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LTC3350

24

3350fc

For more information 

www.linear.com/LTC3350

applicaTions inForMaTion

Compensation

The input current, charge current, V

CAP

 voltage, and V

OUT

 

voltage loops all require a 1nF to 10nF capacitor from the 

VC node to ground. When using the output ideal diode and 

backing up to low voltages (<8V) use 8.2nF to 10nF on 

VC. When not using the output ideal diode 4.7nF to 10nF 

on VC is recommended. For very high backup voltages 

(>15V) 1nF to 4.7nF is recommended.
In addition to the VC node capacitor, the V

OUT

 voltage loop 

requires a phase-lead capacitor, C

FBO1

, for stability and 

improved transient response during input power failure 

(Figure 7). The product of the top divider resistor and the 

phase-lead capacitor should be used to create a zero at 

approximately 2kHz:

   

R

FBO1

C

FBO1

1

2

π

2kHz

(

)

Choose an R

FBO1

 such that C

FBO1

 is ≥ 100pF to minimize 

the effects of parasitic pin capacitance. Because the phase-

lead capacitor introduces a larger ripple at the input of 

the  V

OUT

  transconductance  amplifier,  an  additional  RC 

lowpass filter from the V

OUT

 divider to the OUTFB pin may 

be needed to eliminate voltage ripple spikes. The filter time 

constant should be located at the switching frequency of 

the synchronous controller: 

   

R

FO

C

FO

=

1

2

π

f

SW

with C

FO

 > 10pF to minimize the effects of parasitic pin 

capacitance. For back up applications where the V

OUT

 

regulation voltage is low (~5V to 6V), an additional 1k to 

3k resistor, R

C

, in series with the VC capacitor can improve 

stability and transient response.

Minimum V

CAP

 Voltage in Backup Mode

In backup mode, power is provided to the output from the 

supercapacitors either through the output ideal diode or 

the synchronous controller operating in step-up mode. 

The output ideal diode provides a low loss power path 

from the supercapacitors to V

OUT

. The minimum internal 

(open-circuit)  supercapacitor  voltage  will  be  equal  to 

the minimum V

OUT

 necessary for the system to operate 

plus the voltage drops due to the output ideal diode and 

equivalent series resistance, R

SC

, of each supercapacitor 

in the stack.
Example: System needs 5V to run and draws 1A during 

backup. There are four supercapacitors in the stack, each 

with an R

SC

 of 45mΩ. The output ideal diode forward 

regulation voltage is 30mV (OUTFET R

DS(ON)

 < 30mΩ). 

The minimum open-circuit supercapacitor voltage is: 
  V

CAP(MIN)

 = 5V + 0.030V + (1A

 • 4 • 45

mΩ) = 5.21V

Using the synchronous controller in step-up mode allows 

the supercapacitors to be discharged to a voltage much 

lower than the minimum V

OUT

 needed to run the system. 

The amount of power that the supercapacitor stack can 

deliver at its minimum internal (open-circuit) voltage should 

be greater than what is needed to power the output and 

the step-up converter.
According to the maximum power transfer rule:

   

P

CAP(MIN)

=

V

CAP(MIN)2

4

n

R

SC

>

P

BACKUP

η

In the equation above 

η

 is the efficiency of the synchro-

nous controller in step-up mode and n is the number of 

supercapacitors in the stack.
Example: System needs 5V to run and draws 1A during 

backup. There are four supercapacitors in the stack (n = 4), 

each with an R

SC

 of 45mΩ. The converter efficiency is 

90%. The minimum open-circuit supercapacitor voltage is: 

   

V

CAP(MIN)

=

4

4

45m

Ω

5V

1A

0.9

=

2.0V

In this case, the voltage seen at the terminals of the ca-

pacitor stack is half this voltage, or 1V, according to the 

maximum power transfer rule.

Содержание LTC3350

Страница 1: ...ply Applications n High Efficiency Synchronous Step Down CC CV Charging of One to Four Series Supercapacitors n Step Up Mode in Backup Provides Greater Utilization of Stored Energy in Supercapacitors...

