Description The ZXCT117/9/1 are high side unipolar current sense monitors. These devices eliminate the need to disrupt the ground plane when sensing a load current. The wide common-mode input voltage range and low quiescent current coupled with SOT23 packages make them suitable for a range of applications; including adapters, automotive and systems operating from industrial 24 rails. The device is line powered and as such doesn t need a separate supply rail. Quiescent current is only 3µA thereby minimising current sensing error. One external gain setting resistor increases versatility by permitting wide gain ranges. Features Wide supply and common-mode voltage range: 2.5 to 36 SOT23 packages o 3-pin ZXCT117/9 o 5-pin ZXCT111 Low quiescent current (3µA). Extended industrial temperature range -4 to 125 C AEC-Q1 Grade1 Automotive qualified variants Applications Automotive current measurement Industrial applications current measurement Battery management Over current monitor Power Management Pin Assignments OUT 1 OUT 1 NC 1 GND 2 OUT 3 ZXCT117 Top iew ZXCT119 Top iew ZXCT111 Top iew 2 S- 3 S+ 2 S+ 3 S- 5 S- 4 S+ Typical Application Circuit 1 of 17
Pin Descriptions Package SOT23 SOT23-5 Name ZXCT117 ZXCT119 ZXCT111 Description OUT 1 1 1 1 3 Output pin. Current output. S+ 3 2 4 This is the positive input of the current monitor and has a wide common-mode input range. This also acts as the analog supply and provides power to internal circuitry. The current through this pin varies with differential sense voltage. S- 2 3 5 This is the negative input of the current monitor and has a wide common-mode input range. GND - - 2 Ground pin and substrate connection. NC - - 1 No connection Notes. 1. For the ZXCT117 and ZXCT119 pin 1 (OUT) acts as both the output pin and substrate connection. This means that for the ZXCT117 and ZXCT119 the minimum rail voltage that can be used is 2.5 + OUT (see applications section for more details). Absolute Maximum Ratings Description Rating Unit oltage on S- and S+ relative to OUT (ZXCT117/9) -.3 to 4 oltage on S- and S+ relative to GND (ZXCT111) -.3 to 4 oltage on OUT to GND (ZXCT111) -.3 to S+ 2,3 Differential Sense oltage, -.3 to.8 Current into S+ and S- 3 ±8.5 ma Storage Temperature -55 to 15 C Maximum Junction Temperature 15 C Package Power Dissipation (T A = 25 C) SOT23 SOT23-5 3 (De-rate to Zero at 15 C) 3 (De-rate to Zero at 15 C) ESD Ratings Human Body Model 1 Machine Model 15 Operation above the absolute maximum rating may cause device failure. Operation at the absolute maximum ratings, for extended periods, may reduce device reliability. Notes: 2. = S+ - S- 3. The differential input voltage limit, S+ - S-, may be exceeded provided that the input current limit into S+ or S- is not exceeded. mw Recommended Operating Conditions Notes. Symbol Parameter Min Max Unit ZXCT111 2.5 36 S+ Common-mode input range 4 : OUT(MAX) ZXCT117/9 36 + 2.5 Differential Sense Input voltage range ( S+ - S- ).5 ZXCT111 S- - 1 OUT Output voltage range ( 1m) ZXCT117/9 S+ - 2.5 T A Ambient temperature range -4 125 C 4. For the ZXCT117 and ZXCT119 pin 1 (OUT) acts as both the output pin and substrate connection. This means that for the ZXCT117 and ZXCT119 the minimum rail voltage that can be used is 2.5 + OUT (see applications section for more details). 2 of 17
