SD 5 4 PACKING TYPE TR: TAPE & REEL BG: BAG 1 PACKAGE TYPE V: SOT-23-5 Example: 2 3 SW GND VFB AIC1553CVTR In SOT-23-5 Package & Tape & Reel Packing Type SOT-23-5 MARKING Part No. Marking AIC1553CV EP01 ABSOLUTE MAXIMUM RATINGS (Voltage Referred to GND Pin) VIN Pin Voltage - 0.3 to + 6V SD Voltage (Pin 4) - 0.3 to + 6V VFB Voltage (Pin 3) - 0.3 to + 6V VIN – SW (Max Switch Voltage) 7.0V to - 0.3V Operating Temperature Range -40°C ~ 85°C Junction Temperature Range 125°C Storage Temperature Range - 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 SYMBOL Operating Voltage Range VIN Feedback Pin Input Current IFB Feedback Voltage VFB Reference Voltage Line Regulation Output Voltage Load Regulation Quiescent Current TEST CONDITIONS MIN 2.5 Peak Switch Current Threshold Switch ON Resistance UNIT 5.5 V ±0.1 µA V ΔVLINE REG VIN=2.5V to 5V, ILOAD=200mA 5 15 mV ΔVLOAD REG ILOAD=100mA to 500mA 5 20 mV IQ VSD ISW(PEAK) VFB = 0V RDS(ON) µA 22 Supply Current Shutdown Threshold Low MAX 0.75 Shutdown Mode Input DC Shutdown Threshold High TYP VIN = 3.3V, VFB = 0V 0.25 1 1.4 1.6 µA V 0.3 0.6 0.7 1.1 A 0.6 Ω 3 AIC1553 0.770 600 0.765 575 0.760 Frequency (KHz) Reference Voltage (V) TYPICAL PERFORMANCE CHARACTERISTICS VIN=3.6V 0.755 0.750 0.745 0.740 VIN=3.6V 550 525 500 475 450 425 0.735 400 0.730 -50 0 50 100 150 -50 0 Temperature (°C) 50 100 150 Temperature (°C) Fig. 2 Fig. 2 Reference Voltage vs. Temperature Frequency vs. Temperature ON Resistance (mΩ) 650 600 550 500 450 400 2 3 4 5 6 Supply Voltage (V) Fig. 3 Switch Resistance vs. Supply Voltage 100 95 VOUT=1.5V 95 85 Efficiency (%) Efficiency (%) 90 100 80 VIN=2.5V 75 70 65 60 VIN=3.3V VIN=5V 55 50 VOUT=2.5V V VIN =3.3V IN=3.3V 90 85 80 75 VIN=5V 70 45 65 40 1 10 100 1000 1 10 100 Load Current (mA) Load Current (mA) Fig. 4 Efficiency vs. Load Current Fig. 5 Efficiency vs. Load Current 1000 4 AIC1553 TYPICAL PERFORMANCE CHARACTERISTICS (Continued) 2.60 2.58 VOUT=1.5V Output Voltage (V) Output Voltage (V) 1.54 VIN=3.3V 1.52 1.50 VIN=2.5V 1.48 1.46 VOUT=2.5V 2.56 VIN=5V 2.54 2.52 2.50 VIN=3.3V 2.48 2.46 2.44 2.42 2.40 0 100 200 300 400 500 0 Load Current (mA) 100 200 300 400 500 Load Current (mA) Fig. 7 Load Regulation Fig. 6 Load Regulation 200 Supply Current (µA) 180 VIN=2.5V 160 VOUT=1.5V 140 120 100 80 60 40 20 2 3 4 5 6 Supply Voltage (V) Fig. 8 DC Supply Current 100 2.60 95 Output Voltage (V) VOUT=2.5V 2.55 VOUT=2.5V 90 Efficiency (%) ILOAD=200mA 2.50 ILOAD400mA 2.45 85 ILOAD=100mA 80 75 70 ILOAD=10mA 65 2.40 60 2 3 4 5 6 2 3 Fig. 9 Line Regulation 4 5 6 Supply Voltage (V) Supply Voltage (V) Fig. 10 Efficiency vs. Input Voltage 5 AIC1553 TYPICAL PERFORMANCE CHARACTERISTICS Fig. 11 (Continued) Fig. 12 Load Transient Response Start-up ILOAD =400mA ILOAD=20mA to 400mA VIN =3.3V, VOUT=2.5V VIN=3.3V, VOUT=2.5V BLOCK DIAGRAM Current Limit Comparator VIN + VIN - VIN 0.75V REF Current AMP. + X5 GND Slope Compensation 5Ω - 500KHz Oscillator x1 x20 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. PIN 2: GND - Ground Pin. Connect to the (-) terminal of COUT, the Schottky diode and (-) terminal of CIN. PIN 3: VFB - 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. PIN 5: VIN - Main Power Supply. Main supply pin and the (+) Input to the Current Comparator. Must be closely decoupled to ground. APPLICATION INFORMATION with input voltage feed forward. The fixed Overview switching frequency of typical 500kHz allowing AIC1553 is a step-down DC-DC converter using the use of tiny, small capacitors and inductor. The PWM current mode architecture. The 2.5V to current mode operation achieves excellent line 5.5V input voltage range ideally suited for single and load transient response. At the beginning of Li-ion or 3cell NiMH/NiCd batteries applications. each cycle, the high side P-MOSFET turns on. 0.75V of feedback reference voltage allows low