LT1787

LT1787/LT1787HV Precision, High Side Current Sense Amplifiers FEATURES s s s s s s s s s DESCRIPTIO Input Offset Voltage: 75µV (Max) 60V Supply Operation (LT1787HV) 12-Bit Dynamic Range Operating Current: 60µA User-Selectable External Sense Resistor Bidirectional High Side Current Sensing Unidirectional or Bidirectional Output Input Noise Filtering Available in 8-Lead SO and MSOP Packages APPLICATIO S s s s s s s Battery Monitoring Power Monitoring Portable Phones Cellular Phones Portable Test/Measurement Systems Battery-Operated Systems The LT ®1787 is a complete micropower precision high side current sense amplifier. The LT1787 monitors bidirectional currents via the voltage across an external sense resistor. A current or voltage output depicts the direction and magnitude of the sense current. The LT1787 delivers greater than a 12-bit dynamic range with ultralow 40µV input offset voltage compared to a typical 250mV fullscale input voltage. A fixed gain of 8 is set by onboard precision resistors. Input signal filtering is easily implemented with a capacitor between the FIL– and FIL+ pins. The LT1787HV operates from 2.5V to 60V total supply voltage and the LT1787 operates from 2.5V to 36V total supply voltage. Both versions have a PSRR in excess of 120dB. The LT1787/LT1787HV draw only 60µA and are available in 8-lead SO and MSOP packages. , LTC and LT are registered trademarks of Linear Technology Corporation. TYPICAL APPLICATIO 12-Bit Dynamic Resolution Unidirectional Output into LTC®1286 ADC TO LOAD I = 100A 1 FIL– LT1787HV RSENSE 0.0016Ω FIL+ 8 2.5V TO 60V INPUT OFFSET VOLTAGE (µV) 50 40 30 20 10 0 –10 –20 –30 –40 –50 0 10 30 40 50 20 TOTAL SUPPLY VOLTAGE (V) 60 – 2 VS VS+ 7 3 4 DNC VEE VBIAS 6 ROUT 20k VOUT C2 0.1µF 5 R1 15k C1 1µF VREF VCC CS +IN LTC1286 CLK –IN D GND OUT 5V TO µP VOUT = VBIAS + (8 • ILOAD • RSENSE) LT1634-1.25 1787 TA01 U Input Offset Voltage vs Supply Voltage 1787 TA01b U U 1 LT1787/LT1787HV ABSOLUTE MAXIMUM RATINGS Differential Sense Voltage ...................................... ±10V Total Supply Voltage (LT1787) ................................ 40V Total Supply Voltage (LT1787HV) ........................... 65V Output Voltage ..................... (VEE – 0.3V) to (VEE + 35V) Output Bias Voltage ............. (VEE – 0.3V) to (VEE + 35V) PACKAGE/ORDER INFORMATION TOP VIEW FIL– VS– DNC* VEE 1 2 3 4 8 7 6 5 FIL+ VS+ VBIAS VOUT MS8 PACKAGE 8-LEAD PLASTIC MSOP * DO NOT CONNECT TJMAX = 150°C, θJA = 250°C/ W ORDER PART NUMBER LT1787CMS8 LT1787IMS8 LT1787HVCMS8 LT1787HVIMS8 MS8 PART MARKING LTGM LTGN LTKJ LTKK (Note 4) The q denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. Total supply = (VS– – VEE) = 2.5V to 36V (LT1787), 2.5V to 60V (LT1787HV) unless otherwise specified. SYMBOL VS –, VS + VSENSE VOS PARAMETER CONDITIONS q q q q q q q q q q q q q q q ELECTRICAL CHARACTERISTICS Sense Amplifier Supply Voltage Single Supply Operation (LT1787) Single Supply Operation (LT1787HV) Input Sense Voltage Full Scale Input Offset Voltage (S8) VSENSE = VS+ – VS–, VS = 10V, VBIAS = 5V, AV = 8 ± 10% IOUT = 0, VS Supply = 5V 0°C ≤ TA ≤ 70°C – 40°C ≤ TA ≤ 85°C IOUT = 0 (LT1787) 0°C ≤ TA ≤ 70°C – 40°C ≤ TA ≤ 85°C IOUT = 0 (LT1787HV) 0°C ≤ TA ≤ 70°C – 40°C ≤ TA ≤ 85°C Input Offset Voltage (MS8) IOUT = 0, VS Supply = 5V 0°C ≤ TA ≤ 70°C – 40°C ≤ TA ≤ 85°C IOUT = 0 (LT1787) 0°C ≤ TA ≤ 70°C – 40°C ≤ TA ≤ 85°C IOUT = 0 (LT1787HV) 0°C ≤ TA ≤ 70°C – 40°C ≤ TA ≤ 85°C 2 U U W WW U W (Notes 1, 2) Operating Temperature Range ................ – 40°C to 85°C Specified Temperature Range (Note 3) ... – 40°C to 85°C Storage Temperature Range ..................–65°C to 150°C Lead Temperature (Soldering, 10 sec).................. 300°C TOP VIEW FIL – 1 8 7 6 5 FIL + VS– 2 DNC* 3 VEE 4 VS+ VBIAS VOUT ORDER PART NUMBER LT1787CS8 LT1787IS8 LT1787HVCS8 LT1787HVIS8 S8 PART MARKING 1787 1787I 1787HV 787HVI S8 PACKAGE 8-LEAD PLASTIC SO * DO NOT CONNECT TJMAX = 150°C, θJA = 190°C/ W Consult factory for Military grade parts. MIN 2.5 2.5 500 – 75 – 135 – 200 – 100 – 160 – 225 – 100 – 160 – 225 – 125 – 230 – 250 – 150 – 250 – 280 – 150 – 250 – 280 TYP MAX 36 60 UNITS V V mV µV µV µV µV µV µV µV µV µV µV µV µV µV µV µV µV µV µV ± 40 75 135 200 100 160 225 100 160 225 ± 40 125 230 250 150 250 280 150 250 280 LT1787/LT1787HV ELECTRICAL CHARACTERISTICS SYMBOL VOS TC IOUT(O) VOUT(O) PARAMETER Temperature Coefficient of VOS No-Load Output Current Error No-Load Output Voltage Error (S8) No-Load Output Voltage Error (MS8) gm AV VS PSRR Tranconductance, IOUT/ VSENSE Gain, VOUT/ VSENSE Output Voltage Gain Error VS Supply Rejection Ratio CONDITIONS (Note 4) The q denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. Total supply = (VS – – VEE) = 2.5V to 36V (LT1787), 2.5V to 60V (LT1787HV) unless otherwise specified. MIN TYP 0.5 4 q q q q MAX 2 600 1080 1600 1000 1840 2000 UNITS µV/°C nA µV µV µV µV µV µV µA/V VS Supply = 5V (Note 5) VSENSE = 0V VSENSE = 0V, VS Supply = 5V 0°C ≤ TA ≤ 70°C – 40°C ≤ TA ≤ 85°C VSENSE = 0V, VS Supply = 5V 0°C ≤ TA ≤ 70°C – 40°C ≤ TA ≤ 85°C ± VSENSE = 10mV, 50mV, 100mV, 150mV, 250mV, VS Supply = Total Supply + |VSENSE| ± VSENSE = 100mV, VS Supply = 5V VSENSE = 0V, VS Supply = 2.5V to 36V (LT1787) VSENSE = 0V, VS Supply = 2.5V to 60V (LT1787HV) q q q q q q –600 – 1080 – 1600 – 1000 – 1840 – 2000 400 7.6 –5 120 120 100 100 100 100 8 2 135 135 130 130 130 130 10 50 60 ± 50 VBIAS ±1.024 8.4 5 V/V % dB dB dB dB dB dB VEE PSRR Negative Supply Rejection Ratio VSENSE = 0V, VS Supply = 15V, VBIAS = 0V, VEE = – 1V to – 15V (LT1787) VSENSE = 0V, VS Supply = 40V, VBIAS = 0V, VEE = – 1V to – 15V (LT1787HV) ∆VOS ∆VBIAS IS+(O) IS–(O) IEE(O) IOUT VOUT VOMIN Change in Input Offset Voltage with Change in VBIAS Voltage Positive Input Sense Current Negative Input Sense Current Negative Supply Current Output Current Output Voltage Ripple Rejection Minimum Output Voltage Unipolar Output Saturation Voltage VSENSE = 0V, VS Supply = 36V, VBIAS = 0.5V to 25V (LT1787) q VSENSE = 0V, VS Supply = 60V, VBIAS = 0.5V to 25V (LT1787HV) q VSENSE = 0V VSENSE = 0V VSENSE = 0V VSENSE = ±128mV VSENSE = ± 128mV, VS VS+ – + ≥ 3.3V q q q 20 100 120 µA µA µA µA V dB = VS = 20V, ∆VS Supply = 1V, f = 1kHz q q q q q q 80 88 30 10 32 38 43 49 VS + – 0.75 1.25 20 45 50 55 60 65 VSENSE = 0V, VBIAS = 0V VSENSE = VS+ – VS– = – 128mV, VBIAS = 0V VSENSE = 2mV, VBIAS = 0V VSENSE = 4mV, VBIAS = 0V VSENSE = 5mV, VBIAS = 0V VSENSE = 6mV, VBIAS = 0V Pin 1 to Pin 2, Pin 