DEMO MANUAL DC2156ADescriptionLTC2946Wide Range I2C Power,Charge and Energy MeterDemonstration circuit 2156A features the LTC 2946rail-to-rail system monitor that measures current, voltage,power, energy and charge. It features an operatingrange of 2.7V to 100V and includes a shunt regulator foroperation from supplies above 100V to allow flexibility inthe selection of input supply. The current measurementrange of 0V to 100V is independent of the input supply.An onboard, 0.4% accurate, 12-bit ADC measures loadcurrent, input voltage and an auxiliary external voltage.A 24-bit power value is generated by digitally multiplyingthe measured 12-bit load current and input voltage data.Energy andchargedata aregeneratedby integratingpowerand current. Minimum and maximum values are storedand an overrange alert with programmable thresholdsminimizes the need for software polling. Data is reportedvia a standard I2C interface. Shutdown mode reducespower consumption to 20A.L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks andQuikEval and Linduino are trademarks of Linear Technology Corporation. All other trademarksare the property of their respective owners.The demo board features nested pads for a range of senseresistor package sizes to support currents of up to 15Arange. The full scale sense voltage is 102.4mV. A 20msense resistor is populated on the board for 5.12A fullscale. The full scale current can be changed by populatingRSNS accordingly.The DC2156A was designed to be connected to the DC590andcontrolledthroughtheQuikEval? suiteof software. Allthresholds can be set and ADC registers read back throughthe QuikEval interface, which provides a convenient wayto evaluate the LTC2946.Figure 1. Typical Application CircuitDEMO MANUAL DC2156ADC2156A Pin and Jumper DefinitionsJumper SettingsJP1: Selects the VDD source. It can be set to VIN, INTVCCor EXTVDD (which requires a voltage to be present at theEXTVDD turret.) Please see Powering the DC2156A sectionfor examples of how these different settings are used.JP2 (ADR0), JP3(ADR1): Selects the I2C slave addressof the LTC2946. Any changes here should also be madeinside of QuikEval for communications to persist. Bydefault, both jumpers are set to LOW which correspondsto an address of 0xDE.Turrets and Banana JacksSignal connections are made via the row of turret postsalong the edges of the board.GND: (5 turrets, 2 banana jacks) These turrets are connecteddirectly to the ground planes.VIN: Main Supply Input. The LTC2946 measures the currentflowing from VIN to VOUT.VOUT: Supply Output to Load. The LTC2946 measures thecurrent flowing from VIN to VOUT.INTVCC: Internal Low Voltage Supply Input/Output. Thisturret is directly connected to the INTVCC pin. This turret isused to power internal circuitry and can be configured asa direct input, as a linear regulator from a higher voltageconnected to VDD or as a shunt regulator. In the defaultconfigurationwithJP1 at VIN, INTVCCisinternallygeneratedand is 5V. Please see LTC2946 data sheet for more details.EXTVDD: External Voltage Supply. This turret can be usedto power the LTC2946 independently of the VIN powerpath. Connect to 4V to 100V external supply if this optionis selected through JP1.ADIN: Input Measured by the Onboard ADC. Measuresbetween 0V to 2.048V. ADIN is loaded with a 140k and3k resistive divider to allow voltage measurements of upto 102.4V full scale.VPU: Pull Up Voltage for the LEDs. Derived from a 5Visolated supply on the DC590. It powers the GPIO LEDson the board. If a DC590 is not used and the DC2156Ais operated independently, a 2.5V to 5V supply must beprovided here, in order for the LEDs to work. 5V fromDC590 and the VPU turret input voltage are diode-ORed byD6 to preclude back feeding from one source to the other.SENSE+: Supply Voltage and Current Sense Input. Usedas a Kelvin input for the internal current sense amplifier.The voltage at this pin is also monitored by the onboardADC with a full-scale input range of 102.4V. The full scalecurrent sense voltage is 102.4mV.SENSE–: Current Sense Input. An external 20m senseresistor (RSNS) isconnectedbetweenSENSE+andSENSE–to measure a full scale current of 5.12A. See HardwareSetup section for details.SCL: I2C Clock input.SDA/SDAI: I2C Data Input. Connected to SDAO through0 resistor R14. Remove R14 if opto-isolated I2C functionalityis desired.SDAO: I2C Data Output. Connected to SDAI through 0resistor R14. Remove R14 if opto-isolated I2C functionalityis desired.GPIO1: General Purpose Input/Output 1. Configurablegeneral purpose output and logic input. Configured bydefault as General Purpose Output, pulls low to light D3.GPIO2: General Purpose Input/Output 2. Configurablegeneral purpose output, logic input, and ACC control inputto gate internal accumulators. By default it is configured asACC input and pulled high so that the energy and chargeaccumulation are active. If GPIO2 is configured as anoutput, LED D4 lights up when GPIO2 is asserted low.GPIO3: General Purpose Input/Output 3. Configurablegeneral purpose output, logic input, and ALERT# output.By default it is configured as ALERT#. As ALERT#, it ispulled to ground when a fault occurs to alert the hostcontroller. LED D5 lights when ALERT# is asserted low.3dc2156afDEMO MANUAL DC2156AHardware Setup OptionsFlexible Operating Modes of the LTC2946The LTC2946 current sense inputs, SENSE+ and SENSE–are used to make Kelvin connections to a current senseresistor to measure the output current of a supply or thecurrent consumption of a load. They feature a commonmode