The current flowed the inductor ramps up and is output Switching sensed through an internal circuitry. The high frequency is set at 500kHz, allowing the use of side P-MOSFET turns off until the sensed current tiny, Under causes the PWM comparator to trip or the morning load current AIC1553 operates in PWM inductor current reaches the peak switch current mode with a fixed switching frequency of typical threshold 0.7A. The inductor current flows 500kHz. At light load current, the device through the external Schottky diode to output automatically enters the PFM mode operation, terminal. After the period, the switch turns on and the switching frequency is reducing to decrease the next clock cycle starts again. voltages small down capacitors to and 0.75V. inductor. 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 When the output terminal is short to ground, the input peak current will be limit under the peak switch current threshold 0.7A. sensitive applications. PWM Mode Operation PFM Mode Operation During PWM mode operation the converter uses As the load is relatively light and the peak current a fast response, current mode, controller circuitry doesn’t reach the power save mode threshold, 7 AIC1553 the AIC1553 frequency automatically modulation enters (PFM) a pulse mode. RL =DC resistance of the inductor The switching frequency depends on the loading condition and with a minimum quiescent current Selecting the Output Voltage and maintains high efficiency. The high side P- The output voltage can be set by a resistive MOSFET operates intermittently. When output divider. Use the following equation to calculate: voltage drops, the error comparator enable the PFM controller and the output voltage rises until VOUT=0.75V(1+R2/R1) the error comparator trips. When the output The feedback reference voltage 0.75V allows voltage falls below until the error comparator trips low output voltages from 0.75V to input voltage. again and the next cycle will be started. At no load connection, the quiescent current is typically only 22µA. For stability of feedback compensation, it is required a small bypass capacitor 22pF in parallel to the upper feedback resistor. Inductor Selecting 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. 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: Low Dropout Operation ∆IL = The dropout voltage of buck converter depends VOUT VOUT 1 − f ×L VIN on the maximum duty cycle and the voltage To avoid saturation of the inductor, the rated across the high site switch. AIC1553 offers a low current of the inductor should be less than the input to output voltage difference, while it peak current of the inductor. operates in the 100% duty cycle mode. The IL(PEAK) =IOUT(MAX)+∆L/2 minimum input voltage to maintain regulation, depending on the loading current and output voltage. Input and Output Capacitor Selecting The minimum input voltage can be calculated as: The input capacitor must be sufficient to filter the VIN(MIN)≥VOUT +IOUT(MAX)(RDS(ON)+RL) pulsating input current. A low ESR capacitor provides the Where: input voltage during the transient loading. The input capacitor should be larger than 10µF and IOUT(MAX) = maximum output current RDS(ON) resistance small drop voltage to stabilize the = maximum P-MOSFET turn on 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. ∆VO ≅ Due to the high switching frequency and large transient current, the layout is recommended to have a ground plane and short connections to The output ripple voltage can be calculated as: 1 ∆IL 8COUT Layout Considerations each component. Minimize the length and the + ESR 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) C D L H E e θ1 A A2 SYMBOL MIN MAX A 1.00 1.30 A1 — 0.10 A2 0.70 0.90 b 0.35 0.50 C 0.10 0.25 D 2.70 3.10 E 1.40 1.80 e A1 b 1.90 (TYP) H 2.60 3.00 L 0.37 — θ1 1° 9° 9