Features
Complete and compact lithium-ion pack supervisor
Provides overvoltage, undervoltage, and
overcurrent protection for two series Li-Ion cells
Combines bq2058T with charge/discharge control
FETs
Low side low on-resistance FETs
Designed for battery pack integration
Direct connection for series battery terminals
Measures 1.70 X 0.70 inches
Low standby and operating currents
General Description
The bq2158T provides a complete solution for the super-
vision of two series Li-Ion cells. Designed for battery
pack integration, the bq2158T incorporates a bq2058T
Pack Supervisor, two FETs, and all other components re-
quired to monitor overvoltage, undervoltage, and over-
c u r r e n t c o n d i t i o n s.
T h e b o a r d p r o v i d e s d i r e c t
connections for the negative and positive terminals of
each cell. See Figure 1. Please refer to the bq2058T
data sheet for specific information on the operation of
the bq2058T.
Unitrode configures the bq2158T based on the informa-
tion in Table 1.
Pin Descriptions
B1P
Battery 1 positive input
B1N
Battery 1 negative input
B2N
Battery 2 negative input
POS
Pack positive
NEG
Pack negative
1
Two Series Cell
Li-Ion Pack Supervisor Module
Preliminary
bq2158T
4/99
2
Customer Name: ___________________________________________________________________________
Contact: _________________________________________
Phone: ______________________________
Address: _________________________________________________________________________________
_________________________________________________________________________________
Sales Contact: ____________________________________
Phone: ______________________________
Overvoltage threshold (4.25V)
________________________________________
Charge current (3.8A max.)
________________________________________
Discharge current (3.8A max.)
________________________________________
FAE approval: ____________________________________
Date:________________________________
Table 1. bq2158T Module Configuration
bq2158T
Preliminary
Operation
The bq2158T monitors each series element for under-
voltage, over-voltage, and over-current conditions. If a
cell falls below V
UV
for t
UVD
, the bq2158T enters into
sleep mode. The bq2158T wakes up and enables dis-
charge if a voltage, V
CD
higher than the battery voltage,
is applied across POS and NEG. Charging is disabled if
a cell exceeds V
OV
for t
OVD
, and can resume when the
cell falls below the V
CE
threshold. The bq2158T turns
the discharge FET off if the steady state load current ex-
ceeds I
OC
for t
OCD
and turns it back on if the load is re-
moved.
3
FG2158Tcd.eps
Load
or
Charger
POS
NEG
B1P
B1N
B2N
Note: B1P, B2N, POS, and NEG accomodate a #20 AWG stranded wire.
B1N accomodates a #24 AWG stranded wire.
Figure 1. Module Connection Diagram
Preliminary
bq2158T
4
bq2158t-b6/18/98
bq2158T Schematic
bq2158T
Preliminary
5
.700
.000
2x .055
3x 1.645
2x .055
2x .645
.000
.355
POS
Q3
B1P
B1N
B2N
.068
1.700
U1
TP1
Q1
C7
C3
C8
C2
C5
C6
C4
C1
D1
R1
Q2
R6
R7
R5
R3
R2
R4
NEG
.031
LAYER 1
LAYER 2
bq2158T Board
Preliminary
bq2158T
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