LTC6104 High Voltage, High Side, Bi-Directional Current Sense Amplifi er DESCRIPTION FEATURES APPLICATIONS TYPICAL APPLICATION

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1 FEATUES Wide Supply ange: to 6 with 7 Absolute Maximum Low Offset oltage: ±5µ Maximum Fast esponse: µs esponse Time Gain Configurable with External esistors; Each Direction is Gain Configurable Low Input Bias Current: 7nA Maximum PS: db Minimum Output Current: ± Maximum Low Supply Current: 52µA, = 2 Specified for C to 25 C Temperature ange Available in an 8-Lead MSOP Package APPLICATIONS Current Shunt Measurement Battery Monitoring emote Sensing Power Management, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. LTC6 High oltage, High Side, Bi-Directional Current Sense Amplifi er DESCIPTION The LTC 6 is a versatile, high voltage, high side, bidirectional current sense amplifier. Design fl exibility is provided by the excellent device characteristics: ±5µ maximum offset and only 52µA of current consumption (typical at 2). The LTC6 operates on supplies from to 6. The LTC6 monitors bi-directional current via the voltage across an external sense resistor (shunt resistor). This sense voltage is then translated into a ground referenced signal. Gain is set with three external resistors and can be separately configured for both directions. Low DC offset allows the use of a small shunt resistor and large gain-setting resistors. As a result, power loss in the shunt is minimal. The wide operating supply range and high accuracy make the LTC6 ideal for a wide variety of automotive, industrial and power management applications. A maximum input sense voltage of 5m allows a wide range of currents to be monitored. The fast response makes the LTC6 the perfect choice for load current warnings and shutoff protection control. With very low supply current, the LTC6 is suitable for power sensitive applications. The LTC6 is available in an 8-lead MSOP package. TYPICAL APPLICATION 6-Bit esolution Bi-Directional Output into LTC286 ADC TO CHAGE/LOAD I LOAD Ω Ω 2 Step esponse = m A A B 5 B 6 A LTC6 CUENT MIO 2.5k B EF C2.µF 2.3k C µf EF CC CS LTC286 CLK D LT -2.5 GND 6 TAa 5 TO µp.5 I = µa I = µa TIME (µs/di) = 2 = Ω = 5k = S EF = 6 G5 6f

2 LTC6 ABSOLUTE MAXIMUM ATGS (Note ) Total Supply oltage (B( ) to )...7 Maximum Applied Output oltage ()...9 Input Current...± Output Short-Circuit Duration (to )... Indefi nite Operating Temperature ange LTC6C... C to 85 C LTC6I... C to 85 C LTC6H... C to 25 C Specified Temperature ange (Note 2) LTC6C... C to 7 C LTC6I... C to 85 C LTC6H... C to 25 C Storage Temperature ange C to 5 C Lead Temperature (Soldering, sec)... 3 C PACKAGE/ODE FOMATION NC NC 2 3 ODE PAT NUMBE LTC6CMS8 LTC6IMS8 LTC6HMS8 TOP IEW 8 A 7 A 6 B 5 B/ MS8 PACKAGE 8-LEAD PLASTIC MSOP T JMAX = 5 C, θ JA = 3 C/W MS8 PAT MAKG* LTCMP LTCMP LTCMP Order Options Tape and eel: Add #T Lead Free: Add #PBF Lead Free Tape and eel: Add #TPBF Lead Free Part Marking: Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. ELECTICAL CHAACTEISTICS The denotes the specifi cations which apply over the full operating temperature range, otherwise specifi cations are at. = Ω, = 5k, B( ) 6, =, EF = 2 for 6, EF =.75 for =, unless otherwise noted. SYMBOL PAAMETE CONDITIONS M TYP MAX UNITS Supply ange 6 OS Output Offset oltage = ±5m, LTC6 = ±5m, LTC6C, LTC6I = ±5m, LTC6H ±85 ±5 ±6 ±7 Δ OS /ΔT Input Offset oltage Drift = ±5m ±.5 µ/ C I B Input Bias Current = M for A and B 7 na 25 na (MAX) Input Sense oltage Full Scale 6 6, = k, = 2k, EF = 2 ±5 m (Note 3) =, = k, = k, EF =.5 when ±5 m = 5m, EF = when = 5m PS Power Supply ejection atio = 6 to 6, = 5m 6 db 2 db = 6 to 6, = 5m 2 db 5 db = to 6, = 5m 33 db 5 db = to 6, = 5m 5 db 5 db (MAX) Maximum Output oltage 2 6, = 9m, EF = = 6, = 75m, EF =.8, = 2k =, = 35m, EF =.75, = k (M) Minimum Output oltage 2 6, = 8m, EF = = 6, = 9m, EF =.8, = 2k =, = 75m, EF =.75, = k µ µ µ 2 6f

