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MAX8869EUE10 Datasheet(PDF) 9 Page - Maxim Integrated Products |
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MAX8869EUE10 Datasheet(HTML) 9 Page - Maxim Integrated Products |
9 / 10 page thermal resistance of the package chosen, and θCA is the thermal resistance from the case through the PC board, copper traces, and other materials to the sur- rounding air. Figure 5 shows the allowable power dissi- pation for typical PC boards at +25°C, +50°C, and +70°C ambient temperatures. The MAX8869 TSSOP-EP package features an exposed thermal pad on its underside. This pad lowers the package’s thermal resistance by providing a direct thermal heat path from the die to the PC board. Additionally, the ground pin (GND) also channels heat. Connect the exposed thermal pad and GND to circuit ground by using a large pad (1in2 minimum recom- mended) or multiple vias to the ground plane. Applications Information Capacitor Selection and Regulator Stability Capacitors are required at the MAX8869 input and out- put. Connect 1µF or greater capacitors between IN and GND (CIN) and OUT and GND (COUT). Due to the MAX8869’s relatively high bandwidth, use only surface- mount ceramic capacitors that have low equivalent series resistance (ESR) and high self-resonant frequen- cy (SRF). Make the input and output traces at least 2.5mm wide (the width of the four parallel pins), and connect CIN and COUT within 6mm of the IC to mini- mize the impact of PC board trace inductance. The width of the ground trace should be maximized under- neath the IC to ensure a good connection between pin 10 (GND) and the ground side of the capacitors. The output capacitor’s ESR and SRF can affect stability and output noise. Use capacitors with greater than 5MHz SRF and ESR of 60m Ω or less to ensure stability and optimum transient response. This is particularly true in applications with very low output voltage (<2V) and high output current (>0.5A). Since some capacitor dielectrics may vary over bias voltage and temperature, consult the capacitor manu- facturer specifications to ensure that the capacitors meet these requirements over all voltage and tempera- ture conditions used. Soft-Start Capacitor Selection A capacitor (CSS) connected from SS to GND causes the MAX8869 output current to slowly rise during start- up, reducing stress on the input supply. The rise time to full current limit (tSS) is determined by: tSS = 2.08 ✕ 10-4 ✕ CSS where CSS is in nF. Typical capacitor values between 10nF to 100nF, with a 5V rating, are sufficient. Because this ramp is applied to the current-limit com- parator, the actual time for the output voltage to ramp up depends on the load current and output capacitor. Leave SS open to disable soft-start. Input-Output (Dropout) Voltage A regulator’s minimum input-to-output voltage differen- tial (dropout voltage) determines the lowest usable sup- ply voltage. In battery-powered systems, this determines the useful end-of-life battery voltage. Since a 0.2 Ω P-channel MOSFET is used as the pass device, dropout voltage is the product of RDS(ON) and load current (see Electrical Characteristics and Dropout Voltage vs. Output Current in Typical Operating Characteristics). The MAX8869 operating current remains low in dropout. Noise, PSRR, and Transient Response The MAX8869 is designed to achieve low dropout volt- age and low quiescent current in battery-powered sys- tems while still maintaining good noise, transient response, and AC rejection (see PSRR vs. Frequency in the Typical Operating Characteristics). When operat- ing from very noisy sources, supply noise rejection and transient response can be improved by increasing the values of the input and output capacitors and employ- ing passive postfiltering. MAX8869 output noise is typi- cally 150µVRMS. (see the Output Noise plot in the Typical Operating Characteristics). 1A, MicroCap, Low-Dropout, Linear Regulator _______________________________________________________________________________________ 9 Figure 5. Power Operating Region: Maximum Output Current vs. Input-Output Differential Voltage 0 0.6 0.4 0.2 0.8 1.0 1.2 1 03 24 5 INPUT-OUTPUT DIFFERENTIAL VOLTAGE MAXIMUM CONTINUOUS CURRENT TA = +70 °C TA = +50 °C TA = +25 °C TJ = +150 °C Chip Information TRANSISTOR COUNT: 1088 |
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