Страница 2: ...t 18 Monitor Status Register 19 Charge Status Register 20 Limit Checking and Alarms 20 Die Temperature Sensor 20 General Purpose Input 20 Applications Information 21 Digital Configuration 21 Capacitor...

Страница 3: ...TFB SGND RT GPI ITST CAPRTN VOUTSP VOUTSN INTVCC DRVCC BGATE BST TGATE SW VCC2P5 ICAP VCAP OUTFET PFO PFI CAP_SLCT1 CAP_SLCT0 V IN INFET VOUTM5 CAP1 CAP2 CAP3 CAP4 CFP CFN VCAPP5 23 22 21 20 9 10 11 1...

Страница 4: ...ndervoltage Lockout Rising Threshold Falling Threshold l l 3 75 4 2 3 9 4 35 V V VDUVLO VIN VCAP Differential Undervoltage Lockout Rising Threshold Falling Threshold l l 145 55 185 90 225 125 mV mV VO...

Страница 5: ...oltage 5 2V VIN 35V 5 V VINTVCC Load Regulation IINTVCC 50mA 1 5 2 5 PowerPath Ideal Diodes VFTO Forward Turn On Voltage 65 mV VFR Forward Regulation 30 mV VRTO Reverse Turn Off 30 mV tIF ON INFET Ris...

Страница 6: ...30V 100 1 5 mV VCAP 0V VCAP 10V 100 1 5 mV VGPI 0V Unbuffered VGPI 3 5V Unbuffered 2 1 mV VCAP1 0V VCAP1 2V 2 1 mV VCAP2 0V VCAP2 2V 2 1 mV VCAP3 0V VCAP3 2V 2 1 mV VCAP4 0V VCAP4 2V 2 1 mV VSNSI 0mV...

Страница 7: ...layout the rated package thermal impedance and other environmental factors The junction temperature TJ in C is calculated from the ambient temperature TA in C and power dissipation PD in Watts accord...

Страница 8: ...EFFICIENCY 50 75 7 2 3350 G08 25 0 1 8 3 6 5 4 100 VIN 12V VIN 24V VIN 35V IIN MAX 2A IOUT 0A VCAP V 0 I CHARGE A 2 50 3 75 8 3350 G05 1 25 0 2 4 6 5 00 VIN 12V VIN 24V VIN 35V IIN MAX 2A IOUT 0A IOUT...

Страница 9: ...nless otherwise noted VIN V 10 I Q mA 4 60 4 75 35 3350 G13 4 45 4 30 15 20 25 30 4 90 125 C 25 C 40 C TEMPERATURE C 40 CODE 5470 5475 130 3350 G14 5460 5465 5455 6 28 62 96 5480 VGPI 1V IL A 0 I DRVC...

Страница 10: ...uldalsoKelvintothebottomplateofthecapacitorstack RT Pin 9 Timing Resistor The switching frequency of the synchronous controller is set by placing a resistor RT from this pin to SGND This resistor is a...

Страница 11: ...gate drive receives power from the internal charge pump output VCAPP5 The source of the N channel MOSFETshouldbeconnectedtoVCAPandthedrainshould beconnectedtoVOUTSN IftheoutputidealdiodeMOSFET is not...

Страница 12: ...e input current sense amplifier Decouple this pin with at least 1 F to VOUT INFET Pin 33 Input Ideal Diode Gate Drive Output This pin controls the gate of an external N channel MOSFET used as an ideal...

Страница 13: ...ATE SW CHARGE PUMP DRVCC BGATE CAP4 BIDIRECTIONAL SWITCHING CONTROLLER LOGIC VCC2P5 IIN ICHG VCAP VOUT VIN CAP4 CAP3 CAP2 CAP1 CAPRTN DTEMP CAPGD PFI GPI SGND BANDGAP VREF OSC 2 5V LDO SHUNT CONTROLLE...

Страница 14: ...rotection 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 pu...

Страница 15: ...current is programmed to exceed the allowable input current the input current will not be violated the supercapacitor charger will reduce its current as needed Note that the part s quiescent and gate...

