ETC BQ2903SN

bq2903
Rechargeable Alkaline Charge/Discharge
Controller IC
Features
General Description
➤ Safe charge of three or four rechargeable alkaline batteries
such as Renewal® from Rayovac®
The bq2903 is a cost-effective charge
controller for rechargeable alkaline
batteries such as Renewal batteries
from Rayovac. The bq2903 combines
sensitive, full-charge detection for
three to four rechargeable alkaline
cells, with a low-battery cut-off for
over-discharge protection.
➤ Pulsed charge terminated with
maximum voltage limit
➤ LED outputs indicate charge
status
➤ Automatic charge control simplifies charger design
Designed for integration into a threeor four-cell system, the bq2903 can
improve the service life of the rechargeable alkaline cells by properly
managing the charge and discharge.
The bq2903 requires a voltage-limited
current source to generate the proper
charge pulses for the Renewal cell.
Each cell is individually monitored
to ensure full charge without a damaging overcharge.
➤ Available in 14-pin 300-mil DIP
or 150-mil SOIC
Charge completion is indicated when
the average charge rate falls below
Pin Connections
Pin Names
➤ Selectable end-of-discharge voltage prevents overdischarge and
improves cycle life
➤ Optional external FET drive allows high current loads
➤ Pre-charge qualification indicates
fault conditions
BAT1N
1
14
BAT1P
BAT2N
2
13
DC
BAT3N
3
12
LRTN2
NSEL
4
11
VSS
VSEL
5
10
VSS
DONE
6
9
LRTN1
CHG
7
8
DRV
approximately 6% of the fast charge
rate. Status outputs are provided to
indicate charge in progress, charge
complete, or fault condition.
The bq2903 avoids over-depleting
the battery by using the internal
end-of-discharge control circuitry.
The bq2903 also eliminates the external power switching transistors
needed to separately charge individual Renewal cells.
To reduce external component count,
the discharge and charge control
FETs are internal to the bq2903;
however, if the discharge load is
greater than 400mA, a DRV pin is
provided to drive an external N-FET,
reducing the effective discharge path
resistance for the system.
For safety, charging is inhibited if the
voltage of any cell is greater than
3.0V during charge or if the voltage of
any cell is less than 0.4V when not
charging (open-circuit voltage).
DC
Charging supply input
BAT1N
Battery 1 negative input
CHG
Battery status output 1
BAT2N
Battery 2 negative input
DONE
Battery status output 2
BAT3N
Battery 3 negative input
NSEL
Number of cells input
VSS
Battery 4 negative input/
IC ground
VSEL
End of discharge
voltage select input
LRTN1, 2
System load returns
Battery 1 positive input
DRV
External FET drive
output
BAT1P
14-Pin Narrow DIP
or SOIC
PN290301.eps
6/99 C
1
bq2903
= BAT1P selects an EDV of 1.10V. VSEL floating selects EDV = 1.0V. VSEL =VSS selects EDV
= 0.9V.
Pin Descriptions
DC
DC supply input
BAT1P
This input is used to recharge the rechargeable alkaline cells and power the bq2903
during charge. This input must be connected
to a voltage-limited current source.
CHG
This input connects to the positive terminal
of the battery designated BAT1 (see Figure
3). This pin also provides power to the bq2903
when DC is not present.
Charge status
BAT1N
This open-drain output is used to signify the
battery charging status and is valid only when
DC is applied. See Figure 4 and Table 1.
DONE
Charge done
BAT2N
BAT3N
Number of cells input
Battery 3 negative input
This input connects to the negative terminal
of the battery designated BAT3 (see Figure 3).
VSS
End-of-discharge select input
Battery 4 negative input/IC ground
This input connects to the negative terminal
of the battery designated BAT4 (see Figure 3).
This three-level input selects the desired endof-discharge cut-off voltage for the bq2903. VSEL
DC
Battery 2 negative input
This input connects to the negative terminal
of the battery designated BAT2 (see Figure 3).
This input selects whether the bq2903
charges 3 or 4 cells. NSEL = BAT1P selects 4
cells, and NSEL = VSS selects 3 cells.
VSEL
Battery 1 negative input
This input connects to the negative terminal
of the battery designated BAT1 (see Figure 3).
This open-drain output is used to signify
charge completion and is valid only when DC
is applied.
NSEL
Battery 1 positive input
13
4
NSEL
5
VSEL
6
DONE
14 BAT
1P
Control/Status
Logic
1 BAT
1N
2 BAT
2N
3 BAT
3N
8 DRV
9 LRTN1
12 LRTN
CHG 7
2
10 VSS
11
VSS
BD290301.eps
Figure 1. Functional Block Diagram
2
bq2903
(VOCV<0.4V). If the VOCV of any cell is below VMIN, the
bq2903 enters a charge-pending mode and indicates a
fault (see Table 1).
