Linear Technology LTC3558 Скачать руководство пользователя страница 19

LTC3558

19

3558f

APPLICATIONS INFORMATION

USB and Wall Adapter Power

Although the battery charger is designed to draw power 
from a USB port to charge Li-Ion batteries, a wall adapter 
can also be used. Figure 5 shows an example of how to 
combine wall adapter and USB power inputs. A P-channel 
MOSFET, MP1, is used to prevent back conduction into 
the USB port when a wall adapter is present and Schottky 
diode, D1, is used to prevent USB power loss through the 
1k pull-down resistor.

Typically, a wall adapter can supply signifi cantly  more 
current than the 500mA-limited USB port. Therefore, an 
N-channel MOSFET, MN1, and an extra program resistor are 
used to increase the maximum charge current to 950mA 
when the wall adapter is present.

current. It is not necessary to perform any worst-case 
power dissipation scenarios because the LTC3558 will 
automatically reduce the charge current to maintain the 
die temperature at approximately 105°C. However, the 
approximate ambient temperature at which the thermal 
feedback begins to protect the IC is:

 

T

C P

T

C

V

V

I

A

D JA

A

CC

BAT

BAT

JA

=

°

=

°

(

)

105

105

θ

θ

Example: Consider an LTC3558 operating from a USB port 
providing 500mA to a 3.5V Li-Ion battery. The ambient 
temperature above which the LTC3558 will begin to reduce 
the 500mA charge current is approximately:

 

T

C

V

V

mA

C W

T

C

A

A

=

°

(

) (

)

°

=

°

105

5

3 5

500

68

105

0

– .

/

– ..

/

75

68

105

51

54

W

C W

C

C

T

C

A

°

=

°

°

= °

The LTC3558 can be used above 70°C, but the charge cur-
rent will be reduced from 500mA.  The approximate current 
at a given ambient temperature can be calculated:

 

I

C T

V

V

BAT

A

CC

BAT

JA

=

°

(

)

105

θ

Using the previous example with an ambient tem-
perature of 88°C, the charge current will be reduced to
approximately:

 

I

C

C

V

V

C W

C

C A

BAT

=

°

°

(

)

°

=

°

°

105

88

5

3 5

68

17

102

– .

/

/

II

mA

BAT

=

167

Furthermore, the voltage at the PROG pin will change 
proportionally with the charge current as discussed in 
the Programming Charge Current section.

It is important to remember that LTC3558 applications do 
not need to be designed for worst-case thermal conditions 
since the IC will automatically reduce power dissipation 
when the junction temperature reaches approximately 
105°C.

V

CC

MP1

MN1

1k

1.74k

1.65k

I

BAT

Li-Ion
BATTERY

3558 F05

BATTERY

CHARGER

BAT

USB

POWER

500mA I

CHG

5V WALL

ADAPTER

950mA I

CHG

PROG

+

D1

Figure 5. Combining Wall Adapter and USB Power

Power Dissipation

The conditions that cause the LTC3558 to reduce charge 
current through thermal feedback can be approximated 
by considering the power dissipated in the IC. For high 
charge currents, the LTC3558 power dissipation is
approximately:

 

P

V

V

I

D

CC

BAT

BAT

=

(

)

where P

D

 is the power dissipated, V

CC

 is the input supply 

voltage, V

BAT

 is the battery voltage, and I

BAT

 is the charge 

Содержание LTC3558

Страница 1: ...ange The buck boostregulatorcanregulateitsprogrammedoutputvoltage at its rated deliverable current over the entire Li Ion range without drop out increasing battery runtime TheLTC3558isofferedinalowpro...

Страница 2: ...N 20 19 18 17 16 7 8 TOP VIEW 21 UD PACKAGE 20 LEAD 3mm 3mm PLASTIC QFN 9 10 GND BAT MODE FB1 EN1 EN2 VC2 FB2 SUSP VOUT2 SW1 PV IN1 PV IN2 SWAB2 SWCD2 12 11 13 14 15 4 5 3 2 1 6 V CC CHRG PROG NTC HPW...

Страница 3: ...e Charge Current BAT VTRKL 36 46 56 mA VTRKL Trickle Charge Threshold Voltage BAT Rising 2 8 2 9 3 V VTRKL Trickle Charge Hysteresis Voltage 100 mV VRECHRG Recharge Battery Threshold Voltage Threshold...

Страница 4: ...PD SW Pull Down in Shutdown 13 k Buck Boost Switching Regulator PVIN2 Input Supply Voltage l 2 7 4 2 V IPVIN2 PWM Input Current Burst Mode Input Current Shutdown Current Supply Current in UVLO MODE 0...

Страница 5: ...the BAT pin Total input current is equal to this speci cation plus 1 00125 IBAT where IBAT is the charge current Note 5 IC 10 is expressed as a fraction of measured full charge current with indicated...

Страница 6: ...65 85 VCC 5V IBAT mA 100 V BAT V 4 180 4 190 4 205 4 200 900 3558 G03 4 170 4 160 4 175 4 185 4 195 4 165 4 155 4 150 300 500 700 200 0 400 600 800 1000 VCC 5V HPWR 5V RPROG 845 EN1 EN2 0V VCC V 4 3 4...

Страница 7: ...8 G10 83 107 111 99 35 5 65 85 VCC 5V TEMPERATURE C 55 R DS ON m 500 550 600 85 3558 G11 450 400 300 35 15 5 25 45 65 350 700 650 VCC 4V IBAT 200mA EN1 EN2 0V TEMPERATURE C 55 THRESHOLD V 1 1 5 3558 G...

