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AAT1265 Datasheet(PDF) 10 Page - Advanced Analogic Technologies |
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AAT1265 Datasheet(HTML) 10 Page - Advanced Analogic Technologies |
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10 / 13 page  AAT1265 Low Voltage 2MHz Step-Up DC/DC Converter in SC70JW Package SwitchRegTM PRODUCT DATASHEET 10 1265.2007.12.1.4 www .analogictech.com frequency (Light Load) mode to reduce the dominant switching losses. In addition to Light Load operation, a zero current comparator blocks reverse current in the P-channel synchronous MOSFET, forcing DCM operation at light load. These controls, along with very low quiescent current, help to maintain high efficiency over the com- plete load range without the compromise of increased output voltage ripple during light load conditions. Start-up and Inrush Current Limit The start-up sequence of the AAT1265 varies depending upon whether the input voltage is greater than or less than 2V. Above 1V, a start-up oscillator operating at 25% duty cycle controls the synchronous power stage and charges the output to 2V. For an input voltage greater than 2V, the output is charged at a constant cur- rent of 300mA until the output reaches a voltage level just below the input voltage. The step-up converter then takes control and continues to charge the output to the steady-state voltage. The step-up converter N-channel switch current is limited to 1A and the typical start-up time is 2.5ms. Shutdown and Output Disconnect A typical synchronous step-up (boost) converter has a conduction path from the input to the output via the body diode of the P-channel MOSFET. The AAT1265 design disconnects this body diode from the output and eliminates this conduction path. This enables the AAT1265 to provide true load disconnect during shut- down and inrush current limit at turn-on. Short-Circuit Protection The P-channel synchronous MOSFET body diode discon- nect feature also gives the AAT1265 the ability to pro- vide output short-circuit current limit protection. Applications Information Inductor Selection The AAT1265 is designed to operate with a 2.2μH induc- tor for all input/output voltage combinations. The induc- tor saturation current rating should be greater than the NMOS current limit specification listed in the Electrical Characteristics table. If necessary, the peak inductor cur- rent can exceed the saturation level by a small amount with no significant effect on performance. Table 1 pro- vides a list of some suggested inductor manufacturers and their part numbers. Output and Input Capacitor Selection Surface mount X5R or X7R ceramic capacitors are sug- gested for both the output and the input. For the output capacitor (C1 in Figure 4) a 4.7μF, 10V, X5R ceramic capacitor is necessary for stability, transient response, and ripple performance. The same 0805 sized capacitor is used for the input (C2 of Figure 4). If desired, a smaller, 0603 sized, 4.7μF, 6.3V, X5R ceramic capacitor can be substituted for the input capacitor (C2). Suggested ceramic capacitor suppliers are listed in Table 1. PCB Layout Guidelines Figures 1, 2, and 3 display the evaluation board layout and suggested component placement. Due to the high switching speed of the AAT1265, it is important that the evaluation board layout be followed. Even the best switch-mode power supply design cannot overcome the problems that can be caused by a poor layout. For the AAT1265, it is necessary that C1 and C2 be placed as close as possible to the IC with a good low impedance path to the GND pins of the IC. It is also good practice to minimize the length of the trace from the OUT pin to the output inductor. This prevents switch- ing noise from radiating into other high noise sensitive, high impedance circuits. |
Similar Part No. - AAT1265_07 |
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Similar Description - AAT1265_07 |
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