LTC4001EUF-1#TRPBF Datasheet LTC4001EUF-1#TRPBF | P10-P12

LTC4001-1

40011fa

Soft-Start and Compensation Capacitor Selection

The LTC4001-1 has a low current trickle charger and a

PWM-based high current charger. Soft-start is used when-

ever the high rate charger is initially turned on, preventing

high start-up current. Soft-start ramp rate is set by the

internal 12.8μA pull-up current and an external capacitor.

The control range on the SS pin is approximately 0.3V

to 1.6V. With a 0.1μF capacitor, the time to ramp up to

maximum duty cycle is approximately 10ms.

The external capacitor on the SS pin also sets the compensa-

tion for the current control loop and the ﬂ oat voltage control

loop. A minimum capacitance of 10nF is required.

Charge Current and IDET Programming

The LTC4001-1 has two different charge modes. If the

battery is severely depleted (battery voltage less than

2.9V) a 50mA trickle current is initially used. If the battery

voltage is greater than the trickle charge threshold, high

rate charging is used.

This higher charge current is programmable and is ap-

proximately 915 times the current delivered by the PROG

pin. This current is usually set with an external resistor

from PROG to GNDSENS, but it may also be set with a

current output DAC connected to the PROG pin. The volt-

age on the PROG pin is nominally 1.213V.

For 2A charge current:

PROG

915 •1.213V

 554.9

APPLICATIONS INFORMATION

Figure 1. Programming Charge Current and

IDET Threshold with a Single Resistor

The IDET threshold (a charge current threshold used to

determine when the battery is nearly fully charged) is

programmed in much the same way as the PROG pin,

except that the IDET threshold is 91.5 times the current

delivered by the IDET pin. This current is usually set with

an external resistor from IDET to ground, but it may also

be set with a current output DAC. The voltage on the PROG

pin is nominally 1.213V.

For 200mA IDET current (corresponding to C/10 for a

2AHr battery):

IDET

91.5 •1.213V

0.2A

 554.9

1.10kΩ programs approximately 100mA and 274Ω ap-

proximately 400mA.

For applications where IDET is set to one tenth of the high

rate charge current, and slightly poorer charger current

and IDET threshold accuracy is acceptable, the PROG and

IDET pins may be tied together and a single resistor, R1,

can program both (Figure 1).

R1=

457.5 •1.213

CHARGE

and

IDET =

CHARGE

PROG

LTC4001-1

IDET

274Ω FOR 2A

GNDSENS

40011 F01

LTC4001-1

40011fa

APPLICATIONS INFORMATION

The equations for calculating R1 (used in single resistor

programming) differ from the equations for calculating

PROG

and R

IDET

(2-resistor programming) and reﬂ ect

the fact that the current from both the IDET and PROG

pins must ﬂ ow through a single resistor R1 when a single

programming resistor is used.

CHRG Status Output Pin

When a charge cycle starts, the CHRG pin is pulled to

ground by an internal N-channel MOSFET which is capable

of driving an LED. When the charge current drops below

the end-of-charge (IDET) threshold for at least 4ms,

and the battery voltage is close to the ﬂ oat voltage, the

N-channel MOSFET turns off and a weak 30μA current

source to ground is connected to the CHRG pin. This

weak pull-down remains until the charge cycle ends. After

charging ends, the pin will become high impedance. By

using two different value resistors, a microprocessor can

detect three states from this pin (charging, end-of-charge

and charging stopped). See Figure 2.

To detect the charge mode, force the digital output pin,

OUT, high and measure the voltage on the CHRG pin. The

N-channel MOSFET will pull the pin low even with a 2k

pull-up resistor. Once the charge current drops below

the end-of-charge threshold, the N-channel MOSFET is

turned off and a 30μA current source is connected to the

CHRG pin. The IN pin will then be pulled high by the 2k

resistor connected to OUT. Now force the OUT pin into

a high impedance state, the current source will pull the

pin low through the 390k resistor. When charging stops,

the CHRG pin changes to a high impedance state and the

390k resistor will then pull the pin high to indicate charg-

ing has stopped.

Charge Termination

Battery charging may be terminated several different ways,

depending on the connections made to the TIMER pin. For

time-based termination, connect a capacitor between the

TIMER pin and GNDSENS (C

TIMER

= Time(Hrs) 0.0733μF).

Charging may be terminated when charge current drops

below the IDET threshold by tying TIMER to GNDSENS.

Finally, charge termination may be defeated by tying TIMER

to IDET. In this case, an external device can terminate

charging by pulling the EN pin high.