7 to Pin 8 Pin 5 to Pin 6 mV mV mV mV mV mV V kΩ kΩ VOMAX ROUT Maximum Output Voltage Output Resistor RG1A, RG2A Input Gain-Setting Resistor Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: ESD (Electrostatic Discharge) sensitive devices. Extensive use of ESD protection devices are used internal to the LT1787/LT1787HV, however, high electrostatic discharge can damage or degrade the device. Use proper ESD handling precautions. Note 3: The LT1787C/LT1787HVC are guaranteed to meet specified performance from 0°C to 70° and are designed, characterized and expected to meet these extended temperature limits, but are not tested at – 40°C and 85°C. The LT1787I/LT1787HVI are guaranteed to meet the extended temperature limits. Note 4: Testing done at VBIAS = 1.25V, VEE = 0V unless otherwise specified. Note 5: This parameter is not 100% tested. 3 LT1787/LT1787HV TYPICAL PERFORMANCE CHARACTERISTICS Input Offset Voltage vs Supply Voltage 50 40 INPUT OFFSET VOLTAGE (µV) 30 20 10 0 –10 –20 –30 –40 –50 0 10 30 40 50 20 TOTAL SUPPLY VOLTAGE (V) 60 1787 G01 VS+ = VS– VBIAS = 0V VEE = –1.25V OUTPUT VOLTAGE (µV) OUTPUT CURRENT (nA) TA = 85°C TA = 25°C TA = – 40°C Input Offset Voltage vs Negative Supply Voltage 30 20 10 0 –10 –20 –30 VS+ = VS– = 2.5V VBIAS = 1V TA = 85°C INPUT OFFSET VOLTAGE (µV) INPUT OFFSET VOLTAGE (µV) 20 10 0 –10 –20 –30 –40 OUTPUT VOLTAGE (V) TA = 25°C TA = – 40°C 0 –5 –10 –15 –20 –25 NEGATIVE SUPPLY VOLTAGE (V) Output Voltage vs Sense Voltage (Unidirectional Mode) 1.4 1.2 OUPUT VOLTAGE (V) VS = 2.5V TO 60V TA = – 40°C TO 85°C VBIAS = VEE 1.0 GAIN (V/V) 0.8 0.6 0.4 0.2 0 0 120 SENSE VOLTAGE (VS+ – VS–) (mV) 30 60 90 150 8.165 8.155 8.145 VS+ < VS– GAIN (dB) 4 UW 1787 G04 No Load Output Voltage vs Supply Voltage 400 300 200 100 0 –100 –200 –300 –400 0 50 20 30 40 10 TOTAL SUPPLY VOLTAGE (V) 60 1787 G02 No Load Output Current vs Supply Voltage 10 8 TA = – 40°C TA = 25°C VS+ = VS– VBIAS = 0V VEE = – 1.25V TA = 85°C 6 4 2 0 –2 –4 –6 –8 –10 0 10 30 40 50 20 TOTAL SUPPLY VOLTAGE (V) 60 1787 G03 TA = 25°C TA = 85°C VBIAS = 1V VEE = 0V VS+ = VS– TA = – 40°C Input Offset Voltage vs Temperature 50 40 30 VS+ = VS– VBIAS = 0V VEE = – 1.25V 2.5 2.0 1.5 1.0 0.5 VBIAS –0.5 –1.0 –1.5 –2.0 –2.5 –20 0 20 40 TEMPERATURE (°C) 60 80 85 1787 G05 Output Voltage vs Sense Voltage (Bidirectional Mode) VS = 5.5V TO 60V VBIAS = 2.5V VEE = 0V –30 –50 –40 –250 –150 50 150 –50 SENSE VOLTAGE (VS+ – VS–) (mV) 250 1787 G06 Gain vs Temperature 8.195 VS = (2.5V + |VSENSE|)TO 60V 8.185 VS+ > VS– 8.175 0 –10 –20 –30 –40 20 10 30 Gain vs Frequency VSENSE = 10mV 8.135 –40 –20 0 20 40 TEMPERATURE (°C) 60 80 85 1787 G08 –50 0.1k 1k 10k 100k 1M FREQUENCY (Hz) 10M 100M 1787 G07 1787 G09 LT1787/LT1787HV TYPICAL PERFORMANCE CHARACTERISTICS Supply Current vs Supply Voltage 75 120 NEGATIVE INPUT SENSE CURRENT (µA) 70 SUPPLY CURRENT (µA) 65 60 55 50 45 VS+ = VS– 40 0 TA = 85°C 110 100 90 80 70 60 50 40 POSITIVE INPUT SENSE CURRENT (µA) TA = 25°C TA = – 40°C 20 30 40 50 10 TOTAL SUPPLY VOLTAGE (V) Step Response at VSENSE = 0V to 10mV 10mV 0V 80mV 1V 500mV 0V 0V COUT = 0pF 1787 G12 Step Response at VSENSE = 0V to –128mV 0V – 100mV 0V –100mV 0V – 500mV – 1V COUT = 0 UW 1787 G10 1787 G19 Negative Input Sense