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UC1903L883B 数据表(PDF) 6 Page - Texas Instruments |
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UC1903L883B 数据表(HTML) 6 Page - Texas Instruments |
6 / 16 page OPERATION AND APPLICATION INFORMATION Setting a Fault Window ADJ V 2.5 V ± 4 (1) ( ) S ADJ V ± 10 × V % (2) Hysteresis Fault Window Fault Window NoFault Fault 25 20 15 10 5 0 -5 -10 -15 -20 -25 0 0.5 1 1.5 2 2.5 Window AdjustVoltage(V )atPin4 ADJ 3.125 3 2.875 2.750 2.625 2.5 2.25 2.125 2 2.375 1.875 UC1903 UC2903 UC3903 SLUS233A – OCTOBER 1999 – REVISED SEPTEMBER 2008 ........................................................................................................................................ www.ti.com The fault thresholds on the UC1903 are generated by creating positive and negative offsets, equal in magnitude, that are referenced to the chip’s 2.5-V reference. The resulting fault window is centered around 2.5 V and has a magnitude equal to that of the applied offsets. Simplified schematics of the fault window and reference circuits are shown in Figure 1 along with the Typical Characteristics diagrams. The magnitude of the offsets is determined by the voltage applied at the window adjust pin, Pin 4. A bias cancellation circuit keeps the input current required at Pin 4 low, allowing the use of a simple resistive divider off the reference to set the adjust pin voltage. The adjust voltage at Pin 4 is internally applied across R4, and an 8-k Ω resistor. The resulting current is mirrored four times to generate current sources IOA, IOB, IOC, and IOD, all equal in magnitude. When all four of the sense inputs are inside the fault window, a no-fault condition, Q4 and Q5 are turned on. In combination with D1 and D2 this prevents LOB and LOD from affecting the fault thresholds. In this case, the OV and UV thresholds are equal to VREF + IOA(R5 + R6) and VREF – IOC(R7 + R8) respectively. The fault window can be expressed as: In terms of a sensed nominal voltage level, VS, the window as a percent variation is: When a sense input moves outside the fault window given in Equation 1, the appropriate hysteresis control signal turns off Q4 or Q5. For the under-voltage case, Q5 is disabled and current source IOB flows through D2. The net current through R7 becomes zero as IOB cancels IOC, giving an 8% reduction in the UV threshold offset. The overvoltage case is the same, with Q4 turning off, allowing IOD to cancel the current flow, IOA, through R6. The result is a hysteresis at the sense inputs which is always 8% of the window magnitude. This is shown graphically in Figure 2. Figure 2. Fault Window and Threshold Hysteresis Scale as a Function of the Voltage Applied at Pin 4 6 Submit Documentation Feedback Copyright © 1999–2008, Texas Instruments Incorporated Product Folder Link(s): UC1903 UC2903 UC3903 |
类似零件编号 - UC1903L883B |
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类似说明 - UC1903L883B |
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