9

LTC1729 Series

OVP

BAT

SENSE

GND

OVP

BAT

SENSE

STATUS

NTC

1

2

3

4

8

7

6

5

LTC1729-4.2

1

µF

0.1

µF

1729 F07

10k NTC THERMISTOR

NTHS1206N02 VISHAY/DALE

200

Ω

Figure 7. Terminate Charging at C/10

100

µA

1729 F08

COMP1

LTC1729

SENSE

BAT

+

–

SENSE

RESISTOR

CHARGE

CURRENT

Figure 8. Modify C/10 Indication to Create Charging Indicator

SEPIC Charger with 0.5A Output Current

OVP

BAT

SENSE

GND

STATUS

NTC

S/S

GND

LTC1729-4.2

BOOST

GND

OSC

LV

LTC1044

LT1512

C4

0.22

µF

C1

22

µF

R3

0.2

Ω

R1

29.4k

D2

1/2 BAT85S

D3

1/2 BAT85S

FOR 3.5V TO 14V USE LTC1144

R2

12.4k

L1A**

C6

1

µF

1729 F11

OPTION: TIE R8 TO STATUS FOR

CHARGE TERMINATION AT

LOW CHARGING CURRENT

* TOKIN CERAMIC 1E225ZY5U-C203-F

** L1A, L1B ARE TWO 33

µH WINDINGS ON A

SINGLE INDUCTOR; COILTRONICS CTX33-3

20mA TYPICAL

R8

10k NTC THERMISTOR, NTHS1206N02 VISHAY/DALE

NOTE: EITHER A THERMISTOR OR 10k RESISTOR MUST BE PRESENT

R9

1k

R5

1k

C2*

2.2

µF

R7

100

Ω

10k

R4, 24

Ω

R6

0.2

Ω

L1B**

+

C3

22

µF

C7

10

µF

C8

10

µF

C5

0.1

µF

D1

MBRS130LT3

INPUT POWER

4V TO 9V

4.2V

+

Using Status as a Charging Indicator

In many applications circuits shown in this data sheet, the

STATUS pin is used to indicate when C/10 has occurred

(charge current has dropped to 10% of the full charge

current). This C/10 number is not fixed, but is set by an

external resistor connected to the LTC1729 SENSE pin. A

100

µA bias current through this resistor develops a volt-

age which is compared with the voltage across the charge

current sense resistor. When these voltages are equal, the

open-drain STATUS pin turns off. Connecting an LED to

the STATUS pin will give a visual indication during the

precondition trickle charge and the portion of the main

charge before C/10 has occurred.

By reducing the LTC1729 SENSE pin resistor to 0

Ω, the

STATUS pin function can be changed to a

charging indica-

tor (Figure 8). The LED on the STATUS pin will always go

off after the 3-hour charge cycle is completed, regardless

of the C/10 circuitry.