LTC1759 View Datasheet(PDF) - Linear Technology

Part Name

Description

MFG CO.

LTC1759

Smart Battery Charger

Linear Technology 

Prev 21 22 23 24 25 26 27 28

LTC1759

APPLICATIONS INFORMATION

Charge Termination Issues

Batteries with constant current charging and voltage-

based charger termination might experience problems

with reductions of charger current caused by adapter

limiting. It is recommended that input limiting feature be

defeated in such cases. Consult the battery manufacturer

for information on how your battery terminates charging.

Setting Output Current Limit (Refer to Figure 10)

The LTC1759 current DAC and the PWM analog circuitry

must coordinate the setting of the charger current. Failure

to do so will result in incorrect charge currents.

Table 8. Recommended Resistor Values

IMAX

RSENSE

RSENSE RS1 = RS2

(A) (Ω) 1%

(W)

(Ω) 1%

1.023 0.100

0.25

200

2.046 0.05

0.25

200

4.092 0.025

0.5

200

8.184 0.012

1

200

RSET

(Ω) 1%

3.83k

3.83k

3.83k

4.02k

RILIMIT

(Ω) 1%

0

10k

33k

Open

Warning

DO NOT CHANGE THE VALUE OF RILIMIT DURING OPERA-

TION. The value must remain fixed and track the RSENSE

and RSET values at all times. Changing the current setting

can result in currents that greatly exceed the requested

value and potentially damage the battery or overload the

wall adapter if no input current limiting is provided.

Example Calculations

Setting up the output current to the desired value involves

calculating these values:

1. RSENSE: This resistor is the current sense resistor on the

charger output.

2. RSET: This resistor sets the current DAC output pro-

gramming current scale.

3. RILIMIT: This resistor programs the full-scale value of

the current DAC (IMAX).

The value of RSENSE and RSET are directly related to each

other based on the values chosen for RS1 and RS2. To

prevent current sense op amp input bias errors, the value

of RS1 and RS2 are kept the same, about 200Ω. RSET is

used to scale the PROG pin current relative to the RSENSE

voltage drop to set the maximum current value.

The following example is for a 4A design.

AC

ADAPTER

INPUT

R1

15.8k

+

C9, 0.1µF

C15

10µF

35V VDD

Al

C14

0.1µF

C11, 1µF

C13, 0.33µF

C12, 0.68µF

RVLIMIT, 33k

RILIMIT, 33k

RSET, 3.83k

R4, 1.5k

R7, 1k

VDD

RWEAK RNR

RUR

475k

10k

1k

LTC1759

7

UV

22

DCIN

16

VDD

21

DCDIV

4

SYNC

8

INFET

5

SDB

12

CHGEN

32

VCC

9

CLP

25

VLIMIT

10

CLN

24

ILIMIT

2

TGATE

18

33

DGND BOOSTC

17

ISET

34

GBIAS

28

PROG

1

BOOST

27

VC

3

SW

11

35

COMP1 BGATE

6 AGND

30

SPIN

20

RNR

29

SENSE

19

THERM

31

BAT1

14 SDA

23

BAT2

15

SCL

13

INTB

26

VSET

36

PGND

Q1

C5, 2.2µF

D2

R2

1k

RCL, 0.033Ω

C2

0.47µF

R3

499Ω

C1

1µF

C4, 0.1µF

C6

0.68µF

D2

SYSTEM

POWER

C16

22µF

Q2

L1

15µH

RSENSE

0.025Ω

Q3

D1

RS1, 200Ω

RS2, 200Ω

R6

68Ω

C8

0.047µF C7

0.015µF

D1: MBRS130LT3

D2: FMMD7000

L1: SUMIDA CDRH127-150

Q1: Si3457DV

Q2, Q3: Si3456DV

Figure 10. 4A SMBus Smart Battery Charger

+ C3

22µF

SMART

BATTERY

INTB

SCL

SDA

SMBus

TO

HOST

1759 F10

23

Share Link: