LTC3350_15 Datasheet, PDF(14/46 Page) Linear Technology – High Current Supercapacitor Backup Controller and System Monitor

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LTC3350_15 Datasheet, PDF (14/46 Pages) Linear Technology – High Current Supercapacitor Backup Controller and System Monitor

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LTC3350

Timing Diagram

Definition of Timing for F/S Mode Devices on the I2C Bus

SDA

tLOW

tSU(DAT)

SCL

tHD(SDA)

tHD(DAT)

tHIGH

S = START, Sr = REPEATED START, P = STOP

tSU(STA)

tHD(SDA)

tBUF

tSP

tSU(STO)

3350 TD

Operation

Introduction

The LTC3350 is a highly integrated backup power controller

and system monitor. It features a bidirectional switching

controller, input and output ideal diodes, supercapacitor

shunts/balancers, a power-fail comparator, a 14-bit ADC

and I2C/SMBus programmability with status reporting.

If VIN is above an externally programmable PFI threshold

voltage, the synchronous controller operates in step-down

mode and charges a stack of supercapacitors. A program-

mable input current limit ensures that the supercapacitors

will automatically be charged at the highest possible charge

current that the input can support. If VIN is below the PFI

threshold, then the synchronous controller will run in

reverse as a step-up converter to deliver power from the

supercapacitor stack to VOUT.

The two ideal diode controllers drive external MOSFETs to

provide low loss power paths from VIN and VCAP to VOUT.

The ideal diodes work seamlessly with the bidirectional

controller to provide power from the supercapacitors to

VOUT without backdriving VIN.

The LTC3350 provides balancing and overvoltage protec-

tion to a series stack of one to four supercapacitors. The

internal capacitor voltage balancers eliminate the need

for external balance resistors. Overvoltage protection is

provided by shunt regulators that use an internal switch

and an external resistor across each supercapacitor.

The LTC3350 monitors system voltages, currents, and

die temperature. A general purpose input (GPI) pin is

provided to measure an additional system parameter or

implement a thermistor measurement. In addition, the

LTC3350 can measure the capacitance and resistance of the

supercapacitor stack. This provides indication of the health

of the supercapacitors and, along with the VCAP voltage

measurement, provides information on the total energy

stored and the maximum power that can be delivered.

Bidirectional Switching ControllerâStep-Down Mode

The bidirectional switching controller is designed to charge

a series stack of supercapacitors (Figure 1). Charging

proceeds at a constant current until the supercapacitors

reach their maximum charge voltage determined by the

CAPFB servo voltage and the resistor divider between VCAP

and CAPFB. The maximum charge current is determined

by the value of the sense resistor, RSNSC, used in series

with the inductor. The charge current loop servos the

voltage across the sense resistor to 32mV. When charging

begins, an internal soft-start ramp will increase the charge

current from zero to full current in 2ms. The VCAP voltage

and charge current can be read from the meas_vcap and

meas_ichrg registers, respectively.

For more information www.linear.com/LTC3350

3350fb

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