Страница 16: ...odes The LTC3350 has two ideal diode controllers that drive external N channel MOSFETs The ideal diodes consist of a precision amplifier that drives the gates of N channel MOSFETs whenever the voltage...

Страница 17: ...ults to full scale 1 2V and is programmed via the vcapfb_dac register Supercapacitors lose capacitance as they age By initially setting the VCAP DAC to a low setting the final charge voltage on the su...

Страница 18: ...matsis the 8 bit address of each of these registers The address of the LTC3350 is 0b0001001 The SMBALERT pin is asserted pulled low whenever an enabled limit is exceeded or when an enabled status even...

Страница 19: ...hey must be initiated by setting the ctl_strt_capesr bit in the ctl_reg register This bit will automatically clear once the measurement begins If the cap_esr_per register is set to a non zero value th...

Страница 20: ...ppropriate bit to the msk_alarms register All alarms that have been set and have not yet been cleared may be read in the alarm_reg register Alloftheindividualmeasuredvoltageshaveacorresponding undervo...

Страница 21: ...initial power up VSHUNT serves to limit the voltage on any individual capacitor by turning on a shunt around that capacitor as the voltage approaches VSHUNT CAPRTN CAP1 CAP2 CAP3 and CAP4 must be conn...

Страница 22: ...The input current limit is 32mV RSNSI1 ILOAD RSNSI1 RSNSI2 IINCHG For example suppose that only 2A of input current is de sired to charge the supercapacitors but the system load and charger combined c...

Страница 23: ...r rent RPF1 RPF2 and RPF3 should be between 1k and 100k Setting VOUT Voltage in Backup Mode The output voltage for the controller in step up mode is set by an external feedback resistor divider as sho...

Страница 24: ...to the output from the supercapacitors either through the output ideal diode or the synchronous controller operating in step up mode The output ideal diode provides a low loss power path from the sup...

Страница 25: ...tack is VCAP MIN n VCELL MIN Some of this energy will be dissipated as conduction loss in the ESR of the supercapacitor stack A higher backup power requirement leads to a higher conduction loss for a...

Страница 26: ...account the lifetime degrada tion of ESR and capacitance as well as the maximum discharge current rating of the supercapacitor A list of supercapacitor suppliers is provided in Table 2 Table 2 Superc...

Страница 27: ...unt of high frequency bypass capacitance is needed to minimize voltage ripple The voltage ripple in step up mode is VOUT 1 VCAP VOUT 1 COUT fSW VOUT VCAP RESR IOUT BACKUP Maximumrippleoccursatthelowes...

Страница 28: ...ation for low voltage MOSFETs Both MOSFET switches have conduction loss However transition loss occurs only in the top MOSFET in step down mode and only in the bottom MOSFET in step up mode These loss...

Страница 29: ...sup ply INTVCC powers the gate drivers when connected to DRVCC and much of the LTC3350 s internal circuitry The LDO regulates the voltage at the INTVCC pin to 5V The LDO can supply a maximum current...

Страница 30: ...LTC3350willregulatetheforwardvoltage drop across the input and output ideal diode MOSFETs to 30mVifRDS ON islowenough TherequiredRDS ON canbe calculated by dividing 0 030V by the load current in amps...

Страница 31: ...esistors See Figure 10 6 Thetracefromthepositiveterminaloftheinputcurrent sense resistor RSNSI to the VOUTSP pin carries the part s quiescent and gate drive currents To maintain accurate measurement o...

Страница 32: ...0 35 iin_oc_lvl 0x11 R W 15 0 IIN overcurrent alarm level 0x0000 35 ichg_uc_lvl 0x12 R W 15 0 ICHG undercurrent alarm level 0x0000 35 dtemp_cold_lvl 0x13 R W 15 0 Die temperature cold alarm level 0x00...

Страница 33: ...uc Clear charge undercurrent alarm 12 clr_dtemp_cold Clear die temperature cold alarm 13 clr_dtemp_hot Clear die temperature hot alarm 14 clr_esr_hi Clear ESR high alarm 15 clr_cap_lo Clear capacitanc...