3 LTC6 ELECTICAL CHAACTEISTICS The denotes the specifi cations which apply over the full operating temperature range, otherwise specifi cations are at. = Ω, = 5k, B( ) 6, =, EF = 2 for 6, EF =.75 for =, unless otherwise noted. SYMBOL PAAMETE CONDITIONS M TYP MAX UNITS I (MAX) Maximum Output Current 6 6, = ±m, EF = 2, = k =, = ±27.5m, EF =.75, = k I -GAE Current Mirror Gain Error B > B and A < A (Note ) ±.2 ±.75 % I -OSE Current Mirror Offset Error B > B and A < A (Note ) ±.2 µa t r Input Step esponse (Δ = to 8 6, EF =, = m to m µs 5% on a 5 Output Step) Transient 8 6, EF = 6, = m to m µs Transient 8 6, EF =, = 5m to 5m Transient 3 µs Input Step esponse (Δ = to 5% on a.5 Output Step) =, = 5Ω, Gain = 5, EF =.5, = m to m Transient =, = 5Ω, Gain = 5, EF =, = m to m Transient =, = 5Ω, Gain = 5, EF =.75, = 5m to 5m Transient BW Signal Bandwidth I = 2µA, = 5k I = 2µA, = 5k I =, = 5k I =, = 5k I S Supply Current =, I =, = M = 6, I =, = M = 2, I =, = M = 6, I =, = M LTC6I, LTC6C LTC6H ± ±.25.2 µs.2 µs 3.2 µs khz khz khz khz Note : Stresses beyond those listed under Absolute Maximum atings may cause permanent damage to the device. Exposure to any Absolute Maximum ating condition for extended periods may affect device reliability and lifetime. Note 2: The LTC6C is guaranteed to meet specifi ed performance from C to 7 C. The LTC6C is designed, characterized and expected to meet specified performance from C to 85 C but are not tested or QA sampled at these temperatures. LTC6I is guaranteed to meet specifi ed performance from C to 85 C. The LTC6H is guaranteed to meet specified performance from C to 25 C. Note 3: (MAX) is tested by applying 55m and verifying the gain error is less than %. The % limit is set by the accuracy of high speed test equipment. Gain error is typically dominated by external resistor tolerance. Note : When amplifi er A is active and amplifi er B is inactive, the gain error is entirely due to the external resistors and. When amplifier A is inactive and amplifier B is active, there is an additional gain error from the LTC6 current mirror circuit. This error term is the gain error term, I -GAE plus the offset error term, I -OSE. 6f 3