Current vs Sense Voltage 60 VS = (2.5V + |VSENSE |) TO 60V Positive Input Sense Current vs Sense Voltage VS = (2.5V + |VSENSE |) TO 60V 50 40 30 20 10 0 –128 –96 –64 –32 0 32 64 96 SENSE VOLTAGE (VS+ – VS–) (mV) TA = 85°C TA = 85°C TA = 25°C TA = – 40°C TA = 25°C TA = – 40°C 60 30 –128 –96 –64 –32 0 32 64 96 SENSE VOLTAGE (VS+ – VS–) (mV) 128 128 1787 G11 1787 G17 Step Response at VSENSE = 0V to 128mV 100mV 0V 100mV 0V Step Response at VSENSE = 0V to 128mV 1V 500mV 0V COUT = 0pF 1787 G18 COUT = 1000pF 1787 G13 Step Response at VSENSE = 0V to –128mV 100mV 0V – 100mV Step Response at VSENSE = – 128mV to 128mV 0V –500mV –1V 1V 0V –1V COUT = 1000pF 1787 G14 COUT = 0 1787 G20 5 LT1787/LT1787HV TYPICAL PERFORMANCE CHARACTERISTICS Step Response at VSENSE = 128mV to –128mV 1000 100mV –100mV SUPPLY RIPPLE VOLTAGE (mV) 700 600 500 400 300 200 100 0 100 1k 10k 100k FREQUENCY (Hz) 1M 1787 G16 OUTPUT VOLTAGE (V) 1V 0V –1V COUT = 2200pF PIN FUNCTIONS FIL–, FIL+ (Pins 1, 8): Negative and Positive Filter Terminals. Differential mode noise can be filtered by connecting a capacitor across FIL– and FIL+ . Pole frequency f– 3dB = 1/(2πRC), R = 1.25kΩ. VS – (Pin 2): Negative Input Sense Terminal. Negative sense voltage will result in an output sinking current proportional to the sense current. VS – is connected to an internal gain-setting resistor RG1A and supplies bias current to the internal amplifier. DNC (Pin 3): Do Not Connect. Connected internally. Do not connect external circuitry to this pin. VEE (Pin 4): Negative Supply or Ground for Single Supply Operation. VOUT (Pin 5): Voltage Output or Current Output proportional to the magnitude of the sense current flowing through RSENSE. For bidirectional current sensing operation, VOUT = AV • VSENSE + VOUT(O) + VBIAS, where: VOUT > VBIAS for VS+ > VS– VOUT < VBIAS for VS+ < VS– VOUT(O) is the no load output voltage at VSENSE = 0V. VBIAS (Pin 6): Output Bias Pin. For single supply, bidirectional current sensing operation, VBIAS is connected to an external bias voltage, so that at VSENSE = 0V, VOUT = VOUT(O) + VBIAS. For dual supply, bidirectional current sensing operation, VBIAS is connected to ground. Thus, VOUT = VOUT(O) at VSENSE = 0V. VS+ (Pin 7): Positive Input Sense Terminal. Positive sense voltage will result in an output sourcing current proportional to the sense current. VS + is connected to an internal gain-setting resistor RG2A. Connecting a supply to VS+ and a load to VS– will allow the LT1787 to measure its own supply current. 6 UW 1787 G15 VOUT Error vs Supply Ripple Voltage (VSENSE = ± 128mV) 16 14 12 10 8 6 4 2 0 –2 –4 –6 –8 Output Voltage vs Sense Voltage VS– = 18V VBIAS = 0V VEE = – 18V 900 800 0.5% 5% 1% VOUT ERROR LESS THAN 0.1% 2% 0.4 0.8 1.2 1.6 0 –0.8 –0.4 SENSE VOLTAGE (VS+ – VS–) (V) 2.0 1787 G21 U U U LT1787/LT1787HV BLOCK DIAGRAM W VS– RG1A 1.25k FIL– RG1B 1.25k RG2B 1.25k RSENSE ISENSE VS+ RG2A 1.25k FIL+ – A1 + IOUT VBIAS Q1 Q2 ROUT 20k VOUT VEE CURRENT MIRROR 1787 F 01 Figure 1. LT1787 Functional Diagram APPLICATIONS INFORMATION The LT1787 high side current sense amplifier (Figure 1) provides accurate bidirectional monitoring of current through a user-selected sense resistor. The sense voltage is amplified