Linear Technology LTC3350 Manual
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Linear Technology LTC3350 Manual

High current supercapacitor backup controller and system monitor
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FeaTures

High Efficiency Synchronous Step-Down CC/CV
n
Charging of One to Four Series Supercapacitors
Step-Up Mode in Backup Provides Greater
n
Utilization of Stored Energy in Supercapacitors
14-Bit ADC for Monitoring System Voltages/Currents,
n
Capacitance and ESR
Active Overvoltage Protection Shunts
n
Internal Active Balancers—No Balance Resistors
n
V
: 4.5V to 35V, V
n
IN
CAP(n)
Charge/Backup Current: 10+A
Programmable Input Current Limit Prioritizes System
n
Load Over Capacitor Charge Current
Dual Ideal Diode PowerPath™ Controller
n
All N-FET Charger Controller and PowerPath Controller
n
Compact 38-Lead 5mm × 7mm QFN Package
n

applicaTions

High Current 12V Ride-Through UPS
n
Servers/Mass Storage/High Availability Systems
n

Typical applicaTion

High Current Supercapacitor Charger and Backup Supply
I
(STEP-DOWN)
CHG
V
IN
INFET VOUTSP VOUTSN
PFI
LTC3350
2
I
C
: Up to 5V per Capacitor,
I
BACKUP
OUTFB
OUTFET
V
< V
CAP
OUT
(STEP-UP)
TGATE
SW
BGATE
ICAP
VCAP
CAP4
10F
CAP3
10F
CAP2
10F
CAP1
10F
CAPRTN
CAPFB
For more information
High Current Supercapacitor
Backup Controller and

DescripTion

The
LTC
3350
is a backup power controller that can charge
®
and monitor a series stack of one to four supercapacitors.
The LTC3350's synchronous step-down controller drives
N-channel MOSFETs for constant current/constant voltage
charging with programmable input current limit. In addition,
the step-down converter can run in reverse as a step-up
converter to deliver power from the supercapacitor stack
to the backup supply rail. Internal balancers eliminate the
need for external balance resistors and each capacitor has
a shunt regulator for overvoltage protection.
The LTC3350 monitors system voltages, currents, stack
capacitance and stack ESR which can all be read over
2
the I
C/SMBus. The dual ideal diode controller uses
N-channel MOSFETs for low loss power paths from the
input and supercapacitors to the backup system supply.
The LTC3350 is available in a low profile 38-lead 5mm ×
7mm × 0.75mm QFN surface mount package.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
PowerPath are trademarks of Linear Technology Corporation. All other trademarks are the
property of their respective owners. Patents pending.
V
OUT
V
> V
V
CAP
OUT
OUT
(DIRECT
2V/DIV
CONNECT)
V
CAP
2V/DIV
V
IN
2V/DIV
0V
V
CAP
BACK PAGE APPLICATION CIRCUIT
3350 TA01a
www.linear.com/LTC3350
LTC3350
System Monitor
Backup Operation
P
= 25W
BACKUP
V
OUT
V
CAP
V
IN
400ms/DIV
3350 TA01a
3350fc
1

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Summary of Contents for Linear Technology LTC3350

  • Page 1: Features

    7mm × 0.75mm QFN surface mount package. High Current 12V Ride-Through UPS L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and Servers/Mass Storage/High Availability Systems PowerPath are trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.

  • Page 2: Table Of Contents

    LTC3350 Table oF conTenTs Features ............. 1 Applications Information ........ 21 Applications ..........1 Digital Configuration ..........21 Typical Application ........1 Capacitor Configuration .......... 21 Description..........1 Capacitor Shunt Regulator Programming ....21 Absolute Maximum Ratings ......3 Setting Input and Charge Currents ......21 Order Information ..........

  • Page 3: Absolute Maximum Ratings

    LTC3350 absoluTe MaxiMuM raTings (Note 1) pin conFiguraTion , VOUTSP, VOUTSN ....... –0.3V to 40V VCAP ............–0.3V to 22V TOP VIEW CAP4-CAP3, CAP3-CAP2, CAP2-CAP1, CAP1-CAPRTN .......... –0.3V to 5.5V , OUTFB, CAPFB, SMBALERT, CAPGD, 38 37 36 35 34 33 32 PFO, GPI, SDA, SCL ........

