LTC4425 Linear SuperCap Charger
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To introduce LTC4425 linear supercapacitor charger
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LTC4425 Linear SuperCap Charger
- 6. LTC4425: Block Diagram / Features & Benefits Balancer forces caps to equal voltage (@ low current) PFO goes Hi-Z when VIN good and VOUT good; indicate that backup power is not yet valid when the part is starting up RPROG sets Vin (charge) current limit, VPROG is proportional to IVIN EN pin disconnects VIN from VOUT (IVIN<2uA) Internal current limit profile minimizes thermal/inrush problems during charging VOUT can be regulated or connected directly to VIN through ideal diode Ideal diode operates even with regulated VOUT – prevents reverse conduction into VIN Protection shunts reduce charge current if VCAP gets too high
- 7. LTC4425: Packages/Pinouts PIN CONFIGURATION
- 8. LTC4425: Simple Charging Circuits 3xAA Alkaline to 3.3V Charging USB to 3.3V Charging
Editor's Notes
- Welcome to the training module on LTC4425 Linear SuperCap Charger.
- This training module will introduce LTC4425 linear supercapacitor charger.
- Many electronic systems require a local power source that allows them to ride through brief main power interruptions without shutting down. Some local power sources must be available to carry out a controlled shutdown if the main power input is abruptly removed. A battery backup can supply power in the event of a mains shutdown. Batteries feature good energy density, have OK power density, yet high ESR at cold temperatures. Also, batteries have finite lives of ~2 to 3 years, and the maintenance required for rechargeable batteries is substantial. However supercapacitors have OK energy density, good power density and have low ESR at cold temps. However, supercaps are limited to 2.5V or 2.75V maximum, and may experience high battery insertion inrush currents.
- The LTC4425 is Linear Technology’s 2nd supercapacitor charger - the 1st being the LTC3225/-1, a charge pump doubler with current limiting and automatic cell balancing. The LTC4425 addresses high peak power, data backup and “dying gasp” needs in portable and data storage applications. The device employs a linear CC to CV charger architecture, with onboard ideal diode and thermal limiting to charge two super capacitors in series to a programmable output voltage, from a Li-Ion or Polymer battery, a USB port, or other 2.7V to 5.5V current-limited supplies.
- The LTC4425 features two operating modes: charge current profile or “normal” mode and LDO mode. The device’s charge current profile mode charges the top of the supercap stack to the input voltage VIN with a charge current that varies inversely with the input-to-output voltage differential in order to present excessive heating. The LDO mode charges the stack to an externally programmed output voltage with a fixed charge current that is also externally programmable. Charge current is resistor programmable up to 2A (3A peak), and each capacitor is protected against overvoltage by internal shunts (2.45V/2.7V selectable). The LTC4425’s onboard current-limited ideal diode features extremely low 50 milli Ohm ON-resistance to allow high forward current and to prevent back-driving of VIN, making it suitable for a wide variety of high peak power battery and USB-powered equipment, industrial PDAs, portable instruments and monitoring equipment, power meters, supercap backup circuits and PC card/USB modems. The LTC4425’s automatic cell balancing feature maintains equal voltages across both cells, eliminating the need for balancing resistors while protecting each supercapacitor from overvoltage damage and minimizing current drain on the capacitors. The IC operates with a very low 20uA quiescent current when the output voltage is in regulation and draws only 2uA in shutdown from either VIN or VOUT, whichever is higher. The LTC4425 is available in two compact and thermally enhanced packages, a 12-lead, low-profile (0.75mm) 3mm x 3mm DFN package and a 12-lead MSOP package. The device operates over a -40ºC to 125ºC junction temperature range.
- Key Features and Benefits of the LTC4425: The automatic cell balancing feature maintains equal voltages across both cells, eliminating the need for balancing resistors while protecting each supercapacitor from overvoltage damage and minimizing current drain on the capacitors The ideal diode operates even with regulated VOUT – preventing reverse conduction into VIN. The protection shunts reduce charge current if the supercapacitor voltage gets too high. Current and thermal limiting reduce charge current in cases of excessive temperature. The IC operates with a very low 20uA quiescent current when the output voltage is in regulation and draws only 2uA in shutdown from either VIN or VOUT, whichever is higher, saving battery run time.
- The device comes in 2 compact, thermally enhanced packages – a 3 millimeter by 3 millimeter DFN 12-lead package and a 12-lead MSOP package.
- A typical application to charge 2 series supercaps requires only six external components and is highly compact, offered in both a tiny 9mm squared footprint leadless DFN package and a leaded MSOP package version.
- The LTC4425 is a supercapacitor charger like its little brother IC, the LTC3225/-1. However, aside from the ability to charge 2 series supercaps with automatic cell balancing and low Iq there is not much resemblance between the two parts. The LTC3225/-1 is a charge-pump based IC that may buck or boost charge. It works best for low-current charging from 3.3V, 3xAA or Li-Ion battery sources. On the other hand, the LTC4425 is a CC-CV charger linear charger with ideal diode onboard. It works best when high peak power or low average power is required from 5V USB, Li-Ion or a current-limited 2.7V-5.5V supply.
- Thank you for taking the time to view this presentation on “ LTC4425 Linear SuperCap Charger” . If you would like to learn more or go on to purchase some of these devices, you may either click on the part list link right beside the play button on the TechCast portal, or simply call our sales hotline. For more technical information you may either visit the LINEAR TECHNOLOGY site, or if you would prefer to speak to someone live, please call our hotline number, or even use our ‘live chat’ online facility. You may visit element14 e-community to post your questions.