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MCP1258 bảng dữ liệu(PDF) 13 Page - Microchip Technology |
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MCP1258 bảng dữ liệu(HTML) 13 Page - Microchip Technology |
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13 / 24 page  2006-2013 Microchip Technology Inc. DS21989B-page 13 MCP1256/7/8/9 4.6 Power-Good Output (PGOOD) For the MCP1256/8 devices, the PGOOD output is an open-drain output that sinks current when the regulator output voltage falls below 0.93VOUT (typical). If the reg- ulator output voltage falls below 0.93VOUT (typical) for less than 200 µs and then recovers, glitch immunity cir- cuits prevent the PGOOD signal from transitioning low. A 10 k to 1 M pull-up resistor from PGOOD to V OUT may be used to provide a logic output. If not used, connect PGOOD to GND or leave unconnected. PGOOD is high impedance when the output voltage is in regulation. A logic low is asserted when the output falls 7% (typical) below the nominal value. The PGOOD output remains low until VOUT is within 3% (typical) of its nominal value. On start-up, this pin indicates when the output voltage reaches its final value. PGOOD is high impedance when SHDN is low or when BYPASS is low (MCP1258). 4.7 Low-Battery Output (LBO) For the MCP1257/9 devices, the LBO output is an open-drain output that sinks current when the input voltage falls below a preset threshold. If the input volt- age falls below the preset threshold for less than 200 µs and then recovers, glitch immunity circuits pre- vent the LBO signal from transitioning low. A 10 k to 1M pull-up resistor from LBO to V OUT may be used to provide a logic output. If not used, connect LBO to GND or leave unconnected. LBO is high impedance when the input voltage is above the low-battery threshold voltage. A logic low is asserted when the input falls below the low-battery threshold voltage. The LBO output remains low until VIN is above the low-battery threshold voltage plus the low-battery hysteresis voltage. LBO is high impedance when SHDN is low or when BYPASS is low (MCP1259). 4.8 Soft-Start and Short-Circuit Protection The MCP1256/7/8/9 devices feature fold back short- circuit protection. This circuitry provides an internal soft-start function by limiting inrush current during startup and also limits the output current to 150 mA (typical), if the output is short-circuited to GND. The internal soft-start circuitry requires approximately 175 µs, typical, from either initial power-up, release from Shutdown, or release from BYPASS (MCP1258/9) for the output voltage to be in regulation. 4.9 Thermal Shutdown The MCP1256/7/8/9 devices feature thermal shutdown with temperature hysteresis. When the die temperature exceeds 160°C, the device shuts down. When the die cools by 15°C, the MCP1256/7/8/9 automatically turns back on again. If high die temperature is caused by out- put overload and the load is not removed, the device will turn on and off resulting in a pulsed output. 5.0 APPLICATIONS 5.1 Capacitor Selection The style and value of capacitors used with the MCP1256/7/8/9 family determine several important parameters, such as output voltage ripple and charge pump strength. To minimize noise and ripple, it is rec- ommended that low ESR (0.1 ) capacitors be used for both CIN and COUT. These capacitors should be ceramic and should be 10 µF or higher for optimum performance. If the source impedance to VIN is very low, up to several megahertz, CIN may not be required. Alternatively, a somewhat smaller value of CIN may be substituted for the recommended 10 µF, but will not be as effective in preventing ripple on the VIN pin. The value of COUT controls the amount of output volt- age ripple present on VOUT. Increasing the size of COUT will reduce output ripple at the expense of a slower turn-on time from shutdown and a higher inrush current. The flying capacitors (C1 and C2) control the strength of the charge pump and in order to achieve the maxi- mum rated output current (100 mA), it is necessary to have at least 1 µF of capacitance for the flying capaci- tor. A smaller flying capacitor delivers less charge per clock cycle to the output capacitor resulting in lower available output current. 5.2 PCB Layout Issues The MCP1256/7/8/9 devices transfer charge at high switching frequencies producing fast, high peak, tran- sient currents. As a result, any stray inductance in the component layout will produce unwanted noise in the system. Proper board layout techniques are required to ensure optimum performance. |
Số phần tương tự - MCP1258 |
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Mô tả tương tự - MCP1258 |
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