  • Page 4: Electrical Characteristics

    LTC3350 elecTrical characTerisTics denotes the specifications which apply over the specified operating junction temperature range, otherwise specifications are at T = 25°C (Note 2). V = 12V, V unless otherwise DRVCC INTVCC noted. SYMBOL PARAMETER CONDITIONS UNITS Switching Regulator Input Supply Voltage...
  • Page 5 LTC3350 elecTrical characTerisTics denotes the specifications which apply over the specified operating junction temperature range, otherwise specifications are at T = 25°C (Note 2). V = 12V, V unless otherwise DRVCC INTVCC noted. SYMBOL PARAMETER CONDITIONS UNITS Maximum Duty Cycle Step-Down Mode 99.5...
  • Page 6 LTC3350 elecTrical characTerisTics denotes the specifications which apply over the specified operating junction temperature range, otherwise specifications are at T = 25°C (Note 2). V = 12V, V unless otherwise DRVCC INTVCC noted. SYMBOL PARAMETER CONDITIONS UNITS Analog-to-Digital Converter Measurement Resolution...

  • Page 7: Typical Performance Characteristics

    Continuous operation above the specified maximum operating junction reliability and lifetime. temperature may impair device reliability. Note 2: The LTC3350 is tested under pulsed load conditions such that Note 4: Dynamic supply current is higher due to the gate charge being ≈ T .
  • Page 8 LTC3350 Typical perForMance characTerisTics = 25°C, Application Circuit 4 unless otherwise noted. and I vs V vs V vs V CHARGE CHARGE CHARGE 5.00 5.00 = 1A = 6V 125°C 25°C 3.75 3.75 –40°C CHARGE 2.50 2.50 = 2A = 2A...
  • Page 9 LTC3350 Typical perForMance characTerisTics = 25°C, Application Circuit 4 unless otherwise noted. Current vs Boost Inductor vs V , Pulse Skipping GPI Code vs Temperature Current 4.90 5480 10.0 = 1V 5475 4.75 5470 4.60 5465 = 4V 4.45 125°C 5460 25°C...

  • Page 10: Pin Functions

    LTC3350 pin FuncTions SCL (Pin 1): Clock Pin for the I C/SMBus Serial Port. RT (Pin 9): Timing Resistor. The switching frequency of the synchronous controller is set by placing a resistor, R SDA (Pin 2): Bidirectional Data Pin for the I C/SMBus from this pin to SGND.
  • Page 11 LTC3350 pin FuncTions current around the capacitor to provide balancing and VCAP (Pin 21): Supercapacitor Stack Voltage and Charge prevent overvoltage. If not used this pin should be shorted Current Sense Amplifier Negative Input. Connect this pin to CAP1. The voltage between this pin and CAP1 is digitized to the top of the supercapacitor stack.
  • Page 12 Decouple this pin with at least 1μF to V pad must be connected to a continuous ground plane on the second layer of the printed circuit board by several vias directly under the LTC3350 for rated thermal performance. It must be tied to the SGND pin. 3350fc For more information www.linear.com/LTC3350...

  • Page 13: Block Diagram

    LTC3350 block DiagraM INFET VOUTSP VOUTM5 VOUTSN OUTFET VCAPP5 + – – INTV CHARGE + – PUMP –5V LDO 30mV – 30mV – – VCAP x37 .5 x37.5 ICAP Vcapfb_dac vcapfb_dac[3:0] – CAPFB – OUTFB TGATE – BIDIRECTIONAL SWITCHING CONTROLLER...

  • Page 14: Timing Diagram

    The LTC3350 monitors system voltages, currents, and die temperature. A general purpose input (GPI) pin is The LTC3350 is a highly integrated backup power controller provided to measure an additional system parameter or and system monitor. It features a bidirectional switching implement a thermistor measurement.

  • Page 15: Bidirectional Switching Controller-Step-Up Mode

    Figure 1. Power Path Block Diagram—Power Available from V Bidirectional Switching Controller—Step-Up Mode The LTC3350 provides constant power charging (for a fixed ) by limiting the input current drawn by the switching The bidirectional switching controller acts as a step-up controller in step-down mode.

  • Page 16: Ideal Diodes

    Fast-Off comparator, the output ideal diode also has a Fast- Ideal Diodes On comparator that turns on the external MOSFET when The LTC3350 has two ideal diode controllers that drive drops 65mV below V . The output ideal diode will external N-channel MOSFETs.

  • Page 17: Gate Drive Supply (Drv Cc )

    Charge Status Indication value reported in the meas_cap register, described in the Capacitance and ESR Measurement section of this data The LTC3350 includes a comparator to report the status sheet. of the supercapacitors via an open-drain NMOS transistor on the CAPGD pin. This pin is pulled to ground until the...

  • Page 18: Capacitor Shunt Regulators

    3.6V may be programmed in 183.5µV increments. The voltages and currents, some of these measurements are shunt regulators can be disabled by programming vshunt used by the LTC3350 to balance, protect, and measure to zero (0x0000). The default value is 0x3999, resulting the capacitors in the stack.