Страница 34: ...not repeat if this register is zero vcapfb_dac 0x05 CAPFBREF 37 5mV vcapfb_dac 637 5mV VCAP Regulation Reference This register is used to program the capacitor voltage feedback loop s reference voltag...

Страница 35: ...e this level will trigger an alarm and an SMBALERT iin_oc_lvl 0x11 1 983 V RSNSI per LSB Input Overcurrent Level This is an alarm threshold for the input current If enabled the current rising above th...

Страница 36: ...mber of capacitors programmed minus one VALUE CAPACITORS 0b00 1 Capacitor Selected 0b01 2 Capacitors Selected 0b10 3 Capacitors Selected 0b11 4 Capacitors Selected chrg_status 0x1B Charger Status Regi...

Страница 37: ...nable to charge It is cleared only when power returns and the charger is able to charge 9 mon_power_returned This bit is set when the input is above the PFI threshold and the charger is able to charge...

Страница 38: ...Measured voltage between the CAP2 and CAP1 pins meas_vcap3 0x22 183 5 V per LSB Measured voltage between the CAP3 and CAP2 pins meas_vcap4 0x23 183 5 V per LSB Measured voltage between the CAP4 and CA...

Страница 39: ...FI C1 0 1 F C2 1 F RPF1 80 6k DB B0540WS CB 0 1 F C3 4 7 F C4 0 1 F CCAP 47 F RFBC1 866k RFBC2 118k CF 0 1 F CCP5 0 1 F CAP1 5F CAP1 4 NESSCAP ESHSR 0005C0 002R7 L1 COILCRAFT XAL7070 682ME CFBO1 120pF...

Страница 40: ...P_SLCT0 CAP_SLCT1 VCAPP5 3350 TA03 CFP CAP4 CAP3 CAP2 CAP1 CFN SGND PGND ITST RT T VC GPI DRVCC INTVCC BST BGATE CAP2 360F CAP3 360F CAP4 360F CAPRTN CAPFB Typical Applications Application Circuit 3 1...

Страница 41: ...A PFO CAPGD SMBALERT SCL SDA VOUT 10V 10W IN BACKUP TGATE SW ICAP VCAP CAP_SLCT0 CAP_SLCT1 VCAPP5 3350 TA05 CFP CAP4 CAP3 CAP2 CAP1 CFN SGND PGND ITST RT T VC GPI DRVCC INTVCC BST C6 220pF BGATE CAP2...

Страница 42: ...acitorvoltageismeasured differently it is no longer measured in the meas_vcap register but in the meas_vcap1 register The scale factor for meas_vcap1 must be adjusted for the resistor divider connecte...

Страница 43: ...PFI C1 0 1 F C2 1 F RPF1 30 1k DB B0540WS CB 0 1 F C3 10 F C4 0 1 F CCAP 47 F RFBC1 732k RFBC2 274k CF 0 1 F CCP5 0 1 F CAP1 50F CAP1 2 NESSCAP ESHSR 0050C0 002R7 L1 COILCRAFT XAL7030 102ME CFBO1 100p...

Страница 44: ...N MILLIMETERS PIN 1 TOP MARK SEE NOTE 6 37 1 2 38 BOTTOM VIEW EXPOSED PAD 5 50 REF 5 15 0 10 7 00 0 10 0 75 0 05 R 0 125 TYP R 0 10 TYP 0 25 0 05 UH QFN REF C 1107 0 50 BSC 0 200 REF 0 00 0 05 RECOMME...

Страница 45: ...n Increase page numbers to all entries on the Register Map For meas_vcap change V to mV Change name to Application Circuit 6 4 5 18 20 23 30 32 38 42 C 08 15 Modified Order Information Table for tempe...

Страница 46: ...tors Automatic Cell Balancing Programmable Charging Current to 500mA Single Inductor 1A Dual Inductor 12 Lead 3mm 4mm DFN Package LTC4110 Battery Backup System Manager Complete Backup Battery Manager...

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