range of 0V to 100V so that the output current ofeither a positive or negative supply can be measured, aswell as current in either the positive or negative lead of theload. Thus a potentially bewildering number of measurementconfigurations are possible. To allow such flexibility,the SENSE+ and SENSE– pins cannot be relied upon asa source of power; the LTC2946 features a separate VDDpin for this purpose.Power to operate LTC2946 is obtained from the VDD pinor the INTVCC pin (see the block diagram in Figure 2). Ifa supply of 4V to 100V is available, VDD can be used andan internal series regulator powers the device. If a supplyof 2.7V to 5.9V is available, power may be applied directlyto INTVCC. In the event that no supply of less than 100Vis available, the shunt regulator shown connected acrossINTVCC can be used in conjunction with an external droppingresistor to power the LTC2946.RingingIt comes as a surprise to many that seemingly innocentacts, such as making a connection to a live supply, causeringing. Theory tells us that the amplitude of such ringingreaches approximately 2x the input voltage, but in practicethis limit is sometimes exceeded. For general informationon ringing, see the LTC1647 data sheet.Since the VDD pin current is small, ringing there is easilysuppressed by a 51/100nF RC filter (R1 and C1) withoutany compromise to the input voltage range. The SENSE+and SENSE– pins however are not so easily protected.To protect these pins and to prevent damage to theLTC2946 that might arise from ringing, VIN is clamped byan SMAT70A TVS (D1). D1 has a minimum breakdownvoltage of 77V at room temperature and thus VIN DCinput rating to 75V maximum. While D1 may be removedto operate VIN up to 100V, always remember that anyexcursion above this value may destroy the LTC2946.DC2156A Pin and Jumper DefinitionsConnectorsDC590 Connector (J5): J5 allows connection of theDC2156A to the DC590 demo board through which theLinear Technology? QuikEval software can communicatewith the board. When DC590 is connected, 5V is providedto power the GPIO LEDs through this connector.LEDINTVCC – D2:LightsupgreenwhenbothVPUandLTC2946are powered.ALERT# (GPIO3) – D5: Fault Alert Output. Lights up redon an ALERT condition. Can also be monitored on theALERT (GPIO3) turret.ACC (GPIO2) – D4:Will light up amberwhenACCis Low. ByDefaultGPIO2 is an input, pulled high to VPUby D4 and R7.GPIO1 – D3: General Purpose Output. Lights up greenwhen pulled low. Default state is low.Figure 2. Simplified Supply Block DiagramVDDINTVCCGND735k15k5V LDO LTC2946SENSE– SENSE+4dc2156afDEMO MANUAL DC2156AHardware Setup OptionsPowering The DC2156AThe LTC2946 offers great flexibility in terms of supplyoptions owing to its separate VDD and SENSE pins.Jumper JP1 is used to select the source of power for VDDandallowseasyconfigurationofthevarioussupplyoptions.If JP1 is set to VIN, then VDD is powered from VIN (Figure?3aand Figure?3b). In this configuration, sensing is done onthe same rail which is supplying power to the LTC2946.Provide 4V to 75V at VIN in this configuration to powerthe LTC2946. The 75V limitation is set by the zener clampD1 which protects the LTC2946 against voltage transientsexceeding 100V, while the 4V limitation is the minimumoperating voltage of the VDD pin. D1 can be removed ifthe full voltage range of 100V is desired.Figure 3a. DC2156A Is Powered from VINFigure 3b. LTC2946 Powered from VINSENSE– SENSE+ LOADLTC29465dc2156afDEMO MANUAL DC2156AHardware Setup OptionsIf JP1 is set to EXTVDD then VDD is powered by theEXTVDD turret (Figure 4a and Figure 4b). Providea separate 4V to 100V at the EXTVDD turret in thisconfiguration. The maximum input VIN is limited to75V by D1. D1 can be removed if the full voltage rangeof 100V is desired.Figure 4a. DC2156A Powered from External VDDFigure 4b. LTC2946 Powered from External VDDSENSE– SENSE+ LOADLTC29466dc2156afDEMO MANUAL DC2156AIf JP1 is settoINTVCC, thentheLTC2946’s internal circuitryis powered from INTVCC. A low voltage supply (2.7V to5.9V) connected to INTVCC helps minimize on-chip powerdissipation (Figure 5a and Figure 5b). The device canalso be used as a shunt regulator in this configuration tomonitor rails higher than 100V.Regardlessofwhichconfigurationis selected, ifthe systemis connected properly, the green INTVCC LED should be lit.By default the DC2156A is configured, with VIN providingpower to VDD.In order to support a wide range of applications, theLTC2946 demo board also features multiple nested sensepads to support high current monitoring. These padsare Kelvin sensed. By default the board supports currentmonitoring of up to 5.12A. An appropriate sense resistorcan be used to support monitoring of desired currentlevels up to 20A with an on-board sense resistor. TheSENSE+ and SENSE– turrets may be used to connect toan external sense resistor and power path for any currentlevel. Remove RSNS in this case.Figure 5a. DC2156A Powered from INTVCCFigure 5b. LTC2946 Powered from INTVCCLTC2946Hardware Setup Options7dc2156afDEMO MANUAL DC2156ADC2156A Shunt RegulatorFor supply voltages above 100V, the shunt regulator atINTVCC can be used in both high and low side configurationsto provide power to the LTC2946 through anexternal shunt resistor, RSHUNT. RSHUNT should be sizedaccording to the following equation:VS(MAX) 5.9V35mA≤ RSHUNT ≤VS(MIN) 6.7V1mA +ILOAD(MAX)(1)Figure 6a. Powering DC2156A from High Side Shunt Regulator to Allow for Input Voltage Higher than 100VTO DC590OR DC2026
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