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LTC3226

3226f

TYPICAL APPLICATION

FEATURES DESCRIPTION

2-Cell Supercapacitor

Charger with Backup

PowerPath Controller

The LTC

3226 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 from a 2.5V to 5.3V

input supply. The charger input current limit is program-

mable by an external resistor at up to 315mA.

The internal backup LDO is powered from the superca-

pacitors 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, battery-

powered applications. Internal current limit and thermal

shutdown circuitry allow the device to survive a continu-

ous short-circuit from the PROG or CPO pins to ground.

Automatic Normal-to-Backup

Mode Switchover

3.3V Backup Supply

APPLICATIONS

1x/2x Multimode Charge Pump Supercapacitor

Charger

Automatic Cell Balancing

Ideal Diode Main PowerPath™ Controller

to V

OUT

)

Internal 2A LDO Backup Supply (CPO to V

OUT

)

Automatic Main/Backup Switchover

Input Voltage Range: 2.5V to 5.5V

Programmable SCAP Charge Voltage

Programmable Input Current Limit (315mA Max)

No Load I

VIN

= 55μA (Typical)

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

Smart Power Meters

Battery-Powered Industrial/Medical Equipment

3.3V Solid-State Drives

Industrial Alarms

Data Backup Supplies

Battery Hold-Up Supplies

L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks

and PowerPath is a trademark of Linear Technology Corporation. All other trademarks are the

property of their respective owners.

1.2V

GATE

MPEXT

PFI

2.2µF

1.96M

–

PROG

EN_CHG

PFO

RST

CAPGOOD

GND

CHARGE

PUMP

LTC3226

LDO

CPO

VMID

2.2µF

3.3V

1.21M

OUT

47µF

TO LOAD

(2A)

33.2k

3.83M

1.2F

255k

80.6k

1.21M

3226 TA01a

CPO_FB

LDO_FB

OUT

RST_FB

–

TIME (SECONDS)

VOLTAGE (V)

1.6

3226 TA01b

–1

0.4

0.8

1.2

CPO

2.0

OUT

= 1.2F

OUT

= 47µF

LOAD

= 2A

PFO (2V/DIV)

BACKUP

MODE

(LDO IN

REGULATION)

BACKUP MODE

(LDO IN

DROPOUT)

Summary of content (16 pages)

PAGE 1
LTC3226 2-Cell Supercapacitor Charger with Backup PowerPath Controller DESCRIPTION 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.
PAGE 2
LTC3226 PIN CONFIGURATION VIN, VOUT, VMID, CPO, RST, PFO, CAPGOOD, LDO_FB...................................... –0.3V to 6V EN_CHG, PFI, RST_FB, CPO_FB Voltage.............–0.3V to Max (VIN, CPO) + 0.3V Operating Junction Temperature................. –40 to 125°C Storage Temperature Range.......................
PAGE 3
LTC3226 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C (Note 3). VIN = 3.3V, VCPO = 5V, VOUT = 3.3V, VMID = 1/2 VCPO unless otherwise noted. SYMBOL PARAMETER VIN Input Supply Range CONDITIONS MIN l TYP 2.5 MAX 5.5 UNITS V IVIN(ST) VIN Quiescent Current in Normal Mode VPFI > 1.2V, VCPO_FB > 1.2V, VIN < VCPO 10 µA ICPO(ST) CPO Quiescent Current in Normal Mode VPFI > 1.
PAGE 4
LTC3226 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C (Note 3). VIN = 3.3V, VCPO = 5V, VOUT = 3.3V, VMID = 1/2 VCPO unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS 0.8 0.82 V LDO Minimum CPO Voltage for LDO Operation VLDO_FB IVOUT = 1mA Load Regulation ΔVLDO_FB/ΔIOUT 1mA < IVOUT < 2A LDO FET RDS(ON) ILDO_FB(LEAK) LDO_FB Input Leakage Current ILIM 2.
PAGE 5
LTC3226 TYPICAL PERFORMANCE CHARACTERISTICS LDO Load Regulation 3.310 CPO = 4V VOUT SET TO 3.3V VOUT (V) 3.290 3.285 3.280 3.325 IOUT = 10µA VOUT SET TO 3.3V 3.305 LDO OUTPUT VOLTAGE (V) 3.295 LDO Regulation Voltage vs Temperature LDO Supply Regulation 3.315 3.300 3.295 3.270 0.001 0.01 0.1 IOUT (A) 1 3.290 3226 G01 3.
PAGE 6
LTC3226 TYPICAL PERFORMANCE CHARACTERISTICS VMID Shunt Regulator Voltage vs Current and Temperature 2.70 12 VIN = 3.3V, VCPO = 5V 10 VMID SHUNT REG OFF 2.65 VMID SOURCING CURRENT 6 4 VMID VOLTAGE (V) VMID CURRENT (mA) 8 90°C 25°C –45°C 2 0 –2 VMID SINKING CURRENT –4 –6 –8 0 0.5 1 1.5 2 2.5 3 3.5 VMID VOLTAGE (V) 4 5 ONLY LEAKAGE BALANCER ACTIVE 2.60 VIN = 3.
PAGE 7
LTC3226 PIN FUNCTIONS VOUT (Pin 1): Voltage Output. This pin is used to provide power to an external load from either the primary input supply (VIN) or the supercapacitor (CPO) if the primary input supply is not available. VOUT should be bypassed with a low ESR ceramic capacitor of at least 47µF capacitance to GND. PFO (Pin 2): Open-Drain Power-Fail Status Output. This pin is pulled to ground by an internal N-channel MOSFET when the PFI input is below 1.2V.
PAGE 8
LTC3226 BLOCK DIAGRAM EXTERNAL PFET 5 GATE VIN 2.5V TO 5.5V 13 2 RPF1 3 15mV VIN +– RPF2 1.2V VOUT COUT IDEAL DIODE CONTROLLER PFO PFI – + – LDO_FB LDO + + – – RST_FB 4 RFB1 6 RFB2 0.8V + 0.74V RST 7 DELAY CPO 8 EN_CHG VMID 1x/2x MODE CHARGE PUMP + CPO_FB – 9 – 2.65V CLAMP/ BALANCER 1V 1.11V CAPGOOD 16 14 10 CSC RCP1 RCP2 11 + PROG RPROG GND 17 C+ 15 C– 12 3226 F01 2.2µF Figure 1.
PAGE 9
LTC3226 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.
PAGE 10
LTC3226 OPERATION CAPGOOD Status Output The LTC3226 charge pump includes a comparator to report the status of the supercapacitors via an open-drain NMOS transistor on the CAPGOOD pin. This pin is pulled to ground until the CPO pin voltage rises to within 7.5% of the programmed value. Once the CPO pin is above this threshold, the CAPGOOD pin goes high impedance. PROG Pin Short-Circuit Protection Typically the maximum current that the LTC3226 charge pump can deliver is set by the PROG resistor.
PAGE 11
LTC3226 APPLICATIONS INFORMATION Programming the Supercapacitor Termination Voltage (CPO) Programming the Input Voltage Threshold for the Power-Fail Comparator The termination voltage of the supercapacitor stack on the CPO pin can be programmed for any voltage between 2.5V to 5.
PAGE 12
LTC3226 APPLICATIONS INFORMATION where VF is the forward voltage of the diode. As an example, if RPF1 = 200k, RPF2 = 120k, RH = 2M, and VF = 0.4V, the additional hysteresis provided by this network can be calculated using the above equation as follows: ∆VIN(HYS) = (1.2 + 0.02 – 0.4) V • VOUT VIN RPF1 RH 470k LTC3226 PFI RPF2 200kΩ = 82mV 2MΩ PFO D1 3226 F02 Figure 2.
PAGE 13
LTC3226 APPLICATIONS INFORMATION For the LTC3226 charge pump, the sum of the switch resistances is approximately 2.5Ω in a typical application where VIN = 3.3V and VCPO = 5V. For CFLY = 1µF and fOSC = 1MHz, the effective open-loop output resistance of the charge pump can be approximated from the above equation as follows: ROL ≅ 2 • 2.
PAGE 14
LTC3226 APPLICATIONS INFORMATION Charging a Single Supercapacitor The LTC3226 can also be used to charge a single supercapacitor by connecting two series-connected matched ceramic capacitors with a minimum capacitance of 100µF in parallel with the supercapacitor as shown in Figure 3. Supercapacitor Manufacturers Refer to the following table for supercapacitor manufacturers. Table 1. Supercapacitor Manufacturers CAP-XX www.cap-xx.com NESS CAP www.nesscap.com Maxwell www.maxwell.com Bussmann www.
PAGE 15
LTC3226 PACKAGE DESCRIPTION UD Package 16-Lead Plastic QFN (3mm × 3mm) (Reference LTC DWG # 05-08-1691) 0.70 ±0.05 3.50 ± 0.05 1.45 ± 0.05 2.10 ± 0.05 (4 SIDES) PACKAGE OUTLINE 0.25 ±0.05 0.50 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 3.00 ± 0.10 (4 SIDES) BOTTOM VIEW—EXPOSED PAD PIN 1 NOTCH R = 0.20 TYP OR 0.25 × 45° CHAMFER R = 0.115 TYP 0.75 ± 0.05 15 16 PIN 1 TOP MARK (NOTE 6) 0.40 ± 0.10 1 1.45 ± 0.10 (4-SIDES) 2 (UD16) QFN 0904 0.200 REF 0.00 – 0.05 NOTE: 1.
PAGE 16
LTC3226 TYPICAL APPLICATION Li-Ion Backup Supply TO LOAD MPEXT Li-Ion + C1 4.7µF R1 2.21M VIN GATE VOUT CPO PFI R2 1.21M 5V VMID LTC3226 CFLY 2.2µF H/L C+ CPO_FB C– LDO_FB RST_FB RST PFO CAPGOOD EN_CHG RPROG 33.2k PROG GND CSC 1.2F R4 3.83M R6 1.21M R3 255k 47µF R4 80.