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TS1102-50EG5TP データシート(PDF) 9 Page - Touchstone Semiconductor Inc |
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TS1102-50EG5TP データシート(HTML) 9 Page - Touchstone Semiconductor Inc |
9 / 11 page TS1102 TS1102DS r1p0 Page 9 RTFDS An expression for the TS1102 ’s total output voltage (+ error) is given by: VOUT = [GAIN x (1 ± GE) x VSENSE] ± (GAIN x VOS) A large value for RSENSE permits the use of smaller load currents to be measured more accurately because the effects of offset voltages are less significant when compared to larger VSENSE voltages. Due care though should be exercised as previously mentioned with large values of RSENSE. 4) Circuit Efficiency and Power Dissipation IR losses in RSENSE can be large especially at high load currents. It is important to select the smallest, usable RSENSE value to minimize power dissipation and to keep the physical size of RSENSE small. If the external RSENSE is allowed to dissipate significant power, then its inherent temperature coefficient may alter its design center value, thereby reducing load current measurement accuracy. Precisely because the TS1102 ’s input stage was designed to exhibit a very low input offset voltage, small RSENSE values can be used to reduce power dissipation and minimize local hot spots on the pcb. 5) RSENSE Kelvin Connections For optimal VSENSE accuracy in the presence of large load currents, parasitic pcb track resistance should be minimized. Kelvin-sense pcb connections between RSENSE and the TS1102 ’s RS+ and RS- terminals are strongly recommended. The drawing in Figure 1 illustrates the connections between the current-sense amplifier and the current-sense resistor. The pcb layout should be balanced and symmetrical to minimize wiring-induced errors. In addition, the pcb layout for RSENSE should include good thermal management techniques for optimal RSENSE power dissipation. 6) RSENSE Composition Current-shunt resistors are made available in metal film, metal strip, and wire-wound constructions. Wire-wound current-shunt resistors are constructed with wire spirally wound onto a core. As a result, these types of current shunt resistors exhibit the largest self inductance. In applications where the load current contains high-frequency transients, metal film or metal strip current sense resistors are recommended. Internal Noise Filter In power management and motor control applications, current-sense amplifiers are required to measure load currents accurately in the presence of both externally-generated differential and common- mode noise. An example of differential-mode noise that can appear at the inputs of a current-sense amplifier is high-frequency ripple. High-frequency ripple – whether injected into the circuit inductively or capacitively - can produce a differential-mode voltage drop across the external current-shunt resistor (RSENSE). An example of externally- generated, common-mode noise is the high- frequency output ripple of a switching regulator that can result in common-mode noise injection into both inputs of a current-sense amplifier. Even though the load current signal bandwidth is DC, the input stage of any current-sense amplifier can rectify unwanted, out-of-band noise that can result in an apparent error voltage at its output. This rectification of noise signals occurs because all amplifier input stages are constructed with transistors that can behave as high-frequency signal detectors in the same way pn-junction diodes were used as RF envelope detectors in early radio designs. Against common-mode injected noise, the amplifier’s internal common-mode rejection is usually sufficient. To counter the effects of externally-injected noise, it has always been good engineering practice to add external low-pass filters in series with the inputs of a current-sense amplifier. In the design of discrete current-sense amplifiers, resistors used in the external low-pass filters were incorporated into the circuit’s overall design so errors because of any input-bias current-generated offset voltage errors and gain errors were compensated. With the advent of monolithic current-sense amplifiers, like the TS1102, the addition of external Figure 1: Making PCB Connections to the Sense Resistor. |
同様の部品番号 - TS1102-50EG5TP |
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同様の説明 - TS1102-50EG5TP |
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