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MCP1640T-IMC Datasheet(PDF) 13 Page - Microchip Technology |
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MCP1640T-IMC Datasheet(HTML) 13 Page - Microchip Technology |
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13 / 32 page  2010 Microchip Technology Inc. DS22234A-page 13 MCP1640/B/C/D 4.2.2 PWM MODE OPERATION In normal PWM operation, the MCP1640/B/C/D operates as a fixed frequency, synchronous boost converter. The switching frequency is internally maintained with a precision oscillator typically set to 500 kHz. The MCP1640B/D devices will operate in PWM only mode even during periods of light load operation. By operating in PWM only mode, the output ripple remains low and the frequency is constant. Operating in fixed PWM mode results in lower efficiency during light load operation (when compared to PFM mode (MCP1640/C)). Lossless current sensing converts the peak current sig- nal to a voltage to sum with the internal slope compen- sation. This summed signal is compared to the voltage error amplifier output to provide a peak current control command for the PWM signal. The slope compensation is adaptive to the input and output voltage. Therefore, the converter provides the proper amount of slope compensation to ensure stability, but is not excessive, which causes a loss of phase margin. The peak current limit is set to 800 mA typical. 4.2.3 PFM MODE OPERATION The MCP1640/C devices are capable of operating in normal PWM mode and PFM mode to maintain high efficiency at all loads. In PFM mode, the output ripple has a variable frequency component that changes with the input voltage and output current. With no load, the quiescent current draw from the output is typically 19 µA. The PFM mode can be disabled in selected device options. PFM operation is initiated if the output load current falls below an internally programmed threshold. The output voltage is continuously monitored. When the output voltage drops below its nominal value, PFM operation pulses one or several times to bring the output back into regulation. If the output load current rises above the upper threshold, the MCP1640/C transitions smoothly into PWM mode. 4.2.4 ADJUSTABLE OUTPUT VOLTAGE The MCP1640/B/C/D output voltage is adjustable with a resistor divider over a 2.0V minimum to 5.5V maximum range. High value resistors are recommended to minimize quiescent current to keep efficiency high at light loads. 4.2.5 ENABLE The enable pin is used to turn the boost converter on and off. The enable threshold voltage varies with input voltage. To enable the boost converter, the EN voltage level must be greater than 90% of the VIN voltage. To disable the boost converter, the EN voltage must be less than 20% of the VIN voltage. 4.2.6 INTERNAL BIAS The MCP1640/B/C/D gets its start-up bias from VIN. Once the output exceeds the input, bias comes from the output. Therefore, once started, operation is completely independent of VIN. Operation is only limited by the output power level and the input source series resistance. Once started, the output will remain in regulation down to 0.35V typical with 1 mA output current for low source impedance inputs. 4.2.7 INTERNAL COMPENSATION The error amplifier, with its associated compensation network, completes the closed loop system by comparing the output voltage to a reference at the input of the error amplifier, and feeding the amplified and inverted signal to the control input of the inner current loop. The compensation network provides phase leads and lags at appropriate frequencies to cancel excessive phase lags and leads of the power circuit. All necessary compensation components and slope compensation are integrated. 4.2.8 SHORT CIRCUIT PROTECTION Unlike most boost converters, the MCP1640/B/C/D allows its output to be shorted during normal operation. The internal current limit and overtemperature protection limit excessive stress and protect the device during periods of short circuit, overcurrent and over- temperature. While operating in Bypass mode, the P-Channel current limit is inhibited to minimize quiescent current. 4.2.9 LOW NOISE OPERATION The MCP1640/B/C/D integrates a low noise anti-ring switch that damps the oscillations typically observed at the switch node of a boost converter when operating in the discontinuous inductor current mode. This removes the high frequency radiated noise. 4.2.10 OVERTEMPERATURE PROTECTION Overtemperature protection circuitry is integrated in the MCP1640/B/C/D. This circuitry monitors the device junction temperature and shuts the device off if the junction temperature exceeds the typical +150oC threshold. If this threshold is exceeded, the device will automatically restart once the junction temperature drops by 10oC. The soft start is reset during an overtemperature condition. |
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Similar Description - MCP1640T-IMC |
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