LTC1729 データシートの表示（PDF） - Linear Technology

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LTC1729

Li-Ion Battery Charger Termination Controllers

Linear Technology 

LTC1729 Series

APPLICATIO S I FOR ATIO

Overview

The LTC1729 is a charge termination controller for the

LT1505/LT1510/LT1511/LT1512/LT1513/LT1769 con-

stant-voltage/constant-current battery charger family.

Table 1 details these chargers. The primary function of this

IC is to stop the charger after three hours of constant-

voltage/constant-current charging. The secondary func-

tion of this controller includes an indication when the

charge current (during constant-voltage mode) drops

below a user-selected threshold. A 500kHz Li-Ion cell

phone charger is shown in Figure 1. The LTC1729 requires

only six external components when combined with the

standard LT1510 application. The LTC1729 provides a

complete and tiny solution for cellular phones and other

portable applications.

Table 1. Battery Chargers

LT1505

4A Step-Down Charger with Input Current Limit

LT1510

1.5A Step-Down Charger

LT1510-5

1.5A 500kHz Step-Down Charger

LT1511

3A Step-Down Charger with Input Current Limit

LT1512

2A Switch SEPIC Charger

LT1513

3A Switch SEPIC Charger

LT1769

2A Step-Down Charger with Input Current Limit

Block Diagram

Figure 2 shows the block diagram of the LTC1729. The IC

consists of six comparators, a resistive divider, a UVLO

block and a logic and timer block.

Comparator COMP1 is used to indicate C/10 charge cur-

rent threshold. (“C” is a term used to indicate the Ampere-

hour capacity of a cell.) Figure 3 details the C/10 detection

circuit. The resistor and capacitor on the SENSE pin filter

the signal from the 0.2Ω current sense resistor R1. The

100µA current sink on the SENSE pin develops 20mV

across the 200Ω resistor R2. This sets a 20mV offset on

COMP1 that sense resistor R1 must equal before C/10

current is indicated. The C/10 is not recognized by the logic

until it passes through a 3-second digital filter.

For cases where there are multiple batteries to be charged,

the LTC1729 detects when a battery is removed and resets

the timers for the next charge cycle. The battery present

detection is the primary function of comparator COMP2.

When the battery is disconnected from the LTC1729, the

voltage at the BAT pin will begin ramping upward. This is

due to a current source inside the charger or an external

pull-up resistor. Once the voltage on the BAT pin exceeds

the 4.5V/cell limit, COMP2 signals a VMAX = true to the

logic and turns on a transistor that clamps the voltage.

There is the possibility of an overvoltage transient at the

charging terminals. This occurs if the battery protection

circuit, which is often included in the battery pack, opens

the connection to the battery during high current charging

(constant-current mode). This is a result of energy storage

in the inductor. COMP2 senses the overvoltage and clamps

the VC pin, reducing the duty cycle of the charger. If the

battery protection circuit quickly returns battery connec-

tion to the charger (in less than one second), then the

LTC1729 continues charging without resetting the timers.

CHARGING

CURRENT

+ R1

20mV

–

0.2Ω

+ 20mV –

R2

200Ω

SENSE

C1

1µF BAT

IBIAS

–

COMP1

+

100µA

3-SEC

FILTER

LOGIC

AND

TIMERS

Figure 3. C/10 Detection Circuit

VCC

LTC1729

STATUS

CHARGE

LED

50µA

1729 F03

7

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