4 LTC6 TYPICAL PEFOMANCE CHAACTEISTICS PUT OFFSET (µ) Input OS vs Temperature TWO EPESENTATIE UNITS = Ω = 5k = 5m OS OF TENAL AMPLIFIE A OS OF TENAL AMPLIFIE B TEMPEATUE ( C) 6 G PUT OFFSET (µ) Input OS vs Supply oltage = Ω = 5k = 5m TWO EPESENTATIE UNITS OS OF TENAL AMPLIFIE A OS OF TENAL AMPLIFIE B () 6 G2 MAXIMUM () Input Sense ange vs Supply oltage = 5k = 2.5k T A = C T A = C T A = 7 C T A = 85 C NO LIMITS FO IF < AND () 6 G3 2 Maximum vs Temperature.9 Minimum vs Temperature 6 I Maximum vs Temperature MAXIMUM PUT () = 6 = 2 = 6 = MIMUM PUT () = 6 =, 6, 2 MAXIMUM I () = 6 = 2 = 6 = TEMPEATUE ( C) TEMPEATUE ( C) TEMPEATUE ( C) 6 G 6 G5 6 G6 GA (db) Gain vs Frequency Input Bias Current vs Temperature Supply Current vs Supply oltage 35 I = ± 3 25 I = ±2µA = Ω = 5k k k k M FEQUENCY (Hz) I B (na) = 6 TO = TEMPEATUE ( C) SUPPLY CUENT (µa) T A = 7 C T A = 85 C T A = C T A = C = = M SUPPLY OLTAGE () 6 G8 6 G9 6 G 6f

5 TYPICAL PEFOMANCE CHAACTEISTICS LTC6 Step esponse m to mtep esponse m to mtep esponse 5m to 5m m m 5m 5m = 2 = Ω = 5k = S EF = = 2 = Ω = 5k = S EF = = 2 = Ω = 5k = S EF = 2 TIME (µs/di) TIME (µs/di) TIME (µs/di) 6 G 6 G2 6 G3 Step esponse 5m to 5m Step esponse ising Edge Step esponse ising Edge 5m 5m 6.5 C LOAD pf 6 = m = m I = µa I = µa C LOAD pf.5 = 2 = Ω = 5k = S EF =.5 I = µa I = µa = 2 = Ω = 5k = S EF =.5 = 2 = Ω = 5k = S EF = 6 TIME (µs/di) TIME (µs/di) TIME (µs/di) 6 G 6 G5 6 G6 Step esponse ising Edge Step esponse Falling Edge 5m 5m = m.5 2 = 2 = Ω = 5k = S EF =.5.5 = 2 = Ω = 5k = S EF = I = µa I = µa TIME (µs/di) TIME (µs/di) 6 G7 6 G8 6f 5

6 LTC6 TYPICAL PEFOMANCE CHAACTEISTICS Step esponse Falling Edge I = µa I = µa = 2 = Ω = 5k = S EF = 6 = m TIME (µs/di) 6 G9 5m 5m Step esponse Falling Edge = 2 = Ω = 5k = S EF =.5 TIME (µs/di) 6 G2 PS (db) PS vs Frequency = = 2 6 = Ω = 5k C = 5pF 2 GA = 5 I DC = µa AC = 5m P-P. k k k M FEQUENCY (Hz) 6 G2 P FUNCTIONS (Pin ): Current Output. will source or sink a current that is proportional to the sense voltage into an external resistor. A voltage reference is required to provide the proper positive offset voltage so that the output can swing both positive and negative. (Pin ): Negative Supply (or Ground for Single-Supply Operation). B/ (Pin 5): The positive input of the internal sense amplifier B. It also works as the positive supply input. Supply current is drawn through this pin. B (Pin 6): The negative input of the internal sense amplifier B. The internal sense amplifi er will drive B to the same potential as B when is negative. A resistor ( ) tied from one end of to B sets the output current I = /. is the voltage developed across the external (Figure ). A (Pin 7): The negative input of the internal sense amplifi er A. The internal sense amplifi er will drive A to the same potential as A when is positive. A resistor ( ) tied from one end of to A sets the output current I = /. A (Pin 8): The positive input of the internal sense amplifi er A. 6 6f