  • Page 19: Monitor Status Register

    This allows reduced polling where R is the charge current sense resistor in series of the LTC3350 when waiting for a capacitance or ESR SNSC with the inductor. measurement to complete.

  • Page 20: Charge Status Register

    The LTC3350 has an integrated die temperature sensor monitored by the ADC and digitized to the meas_dtemp The LTC3350 has a limit checking function that will check register. An alarm may be set on die temperature by each measured value against I...

  • Page 21: Applications Information

    For this reason, V should be programmed SHUNT The LTC3350 may be used with one to four supercapaci- as high as possible to reduce the likelihood of it activating tors. If less than four capacitors are used, the capacitors during a charge cycle.

  • Page 22: Low Current Charging And High Current Backup

    PCB pad area Low Current Charging and High Current Backup between them as the system load current is pulled from the The LTC3350 can accommodate applications requiring trace connecting the two sense resistors. low charge currents and high backup currents. In these Note that the backup current will flow through R .

  • Page 23: Setting V Out Voltage In Backup Mode

    LTC3350 3350 F04 Figure 4. V Voltage Feedback Divider LTC3350 bidirectional controller switches to step-up mode is programmed using a resistor divider from the V to SGND via the PFI pin such that: 3350 F06 Figure 6. PFI Threshold Divider with Added Hystersis ⎛...

  • Page 24: Compensation

    LTC3350 applicaTions inForMaTion Compensation The output ideal diode provides a low loss power path from the supercapacitors to V . The minimum internal The input current, charge current, V voltage, and V (open-circuit) supercapacitor voltage will be equal to voltage loops all require a 1nF to 10nF capacitor from the...

  • Page 25: Optimizing Supercapacitor Energy Storage Capacity

    LTC3350 applicaTions inForMaTion Note the minimum V voltage can also be limited by the where: peak inductor current limit (180% of maximum charge cur- •P rent) and the maximum duty cycle in step-up mode (~90%). BACKUP = 1+ 1– and, γ...

  • Page 26: Capacitor Selection Procedure

    4. Choose a desired utilization ratio, α , for the superca- For the LTC3350, the best overall performance will be pacitor (e.g., 80%). attained if the inductor is chosen to be: 5.

  • Page 27: Cout Cap Capacitance

    LTC3350 applicaTions inForMaTion Using the above equation, the inductor may be too large Maximum ripple occurs at the lowest V that can supply to provide a fast enough transient response to hold up . Multilayer ceramics are recommended for OUT(BACKUP) when input power goes away.

  • Page 28: Power Mosfet Selection

    (5V) or an external LDO whose output voltage must be The power is lost to the internal LDO and gate drivers within less than 5.5V. the LTC3350. The power lost due to charging the gates is: MOSFET power losses are determined by R DS(ON) ≈...

  • Page 29: Top Mosfet Driver Supply (C B , D B )

    (when connected to ted if the efficiency loss can be tolerated. The diode can ) and much of the LTC3350’s internal circuitry. The be rated for about one-third to one-fifth of the full load LDO regulates the voltage at the INTV pin to 5V.

  • Page 30: Minimum On-Time Considerations

    Minimum on-time, t , is the smallest time dura- ON(MIN) tion that the LTC3350 is capable of turning on the top During backup mode, the output ideal diode shuts off MOSFET in step-down mode. It is determined by internal when the voltage on OUTFB falls below 1.3V. For high timing delays and the gate charge required to turn on the backup voltages (>8.4V), the output ideal diode will...
  • Page 31 DC/DC converter layouts. Orient power components and should be kept on the output side of the LTC3350. such that switching current paths in the ground plane 9. The input ideal diode senses the voltage between V do not cross through the SGND pin and exposed pad and VOUTSP.

  • Page 32: Register Map

    LTC3350 regisTer Map REGISTER SUB ADDR BITS DESCRIPTION DEFAULT PAGE clr_alarms 0x00 15:0 Clear alarms register 0x0000 msk_alarms 0x01 15:0 Enable/mask alarms register 0x0000 msk_mon_status 0x02 Enable/mask monitor status alerts 0x0000 cap_esr_per 0x04 15:0 Capacitance/ESR measurement period 0x0000 vcapfb_dac 0x05...