by a fixed gain of 8 and level shifted from the positive power supply to the ground referenced outputs. The output signal may be used in a variety of ways to interface with subsequent signal processing circuitry. Input and output filtering are easily implemented to eliminate aliasing errors. Theory of Operation Inputs VS+ and VS– apply the sense voltage to matched resistors RG1 and RG2. The opposite ends of resistors RG1 and RG2 are forced to be at equal potentials by the voltage gain of amplifier A1. The currents through RG1 and RG2 are forced to flow through transistors Q1 and Q2 and are summed at node VOUT by the 1:1 current mirror. The net current from RG1 and RG2 flowing through resistor ROUT gives a voltage gain of eight. Positive sense voltages result in VOUT being positive with respect to pin VBIAS. Pins VEE, VBIAS and VOUT may be connected in a variety of ways to interface with subsequent circuitry. Split supply and single supply output configurations are shown in the following sections. Supply current for amplifier A1 is drawn from the VS– pin. The user may choose to include this current in the monitored current through RSENSE by careful choice of connection polarity. Selection of External Current Sense Resistor External RSENSE resistor selection is a delicate trade-off between power dissipation in the resistor and current measurement accuracy. The LT1787 makes this decision less difficult than with competitors’ products. The maximum sense voltage may be as large as ± 500mV to get maximum resolution, however, high current applications will not want to suffer this much power dissipation in the sense resistor. The LT1787’s input offset voltage of 40µV gives high resolution for low sense voltages. This wide operating dynamic range gives the user wide latitude in tailoring the range and resolution of his supply monitoring function. U W U U 7 LT1787/LT1787HV APPLICATIONS INFORMATION Kelvin connection of the LT1787’s VS+ and VS– inputs to the sense resistor should be used in all but the lowest power applications. Solder connections and PC board interconnect resistance (approximately 0.5mΩ per square) can be a large error in high current systems. A 5-Amp application might choose a 20mΩ sense resistor to give a 100mV full-scale input to the LT1787. Input offset voltage will limit resolution to 2mA. Neglecting contact resistance at solder joints, even one square of PC board copper at each resistor end will cause an error of 5%. This error will grow proportionately higher as monitored current levels rise to tens or hundreds of amperes. Input Noise Filtering The LT1787 provides input signal filtering pins FIL+ and FIL– that are internally connected to the midpoint taps of resistors RG1 and RG2. These pins may be used to filter the input signal entering the LT1787’s internal amplifier, and should be used when fast current ripple or transients may flow through the sense resistor. High frequency signals above the 300kHz bandwidth of the LT1787’s internal amplifier will cause errors. A capacitor connected between FIL+ and FIL– creates a single pole low pass filter with corner frequency: f –3dB = 1/(2π RC) where R = 1.25k. A 0.01µF capacitor creates a pole at 