LTC4059AEDC#TRMPBF Datasheet LTC4059EDC#TRMPBF, LTC4059AEDC#TRMPBF, LTC4059EDC#TRPBF | P7-P9

LTC4059/LTC4059A

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OPERATIO

The LTC4059/LTC4059A are linear battery chargers de-

signed primarily for charging single cell lithium-ion bat-

teries. Featuring an internal P-channel power MOSFET,

the chargers use a constant-current/constant-voltage

charge algorithm with programmable current. Charge

current can be programmed up to 900mA with a final float

voltage accuracy of ±0.6%. No blocking diode or external

sense resistor is required; thus, the basic charger circuit

requires only two external components. The ACPR pin

(LTC4059A) monitors the status of the input voltage with

an open-drain output. The Li CC pin (LTC4059) disables

constant-voltage operation and turns the LTC4059 into a

precision current source capable of charging Nickel chem-

istry batteries. Furthermore, the LTC4059/LTC4059A are

designed to operate from a USB power source.

An internal thermal limit reduces the programmed charge

current if the die temperature attempts to rise above a

preset value of approximately 115°C. This feature protects

the LTC4059/LTC4059A from excessive temperature, and

allows the user to push the limits of the power handling

capability of a given circuit board without risk of damaging

the LTC4059/LTC4059A or external components. Another

benefit of the thermal limit is that charge current can be set

according to typical, not worst-case, ambient tempera-

tures for a given application with the assurance that the

charger will automatically reduce the current in worst-

case conditions.

The charge cycle begins when the voltage at the V

rises approximately 150mV above the BAT pin voltage, a

program resistor is connected from the PROG pin to

ground, and the EN pin is pulled below the shutdown

threshold (typically 0.92V).

If the BAT pin voltage is below 4.2V, or the Li CC pin is

pulled above V

Li CC

(LTC4059 only), the LTC4059 will

charge the battery with the programmed current. This is

constant-current mode. When the BAT pin approaches the

final float voltage (4.2V), the LTC4059 enters constant-

voltage mode and the charge current begins to decrease.

To terminate the charge cycle the EN should be pulled

above the shutdown threshold. Alternatively, reducing the

input voltage below the BAT pin voltage will also terminate

the charge cycle.

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Programming Charge Current

The charge current is programmed using a single resistor

from the PROG pin to ground. The battery charge current

is 1000 times the current out of the PROG pin. The

program resistor and the charge current are calculated

using the following equations:

PROG

CHG

PROG

==1000

121

1000

121

•

,•

For best stability over temperature and time, 1% metal-

film resistors are recommended.

The charge current out of the BAT pin can be determined

at any time by monitoring the PROG pin voltage and using

the following equation:

BAT

PROG

= • 1000

Undervoltage Lockout (UVLO)

An internal undervoltage lockout circuit monitors the input

voltage and keeps the charger in undervoltage lockout until

rises approximately 150mV above the BAT pin voltage.

The UVLO circuit has a built-in hysteresis of 115mV. If the

BAT pin voltage is below approximately 2.75V, then the

charger will remain in undervoltage lockout until V

rises

above approximately 3V. During undervoltage lockout

conditions, maximum battery drain current is 4µA.

Power Supply Status Indicator

(ACPR, LTC4059A Only)

The power supply status output has two states: pull-down

and high impedance. The pull-down state indicates that

is above the undervoltage lockout threshold (see

Undervoltage Lockout). When this condition is not met,

the ACPR pin is high impedance indicating that the

LTC4059A is unable to charge the battery.

LTC4059/LTC4059A

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Shutdown Mode

Charging can be terminated by pulling the EN pin above the

shutdown threshold (approximately 0.92V). In shutdown

mode, the battery drain current is reduced to less than 1µA

and the supply current to 10µA.

USB and Wall Adapter Power

Although the LTC4059

/LTC4059A

allow charging from a

USB port, a wall adapter can also be used to charge Li-Ion

batteries. Figure 3 shows an example of how to combine

wall adapter and USB power inputs. A P-channel MOSFET,

MP1, is used to prevent back conducting 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 significantly more

current than the 500mA limited USB port. Therefore, an

N-channel MOSFET, MN1, and an extra program resistor

are used to increase the charge current to 850mA when the

wall adapter is present.

ance of the current source pair, M1 and M2 (note that M1

is the internal P-channel power MOSFET). It ensures that

the drain current of M1 is exactly 1000 times greater than

the drain current of M2.

Amplifiers CA and VA are used in separate feedback loops

to force the charger into constant-current or voltage

mode, respectively. Diodes D1 and D2 provide priority to

either the constant-current or constant-voltage loop;

whichever is trying to reduce the charge current the most.

The output of the other amplifier saturates low which

effectively removes its loop from the system. When in

constant-current mode, CA servos the voltage at the

PROG pin to be 1.21V. VA servos its inverting input to

precisely 1.21V when in constant-voltage mode and the

internal resistor divider made up of R1 and R2 ensures

that the battery voltage is maintained at 4.2V. The PROG

pin voltage gives an indication of the charge current

during constant-voltage mode as discussed in the Pro-

gramming Charge Current section.