LRTN1, 2 Load returns
These open-drain pull-down outputs are typically used as low-side load switches.
High-side load switching is also possible
with the addition of an external P-FET
DRV
If all cells are above VMIN and the minimum operating
voltage VOP(min)=2.7V at the DC pin is met, the bq2903
will initiate a charge cycle. A charge cycle consists of
pulse charging the battery and then checking for a termination condition.
External FET drive output
This push-pull output drives an optional external N-FET (see Figure 4). See page 5 for a
full description.
Charge Termination
Once a charge cycle begins, the bq2903 terminates
charge when the average charge rate falls below 6% of
the maximum charge rate. The bq2903 also terminates
charge when the closed-circuit voltage (VCCV) of any cell
exceeds 3.0V (VFLT) during charge and indicates a fault
condition on the CHG output (see Table 1).
Functional Description
Figure 1 is a block diagram outlining the major components of the bq2903. Figure 2 illustrates the charge control and display status during a bq2903 cycle. Table 1
outlines the various operational states and their associated conditions which are described in detail in the following section.
Charge Re-Initiation
If DC remains valid, the bq2903 will suspend all charge activity after full-charge termination. A charge cycle is reinitiated when all cell potentials fall below 1.4V. The rechargeable alkaline cells, unlike other rechargeable chemistries, do not require a maintenance charge to keep the cells
in a fully charged state. The self-discharge rate for the Renewal cells is typically 4% per year at room temperature.
DC Input
This input is used to charge the rechargeable alkaline cells
and power the bq2903 during a charge. To charge the batteries, this input should be connected to a current source
limited to 300mA. If the DC input current is greater than
300mA, the power dissipation limits of the package will be
exceeded. The DC input should also be capable of supplying a minimum of 2.0V*N, where N is the number of cells
to be charged. The DC input should not exceed 10V.
Charge Status Indication
Table 1 and Figure 2 outline the various charge action
states and the associated BAT1P, CHG, and DONE output states. The charge status outputs are designed to
work with individual or tri-color LED indicators. In all
cases, if the voltage at the DC pin is less than the voltage at the BAT1P pin, CHG and DONE outputs are held
in a high-impedance condition.
Charge Pre-Qualification
After DC is applied, the bq2903 checks the open-circuit
voltage (VOCV) of each cell for an undervoltage condition
Table 1. bq2903 Operational Summary
Charge Action
State
DC absent
Charge initiation
Charge pending/
fault
BAT1P Input
CHG
Output
DONE
Output
VDC < VBAT1P
-
Z
Z
DC applied
-
-
-
Conditions
1
VOCV < 0.4V or VCCV > 3.0V
2
-
1
6 sec = Low
1 sec = Z
6
Z
Charge pulse
VOCV ≤ 1.63V before pulse
Charge pulsed @ 100Hz per Figure 1
Low
Z
Pulse skip
VOCV > 1.63V before pulse
Pulse skipped per Figure 1
Low
Z
Average charge rate falls below
6% of the fast charge rate
Charge complete
Z
Low
Charge complete
Notes:
1. VOCV = Open-circuit voltage of each cell between positive and negative leads.
2. VCCV = Closed-circuit voltage.
3
bq2903
Charging
End-of-Discharge Control
The bq2903 controls charging by periodically connecting
the DC current source to the battery stack, not to the individual battery cells. The charge current is pulsed from
the internal clock at approximately a 100 Hz rate on the
BAT1P pin.
When DC is less than the voltage on BAT1P, the bq2903
is powered by the battery at BAT1P. In this state, the
batteries discharge down to the level determined by the
VSEL pin. The end-of-discharge voltage (VEDV) is selectable by connecting the VSEL pin as outlined in Table 2. If
the voltage across any cell is below the voltage specified
by the VSEL input, the bq2903 disconnects the battery
stack from the load by turning the internal discharge
FET off. The DRV output is also driven low, disabling
the external FET. After disconnecting power (the battery stack) to the load, the standby current in the
bq2903 is reduced to less than 1µA. Typically, higher
discharge loads (>200mA) should use a lower discharge
voltage cut-off to maximize battery capacity.
The bq2903 pulse charges the battery for approximately
7.5ms of every 10ms, when conditions warrant. The
bq2903 measures the open circuit voltage (VOCV) of each
battery cell during the idle period. If a single-cell potential of any battery is above the maximum open-circuit
voltage (VMAX = 1.63V ±3%), the following pulses are
skipped until all cell potentials fall below the VMAX
limit. Charging is terminated when the average charge
rate falls below approximately 6% of the maximum
charge rate. Once charging is terminated, the internal
charging FET remains off, and the DONE output becomes active per Table 1 and Figure 2. With DC applied,
the internal discharge FET will always remain on, and
the DRV output will remain high.
