Texas Instruments BQ2057SN-C1TR, BQ2057SN-C1, BQ2057PN-C1, BQ2057CTS-C1TR, BQ2057CTS-C1 Datasheet
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1
Features
➤
Ideal for single- and dual-cell Li-Ion
packs with coke or graphite anodes
➤
Dropout voltage as low as 0.3V
➤
AutoComp™ dynamic compensa
-
tion of battery pack’s internal im
-
pedance
➤
Optional temperature-monitoring
before and during charge
➤
Integrated voltage and current
regulation with programmable
charge-current and high- or
low-side current sensing
➤ Integrated cell conditioning for
reviving deeply discharged cells
and minimizing heat dissipation
during initial stage of charge
➤ Better than ±1% voltage regula-
tion accuracy
➤ Charge status output for LED or
host processor interface
➤ Automatic battery-recharge feature
➤
Charge termination by minimum
current
➤
Low-power sleep mode
➤
Packaging: 8-pin SOIC, 8-pin
TSSOP
General Description
The BENCHMARQ bq2057 series
advanced Li-Ion linear charge-man
agement ICs are designed for
cost-sensitive and compact portable
electronics. They combine high-accu
racy current and voltage regulation,
battery conditioning, temperature
monitoring, charge termination,
charge-status indication, and
AutoComp charge-rate compensation in a single 8-pin IC.
The bq2057 continuously measures
battery temperature using an exter
nal thermistor. For safety reasons,
the bq2057 inhibits charge until the
battery temperature is within
user-defined thresholds. The bq2057
then charges the battery in three
phases: conditioning, constant current, and constant voltage. If the
battery voltage is below the
low-voltage threshold V
MIN
, the
bq2057 trickle-charges to condition
the battery. The conditioning charge
rate is set at 10% of the regulation
current. The conditioning current
also minimizes heat dissipation in
the external pass-element during
the initial stage of charge.
After conditioning, the bq2057 ap
-
plies a constant current to the bat
-
tery. An external sense-resistor sets
the magnitude of the current. The
sense-resistor can be on either the
low or the high side of the battery
without additional components. The
constant-current phase continues
until the battery reaches the
charge-regulation voltage.
The bq2057 then begins the con
stant-voltage phase. The accuracy of
the voltage regulation is better than
±1% over the operating-temperature
and supply-voltage ranges. For sin
gle and dual cells with either coke
or graphite anodes, the bq2057 is of
fered in four fixed-voltage versions:
4.1V, 4.2V, 8.2V, and 8.4V. Charge
stops when the current tapers to the
charge termination threshold,
V
TERM
. The bq2057 automatically
restarts the charge if the battery
voltage falls below the V
RCH
thresh-
old.
The designer also may use the
AutoComp feature to reduce charging time. This proprietary technique
allows safe and dynamic compensation for the internal impedance of
the battery pack during charge.
bq2057
Pin Connections
Advanced Li-Ion Linear Charge
Management IC
1
PN-205701.eps
8-Pin PDIP, Narrow SOIC, or TSSOP
2
3
4
8
7
6
5
SNS
BAT
V
CC
TS
COMP
CC
V
SS
STAT
Pin Names
SNS Current-sense input
BAT Battery-voltage input
V
CC
Supply voltage
TS Temperature sense
input
STAT Charge status output
V
SS
Ground input
CC Charge control output
COMP Charge-rate
compensation input
SLUS025A – JANUARY 2000 - REVISED MAY 2000
Pin Descriptions
SNS Current-sense input
Battery current is sensed via the voltage de
-
veloped on this pin by an external sense re
-
sistor.
BAT Battery voltage input
Voltage sense-input tied directly to the posi
-
tive side of the battery.
V
CC
VCCsupply input
TS Temperature sense input
Input for an external battery-temperature
monitoring circuit. Connecting this input to
Vcc/2 disables this feature.
STAT Charge status output
Tri-state indication of charge-in-progress,
charge-complete, and temperature fault.
V
SS
Ground input
CC Charge-control output
Source-follower output that drives an exter
nal pass-transistor for current and voltage
regulation.
COMP Charge-rate compensation input
Sets the charge-rate compensation level. The
voltage-regulation output may be pro
grammed to vary as a function of the charge
current delivered to the battery.
