AS1322 Low Voltage, Micropower, DC-DC Step-Up Converters 1 General Description 2 Key Features 95% Efficiency The AS1322A and the AS1322B are synchronous, fixed frequency, very high-efficiency DC-DC boost converters capable of supplying Single-Cell Operation 3.3V at 150mA from a single AA-supply. Compact size and minimum external parts requirements make these devices perfect for modern Delivers 160mA 3.3V (from Single AA Cell) portable devices. Delivers 220mA 5.0V (from Two AA Cells) High-speed switching frequency (1.2MHz) and internally compensated PWM current mode design provide highly-reliable DC- Delivers 570mA 3.3V (from Two AA Cells) DC conversion, especially when driving white LEDs. The converters are available as the standard products listed in Table Low Start-Up Voltage: 0.85V 1. High-Speed Fixed-Frequency: 1.2MHz Table 1. Standard Products Internal PMOS Synchronous Rectifier Model Light Load Switching AS1322A Automatic Powersave Operation Automatic Powersave Operation (AS1322A) AS1322B Continuous Switching Continuous Switching at Light Loads (AS1322B) Anti-Ringing Control Minimizes EMI The devices contain two internal MOSFET switches: one NMOS switch and one PMOS synchronous rectifier. Logic Controlled Shutdown (< 1A) Anti-ringing control circuitry reduces EMI by damping the inductor in discontinuous mode, and the devices exhibit extremely low Output Range: 2.5 to 5.0V quiescent current (< 1A) in shutdown. 6-pin TSOT-23 Package In shutdown mode the battery is connected to the output and VOUT is held at approximately VIN - 0.6V. 3 Applications The AS1322 is available in a 6-pin TSOT-23 package. The AS1322 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 Synchronous Boost Converter and PC cards. L1 4.7H 1 SW VOUT 6 5 3.3V AA Battery 160mA VOUT VIN C2 C1 10F R1 10F 1.02M AS1322 1% On 4 3 Off SHDNN FB R2 604k 2 GND 1% www.ams.com/DC-DC Step-Up/AS1322 Revision 1.10 1 - 18AS1322 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 AS1322 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. Bias is derived from VOUT when VOUT exceeds VIN. PCB trace length from VOUT to the 5 VOUT output filter capacitor(s) should be as short and wide as is practical. VOUT is held at approximately VIN - 0.6V during shutdown. Input Voltage. The AS1322 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/AS1322 Revision 1.10 2 - 18