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SI9122A 数据表(PDF) 8 Page - Vishay Siliconix |
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SI9122A 数据表(HTML) 8 Page - Vishay Siliconix |
8 / 15 page Si9122A Vishay Siliconix www.vishay.com 8 Document Number: 73492 S–51921—Rev. A, 12-Sep-05 Figure 4. Detailed Si9122A Block Diagram Timer + – 132 k W EP + – Bandgap Reference 3.3 V Voltage Feedforward Frequency Foldback OSC Loop Control 160 _C Temp Protection High Voltage Interface VSD VUV VUVLO Logic Clock OTP VREF VINDET – + CL_CONT ROSC Oscillator Clock 60 k W VREF/2 PWM Generator – + – + VUV VSD VREF 550 mV Logic DH BST LX High-Side Primary Driver DL SRH SRL PGND Low-Side Driver Synchronous Driver (High) Synchronous Driver (Low) GND BBM Current Control Gain 100 mV CS2 CS1 Blanking CL_CONT VCC 20 mA Soft-Start SS Enable SS Si9122A 8 V – + – + VREG 9.1 V VCC VIN Pre-Regulator VUVLO 8.6 V 9.1 V VCC VCC VCC DETAILED OPERATION Start-Up When VINEXT rises above 0 V, the internal pre-regulator begins to charge up the Vcc capacitor. Current into the external VCC capacitor is limited to typically 40 mA by the internal DMOS device. When Vcc exceeds the UVLO voltage of 8.8 V a soft-start cycle of the switch mode supply is initiated. The VCC supply continues to be charged by the pre-regulator until VCC equals VREG. During this period, between VUVLO and VREG, excessive load current will result in VCC falling below VUVLO and stopping switch mode operation. This situation is avoided by the hysteresis between VREG and VUVLO and correct sizing of the VCC capacitor, bootstrap capacitor and the soft-start capacitor. The value of the VCC capacitor should therefore be chosen to be capable of maintaining switch mode operation until the required VCC current can be supplied from the external circuit (e.g via a power transformer winding and zener regulator). Feedback from the output of the switch mode supply charges VCC above VREG and fully disconnects the pre-regulator, isolating VCC from VIN. VCC is then maintained above VREG for the duration of switch mode operation. In the event of an over voltage condition on VCC, an internal voltage clamp turns on at 14.5 V to shunt excessive current to GND. |
类似零件编号 - SI9122A |
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类似说明 - SI9122A |
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