Battery Temperature Detection

When battery temperature is out of range (either too hot

or too cold) charging is temporarily halted and the FAULT

pin is driven high. In addition, if the battery is still charg-

ing at a high rate (greater than the IDET current) when a

temperature fault occurs, the CHRG pin NMOS turns on

and off at approximately 50kHz, alternating between a

high and low duty factor at an approximate rate of 1.5Hz

(Figure 3). This provides a low rate visual indication (1.5Hz)

when driving an LED from the CHRG pin while providing

a fast temperature fault indication (20μs typical) to a mi-

croprocessor by tying the CHRG pin to an interrupt line.

Serrations within this pulse are typically 500ns wide.

Figure 2. Microprocessor Interface Figure 3. CHRG Temperature Fault Waveform

LTC4001-1

OUT

μPROCESSOR

CHRG

390k

40011 F02

20μs

40011 F03

667ms

LTC4001-1

40011fa

APPLICATIONS INFORMATION

The battery temperature is measured by placing a negative

temperature coefﬁ cient (NTC) thermistor close to the bat-

tery pack. To use this feature, connect the NTC thermistor,

NTC

, between the NTC pin and GNDSENS and the resistor,

NOM

, from the NTC pin to V

INSENSE

. R

NOM

should be a 1%

resistor with a value equal to the value of the chosen NTC

thermistor at 25°C. The LTC4001-1 goes into hold mode

when the resistance, R

HOT

, of the NTC thermistor drops to

0.41 times the value of R

NOM

. For instance for R

NTC

= 10k.

(The value for a Vishay NTHS0603N02N1002J thermistor

at 25°C) hold occurs at approximately 4.1k, which occurs

at 50°C. The hold mode freezes the timer and stops the

charge cycle until the thermistor indicates a return to a

valid temperature. As the temperature drops, the resistance

of the NTC thermistor rises. The LTC4001-1 is designed to

go into hold mode when the value of the NTC thermistor

increases to 2.82 times the value of R

NOM

. This resistance

is R

COLD

. For the Vishay 10k thermistor, this value is 28.2k,

which corresponds to approximately 0°C. The hot and cold

comparators each have approximately 3°C of hysteresis

to prevent oscillation about the trip point. Grounding the

NTC pin disables the NTC function.

Thermistors

The LTC4001-1 NTC trip points were designed to work with

thermistors whose resistance temperature characteristics

follow Vishay Dale’s “R-T Curve 2.” However, any thermis-

tor whose ratio of R

COLD

to R

HOT

is about 7 will also work

(Vishay Dale R-T Curve 2 shows a ratio of R

COLD

to R

HOT

of 2.815/0.4086 = 6.89).

Power conscious designs may want to use thermistors

whose room temperature value is greater than 10k. Vishay

Dale has a number of values of thermistor from 10k to 100k

that follow the “R-T Curve 1.” Using these as indicated

in the NTC Thermistor section will give temperature trip

points of approximately 3°C and 47°C, a delta of 44°C. This

delta in temperature can be moved in either direction by

changing the value of R

NOM

with respect to R

NTC

. Increasing

NOM

will move the trip points to higher temperatures. To

calculate R

NOM

for a shift to lower temperature for example,

use the following equation:

NOM

COLD

2.815

•R

NTC

at 25°C

where R

COLD

is the resistance ratio of R

NTC

at the desired

cold temperature trip point. If you want to shift the trip points

to higher temperatures use the following equation:

NOM

HOT

0.4086

•R

NTC

at 25°C

where R

HOT

is the resistance ratio of R

NTC

at the desired

hot temperature trip point.

Here is an example using a 100k R-T Curve 1 thermistor

from Vishay Dale. The difference between trip points is

44°C, from before, and we want the cold trip point to be

0°C, which would put the hot trip point at 44°C. The R

NOM

needed is calculated as follows:

NOM

COLD

2.815

•R

NTC

at 25°C

3.266

2.815

• 100k = 116k

The nearest 1% value for R

NOM

is 115k. This is the value

used to bias the NTC thermistor to get cold and hot trip

points of approximately 0°C and 44°C respectively. To

extend the delta between the cold and hot trip points a

resistor, R1, can be added in series with R

NTC

(see Figure 4).

The values of the resistors are calculated as follows:

NOM

COLD

–R

HOT

2.815 – 0.4086

R1=

0.4086

2.815 –

0.4086

•R

COLD

–R

HOT

()

–R

HOT

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LTC4001EUF-1#TRPBF

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Manufacturer:

Analog Devices / Linear Technology

Description:

Battery Management 2A Sync Buck Li-Ion Chr

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