Electrical Characteristics (T A = 25 C, S+ = 2, 5 = 1m, R GAIN = unless otherwise stated) ZXCT117, ZXCT119 Symbol Parameter Conditions T A Min Typ Max Units 25 C 19 1 I S- S- input current 5 = -4 C 16 na 125 C 35 25 C 1 3 1 5 = m -4 C 2.2 125 C 5.5 25 C 37 45 54 5 = 1m -4 C 42 125 C 49 25 C 115 124 134 5 = 3m -4 C 119 µa I OUT Output current 6 125 C 129 25 C 394 48 422 5 = 1m -4 C 396 125 C 42 25 C 787 81 832 5 = 2m -4 C 785 125 C 832 25 C 1.965 2.15 2.64 5 = 5m -4 C 1.965 ma 125 C 2.65 I OUT -TC Output current temperature coefficient full range 37 ppm/ºc 25 C.1.4 CMSR Common-Mode Sense rejection S+ = 2.5 to 36-4 C.13 µa/ 125 C.5 BW -3dB Small Signal Bandwidth 5 (AC) = 1m PP R GAIN = 2.5kΩ 25 C.65 MHz 3 of 17
Electrical Characteristics (T A = 25 C, S+ = 2, 5 = 1m, R GAIN = unless otherwise stated) (cont.) ZXCT111 Symbol Parameter Conditions T A Min Typ Max Units I Q I S- GND pin current S- input current 5 = CMSR Common-Mode Sense rejection S+ = 2.5 to 36 I OO Output Offset current 6,7 5 = 1m G T GE Transconductance Transconductance error 5 = 1m to 15m 5 = 1m to 15m 25 C 3 5-4 C 2.2 125 C 5.8 25 C 19 1-4 C 16 125 C 35 25 C.1.4-4 C.13 125 C.5 25 C ±4-4 C -1.8 125 C +2.5 25 C 3.928 4 4.72-4 C 3.9 125 C 4.8 µa na µa/ µa ma/ 25 C -1.8 1.8 % I OUT G T-TC Transconductance temp.co 25 C 265 ppm/ºc OUTH Output relative to S- 25 C -1 -.78-4 C -.88 125 C -.63 BW -3dB Small Signal Bandwidth 5 (AC) = 1m PP, R GAIN = 2.5kΩ 25 C.65 MHz Notes. 5. = + - 6. Output current characteristic measured with low impedance ammeter connected to GND 7. Defined as difference between actual output current and 4 µa; measured at =1m. This will include an error due to bias currents of the device. 8. For > 1m, the internal voltage-current converter is fully linear. This enables a true offset to be defined and used. 4 of 17
Typical Characteristics 12 1 OUT = = T = 125 C A 9. 8. 7. = OUT = = 2 S+ 8 6. I S+ (µa) 6 4 2 T = C A T = 85 C A T = 25 C A T = -4 C A 1 2 3 4 S+ () Input Current vs. S+ I S+ (µa) 5. 4. 3. 2. 1. = 3.7 S+. -4-25 -1 5 2 35 5 65 8 95 11 125 TEMPERATURE ( C) Input Current vs. Ambient Temperature 4. 3.5 3. 1.8 1.6 1.4 T A = 25 C OUT = = I S+ (µa) 2.5 2. 1.5 I S- (na) 1.2 1..8.6 1..5 T A = 25 C OUT = =.4.2. 1 2 3 4 S+ () I S+ Current vs. S+. 1 2 3 4 S+ () I S- Current vs. S+ 25 2 S+ = 2 OUT = T = 125 C A T = 85 C A 45 4 35 I OUT (µa) 15 1 5 T = -4 C A T =25 C A T = C A OUTPUT CURRENT (µa) 3 25 2 15 1 5 1 2 3 4 5 6 (m) Output Current vs. 5 of 17..5 1. 1.5 2. 2.5 3. 3.5 4. OUTPUT OLTAGE () Output Current vs. Output oltage
Typical Characteristics (cont.) 7 25 6 5 2 I OUT (µa) 4 3 2 1-4 -25-1 5 2 35 5 65 8 95 11 125 TEMPERATURE( C) Output Current vs. Ambient Temperature I OUT (µa) 15 1 5-4 -25-1 5 2 35 5 65 8 95 11 125 TEMPERATURE( C) Output Current vs. Ambient Temperature I OUT (µa) 7 6 5 4 3 2 1 I OUT (µa) 25 2 15 1 5 T A = 25 C OUT = = 5m = 5m = 1m = 15m = 3m = 1m = 5m DIFFERENTIAL GAIN (ma/) 4.2 4.15 4.1 4.5 4. 3.95 3.9 1 2 3 4 S+ () Output Current vs. S+ S+ = 2 OUT = T A = 125 C T 85 C A T = 25 C A T = C A T = -4 C A 3.85 1 2 3 4 5 6 (m) Differential Gain vs. I OUT Error [ S+ = 2] (%) -.5% -.1% 1 2 3 4 S+ () Output Current vs. S+.25%.2%.15%.1%.5%.% = 1m = 15m = 5m -.15% = 3m -.2% = 5m T A = 25 C OUT = -.25% 1 2 3 4 S+ () Output Current Error vs. S+ 6 of 17
