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MIC5209-3.3BM Datasheet(PDF) 9 Page - Micrel Semiconductor |
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MIC5209-3.3BM Datasheet(HTML) 9 Page - Micrel Semiconductor |
9 / 13 page June 2006 9 M9999-060906 MIC5209 Micrel, Inc. Applications Information Enable/Shutdown Enable is available only on devices in the SO-8 (M) and TO-263-5 (U) packages. ForcingEN(enable/shutdown)high(>2V)enablestheregula- tor. EN is compatible with CMOS logic. If the enable/shutdown feature is not required, connect EN to IN (supply input). Input Capacitor A 1µF capacitor should be placed from IN to GND if there is more than 10 inches of wire between the input and the ac filter capacitor or if a battery is used as the input. Output Capacitor An output capacitor is required between OUT and GND to prevent oscillation. The minimum size of the output capacitor is dependent upon whether a reference bypass capacitor is used. 1µF minimum is recommended when CBYP is not used (see Figure 1). 2.2µF minimum is recommended when CBYP is 470pF (see Figure 2). Larger values improve the regulator’s transient response. The output capacitor should have an ESR (equivalent series resistance) of about 1Ω and a resonant frequency above 1MHz. Ultra-low-ESR capacitors can cause a low amplitude oscillation on the output and/or underdamped transient re- sponse. Most tantalum or aluminum electrolytic capacitors are adequate; film types will work, but are more expensive. Since many aluminum electrolytics have electrolytes that freeze at about –30°C, solid tantalums are recommended for operation below –25°C. At lower values of output current, less output capacitance is needed for output stability. The capacitor can be reduced to 0.47µF for current below 10mA or 0.33µF for currents below 1mA. No-Load Stability The MIC5209 will remain stable and in regulation with no load (other than the internal voltage divider) unlike many other voltage regulators. This is especially important in CMOS RAM keep-alive applications. Reference Bypass Capacitor BYP (reference bypass) is available only on devices in SO-8 and TO-263-5 packages. BYP is connected to the internal voltage reference. A 470pF capacitor (CBYP) connected from BYP to GND quiets this reference, providing a significant reduction in output noise (ultra-low-noise performance). Because CBYP reduces the phase margin, the output capacitor should be increased to at least 2.2µF to maintain stability. The start-up speed of the MIC5209 is inversely proportional to the size of the reference bypass capacitor. Applications requiring a slow ramp-up of output voltage should consider larger values of CBYP. Likewise, if rapid turn-on is necessary, consider omitting CBYP. If output noise is not critical, omit CBYP and leave BYP open. Thermal Considerations The SOT-223 has a ground tab which allows it to dissipate more power than the SO-8. Refer to “Slot-1 Power Supply” for details. At 25°C ambient, it will operate reliably at 2W dissipation with “worst-case” mounting (no ground plane, minimum trace widths, and FR4 printed circuit board). Thermal resistance values for the SO-8 represent typical mounting on a 1”-square, copper-clad, FR4 circuit board. For greater power dissipation, SO-8 versions of the MIC5209 feature a fused internal lead frame and die bonding arrange- ment that reduces thermal resistance when compared to standard SO-8 packages. Package θJA θJC SOT-223 (S) 50°C/W 8°C/W SO-8 (M) 50°C/W 20°C/W TO-263-5 (U) — 2°C/W 3x3 MLF (ML) 63°C/W 2°C/W Table 1. MIC5209 Thermal Resistance Multilayer boards with a ground plane, wide traces near the pads, and large supply-bus lines will have better thermal con- ductivity and will also allow additional power dissipation. For additional heat sink characteristics, please refer to Mi- crel Application Hint 17, “Designing P.C. Board Heat Sinks”, included in Micrel’s Databook. For a full discussion of heat sinking and thermal effects on voltage regulators, refer to Regulator Thermals section of Micrel’s Designing with Low- Dropout Voltage Regulators handbook. Low-Voltage Operation The MIC5209-1.8 and MIC5209-2.5 require special con- sideration when used in voltage-sensitive systems. They may momentarily overshoot their nominal output voltages unless appropriate output and bypass capacitor values are chosen. During regulator power up, the pass transistor is fully satu- rated for a short time, while the error amplifier and voltage reference are being powered up more slowly from the output (see “Block Diagram”). Selecting larger output and bypass capacitors allows additional time for the error amplifier and reference to turn on and prevent overshoot. To ensure that no overshoot is present when starting up into a light load (100µA), use a 4.7µF output capacitance and 470pF bypass capacitance. This slows the turn-on enough to allow the regulator to react and keep the output voltage from exceeding its nominal value. At heavier loads, use a 10µF output capacitance and 470pF bypass capacitance. Lower values of output and bypass capacitance can be used, depending on the sensitivity of the system. Applications that can withstand some overshoot on the output of the regulator can reduce the output capacitor and/or reduce or eliminate the bypass capacitor. Applications that are not sensitive to overshoot due to power-on reset delays can use normal output and bypass capacitor configurations. Please note the junction temperature range of the regulator at 1.8V output (fixed and adjustable) is 0˚C to +125˚C. SOT-223 (S) 50°C/W 8°C/W SO-8 (M) 50°C/W 20°C/W TO-263-5 (U) — 2°C/W 3x3 MLF (ML) 63°C/W 2°C/W Package SO-8 (M) 50°C/W 20°C/W 3x3 MLF (ML) 63°C/W 2°C/W |
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