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ISL28005FH-20EVAL1Z датащи(PDF) 11 Page - Intersil Corporation |
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ISL28005FH-20EVAL1Z датащи(HTML) 11 Page - Intersil Corporation |
11 / 14 page ISL28005 11 FN6973.4 July 1, 2011 Hysteretic Comparator The input trans-conductance amps are under control of a hysteretic comparator operating from the incoming source voltage on the RS+ pin (see Figure 20). The comparator monitors the voltage on RS+ and switches the sense amplifier from the low-side gm amp to the high-side gm amplifier whenever the input voltage at RS+ increases above the 1.35V threshold. Conversely, a decreasing voltage on the RS+ pin, causes the hysteric comparator to switch from the high-side gm amp to the low-side gm amp as the voltage decreases below 1.35V. It is that low-side sense gm amplifier that gives the ISL28005 the proprietary ability to sense current all the way to 0V. Negative voltages on the RS+ or RS- are beyond the sensing voltage range of this amplifier. Typical Application Circuit Figure 22 shows the basic application circuit and optional protection components for switched-load applications. For applications where the load and the power source is permanently connected, only an external sense resistor is needed. For applications where fast transients are caused by hot plugging the source or load, external protection components may be needed. The external current limiting resistor (RP) in Figure 22 may be required to limit the peak current through the internal ESD diodes to < 20mA. This condition can occur in applications that experience high levels of in-rush current causing high peak voltages that can damage the internal ESD diodes. An RP resistor value of 100Ω will provide protection for a 2V transient with the maximum of 20mA flowing through the input while adding only an additional 13µV (worse case over-temperature) of VOS. Refer to the following formula: ((RP x IRS-) = (100Ω x 130nA) = 13µV) Switching applications can generate voltage spikes that can overdrive the amplifier input and drive the output of the amplifier into the rails, resulting in a long overload recovery time. Capacitors CM and CD filter the common mode and differential voltage spikes. Error Sources There are 3 dominant error sources: gain error, input offset voltage error and Kelvin voltage error (see Figure 21). The gain error is dominated by the internal resistance matching tolerances. The remaining errors appear as sense voltage errors at the input to the amplifier. They are VOS of the amplifier and Kelvin voltage errors. If the transient protection resistor is added, an additional VOS error can result from the IxR voltage due to input bias current. The limiting resistor should only be added to the RS- input, due to the high-side gm amplifier (gmHI) sinking several micro amps of current through the RS+ pin. Layout Guidelines Kelvin Connected Sense Resistor The source of Kelvin voltage errors is illustrated in Figure 21. The resistance of 1/2 oz. copper is ~1m Ω per square with a TC of ~3900ppm/°C (0.39%/°C). When you compare this unwanted parasitic resistance with the total of 1m Ω to 10mΩ resistance of the sense resistor, it is easy to see why the sense connection must be chosen very carefully. For example, consider a maximum current of 20A through a 0.005 Ω sense resistor, generating a VSENSE = 0.1 and a full scale output voltage of 10V (G = 100). Two side contacts of only 0.25 square per contact puts the VSENSE input about 0.5 x 1mΩ away from the resistor end capacitor. If only 10A the 20A total current flows through the kelvin path to the resistor, you get an error voltage of 10mV (10A x 0.5sq x 0.001 Ω/sq. = 10mV) added to the 100mV sense voltage for a sense voltage error of 10% (0.110V - 0.1)/0.1V) x 100. FIGURE 20. GAIN ACCURACY vs VRS+ = 0V TO 2V VRS+ (V) -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 FIGURE 21. PC BOARD CURRENT SENSE KELVIN CONNECTION PC Board Non-uniform Current Flow Current Sense Resistor 1 to 10mO Current In Current Out Kelvin V S Contacts Copper Trace 30mO/Sq. PC Board Non-uniform Current Flow Current Sense Resistor 1 to 10mO Current In Current Out Kelvin V S Contacts Copper Trace 30mO/Sq. CURRENT SENSE RESISTOR 1mΩ TO 10mΩ 1mΩ /SQ CURRENT OUT CURRENT IN NON-UNIFORM CURRENT FLOW PC BOARD KELVIN VS CONTACTS 1/2 Oz COPPER TRACE |
Аналогичный номер детали - ISL28005FH-20EVAL1Z |
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Аналогичное описание - ISL28005FH-20EVAL1Z |
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