  • Page 33: Register Descriptions

    LTC3350 regisTer DescripTions clr_alarms (0x00) Clear Alarms Register: This register is used to clear alarms caused by exceeding a programmed limit. Writing a one to any bit in this register will cause its respective alarm to be cleared. The one written to this register is automatically cleared when its respective alarm is cleared.
  • Page 34 LTC3350 regisTer DescripTions msk_mon_status (0x02) Mask Monitor Status Register: Writing a one to any bit in this register enables a rising edge of its respective bit in the mon_status register to trigger an SMBALERT. BIT(S) BIT NAME DESCRIPTION msk_mon_capesr_active Set the SMBALERT when there is a rising edge on mon_capesr_active...
  • Page 35 LTC3350 regisTer DescripTions vin_uv_lvl (0x0B) 2.21mV per LSB Undervoltage Level: This is an alarm threshold for the input voltage. If enabled, the voltage falling below this level will trigger an alarm and an SMBALERT. vin_ov_lvl (0x0C) 2.21mV per LSB Overvoltage Level: This is an alarm threshold for the input voltage. If enabled, the voltage rising above this level will trigger an alarm and an SMBALERT.
  • Page 36 LTC3350 regisTer DescripTions ctl_reg (0x17) Control Register: Several Control Functions are grouped into this register. BIT(S) BIT NAME DESCRIPTION ctl_strt_capesr Begin a capacitance and ESR measurement when possible; this bit clears itself once a cycle begins. ctl_gpi_buffer_en A one in this bit location enables the input buffer on the GPI pin. With a zero in this location the GPI pin is measured without the buffer.
  • Page 37 LTC3350 regisTer DescripTions mon_status (0x1C) Monitor Status: This register provides real time status information about the state of the monitoring system. Each bit is active high. BIT(S) BIT NAME DESCRIPTION mon_capesr_active Capacitance/ESR measurement is in progress mon_capesr_scheduled Waiting programmed time to begin a capacitance/ESR measurement...
  • Page 38 LTC3350 regisTer DescripTions meas_cap (0x1E) 336µF • R per LSB Measured capacitor stack capacitance value. When ctl_cap_scale is set to one the constant is 3.36µF • R meas_esr (0x1F) /64 per LSB SNSC Measured capacitor stack equivalent series resistance (ESR) value meas_vcap1 (0x20) 183.5µV per LSB...

  • Page 39: Typical Applications

    LTC3350 Typical applicaTions Application Circuit 1. 25V to 35V, 6.4A Supercapacitor Charger with 2A Input Current Limit and 28V, 50W Backup Mode SNSI 0.016 SiS434DN 25V TO 35V 50W IN BACKUP 1µF 25V RISING THRESHOLD 0.1µF 22V FALLING THRESHOLD INFET...
  • Page 40 LTC3350 Typical applicaTions Application Circuit 2. 11V to 20V, 16A Supercapacitor Charger with 6.4A Input Current Limit and 10V, 60W Backup Mode SNSI 0.005 SiR422DP 11V TO 20V 60W IN BACKUP 1µF 0.1µF OUT2 OUT1 FBO1 FBO1 22µF 82µF INFET...
  • Page 41 LTC3350 Typical applicaTions Application Circuit 4. 11V to 35V, 4A Supercapacitor Charger with 2A Input Current Limit and 10V, 1A Backup Mode SNSI 0.016 SiR426DP 11V TO 35V 10W IN BACKUP 1µF 0.1µF OUT2 10µF FBO1 FBO1 OUT1 INFET VOUTM5 VOUTSP...
  • Page 42 R is the top divider resistor from CAPTOP LTC3350 is configured. The capacitor voltage is measured the capacitor to CAP1 and R is the bottom divider CAPBOT differently, it is no longer measured in the meas_vcap resistor from CAP1 to ground.
  • Page 43 LTC3350 Typical applicaTions Application Circuit 7. 4.8V to 12V, 10A Supercapacitor Charger with 6.4A Input Current Limit and 5V, 30W Backup Mode SNSI 0.005 SiS452DN 4.8V TO 12V 30W IN BACKUP 1µF 50µs FALLING EDGE FILTER 0.1µF OUT2 OUT1 FBO1 FBO1 100µF...

  • Page 44: Package Description

    ON THE TOP AND BOTTOM OF PACKAGE 3350fc Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa- For more information www.linear.com/LTC3350 tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.

  • Page 45: Revision History

    LTC3350 revision hisTory DATE DESCRIPTION PAGE NUMBER 09/14 Modified I equations in C and C Capacitance section Changed 5V to 6V in back-up mode under the Power MOSFET Selection section Changed V voltage reference DAC setting Modified Application Circuit 01/15...

  • Page 46: Typical Application

    Shutdown Current <2μA. 12-Pin 3mm × 3mm DFN or 12-Lead MSOP Package 3350fc Linear Technology Corporation LT 0815 REV C• PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 For more information www.linear.com/LTC3350 (408) 432-1900 FAX: (408) 434-0507 www.linear.com/LTC3350  LINEAR TECHNOLOGY CORPORATION 2014 ● ●...

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