After disconnecting the battery stack from the load, the
internal discharge FET remains off, and the DRV output
remains low until the batteries are replaced or DC is reapplied, initiating a new charge cycle.
DC Valid
Charge
Complete
Charging 2
Pending 1
tP
10ms
tPW
7.5ms
3
4
BAT1P
1/6 sec.
CHG
DONE
Notes:
1.
2.
3.
4.
Charging Pending: 0.4 < VOCV < 0.4V per cell, VCCV > 3.0V per cell.
Charging: 0.4 < VOCV < 1.63V, VCCV < 3.0V.
Pulses skipped when VOCV > 1.63V.
Charge complete when average charge rate falls below approximately 6% of the fast charge rate.
Figure 2. bq2903 Example of Charge Action Events
4
bq2903
DRV Pin
Table 2. bq2903 EDV Selections
End-of-Discharge Voltage
Pin Connection
1.10V
VSEL = BAT1P
1.00V
VSEL = Z
0.90V
VSEL = VSS
The bq2903 controls battery discharge with two internal
FETs between LRTN1, LRTN2, and VSS. The current
through each switch should be limited to 200mA.
LRTN1 can be tied to LRTN2 for discharge current of up
to 400mA. To reduce the effective discharge switch resistance, or for high current loads, the DRV pin can control
an external N-FET, as shown in Figure 4. DRV is “high”
when a valid charging voltage is applied to the DC pin
and remains “high” during discharge. DRV goes “low”
during discharge to turn off the external FET when an
end-of-discharge condition is met. This pin should not
be connected if the external FET option is not used.
Number-of-Cell Selection
NSEL is used to select whether the bq2903 will charge 3
or 4 cells. Figure 3 shows the proper connection for a 3or 4-cell system. For 4 cell operation, NSEL = BAT1P. For
3 cell operation, NSEL = VSS and the BAT2N pin should
be connected to the BAT3N pin.
BAT1P
BAT1
BAT2
BAT3
BAT4
BAT1P
BAT1
NSEL
BAT1N
BAT2
BAT2N
NSEL
BAT1N
BAT2N
BAT3N
BAT3
VSS
BAT3N
VSS
bq2903
bq2903
4-Cell
3-Cell
FG290301.eps
Figure 3. NSEL Connection Diagram
5
bq2903
DC+
R1
C1
D1
CHG/RED
D2
DONE/GREEN
13
7
6
4
5
10
11
DC
CHG
DONE
NSEL
VSEL
VSS
VSS
14
1
2
3
8
9
12
BAT1P
BAT1N
BAT2N
BAT3N
DRV
LRTN1
LRTN2
C2
R2
C3
C4
R3
R4
Load
C5
bq2903
DCQ1
IRF7102
Dual N-Channel
MOSFET
Optional for Higher
Discharge Current or
Lower Series Loss
Battery
and
Load
Note: Load must be disconected
from battery stack while
changing
FG290302.eps
Figure 4. bq2903 Application Example,
4–Cell and 1.0V EDV
6
bq2903
Absolute Maximum Ratings
Symbol
Parameter
Minimum
Maximum
Unit
Notes
DCIN
VDC
-0.3
11.0
V
VT
DC threshold voltage applied on any
pin, excluding DC pin
-0.3
11.0
V
TOPR
Operating ambient temperature
0
+70
°C
TSTG
Storage temperature
-40
+85
°C
TSOLDER
Soldering temperature
-
+260
°C
IDC
DC charging current
-
400
mA
ILOAD
Discharge current
-
500
mA
No external FET
IOL
Output current
-
20
mA
CHG, DONE
Note:
Commercial
10 sec max.
Permanent device damage may occur if Absolute Maximum Ratings are exceeded. Functional operation
should be limited to the Recommended DC Operating Conditions detailed in this data sheet. Exposure to conditions beyond the operational limits for extended periods of time may affect device reliability.
7
bq2903
DC Thresholds
Symbol
VMAX
VEDV
(TA = 25°C; VDC =10V)
Parameter
Maximum open-circuit
voltage
End-of-discharge voltage
Rating
Tolerance
Unit
Notes
1.63
± 3%
V
VOCV > VMAX inhibits or terminates
charge pulses
0.90
± 5%
V
VSEL = VSS
1.00
± 5%
V
VSEL = Z
1.10
± 5%
V
VSEL = BAT1P
VFLT
Maximum closed-circuit
voltage
3.00
± 5%
V
VCCV > VFLT terminates charge, indicates fault
VMIN
Minimum battery
voltage
0.40
± 5%
V
VOCV < VMIN inhibits charge
VCE
Charge enable
1.40
± 5%
V
VOCV < VCE on all cells re-initiates
charge
Note:
Each parameter above has a temperature coefficient associated with it. To determine the coefficient for
each parameter, use the following formula:
Tempco =
ParameterRating
* -0.5mV/°C
1.63
The tolerance for these temperature coefficients is 10%.