7 LTC6 BLOCK DIAGAM I LOAD B A A A B B 5k 5k 5k 5k A B = EF EF 6 F Figure. LTC6 Block Diagram THEOY OF OPEATION When is positive, an internal sense amplifier loop forces A to have the same potential as A. Connecting an external resistor, A, in series with A causes a current, / A, to flow through A. The high impedance inputs of the sense amplifier will not conduct this input current, so the current will fl ow through an internal MOSFET to the pin. The output current can be transformed into a voltage by adding a resistor from to a reference voltage ( EF ). The output voltage is then = ( / A ) EF. When operating on a dual supply, can be tied to ground. The output voltage is then = ( / A ). Only one amplifier is active at a time in the LTC6. If the load current direction ( is negative) activates the B amplifi er, the A amplifi er will be inactive. The signal current goes into the B pin, through the MOSFET, and into the current mirror. The mirror reverses the polarity of the signal so that current flows into the pin, causing the output voltage to change polarity. The magnitude of the output is then / B EF. Keep in mind that the voltage cannot swing below, even though it s sinking current. A proper EF and need to be chosen so that the designed voltage swing does not go beyond the specifi ed voltage range of the output. Supply current is drawn from B pin. The user may choose to include this current in the monitored current through by careful choice of connection polarity. 6f 7

8 LTC6 APPLICATIONS FOMATION Selection of External Current Sense esistor The external sense resistor,, has a significant effect on the function of a current sensing system and must be chosen with care. First, the power dissipation in the resistor should be considered. The system load current will cause both heat and voltage loss in. As a result, the sense resistor should be as small as possible while still providing the input dynamic range required by the measurement. Note that input dynamic range is the difference between the maximum input signal and the minimum accurately reproduced signal, and is limited primarily by input DC offset of the internal amplifier of the LTC6. In addition, must be small enough that does not exceed the maximum input voltage specified by the LTC6, even under peak load conditions. As an example, an application may require that the maximum sense voltage be ±m. If this application is expected to draw ±2A at peak load, should be no more than 5mΩ. 8 = m m I = 2A = 5 Ω PEAK Once the maximum value is determined, the minimum sense resistor value will be set by the resolution or dynamic range required. The minimum signal that can be accurately represented by this sense amp is limited by the input offset. As an example, the LTC6 has a typical input offset of ±85µ. If the minimum current is ±2, a sense resistor of.25mω will set to ±85µ. This is the same value as the input offset. A larger sense resistor will reduce the error due to offset by increasing the sense voltage for a given load current. Choosing a 5mΩ will maximize the dynamic range and provide a system that has ±m across the sense resistor at peak load (±2A), while input offset causes an error equivalent to only ±.7 of load current. Peak dissipation in the sense resistor is 2mW in this example. If instead a 5mΩ sense resistor is employed, then the effective current error is ±7, while the peak sense voltage is reduced to ±m at ±2A, dissipating only 2mW. The low offset and corresponding large dynamic range of the LTC6 make it more fl exible than other solutions in this respect. The ±85µ typical offset gives 6dB of dynamic range for a sense voltage that is limited to ±85m max, and over 75dB of dynamic range if the rated input maximum of ±5m is allowed. Sense esistor Connection Kelvin connection of the A/B and A/B inputs to the sense resistor should be used in all but the lowest power applications. Solder connections and PC board interconnections that carry high current can cause signifi cant error in measurement due to their relatively large resistances. One mm mm square trace of one-ounce copper is approximately.5mω. A m error can be caused by as little as 2A flowing through this small interconnect. This will cause a % error in a m signal. A A load current in the same interconnect will cause a 5% error for the same m signal. By isolating the sense traces from the high current paths, this error can be reduced by orders of magnitude. A sense resistor with integrated Kelvin sense terminals will give the best results. Figure 2 illustrates the recommended method. TO CHAGE/LOAD I LOAD LTC A A B A CUENT MIO EF B 5 B 6 F2 Figure 2. Kelvin Input Connections Preserve Accuracy Despite Large Load Currents 6f