Typical Characteristics (cont.) I OUT ERROR [ S+ = 2] (%) 4.% 3.% 2.% 1.%.% -1.% -2.% -3.% = 1m, OUT = T = 125 C A T = 85 C A T = 25 C A T = C A T = -4 C A -4.% 1 2 3 4 S+ () Output Current Error vs. S+ 7 of 17
Typical AC Characteristics OLTAGE (m) -1-2 -3-4 -5-6 Output Input S+ =, GND = -3.7 R GAIN = 1k -.5-1.5-2.5-7 -3.5 5 1 15 2 25 3 35 4 45 5 TIME (µs) Small Signal Pulse Response -1-2 -3 OUTPUT OLTAGE () OLTAGE (m) -5-1 -15-2 Output Input S+ =, GND = -2 R GAIN = 1k -13-17 -21-25 -25 5 1 15 2 25 3 35 4 45 5 TIME (µs) Large Signal Pulse Response -5-9 OUTPUT OLTAGE () -5 Output S+ =, GND = -2 R GAIN = 1k -1-12 -5-18 S+ =, GND = -2 R GAIN = 1k OLTAGE (m) -1-15 -2 Input -14-16 -18 OUTPUT OLTAGE () OLTAGE (m) -1-15 -2 Input Output -19 OUTPUT OLTAGE () -25-2 5 1 15 2 25 3 35 4 45 5 TIME (µs) Large Signal Pulse Response -25-2 5 1 15 2 25 3 35 4 45 5 TIME (µs) Small Signal Pulse Response OLTAGE (m) -88-9 -92-94 -96-98 -1 Input Output S+ =, GND = -2 R GAIN = 1k -15-15.5-16 -16.5-12 5 1 15 2 25 3 35 4 45 5-17 TIME (µs) Small Signal Pulse Response OUTPUT OLTAGE () OLTAGE (m) -98-1 -12-14 -16-18 -11 Input Output S+ =, GND = -2 R GAIN = 1k -15-15.2-15.4-15.6-15.8-16 -16.2-16.4-16.6-16.8-112 5 1 15 2 25 3 35 4 45 5-17 TIME (µs) Small Signal Pulse Response OUTPUT OLTAGE () 8 of 17
Typical AC Characteristics (cont.) Test Circuit for Pulse Response 8 7 6 5 CMRR (db) 4 3 2 1 1 1 1 1k 1k 1k 1M 1M FREQUENCY (Hz) Common Mode Rejection Ratio CMRR Test circuit for CMRR 3 2 1 GAIN (db) -1 T A =25 C S+ = 2 = 1m -2 DC AC = 1mpp R GAIN = 2.5K -3 1 1 1k 1k 1k 1M 1M FREQUENCY (Hz) Small Signal Bandwidth Test circuit for Small signal bandwidth 9 of 17
Application Information Description The current monitor ICs ZXCT117, ZXCT119 and ZXCT111 all use a similar application circuit topology for high-side current sensing, with small differences. The ZXCT111 has a separate ground pin whereas the ZXCT117 and ZXCT119 do not. The use of ZXCT111 allows reduction of the absolute current measurement error in some applications by providing a reduced output offset current. The ZXCT117 provides a mirror image pin assignment of the ZXCT119 to ease PCB layout in very small equipment designs. The basic application circuit for each device is shown in Figure 1. Two external resistors are required. The resistor R is connected in the path of the current to be monitored. The resistor R GAIN converts the device output current to a voltage for convenient processing by a further device, such as a comparator, amplifier or analog-to-digital converter within a microcontroller system. The current monitor output current is defined through the nominal transconductance of 4mA/. I OUT =.4 * Amp Equation 1 Then the resistors determine the output voltage as described below. SUPPLY R I LOAD ZXCT111 S+ S- GND OUT OUTPUT LOAD GND R GAIN OUT Figure 1. Basic Application Circuit Calculation of Resistor alues In order to select R, a choice of sense voltage is required. This often involves a compromise between power efficiency and accuracy for the given temperature range. The resistor must be small enough to avoid excessive volt drop between the power supply and the load. However, the resistor must be large enough to avoid excessive current measurement error, particularly random