AS1329 Low Voltage, Micropower, DC-DC Step-Up Converters 1 General Description 2 Key Features Low Start-Up Voltage: 0.85V The AS1329A, AS1329B and the AS1329C are synchronous, fixed frequency, very high-efficiency DC-DC boost converters capable of Output Range: 2.5V to 5.0V supplying 3.3V at 160mA from a single AA-supply. Compact size and minimum external parts requirements make these devices perfect for Single-Cell Operation modern portable devices. Operating with coils down to 2.2H High-speed switching frequency (1.2MHz) and internally compensated PWM current mode design provide highly-reliable DC- Delivers 160mA 3.3V (from Single AA Cell) DC conversion, especially when driving white LEDs. The converters are available as the standard products listed in Table 1. Delivers 220mA 5.0V (from Two AA Cells) Table 1. Standard Products Delivers 570mA 3.3V (from Two AA Cells) Model Light Load Switching 95% Efficiency Medium Load AS1329A Automatic Powersave Operation High-Speed Fixed-Frequency: 1.2MHz AS1329B Light Load Automatic Powersave Operation Internal PMOS Synchronous Rectifier AS1329C Continuous Switching Automatic Powersave Operation (AS1329A&B) The devices contain two internal MOSFET switches: one NMOS Continuous Switching at Light Loads (AS1329C) switch and one PMOS synchronous rectifier. Anti-ringing control circuitry reduces EMI by damping the inductor in discontinuous Logic Controlled Shutdown (< 1A) mode, and the devices exhibit extremely low quiescent current (< 1A) in shutdown. 6-pin TSOT-23 Package In shutdown mode the battery is connected directly to the output enabling the supply of real-time-clocks. The AS1329 is available in a 3 Applications 6-pin TSOT-23 package. The AS1329 is ideal for low-power applications where ultra-small size is critical as in medical diagnostic equipment, hand-held instruments, pagers, digital cameras, remote wireless transmitters, MP3 players, LCD bias supplies, cordless phones, GPS receivers, Figure 1. Typical Application Diagram Single Cell to 3.3V and PC cards. Synchronous Boost Converter L1 4.7H 1 SW VOUT 6 5 3.3V AA Battery 160mA VOUT VIN C2 C1 10F R1 10F 1.02M AS1329 1% On 4 3 Off SHDNN FB R2 604k 2 GND 1% www.ams.com/DC-DC Step-Up/AS1329 Revision 1.12 1 - 20AS1329 Datasheet - P in A s s ig n me nt s 4 Pin Assignments Figure 2. Pin Assignments (Top View) SW VIN 1 6 GND VOUT 2 5 AS1329 FB 3 4 SHDNN 4.1 Pin Descriptions Table 2. Pin Descriptions Pin Number Pin Name Description Switch Pin. Connect an inductor between this pin and VIN. Keep the PCB trace lengths as short and wide as is practical to reduce EMI and voltage overshoot. If the inductor current falls to zero, or pin SHDNN is low, an internal 100 anti-ringing switch is connected from this 1 SW pin to VIN to minimize EMI. Note: An optional Schottky diode can be connected between this pin and VOUT. Signal and Power Ground. Provide a short, direct PCB path between this pin and the 2 GND negative side of the output capacitor(s). Feedback Pin. Feedback input to the gm error amplifier. Connect a resistor divider tap to this 3 FB pin. The output voltage can be adjusted from 2.5 to 5V by: VOUT = 1.23V 1 + (R1/R2) Shutdown Pin. Logic controlled shutdown input. 1 = Normal operation, 1.2MHz typical operating frequency. 4 SHDNN 0 = Shutdown quiescent current <1A. If SHDNN is undefined, pin SW may ring. Note: In a typical application, SHDNN should be connected to VIN through a 1M pull-up resistor. Output Voltage Sense Input and Drain of the Internal PMOS Synchronous Rectifier. 5 VOUT Bias is derived from VOUT when VOUT exceeds VIN. PCB trace length from VOUT to the output filter capacitor(s) should be as short and wide as is practical. Input Voltage. The AS1329 gets its start-up bias from VIN unless VOUT exceeds VIN, in which case the bias is derived from VOUT. Thus, once started, operation is completely 6 VIN independent from VIN. Operation is only limited by the output power level and the internal series resistance of the supply. www.ams.com/DC-DC Step-Up/AS1329 Revision 1.12 2 - 20