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SI9176DH-T1 数据表(PDF) 6 Page - Vishay Siliconix |
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SI9176DH-T1 数据表(HTML) 6 Page - Vishay Siliconix |
6 / 12 page Si9176 Vishay Siliconix New Product www.vishay.com 6 Document Number: 71753 S-21825—Rev. A, 07-Oct-02 The error amplifier and comparator control the duty cycle of the PMOS MOSFET to continuously force the REF pin and FB pin voltages to be equal. As the input-to-output voltage difference drops, the duty cycle of the PMOS MOSFET can reach 100% to allow system designers to extract the maximum stored energy from the battery. The dropout voltage is 190 mV at 600 mA. During each cycle, the PMOS switch current is limited to a maximum of 1.5 A (typical) thereby protecting the IC while continuing to force maximum current into the load. Pulse Skipping Mode (MODE pin = OPEN) By leaving the MODE pin open-circuit, the converter runs in pulse skipping mode (PSM). In PSM mode the oscillator continues to operate, but switching only occurs if the FB pin voltage is below the REF voltage at the start of each clock cycle. Clock cycles are skipped thereby reducing the switching frequency to well below 100 kHz and minimizing switching losses for improved efficiency at loads under 150 mA. Although PSM mode switching frequency varies with line and load conditions, the minimum PSM frequency will be kept above 20 kHz for load currents of 30 mA or more to prevent switching noise from reaching the audio frequency range. Each time the PMOS switch is turned on, the inductor current is allowed to reach 300 mA. Once achieved, the PMOS switch is turned off and the NMOS switch is turned on in the normal manner. However, unlike PWM mode, the NMOS switch, turns off as the switch current approaches zero current to maximize efficiency. The PMOS switch remains on continuously (100% duty cycle) when the input-voltage-to-output-voltage difference is low enabling maximum possible energy extraction from the battery. PSM mode is recommend for load currents of 150 mA or less. Auto Mode When the MODE pin grounded, the converter is set to Auto mode. Switching between PWM mode and PSM modes takes place automatically without an external control signal. For heavy load operation, the converter will operate in PWM mode to achieve maximum efficiency. When delivering light load currents, the converter operates in PSM mode to conserve power. The switchover threshold between the two modes is determined by the peak inductor current, which is 300 mA nominal. There is hysteresis in the switchover threshold to provide smooth operation. Thus, the mode PSM-to-PWM mode switchover current for increasing load currents is higher than that of PWM-to-PSM mode switchover for decreasing load currents. Oscillator The internal oscillator provides for a fixed 2-MHz switching frequency. Dynamic Output Voltage Control (REF) The Si9176 is designed with an adjustable output voltage which has a change of VFB to VIN -- VDROP.VOUT is defined according to the following relationship: VOUT = 1+R1 R2 ×V FB Converter Shutdown (SD pin) With logic LOW level on the SD pin, the Si9176 is shutdown. Shutdown reduces current consumption to less than 2-mAby shutting off all of the internal circuits. Both the PMOS and NMOS transistors are turned off. A logic HIGH enables the IC to start up as described in “Start-up” section. Thermal Shutdown The Si9176 includes thermal shutdown circuitry, which turns off the regulator when the junction temperature exceeds 165_C. Once the junction temperature drops below 145_C, the regulator is enabled. If the condition causing the over temperature, the Si9176 begins thermal cycling, turning the regulator on and off in response to junction temperature. Restart from a thermal shutdown condition is the same as described in the “Start-up” section. |
类似零件编号 - SI9176DH-T1 |
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类似说明 - SI9176DH-T1 |
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