9 APPLICATIONS FOMATION Selection of External Input esistor, The external input resistor,, controls the transconductance of the current sense circuit. Since I =, transconductance gm = For example, if = Ω, then I S = ENSE or Ω I =± for =± m. should be chosen to allow the required resolution while limiting the output current. At low supply voltage, I may be as much as ±. By setting such that the largest expected sense voltage gives I = ±, then the maximum output dynamic range is available. Output dynamic range is limited by both the maximum allowed output current and the maximum allowed output voltage, as well as the minimum practical output signal. If less dynamic range is required, then can be increased accordingly, reducing the maximum output current and power dissipation. If low sense currents must be resolved accurately in a system that has very wide dynamic range, a smaller than the maximum current specification allows may be used if the maximum current is limited in another way, such as with a Schottky diode across (Figure 3). This will reduce the high current measurement accuracy by limiting the result, while increasing the low current measurement resolution. This approach can be helpful in cases where occasional large burst currents may be ignored. Care should be taken when designing the printed circuit board layout to minimize input trace resistance (to Pins 5, 6, 7 and 8). Trace and interconnect impedances to the LOAD D 6 F3 BATTEY Figure 3. Shunt Diodes Limit Maximum Input oltage to Allow Better Low Input esolution Without Overranging LTC6 terminals will increase the effective value, causing a gain error, especially for small values. In addition, internal device resistance will add approximately.3ω to. Trace and interconnect impedances to the B terminal will have an effect on offset error. These errors are described in more detail later in this data sheet. Selection of External Output esistor, The output resistor,, determines how the output current is converted to voltage. is simply I EF. In choosing an output resistor, the maximum output voltage range must first be considered. If the circuit that is driven by the output does not limit the output voltage range, then must be chosen such that the maximum output voltage range does not exceed the LTC6 maximum output voltage range (see Electrical Characteristics). If the following circuit is a buffer or ADC with limited input range, then must be chosen so that is in the allowed maximum input range of this circuit. In addition, the output impedance is determined by. If the circuit to be driven has high enough input impedance, then almost any useful output impedance will be acceptable. However, if the driven circuit has relatively low input impedance, or draws spikes of current, such as an ADC might do, then a lower value may be required in order to preserve the accuracy of the output. As an example, if the input impedance of the driven circuit is times, then the accuracy of will be reduced by % since: EF = I ( DIEN) ( DIEN) = I =. I 99 Selection of External oltage eference, EF Selection of external reference voltage should be considered together with selection of. Example: Given the conditions: I = to, = 2. 6f 9

10 LTC6 APPLICATIONS FOMATION From the Electrical Characteristics of the LTC6, the output voltage range is.3 to 8. If the circuit that is driven by the output limits the maximum output voltage to 5, to achieve maximum dynamic range, should be.3 for I and 5 for I. EF 5. 3 = = 235. k, 2 = = A standard 2.5 reference could be used in this example. With I = ± and = 2.2k, the output voltage range would equal.3 to.7 EF Considerations EF as shown in Figure, provides a positive offset so that the output can swing above and below this point. It is recommended that this is an accurate voltage reference. Most voltage references will work in this application as long as they are able to sink and source current. Make sure that the device maintains the required voltage accuracy as the current varies through its entire range. Error Sources The current sense system uses an amplifier and resistors to apply gain and level shift the result. The output is then dependent on the characteristics of the amplifier, such as gain and input offset, as well as resistor matching. Ideally, the circuit output is: EF = I =, = I In this case, the only error is due to resistor mismatch, which provides an error in gain only. However, offset voltage, bias current and finite gain in the amplifier cause additional errors. Output Error, E, Due to the Amplifi er DC Offset oltage, OS E ( OS) = OS The DC offset voltage of the amplifier adds directly to the value of the sense voltage,. This is the dominant error of the system and it limits the available dynamic range. The section, Selection of External Current Sense esistor, provides details. Output Error, E, Due to the Bias Currents, I B and I B The bias current I B fl ows into the positive input of the internal op amp. I B fl ows into the negative input. E IBIAS I ( ) = B IB Since I B I B = I BIAS, if << then: E (IBIAS) I BIAS For instance if I BIAS is na and is k, the output error is.m. Output Error, E, Due to the Finite DC Open-Loop Gain, A OL, of the LTC6 Amplifi er This error is inconsequential as the A OL of the LTC6 is very large. Example: If an I range = (± to ±A) and = 3 I A Then, from the Electrical Characteristics of the LTC6: ( MAX) 5m = = 5mΩ I A ( MAX) Gain ( MAX) 3 = = = = 6 5m ( MAX) 6f

