Description

The LTC3226 is a 2-cell series supercapacitor charger with a backup PowerPath controller. It includes a charge pump supercapacitor charger with programmable output voltage, a low dropout regulator, and a power-fail comparator for switching between normal and backup modes.

The constant input current supercapacitor charger is designed to charge two supercapacitors in series to a resistor-programmable output voltage of 2.5V to 5.3V. The charger input current limit is programmable by an external resistor at up to 315mA.

The internal backup LDO is powered from the supercapacitors and provides up to 2A peak output current with an adjustable output voltage. When the input supply falls below the power-fail threshold, the LTC3226 automatically enters a backup state in which the supercapacitors power the output through the LDO. The input supply power-fail voltage level is programmed by an external resistor divider.

Low input noise, low quiescent current and a compact footprint make the LTC3226 ideally suited for small, batterypowered applications. Internal current limit and thermal shutdown circuitry allow the device to survive a continuous short-circuit from the PROG or CPO pins to ground.

 

FEATURES

1x/2x Multimode Charge Pump Supercapacitor Charger

Automatic Cell Balancing

Ideal Diode Main PowerPath™ Controller  (VIN to VOUT)

Internal 2A LDO Backup Supply (CPO to VOUT)

Automatic Main/Backup Switchover

Input Voltage Range: 2.5V to 5.5V

Programmable SCAP Charge Voltage

Programmable Input Current Limit (315mA Max)

No Load IVIN = 55μA (Typical)

Low Profile, 16-Lead 3mm × 3mm QFN Package

 

APPLICATIONS

Smart Power Meters

Battery-Powered Industrial/Medical Equipment

3.3V Solid-State Drives

Industrial Alarms

Data Backup Supplies

Battery Hold-Up Supplies

 

OPERATION

The LTC3226 is a 2-cell series supercapacitor charger designed to back up a Li-ion battery or any system rail in the range of 2.5V to 5.3V. It has four principal circuit components: a dual mode (1x/2x) charge pump with an integrated balancer and a voltage clamp, an LDO to supply the load current from the charge stored on the supercapacitor, an ideal diode controller to control the gate of the external FET between VIN and VOUT, and a PFI comparator to decide whether to activate the charge pump to charge the supercapacitor stack or to activate the LDO to supply the load when VIN falls below an externally programmed value.

The LTC3226 has two modes of operation: normal and backup. If VIN is above an externally programmable PFI threshold voltage, the part is in normal mode in which power flows from VIN to VOUT through the external FET and the internal charge pump stays on to top off the supercapacitor stack. If VIN is below this PFI threshold, the part is in backup mode. In this mode, the internal charge pump is turned off, the external FET is turned off and the LDO is turned on to supply the load current from the stored charge.

 

Voltage Clamp

The LTC3226 charge pump is equipped with circuitry to limit the voltage across any supercapacitor in the stack to a maximum allowable preset voltage of 2.65V. If the voltage across the top capacitor (VMID-VCPO) ever gets to 2.65V before the CPO pin reaches the target voltage, the charge pump stops charging the top of the stack via the CPO pin, switches to 1x mode and delivers charge directly to the bottom capacitor via the VMID pin until the stack voltage reaches its programmed value. If the voltage across the bottom capacitor reaches 2.65V before the stack gets to its target value, the charge pump continues to deliver charge to the top of the stack via the CPO pin and a shunt regulator turns on to bleed charge off of the bottom capacitor and prevents the VMID pin voltage from rising any further. The shunt regulator is able to shunt the maximum allowable charge current which is approximately 315mA (in 1x mode). In the event both capacitors exceed 2.65V, the charge pump enters sleep mode by turning off most of its circuitry.