C ELL

B1

B2

MC V

V

R

=

N

1

R

V

æ

ö

´

-

ç

÷

è

ø

BAT+

Q1

FMMT718

D2

ZHCS1000

L1

47 H

m

C9

1000pF

R12

120 W

Q2

MMBT3904LT1

C6

47 F

m

D5

MMSD914LT

D3

MMSD914LT

D4

S1A

DC-

R10

1kW

D1

RED

R2

2kW

C3

10 F

m

D6

BZT52-C5V1

R1

100kW

RC 6

LED

3

BAT

4

VSS

2

TS

5

VCC 7

SNS

1

MOD 8

U1

bq2000T

C4

0.0022 F

m

R4

12.4kW

VCC

C7

4.7pF

C8

0.33 F

m

Q3

MMBT3904LT1

R11

220 W

R6

210kW

C5

10 F

m

BAT-

THERM

CHEMISTRY

R7

200kW

R9

221kW

R5

20kW

C1

0.1 mF

R8

6.81kW

C2

0.1 mF

NOTES:

1.ForLi-Ion,CHEMISTRY isleftfloating.

ForNiCd/NiMH,CHEMISTRY istiedtoBAT-

2.DCinputvoltage:9–16V

4.L1:3L GlobalP/NPKSMD-1005-470K-1A

3.Chargecurrent:1A

R13

1.1kW

R3

0.05 W

DC+

bq2000T

www.ti.com

SLUS149D – MAY 1999 – REVISED JANUARY 2010

BATTERY VOLTAGE INPUT

As shown in Figure 3, a resistor voltage-divider between the battery pack's positive terminal and VSS scales the

battery voltage measured at the BAT pin.

For Li-Ion battery packs, the resistor values RB1 and RB2 are calculated by the following equation:

(5)

where N is the number of cells in series and VCELL is the manufacturer-specified charging voltage. RB1 + RB2

should be at least 200 k

Ω and no more than 1 MΩ.

A NiCd or NiMH battery pack consisting of N series cells may benefit by the selection of the RB1 value to be N–1

times larger than the RB2 value. This sets the per cell regulation voltage (VCELL) equal to VMCV. It is critical that

VCELL be set high enough that the nickel pack not reach voltage regulation, thus allowing proper termination by

ΔT/Δt. The typical VCELL setting for a nickel pack is between 1.7 V and 2 V.

In a mixed-chemistry design, a common voltage-divider is used as long as the maximum charge voltage of the

nickel-based pack is below that of the Li-Ion pack. Otherwise, different scaling is required. See Figure 11 for an

example.

Figure 11. Single-Cell Li-Ion, 3-Cell NiCd/NiMH 1-A Charger

Copyright © 1999–2010, Texas Instruments Incorporated

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