Transconductance amplifier, TA, limits the die tempera-

ture to approximately 115°C when in constant-tempera-

ture mode. TA acts in conjunction with the constant-current

loop. When the die temperature exceeds approximately

115°C, TA sources current through R3. This causes CA to

reduce the charge current until the PROG pin voltage plus

the voltage across R3 equals 1.21V. Diode D3 ensures that

TA does not affect the charge current when the die tem-

perature is below approximately 115°C. The PROG pin

voltage continues to give an indication of the charge

current.

In typical operation, the charge cycle begins in constant-

current mode with the current delivered to the battery

equal to 1210V/R

PROG

. If the power dissipation of the

LTC4059

/LTC4059A

results in the junction temperature

approaching 115°C, the amplifier (TA) will begin decreas-

ing the charge current to limit the die temperature to

approximately 115°C. As the battery voltage rises, the

LTC4059

/LTC4059A

either return to constant-current mode

or enter constant-voltage mode straight from constant-

temperature mode. Regardless of mode, the voltage at the

PROG pin is proportional to the current delivered to the

battery.

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Figure 3. Combining Wall Adapter and USB Power

BAT

LTC4059

3.4k

2.43k1k MN1

MP1

5V WALL

ADAPTER

850mA I

CHG

USB

POWER

500mA I

CHG

Li-Ion

BATTERY

4059 F03

SYSTEM

LOAD

PROG

Constant Current/Constant Voltage/

Constant Temperature

The LTC4059

/LTC4059A

use a unique architecture to

charge a battery in a constant-current, constant-voltage

and constant-temperature fashion. Figures 1 and 2 show

simplified block diagrams of the LTC4059 and LTC4059A

respectively. Three of the amplifier feedback loops shown

control the constant-current, CA, constant-voltage, VA,

and constant-temperature, TA modes. A fourth amplifier

feedback loop, MA, is used to increase the output imped-

LTC4059/LTC4059A

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Power Dissipation

The conditions that cause the LTC4059

/LTC4059A

reduce charge current through thermal feedback can be

approximated by considering the power dissipated in the

IC. For high charge currents, the LTC4059 power dissipa-

tion is approximately:

= (V

– V

BAT

) • I

BAT

where P

is the power dissipated, V

is the input supply

voltage, V

BAT

is the battery voltage and I

BAT

is the charge

current. It is not necessary to perform any worst-case

power dissipation scenarios because the LTC4059

LTC4059A

will automatically reduce the charge current to

maintain the die temperature at approximately 115°C.

However, the approximate ambient temperature at which

the thermal feedback begins to protect the IC is:

= 115°C – P

= 115°C – (V

– V

BAT

) • I

BAT

• θ

Example: Consider an LTC4059 operating from a 5V wall

adapter providing 900mA to a 3.7V Li-Ion battery. The

ambient temperature above which the LTC4059

/LTC4059A

begin to reduce the 900mA charge current is approximately:

= 115°C – (5V – 3.7V) • (900mA) • 50°C/W

= 115°C – 1.17W • 50°C/W = 115°C – 59°C

= 56°C

The LTC4059 can be used above 56°C, but the charge

current will be reduced from 900mA. The approximate

current at a given ambient temperature can be calculated:

BAT

CC BAT JA

()

115 –

–•θ

Using the previous example with an ambient temperature

of 65°C, the charge current will be reduced to approximately:

VV CW

ImA

BAT

°°

()

115 65

537 50

770

–

–. • / /

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 LTC4059

/LTC4059A

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 115°C.

Board Layout Considerations

In order to be able to deliver maximum charge current

under all conditions, it is critical that the exposed metal

pad on the backside of the LTC4059

/LTC4059A

package is

soldered to the PC board ground. Correctly soldered to a

2500mm

double sided 1oz copper board the LTC4059

LTC4059A

have a thermal resistance of approximately

60°C/W. Failure to make thermal contact between the

exposed pad on the backside of the package and the

copper board will result in thermal resistances far greater

than 60°C/W. As an example, a correctly soldered LTC4059

LTC4059A

can deliver over 900mA to a battery from a 5V

supply at room temperature. Without a backside thermal

connection, this number could drop to less than 500mA.

Stability Considerations

The LTC4059 contains two control loops: constant voltage

and constant current. The constant-voltage loop is stable

without any compensation when a battery is connected

with low impedance leads. Excessive lead length, how-

ever, may add enough series inductance to require a

bypass capacitor of at least 1µF from BAT to GND. Further-

more, a 4.7µF capacitor with a 0.2Ω to 1Ω series resistor

from BAT to GND is required to keep ripple voltage low

when the battery is disconnected.

High value capacitors with very low ESR (especially ce-

ramic) reduce the constant-voltage loop phase margin.

Ceramic capacitors up to 22µF may be used in parallel with

a battery, but larger ceramics should be decoupled with

0.2Ω to 1Ω of series resistance.

n constant-current mode, the PROG pin is in the feedback

loop, not the battery. Because of the additional pole

created by PROG pin capacitance, capacitance on this pin

must be kept to a minimum. With no additional capaci-

tance on the PROG pin, the charger is stable with program

resistor values as high as 12k. However, additional ca-

pacitance on this node reduces the maximum allowed

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LTC4059AEDC#TRMPBF

Mfr. #:

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Manufacturer:

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Description:

Battery Management LTC4059 w/ Pin 2 assigned for ACPR Output

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