12.7kHz, a good choice for many applications. Common mode filtering from the FIL+ and FIL– pins should not be attempted, as mismatch in the capacitors from FIL+ and FIL– will create AC common mode errors. Common mode filtering must be done at the power supply output. Output Signal Range The LT1787’s output signal is developed by summing the net currents through RG1 and RG2 into output resistor ROUT. The pins VOUT and VBIAS may be connected in numerous configurations to interface with following circuitry in either single supply or split supply applications. Care must be used in connecting the output pins to preserve signal accuracy. Limitations on the signal swing at VOUT are imposed by the negative supply, VEE, and the input voltage VS+. In the negative direction, internal circuit saturation with loss of accuracy occurs for VOUT < 70mV with absolute minimum swing at 30mV above VEE. VOUT may swing positive to within 0.75V of VS+ or a maximum of 35V, a limit set by internal junction breakdown. Within these contraints, an amplified, level shifted representation of the RSENSE voltage is developed across ROUT. Split Supply Bipolar Output Swing Figure 2 shows the LT1787 used with split power supplies. The VBIAS pin is connected to ground, and the output signal appears at the VOUT pin. Bidirectional input currents can be monitored with the output swinging positive for current flow from VS+ and VS–. Input currents in the opposite direction cause VOUT to swing below ground. Figure 2 shows an optional output capacitor connected from VOUT to ground. This capacitor may be used to filter the output signal before it is processed by other circuitry.Figure 3 shows the voltage transfer function of the LT1787 used in this configuration. Single Supply with Shifted VBIAS Figure 4 shows the LT1787 used in a single supply mode with the VBIAS pin shifted positive using an external LT1634 voltage reference. The VOUT output signal can swing above and below VBIAS to allow monitoring of positive or negative currents through the sense resistor, as shown in Figure 5. The choice of reference voltage is not critical except for the precaution that adequate headroom must be provided for VOUT to swing without saturating the internal circuitry. The component values shown in Figure 4 allow operation with VS supplies as low as 3.1V. Operation with A/D Converter Figure 6 shows the LT1787 operating with the LTC1286 A/D converter. This low cost circuit is capable of 12-bit resolution of unipolar currents. The – IN pin of the A/D converter is biased at 1V by the resistor divider R1 and R2. This voltage increases as sense current increases, with the 8 U W U U LT1787/LT1787HV APPLICATIONS INFORMATION TO CHARGER/ LOAD 1 FIL– LT1787 RSENSE C1 1µF 15V 8 FIL+ VS + 7 VBIAS 6 ROUT 5 VOUT C3* 1000pF – 2 VS 3 4 –5V C2 1µF DNC VEE *OPTIONAL Figure 2. Split Supply Operation OUTPUT VOLTAGE – OUTPUT BIAS VOLTAGE (V) 1.5 1.0 OUTPUT VOLTAGE (V) VS = 3.3V TO 60V TA = – 40°C TO 85°C 0.5 0 –0.5 –1.0 –1.5 –128 –96 –64 –32 0 32 64 96 SENSE VOLTAGE (VS+ – VS–) (mV) 128 1787 F03 Figure 3. Split Supply Output Voltage amplified sense voltage appearing between the A/D converters –IN and +IN terminals. The front page of the data sheet