errors. In a typical application, a digital system, perhaps a microcontroller, is set up to monitor the current. At a certain threshold current level, I LOADT, the system is required to disconnect the load or report a fault. At this current level, the current measurement error must be limited to a known value. The total percentage error comprises the inherent error in the device and the tolerances of the two resistors R and R GAIN. The ZXCT117/ZXCT119 absolute error is shown in Table 1 with error limits drawn from the table of Electrical Characteristics above. This error varies with. 1 of 17
Application Information (cont.) The ZXCT111 is highly linear and has a transconductance of 4mA/ ±1.8% and an output of 4µA ±4µA at =1m. The output current can therefore be calculated (Standard International Units) as: I OUT = (4 +/-4)*1-6 + ( -.1)*(.4 +/-.72) Amp The worst-case current error is then I OUTERROR = I OUT I OUTIDEAL = +/- { 4*1-6 + ( -.1) *.72 } Amp or I OUTERROR = +/- { 3.28*1-6 + *.72 } A The percentage error is Then I ε = I OUTERROR OUTIDEAL 3.28 *1 ε = ± I *1% = 4 + *1% *.4 OUTERROR *.72 % *.4.82 or ε = ± ± 1.8% Equation 2 This shows that the error is reduced with increasing. Then the minimum required to give the error ±ε % is.82 = [only for ZXCT111] Equation 3 ε 1.8 In the application, the effect of the external resistor tolerances must also be taken into account. Table 1: ZXCT117/ZXCT119 Error Mean I OUT Error Band Percent Error 1m 45.5 µa ±8.5µA ±18.7% 3m 124.5 µa ±7.6µA ±7.6% 1m 48 µa ±3.4µA ±3.4% 2m 89.8 µa ±22.5µA ±2.8% Table 2: ZXCT111 Error Mean I OUT Error Band Percent Error 1m 4µA ±4µA ±1% 3m 12µA ±5.44µA ±4.53% 1m 4µA ±1.48µA ±2.62% 2m 8µA ±17.68µA ±2.21% 11 of 17
Application Information (cont.) Note that in order to avoid additional error, SUPPLY must be at least 1.5 greater than OUT. This margin depends on the value of. For = 1m, this margin can be reduced to 1.. R is chosen based on the threshold T of sense voltage selected as above, for the chosen threshold load current, I LOADT. T R = Equation 4 ILOADT R GAIN is chosen to give the required threshold output voltage, OUTT. From Equation 1, the threshold output current is I OUTT =.4 * T Equation 1a R GAIN = I OUTT OUTT or OUTT R GAIN = Equation 5.4 * T Design Example A current monitor is required to provide an output voltage of 2 ±6% when the load current of a 12 supply is 2A. Resistors are available with 1% tolerance. The sense and output resistors will contribute a total possible error of 2%, so the ZXCT11xx error must not exceed 4%. From Table 1, the error of ZXCT117/119 will be 3.4% if the sense voltage is 1m. This satisfies the total error requirement of 6%. Equation 4 gives R = 1m/2A = 5mΩ Equation 5 gives 2 R GAIN = = 5kΩ.4 *.1 A suitable preferred value is 5.1kΩ. This gives a systematic error of +2%, which can be compensated elsewhere in the system if desired. Figure 2 shows the resulting schematic. Figure 2. Example Circuit using ZXCT117/ZXCT119 12 of 17
