BQ2000T_15 Datasheet, PDF (13/29 Pages) Texas Instruments – Programmable Multi-Chemistry Fast-Charge Management IC

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 V_SS scales the
battery voltage measured at the BAT pin.
For Li-Ion battery packs, the resistor values R_B1 and R_B2 are calculated by the following equation:
R_B1
=
æ
ç^N
´
V_CELL
ö
÷ ^-1
R_{B2 è}
V_{MCV ø}
(5)
where N is the number of cells in series and V_CELL is the manufacturer-specified charging voltage. R_B1 + R_B2
should be at least 200 kΩ and no more than 1 MΩ.
A NiCd or NiMH battery pack consisting of N series cells may benefit by the selection of the R_B1 value to be N–1
times larger than the R_B2 value. This sets the per cell regulation voltage (V_CELL) equal to V_MCV. It is critical that
V_CELL be set high enough that the nickel pack not reach voltage regulation, thus allowing proper termination by
ΔT/Δt. The typical V_CELL 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.
DC+
D3
MMSD914LT
D4
S1A
C6
47 mF
R10
1 kW
VCC
D6
BZT52-C5V1
R2
2 kW
C3
10 mF
D1
RED
C2
0.1 mF
C7
C4
4.7 pF
0.0022 mF
R1
U1
1
2
3
4
SNS
VSS
LED
BAT
100 kW
MOD
VCC
RC
TS
8
7
6
5
bq2000T
C8
0.33 mF
C1
0.1 mF
Q1
FMMT718
Q2
MMBT3904LT1
D5
MMSD914LT
C9
R12
120 W
1000 pF
L1
47 mH
D2
ZHCS1000
Q3
MMBT3904LT1
R11
220 W
R6
210 kW
R4
12.4 kW
R8
6.81 kW
R5
20 kW
BAT+
C5
10 mF
THERM
R9
221 kW
CHEMISTRY
R7
200 kW
BAT-
R13
1.1 kW
DC-
NOTES:
1. For Li-Ion, CHEMISTRY is left floating.
For NiCd/NiMH, CHEMISTRY is tied to BAT-
2. DC input voltage: 9–16V
3. Charge current: 1A
4. L1: 3L Global P/N PKSMD-1005-470K-1A
Figure 11. Single-Cell Li-Ion, 3-Cell NiCd/NiMH 1-A Charger
R3
0.05 W
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