11 APPLICATIONS FOMATION If the maximum output current, I, is limited to, equals 3/ = 3k and = 3k/6.3Ω (internal device resistance) = 99.7Ω. The output error due to DC offset is ±5µ (typ) and the error due to offset current, I OS, is 3k na = 3µ(typ). The maximum output error can therefore reach ±8µ or.27% (7dB) of the output full scale. Considering the system input 6dB dynamic range (I = ± to ±A), the 7dB performance of the LTC6 makes this application feasible. Output Error, E, Due to the Current Mirror Errors, I -GAE and I -OSE When is negative, amplifier B would be on and amplifier A off. The output of amplifier B drives an internal current mirror which is connected to the pin. This current mirror has some error associated with it, and this error can be calculated as follows: I -GAE = ±.2% I, with I = ±, I -GAE(MAX) = ±2μA I -OSE = ±.2μA I -E(MAX) = I -GAE I -OSE = ±2μA ±.2μA = ±2.2μA E -E(MAX) = I -E(MAX) The combined effect of amplifier offset and current mirror errors is shown graphically in Figure. LTC6 Output Error, E, Due to Trace esistance The LTC6 uses the B pin for both the positive B amplifi er input and the positive supply input for both amplifi ers. If trace resistance ( T ) become significant (Figure 5), this supply current can cause an input offset error, which can be calculated as follows: E( OFFSET) = T IS Trace resistances to the terminals will increase the effective value, causing a gain error (Figure 5). In addition, internal device resistance will add approximately.3ω to. Gain error equals: A ( EO) = 3Ω. T Minimizing resistance in the input traces is important and care should be taken in the PCB layout. Make the trace short and wide. Kelvin connection to the shunt resistor pad should be used. Avoid tapping into this signal along TO CHAGE/LOAD I LOAD T T T T PUT EO (%). = Ω = 5k MAXIMUM TYPICAL LTC A A B A CUENT MIO I B 5 B 6 F5 I S (m) 6 F Figure. Output Error vs Input oltage EF Figure 5. Errors from PCB Traces and Other Parasitic esistances 6f

12 LTC6 APPLICATIONS FOMATION the high current path, as this will increase the voltage drop and escalate this error. Output Current Limitations Due to Power Dissipation The LTC6 can deliver up to ± continuous current to the output pin. This current fl ows through and enters the current sense amp via the pin. The power dissipated in the LTC6 due to the output signal is: P I There is also power dissipated due to the quiescent supply current: P Q = I S The total power dissipated is the output dissipation plus the quiescent dissipation: P TOTAL = P P Q At maximum supply and maximum output current, the total power dissipation can exceed mw. This will cause significant heating of the LTC6 die. In order to prevent damage to the LTC6, the maximum expected dissipation in each application should be calculated. This number can be multiplied by the θ JA value to find the maximum expected die temperature. This must not be allowed to exceed 5 C, or performance may be degraded. As an example, if an LTC6 in the MS8 package is to be run at 55 ±5 supply with output current at 8 C: P Q(MAX) = I S(MAX) (MAX) =.2 6 = 72mW P (MAX) = I (MAX) = 6 = 6mW θ JA = 3C /W T ISE = θ JA P TOTAL(MAX) = 3C /W (72mW 6mW) = 39.6 C T MAX = T AMBIENT T ISE = 8 C 39.6 C = 9.6 C P TOTAL(MAX) 32mW and the max die temp will be 9.6 C T MAX must be <5 C If this same circuit must run at 25 C, the maximum die temperature will exceed 5 C. (Note that supply current, and therefore P Q, is proportional to temperature. efer to Typical Performance Characteristics.) In this condition, the maximum output current should be reduced to avoid device damage. It is important to note that the LTC6 has been designed to provide at least ± to the output when required, and can deliver more depending on the conditions. Care must be taken to limit the maximum output current by proper choice of sense resistor and, if input fault conditions exist, external clamps. Output Filtering The output voltage,, is simply I Z. This makes filtering straightforward. Any circuit may be used which generates the required Z to get the desired filter response. For example, a capacitor in parallel with will give a lowpass response. This will reduce unwanted noise from the output, and may also be useful as a charge reservoir to keep the output steady while driving a switching circuit such as a MUX or ADC. This output capacitor in parallel with an output resistor will create a pole in the output response at: f 3dB = 2 π C Useful Equations Input oltage: = I oltage Gain: Current Gain: I I Transconductance: = = I = Transimpedance: = I 2 6f