2
bq2057
VCC
CC
CONTROL
BLOCK
V
REG
V
SS
V
CC
COMP
BAT
POWER
RESET
ON
SNS
2057FBD.eps
TS
V
TS1
, V
TS2
V
SNS
LED
STAT
STAT
K
COMP
Figure 1. Functional Block Diagram
Functional Description
Figure 1 is a functional block diagram, Figure 2 an oper
-
ational flow chart, and Figure 3 a typical charger sche
-
matic for the bq2057.
Charge Qualification and Conditioning
When power is applied, the bq2057 starts a charge-cycle
if a battery is already present or when a battery is in
-
serted. Charge qualification is based on battery temper
-
ature and voltage. The bq2057 suspends charge if the
battery temperature is outside the V
TS1
to V
TS2
range
and suspends charge until the battery temperature is
within the allowed range. The bq2057 also checks the
battery voltage. If the battery voltage is below the
low-voltage threshold V
MIN
, the bq2057 uses
trickle-charge to condition the battery. The conditioning
charge rate I
COND
is set at 10% of the regulation cur
-
rent. The conditioning current also minimizes heat dis
-
3
bq2057
VCC > V
BAT
Temperature
Check
TS > V
TS1
TS < V
TS2
V
BAT
≤ V
MIN
I
BAT
≤ V
BAT
≤ V
RCH
Sleep Mode
LED = Hi-Z
NO
YES
YES
NO
NO
NO
2057OFC.eps
NO
YES
YES
YES
Current
Regulation
Phase
LED = High
Voltage
Regulation
Phase
LED = HIGH
Charge
Complete
LED = LOW
Temperature
Fault
LED = Hi-Z
Conditioning
Phase
LED = High
I
REG
10
Figure 2. bq2057 Operational Flow Chart
sipation in the external pass-element during the initial
stage of charge. See Figure 4 for a typical charge-algorithm.
Current Regulation
The bq2057 regulates current while the battery-pack
voltage is less than the regulation voltage, V
REG
. The
bq2057 monitors charge current at the SNS input by the
voltage drop across a sense-resistor, R
SNS
, in series with
the battery pack. In high-side current sensing configura
-
tion (Figure 5), R
SNS
is placed between the Vcc and SNS
pins, and in low-side sensing (Figure 6) the R
SNS
is
placed between Vss (battery negative) and SNS (charger
ground) pins.
Charge-current feedback, applied through pin SNS, main
-
tains regulation around a threshold of V
SNS
. The follow
-
ing formula calculates the value of the sense resistor:
R
SNS
=
V
I
SNS
REG
where I
REG
is the desired charging current.
Voltage Monitoring and Regulation
Voltage regulation feedback is through pin BAT. This in
put is tied directly to the positive side of the battery
pack. The bq2057 monitors the battery-pack voltage be
tween the BAT and V
SS
pins. The bq2057 is offered in
four fixed-voltage versions for single- and dual-cells with
either coke or graphite anodes: 4.1V, 4.2V, 8.2V, and
8.4V.
Other regulation voltages can be achieved by adding a
voltage divider between the positive and negative terminals of the battery pack. The voltage divider presents a
scaled battery pack voltage to BAT input. (See Figures 7
and 8.) The resistor values R
B1
and RB2for the voltage
divider are calculated by the following equation:
R
R
N
V
V
B1
B2
CELL
REG
=∗
− 1
where
N = Number of cells in series
V
CELL
= Desired regulation voltage per cell
Charge Termination and Re-Charge
The bq2057 monitors the charging current during the
voltage-regulation phase. The bq2057 declares a “batterycomplete” condition and terminates charge when the
current tapers off to the charge termination threshold,
V
TERM
. A new charge cycle begins when the battery volt
-
age falls below the
VRCH threshold.
4
bq2057
2057ldc.eps
PACK+
Q1
FZT788B
D2
bq2057
CC
Battery
Pack
V
CC
V
CC
R
T1
R
T2
NTC
C1
0.1µF
C2
0.1µF
R2
2kΩ
R
SNS
0.2Ω
R1
1kΩ
D1
SNS
V
CC
V
SS
COMP
BAT
TS
STAT
DC+
DC-
TEMP
PACK-
78
2
4
5
1
3
6
Figure 3. Low-Dropout Single- or Dual-Cell Li-Ion Charger
*
* Optional.
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