Timing
Symbol
(TA = 25°C)
Parameter
Minimum
Typical
Maximum
Unit
Notes
tP
Pulse period
-
10
-
ms
See Figure 2
tPW
Pulse width
-
7.5
-
ms
See Figure 2
8
bq2903
DC Electrical Characteristics (TA = TOPR)
Symbol
Parameter
Minimum
Typical
Maximum
Unit
Notes
VIH
Logic input high
VBAT1P - 0.1
-
VBAT1P
V
VSEL, NSEL
VIL
Logic input low
VSS
-
VSS + 0.1
V
VSEL, NSEL
VOL
-
-
1.0
V
Logic output low
DONE, CHG,
IOL = 5mA
-
-
0.4
V
IOL = 1.0mA, DRV
(Greater of
VBAT1P or
VDC) - 1.0
-
-
V
DRV, IOH = -1.0mA
5
-
-
mA
VOL = VSS + 1.0V,
DONE
1
-
-
mA
DRV = VSS + 1.0V
VOH
Gate drive output
IOL
Output current
CHG,
IDC
Supply current
-
35
250
µA
Outputs unloaded,
VDC = 10.0V
ISB1
Standby current
-
25
40
µA
VDC = 0, VOCV > VEDV,
BAT1P-3N
ISB2
End-of-discharge
standby current
-
-
1
µA
VDRV = 0V, VDC = 0
IL
Input leakage
-
-
±1
µA
NSEL
IOZ
Output leakage in
high-Z state
-
-
±5
µA
CHG, DONE
RDSON
Discharge on resistance
-
0.5
-
Ω
ILOAD
Discharge current without external N-FET
-
-
400
mA
No external FET; LRTN1
(pin 9) must be tied to
LRTN2 (pin 12).
IIL
Logic input low
-
-
70
µA
V= GND to GND + 0.5V,
VSEL
IIH
Logic input high
-70
-
-
µA
V = VDC -0.5 to VDC, VSEL
IIZ
Logic input float
-2
-
2
µA
VSEL
IDC
DC charging current
-
-
300
mA
VOP
Operating voltage
2.7
-
10
V
Note:
All voltages relative to VSS.
9
Discharge FETs;
VBAT1P = 2.7V, LRTN1 (pin 9)
must be tied to LRTN2 (pin 12)
bq2903
PN: 14-Pin DIP (0.300")
14-Pin PN (0.300" DIP)
Inches
Dimension
Millimeters
Min.
Max.
Min.
Max.
A
0.160
0.180
4.06
4.57
A1
0.015
0.040
0.38
1.02
B
0.015
0.022
0.38
0.56
B1
0.055
0.065
1.40
1.65
C
0.008
0.013
0.20
0.33
D
0.740
0.770
18.80
19.56
E
0.300
0.325
7.62
8.26
E1
0.230
0.280
5.84
7.11
e
0.300
0.370
7.62
9.40
G
0.090
0.110
2.29
2.79
L
0.115
0.150
2.92
3.81
S
0.070
0.090
1.78
2.29
SN: 14-Pin SN (0.150" SOIC)
14-Pin SN (0.150" SOIC)
Inches
Dimension
10
Millimeters
Min.
Max.
Min.
Max.
A
0.060
0.070
1.52
1.78
A1
0.004
0.010
0.10
0.25
B
0.013
0.020
0.33
0.51
C
0.007
0.010
0.18
0.25
D
0.335
0.350
8.51
8.89
E
0.150
0.160
3.81
4.06
e
0.045
0.055
1.14
1.40
H
0.225
0.245
5.72
6.22
L
0.015
0.035
0.38
0.89
bq2903
Data Sheet Revision History
Change No.
Page No.
1
1
Pin connections
LRTN1 (pin 9) was LRTN, LRTN2 (pin 12) was
LRTN
1
2
Functional block diagram
Updated block diagram
1
3
Pin description
Added descriptions for LRTN1 and LRTN2
1
5
DRV pin
Clarified LRTN1 and LRTN2 description
1
6
Application example
Corrected schematic
1
9
RDSON and ILOAD specification
Added notes on LRTN1 and LRTN2
2
7
TOPR
Deleted industrial temperature range
Notes:
Description
Nature of Change
Change 1 = May 1999 B changes from July 1996.
Change 2 = June 1999 C changes from May 1999 B
Ordering Information
bq2903
Package Option:
PN = 14-pin narrow plastic DIP
SN = 14-pin narrow SOIC
Device:
bq2903 Rechargeable Alkaline Charge/Discharge Controller IC
11
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