13 APPLICATIONS FOMATION everse Supply Protection Some applications may be tested with reverse-polarity supplies due to an expectation of this type of fault during operation. The LTC6 is not protected internally from external reversal of supply polarity. To prevent damage that may occur during this condition, a Schottky diode should be added in series with (Figure 6). This will limit the reverse current through the LTC6. Note that this diode will limit the low voltage performance of the LTC6 by effectively reducing the supply voltage to the part by D. Keep this in mind when choosing an output resistor and voltage reference. In addition, if the output of the LTC6 is wired to a device that will effectively short it to high voltage (such as through an ESD protection clamp) during a reverse supply condition, the LTC6 s output should be connected through a resistor or Schottky diode (Figure 7). esponse Time The LTC6 is designed to exhibit fast response to inputs for the purpose of circuit protection or signal transmission. This response time will be affected by the external circuit in two ways: delay and speed. LTC6 For unidirectional applications, if the output current is very low and an input transient occurs, there may be an increased delay before the output voltage starts to change. This can be improved by increasing the minimum output current, either by increasing or by decreasing. The effect of increased output current is illustrated in the step response curves in the Typical Performance Characteristics section of this datasheet. Note that the curves are labeled with respect to the initial output currents. For bidirectional applications, there is a delay when output current changes polarity. The delay time can be found in the step response curves in the Typical Performance Characteristics section of this data sheet. Speed is also affected by the external circuit. In this case, if the input changes very quickly, the internal amplifier and the internal output FET (Figure ) will attempt to maintain the internal loop, but may be slew rate limited. This results in current flowing through and the internal FET. This current slew rate will be determined by the amplifier and FET characteristics as well as the input resistor,. Using a smaller will allow the output current to increase more quickly, decreasing the response time at the output. This will also have the effect of increasing the maximum output current. Using a larger will TO CHAGE/LOAD I LOAD TO CHAGE/LOAD I LOAD A A B A 5 B A A B B I S 5 B A B LTC6 CUENT MIO 6 F6 ADC LTC6 CUENT MIO 6 F7 D D EF EF Figure 6. Schottky Prevents Damage During Supply eversal Figure 7. Additional esistor Protects Output During Supply eversal 6f 3

14 LTC6 APPLICATIONS FOMATION decrease the response time, since = I. educing and increasing will both have the effect of increasing the voltage gain of the circuit. Use of Dual Sense esistors The dual amplifi er topology offers signifi cant advantages for controlling gain, dynamic range and shunt current. As an example, separate shunt resistors can be advantageous for an H-bridge current monitor (see H-Bridge Load Current Monitor application). It can also be a significant advantage for battery-operated systems, where battery discharge and charge current can be significantly different. With different current range requirements, a charge shunt resistor can be connected from the charger to the battery and a separate discharge shunt resistor can be connected from the battery to the load. Other applications can benefit from similar topologies where different shunt resistors enable the user to trade off accuracy and shunt power consumption. Finally, since each amplifier has an independent input resistor, gain for each channel can be set to suit the application. The only limitation to observe in this type of application is that since the power for both sense amplifiers is furnished via the B pin, the input protection for both sections is referenced to this one pin. Normal operation of section A is maintained for A and A voltages within the range of.5 above B to.5 below B. As long as both sense resistors are connected to a common potential and voltage drops are small (like <5m, for example), as in Figure 8 or the H-bridge application, this condition will be met. CHAGE LOAD EF LTC6 SHUNTA A B A CUENT MIO Figure 8 SHUNTB B 6 F8 BATTEY TYPICAL APPLICATION H-Bridge Load Current Monitor 3 TO 8.µF BATTEY (8 TO 6) LT µf m 29Ω Ω 8 5 LTC6 2 m 2.99k O O = 2.5 ±2 (±A FS) PWM* PWM* I M 6 TA2 *USE SIGN-MAGNITUDE PWM FO ACCUATE LOAD CUENT CONTOL AND MEASUEMENT 6f

