Linear Technology Launches 150mA Supercapacitor Charger
9mm² Package, PowerPath Control & Automatic Cell Balancing Features

July 29, 2011 – Linear Technology Korea (CEO Hong Sa-kwak, www.linear.com ) announced the release of an inductless supercapacitor charger (product name: LTC3226) featuring a backup PowerPath™ controller for lithium-ion or other low-voltage system rails in applications requiring short-term backup power. This device utilizes a low-noise dual-mode (1x/2x) charge pump architecture with a constant current input for charging two series supercapacitors from a 2.5V to 5.5V input supply to a programmable capacitor charging voltage between 2.5V and 5.3V. The charging current is resistor-programmable up to 150mA. The device's automatic cell balancing and voltage clamping features maintain equal voltages on both cells without the need for balancing resistors. This protects each supercapacitor from overvoltage damage caused by mismatch in cell capacitance or leakage while minimizing current drainage from the capacitor.

The LTC3226 provides two operating modes (normal and backup). The operating mode is determined by a PFI (programmable power fail) comparator. In normal mode (high PFI), power flows from VIN to VOUT through a low-loss external FET fault diode. In backup mode (low PFI), the charge pump is turned off while the external fault diode prevents reverse current flowing to VIN, and the internal LDO is turned on to supply the VOUT load current from the stored supercapacitor charge. A maximum backup current of 2A is supplied from the supercapacitor through an internal LDO.

The LTC3226 operates with a very low standby current of 55µA when the output voltage is regulated. The basic charging circuit requires only a few external components and does not take up much space. This IC is available in an ultra-small 3mm x 3mm QFN package, and its high operating frequency of 900kHz allows for the use of ultra-small external components. Through internal current limiting and over-temperature shutdown circuits, the device is protected from continuous short circuits leading to ground from the PROG, VOUT, or CPO pins. Other features include CAP PGOOD and VIN PFO (power fail) outputs, and a VOUT RST output for system housekeeping.

The LTC3226 is housed in a compact 16-pin low-profile (0.75mm) 3mm x 3mm QFN package and operates over a temperature range of -40°C to 125°C. Pricing for Class E and I devices starts at $2.67 and $3.07 per unit, respectively, based on a unit-to-unit ratio of 1,000. For more information, please refer to www.linear.com/product/LTC3226 .

Photo Caption: 150mA Supercap Charger with PowerPath™ Control & Auto Cell Balancing

Product Features: LTC3226

• 1x/2x Multimode Low Noise Charge Pump Supercapacitor Charger
• Protects capacitor overvoltage during charging with automatic cell balancing
• Ideal diode main PowerPath controller (VIN ~ VOUT)
• Internal 2A LDO Backup Supply (CPO ~ VOUT)
• Automatic main/backup switchover
• Input voltage range: 2.5V ~ 5.5V
• Programmable SCAP charging voltage
• Programmable SCAP input current limit (max. 315mA)
• No-load IVIN = 55μA
• Compact low-profile (0.75mm) 3mm × 3mm 16-pin QFN package