Страница 8: ...5 5 65 85 105 50 FB1 0 85V PVIN1 4 2V PVIN1 2 7V Buck and Buck Boost Regulator Undervoltage Thresholds vs Temperature ILOAD mA 30 EFFICIENCY 90 100 20 10 80 50 70 60 40 0 1 10 100 1000 3558 G25 0 1 VO...

Страница 9: ...DIV AC LOAD STEP 5mA TO 290mA PVIN1 3 8V 50 s DIV 3558 G32 INDUCTOR CURRENT IL 200mA DIV Buck Boost Regulator Input Current vs Temperature Buck Boost Regulator Input Current vs Temperature Buck Boost...

Страница 10: ...OAD mA 3 27 V OUT V 3 29 3 31 3 33 3 35 0 10 10 100 1000 3 24 3 25 1 3 36 3 28 3 30 3 32 3 34 3 26 3558 G39 PWM MODE Burst Mode OPERATION PVIN2 3 6V 2 700 3 300 3 900 4 200 3 000 3 600 PVIN2 V V OUT V...

Страница 11: ...by a resistor divider connected across the output VC2 Pin 14 Output of the Error Ampli er and Voltage Compensation Node for the Buck Boost Regulator Ex ternal Type I or Type III compensation to FB2 co...

Страница 12: ...ed Pad must be soldered to PCB ground to provide electrical contact and rated thermal performance PIN FUNCTIONS 19 TA 800x BAT 1x TDIE TDIE PVIN1 OT CA NTCA NTC REF LOGIC CHRG 20 2 PROG BATTERY CHARGE...

Страница 13: ...has a linear battery charger designed to charge single cell lithium ion batteries The charger uses a constant current constant voltage charge algorithm with a charge current programmable up to 950mA A...

Страница 14: ...lt in safety timer that sets the total charge time for 4 hours Once the battery voltage rises above VRECHRG typically 4 105V and the charger entersconstant voltagemode the4 hourtimerisstarted After th...

Страница 15: ...lled low and remains low for the duration of a normal charge cycle When the charge current has dropped to below 10 of the full scale current the CHRG pin is released high impedance If a fault occurs a...

Страница 16: ...valid temperature As the temperature drops the resistance of the NTC thermistor rises The battery charger is also designed to pause charging when the value of the NTC thermistor increases to 3 25 time...

Страница 17: ...e thermistor at the hot trip point rCOLD Ratio of RNTC COLD to R25 rHOT Ratio of RNTC HOT to R25 RNOM Primary thermistor bias resistor see Figure 3 R1 Optional temperature range adjustment resistor se...

Страница 18: ...45 C with a Vishay Curve 1 thermistor choose R k k NOM 3 266 0 4368 2 714 100 104 2 the nearest 1 value is 105k R1 0 536 105k 0 4368 100k 12 6k the nearest 1 value is 12 7k The nal solution is shown i...

Страница 19: ...duce the 500mA charge current is approximately T C V V mA C W T C A A 105 5 3 5 500 68 105 0 75 68 105 51 54 W C W C C T C A The LTC3558 can be used above 70 C but the charge cur rentwillbereducedfrom...

Страница 20: ...herthaninstantaneous batterycurrentmaybe of interest to the user For example if a switching power supply operating in low current mode is connected in parallel with the battery the average current bei...

Страница 21: ...Do not drive the buck switching regulator from a voltage other than BAT A 10 F decoupling capacitor from the PVIN1 pin to GND is recommended Buck Switching Regulator Output Voltage Programming The buc...

Страница 22: ...tion theoutputcapacitorischargedtoa voltage slightly higher than the regulation point The buck switching regulator then goes into sleep mode during which the output capacitor provides the load current...

Страница 23: ...work with inductors in the range of 2 2 H to 10 H but for most applications a 4 7 H inductor is suggested Larger value inductors reduce ripple current which improves output ripple voltage Lower value...

Страница 24: ...ponse and stability the output capacitor should retain at least 4 F of capacitance over operating temperature and bias volt age Thebuckswitchingregulatorinputsupplyshouldbe bypassed with a 10 F capaci...

Страница 25: ...d output If the input voltage is close to the programmed output voltage then the converter will operate in four switch mode While operating in four switch mode switches turn on as per the following se...

Страница 26: ...oost Switching Regulator Output Voltage Programming The buck boost switching regulator can be programmed foroutputvoltagesgreaterthan2 75Vandlessthan5 45V To program the output voltage a resistor divi...

Страница 27: ...f phase lag from the LC double pole combined with the 90 of phase lag from the right half plane zero will result in negating the phase bump of the compensator The compensator zeros should be placed ei...

Страница 28: ...cycle is not triggered by changing operating modes This allows seamless output operation when transitioning between Burst Mode operation and PWM mode operation Buck Boost Switching Regulator Inductor...

Страница 29: ...utput Capacitor Selec tion section PCB Layout Considerations In order to deliver maximum charge current under all conditions it is critical that the backside of the LTC3558 be soldered to the PC board...

Страница 30: ...A 1 resistor in series with a 4 7 F capacitor at the BAT pin ensures battery charger stability 10 F VCC decoupling capacitors arerequiredforproperoperationoftheDC DCconverters A three resistor bias ne...

Страница 31: ...TO AREAS THAT ARE NOT SOLDERED 1 65 0 05 NOTE 1 DRAWING IS NOT A JEDEC PACKAGE OUTLINE 2 DRAWING NOT TO SCALE 3 ALL DIMENSIONS ARE IN MILLIMETERS 4 DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO N...

Страница 32: ...g 500mA 100mA Pin Selectable Burst Mode Operation Hot SwapTM Output for SDIO and Memory Cards 4mm 4mm QFN 24 Package LTC3456 2 Cell Multi Output DC DC Converter with USB Power Manager Seamless Transit...

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