shows a similar circuit which uses a voltage reference for improved accuracy and signal range. The LTC1286 converter uses sequential sampling of its –IN and +IN inputs. Accuracy is degraded if the inputs move between sampling intervals. A filter capacitor from FIL+ to FIL– as well as a filter capacitor from VBIAS to VOUT may be necessary if the sensed current changes more than 1LSB within a conversion cycle. U W U U TO CHARGER/ LOAD 1 FIL– – RSENSE C1 1µF 3.3V TO 60V 3.3V 20k 5% C2 1µF C3* 1000pF OUTPUT 1787 F04 FIL+ LT1787HV VS + 8 7 2 VS 3 4 DNC VEE VBIAS 6 ROUT VOUT 5 OUTPUT LT1634-1.25 1787 F02 *OPTIONAL Figure 4. Charge/Discharge Current Monitor on Single Supply with VBIAS = 1.25V 1.5 1.0 0.5 0 –0.5 –1.0 –1.5 –128 –96 –64 –32 0 32 64 96 SENSE VOLTAGE (VS+ – VS–) (mV) VS = 3.3V TO 60V TA = – 40°C TO 85°C 128 1787 F05 Figure 5. Single Supply Output Voltage with VBIAS = 1.25V RSENSE 5V 1 FIL– LT1787 8 FIL+ VS + 7 VBIAS 6 IOUT ROUT VEE VOUT R2 5k 5% 5 R1 20k 5% C1 1µF 5V – 2 VS 3 4 DNC VCC CS LTC1286 CLK –IN D VREF GND OUT +IN TO µP 1787 F06 Figure 6. Unidirectional Output into A/D with Fixed Supply at VS+ 9 LT1787/LT1787HV APPLICATIONS INFORMATION Buffered Output Operation Figure 7 shows the LT1787’s outputs buffered by an operational amplifier configured as an I/V converter. This configuration is ideal for monitoring very low voltage supplies. The LT1787’s VOUT pin is held equal to the reference voltage appearing at the op amp’s noninverting input. This allows monitoring VS supplies as low as 2.5V. The op amp’s output may swing from ground to its positive supply voltage. The low impedance output of the op amp may drive following circuitry more effectively than the high output impedance of the LT1787. The I/V converter configuration also works well with split supply voltages. Single Supply Unidirectional Operation Figure 8 shows the simplest connection in which the LT1787 may be used. The VBIAS pin is connected to ground, and the VOUT pin swings positive with increasing sense current. The LT1787’s outputs can swing as low as 30mV as shown in Figure 9. Accuracy is sacrificed at small TO CHARGER/ LOAD 1 FIL– LT1787 RSENSE ISENSE 0.30 8 C1 1µF 2.5V + VSENSE(MAX) 0.25 FIL+ – 2 VS VS+ 7 VBIAS 6 ROUT 5 C3 1000pF 2.5V OUTPUT VOLTAGE (V) 3 4 DNC VEE VOUT 2.5V 1M 5% – A1 + LT1389-1.25 LT1495 0 1787 F07 Figure 7. Single Supply 2.5V Bidirectional Operation with External Voltage Reference and I/V Converter 10 U W U U output levels, but this is not a limitation in protection circuit applications or where sensed currents do not vary greatly. Increased low level accuracy can be obtained by level shifting VBIAS above ground. The level shifting may be done with resistor dividers, voltage references or a simple diode. Accuracy is ensured if the output signal is sensed differentially between VBIAS and VOUT. TO LOAD RSENSE C 0.1µF 2.5V TO 60V 8 FIL+ LT1787HV + – VS 7 2 VS 1 FIL– 3 4 DNC VEE VBIAS 6 ROUT VOUT 1787 F08 5 VOUT Figure 8. Unidirectional Current Sensing Mode 0.20 0.15 0.10 0.05 IDEAL 0 0.005 0.010 0.015 0.020 VS+ – VS– (V) 0.025 0.030 1787 F09 VOUT A Figure 9. Expanded Scale of Unidirectional Output LT1787/LT1787HV APPLICATIONS INFORMATION Adjusting Gain Setting The