15 PACKAGE DESCIPTION MS8 Package 8-Lead Plastic MSOP (eference LTC DWG # ) LTC6.889 ±.27 (.35 ±.5) 5.23 (.26) M (.26.36).2 ±.38 (.65 ±.5) TYP.65 (.256) BSC 3. ±.2 (.8 ±.) (NOTE 3) (.25) EF ECOMMENDED SOLDE PAD LAY GAUGE PLANE.8 (.7).25 (.) DETAIL A NOTE:. DIMENSIONS MILLIMETE/(CH) 2. DAWG NOT TO SCALE 6 TYP.53 ±.52 (.2 ±.6) DETAIL A SEATG PLANE.9 ±.52 (.93 ±.6). (.3) MAX (.9.5) TYP.65 (.256) BSC DIMENSION DOES NOT CLUDE MOLD FLASH, POTUSIONS O GATE BUS. MOLD FLASH, POTUSIONS O GATE BUS SHALL NOT EXCEED.52mm (.6") PE SIDE. DIMENSION DOES NOT CLUDE TELEAD FLASH O POTUSIONS. TELEAD FLASH O POTUSIONS SHALL NOT EXCEED.52mm (.6") PE SIDE 5. LEAD COPLANAITY (BOTTOM OF LEADS AFTE FOMG) SHALL BE.2mm (.") MAX 3. ±.2 (.8 ±.) (NOTE ).86 (.3) EF.27 ±.76 (.5 ±.3) MSOP (MS8) 2 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. 6f 5

16 LTC6 TYPICAL APPLICATION LTC6 Bi-Directional Current Sense Circuit with Combined Charge/Discharge Output CHAGE I CHAGE I DISCHAGE I LOAD LOAD A A B A B 5 B LTC6 CUENT MIO EF 6 TA3 ELATED PATS PAT NUMBE DESCIPTION COMMENTS LT636 ail-to-ail Input/Output, Micropower Op Amp CM Extends Above EE, 55µA Supply Current, Shutdown Function LT637/LT638 LT639 Single/Dual/Quad, ail-to-ail, Micropower Op Amp CM Extends Above EE,./µs Slew ate, >MHz Bandwidth, <25µA Supply Current per Amplifi er LT787/LT787H Precision, Bidirectional, High Side Current Sense Amplifi er 2.7 to 6 Operation, 75µ Offset, 6µA Current Draw LTC92 Dual 8upply and Fuse Monitor ±2 Transient Protection, Drives Three Optoisolators for Status LT99 High oltage, Gain Selectable Difference Amplifi er ±25 Common Mode, Micropower, Pin Selectable Gain =, LT99 Precision, Gain Selectable Difference Amplifi er 2.7 to ±8, Micropower, Pin Selectable Gain = 3 to LTC25/LTC25 Single/Dual/Quad Zero-Drift Op Amp 3µ Offset, 3n/ C Drift, Input Extends Down to LTC252 LTC5 Coulomb Counter/Battery Gas Gauge Indicates Charge Quantity and Polarity LT6 Gain-Selectable High Side Current Sense Amplifier. to 8 Operation, Pin-Selectable Gain:, 2.5, 2, 25,, 5/ LTC6/LTC6H High oltage, High Side Current Sense Amplifi er High oltage 5 to Operation, SOT23 LTC63 High Side Bidirectional Current Sense Amplifi er to 6 Operation, Gain Confi gurable with External esistors 6 LT 7 PTED USA Linear Technology Corporation 63 McCarthy Blvd., Milpitas, CA (8) 32-9 FAX: (8) LEA TECHNOLOGY COPOATION 27 6f