Application Information (cont.) Alternatively, the ZXCT111 may be used with a reduced sense voltage if desired. From Equation 3, with ε=4%, Equation 4 gives.82 = =.82/(4-1.8) = 37.2m ε 1.8 R = 37.2m/2A = 18.6mΩ A suitable preferred value is 2mΩ. Then the sense voltage will be 2A * 2mΩ = 4m. Equation 5 gives 2 R GAIN = = 125Ω.4 *.4 A suitable preferred value is 13kΩ. The alternative example circuit using the ZXCT111 with a sense voltage of 4m is shown in Figure 3, giving the required overall accuracy of ±6%. SUPPLY 2mΩ I LOAD ZXCT111 S+ S- GND OUT OUTPUT LOAD GND 13k OUT Figure 3. Example Circuit using ZXCT111 Protection Against Load Short Circuit In the event of a load short circuit or overload, a large proportion of the supply voltage may appear between the sense terminals. The supply may be current limited, but there is normally a large reservoir capacitor which can deliver enough energy to damage the ZXCT11xx before the supply voltage falls to a safe level due to current limit activation. The ZXCT11xx is rated for a maximum sense voltage of +.8, but is safe if the input current is limited to ±8.5mA. In Figure 4, the resistor R PROT limits the current and therefore protects the current monitor device against load short circuit without introducing significant current measurement error. 13 of 17
Application Information (cont.) Figure 4. Protection and EMC Filtering EMC Susceptibility In many applications, the circuit is required to operate in the presence of RF radiation. This radiation is coupled into the circuit via the supply or load connections and will often cause significant bias shift due to rectification within the integrated circuit. The bias shift may lead to erroneous operation of the integrated circuit. In Figure 4, a low pass filter, R PROT and C1, provides significant attenuation in the HF and UHF regions. The value of C1 is recommended to be in the range of 1pF to 47pF, leadless ceramic type. PCB Layout Considerations It is necessary to take into account a small volt drop in the PCB copper and solder joints to R. Such volt drops can create noticeable error at currents of the order of 1A and greater. The PCB must be designed to provide the maximum possible copper carrying current via the sense resistor, and the traces from the S+ and S- pins must be connected only to the resistor pads. In this way, the effect of the copper is minimized. If used, the capacitor C1 should be placed very close the input pins S+ and S-. Application: High oltage Current Monitor The schematic of Figure 5 shows how the current monitor may be used in a high voltage application such as a T LED backlight system. In this configuration the 5 PNP transistor Q1 drops a large proportion of the supply voltage. Diode D2 limits the differential input voltage to a safe level under overload conditions. The voltage across U1 is limited by the zener diode D1. The output current of U1 is limited to about 3mA by the D2. As R GAIN is typically a few kω, the output voltage is therefore limited to a few volts. An additional output clamping diode may be required for higher gains. R1 is chosen to give a suitable bias current in D1 for the given supply voltage range. 14 of 17
Figure 5. 45 Current Monitor 15 of 17
Ordering Information Order Reference Package Device Quantity Tape Width Reel Size Marking Per Reel (mm) ZXCT117SA-7 SOT23 117 7, 18mm 3 8 ZXCT119SA-7 SOT23 119 7, 18mm 3 8 ZXCT111W5-7 SOT23-5 111 7, 18mm 3 8 Package Outline Dimensions (All Dimensions in mm) Package type: SOT23 Package type: SOT23-5 16 of 17
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