LT1787 may be used in all operating modes with an external resistor used in place of the internal 20k ROUT resistor. When an external resistor is used, leave the VBIAS pin floating or connected to the VOUT pin. This will remove the internal ROUT from the circuit. The voltage gain will be gm • ROUT where gm is the LT1787’s transconductance, 400µA/V typical. A nominal gain of 40 may be obtained with an external 100k resistor used in place of the internal 20k ROUT: AV = gm • ROUT = 400µA/V • 100k = 40 The transconductance gm is set by on-chip resistors on the LT1787. These resistors match well but have loose absolute tolerance. This will normally require that the external gain setting resistor be trimmed for initial accuracy. After trimming, the temperature stability of the gm and therefore gain will be –200ppm/°C. The only limitations placed upon the resistor choice is care must be taken not to saturate the internal circuitry by violating the VOMAX specification of VS + –0.75V. PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. 0.040 ± 0.006 (1.02 ± 0.15) 0.007 (0.18) 0.021 ± 0.006 (0.53 ± 0.015) 0° – 6° TYP SEATING PLANE 0.012 (0.30) 0.0256 REF (0.65) BSC * DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE ** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE S8 Package 8-Lead Plastic Small Outline (Narrow 0.150) (LTC DWG # 05-08-1610) 0.189 – 0.197* (4.801 – 5.004) 0.010 – 0.020 × 45° (0.254 – 0.508) 0.008 – 0.010 (0.203 – 0.254) 0°– 8° TYP 0.053 – 0.069 (1.346 – 1.752) 8 0.004 – 0.010 (0.101 – 0.254) 0.228 – 0.244 (5.791 – 6.197) 0.150 – 0.157** (3.810 – 3.988) 7 6 5 0.014 – 0.019 (0.355 – 0.483) TYP *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE 0.016 – 0.050 (0.406 – 1.270) Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. U U W U U MS8 Package 8-Lead Plastic MSOP (LTC DWG # 05-08-1660) 0.034 ± 0.004 (0.86 ± 0.102) 0.118 ± 0.004* (3.00 ± 0.102) 8 76 5 0.006 ± 0.004 (0.15 ± 0.102) 0.193 ± 0.006 (4.90 ± 0.15) 0.118 ± 0.004** (3.00 ± 0.102) MSOP (MS8) 1098 1 23 4 0.050 (1.270) BSC 1 2 3 4 SO8 1298 11 LT1787/LT1787HV TYPICAL APPLICATION Split or Single Supply Operation, Bidirectional Output into A/D 1Ω 1% 1 FIL– LT1787 8 FIL+ VS+ 7 VBIAS 6 20k VOUT 5 VOUT (±1V) OPTIONAL SINGLE SUPPLY OPERATION: DISCONNECT VBIAS FROM GROUND AND CONNECT IT TO VREF. REPLACE –5V SUPPLY WITH GROUND. OUTPUT CODE FOR ZERO CURRENT WILL BE ~2430 1 CONV 2 3 7 CLOCKING CIRCUITRY VCC 5V 10µF 16V IS = ± 125mA VSRCE ≈ 4.75V – 2 VS 3 DNC VEE 4 VEE –5V RELATED PARTS PART NUMBER LTC1043 LT1490/LT1491 LT1620/LT1621 DESCRIPTION Dual Precision Instrumentation Switched Capacitor Building Block Dual and Quad Micropower Rail-to-Rail Input and Output Op Amps Rail-to-Rail Current Sense Amplifiers COMMENTS 120dB CMRR, 3V to 18V Operation 50µA Amplifier, 2.7V to 40V Operation, Over-The-TopTM Inputs Accurate Output Current Programming, Battery Charging to 32V Over-The-Top is a trademark of Linear Technology Corporation. 12 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408)432-1900 q FAX: (408) 434-0507 q www.linear-tech.com U 6 AIN LTC1404 CLK VREF 5 DOUT GND 10µF 16V 4 8 10µF 16V VEE –5V DOUT 1787 TA02 1787f LT/TP 0100 4K • PRINTED IN USA © LINEAR TECHNOLOGY CORPORATION 1999