DALLAS DS2715Z

DS2715
NiMH Battery Pack Charge Controller
www.maxim-ic.com
DESCRIPTION
PIN CONFIGURATION
The DS2715 is well suited for cost-sensitive charger
applications where the battery is either internal or in a
unique battery pack. It has been optimized for safe
reliable charging of 1 to10 NiMH cells in series. The
DS2715 has an internal gain block that can be
selected as either a comparator or transconductance
amplifier for charge current regulation. The DS2715 is
configurable as a switched DC charger, a linear
current regulator, or a switchmode current source.
The DS2715 pre-conditions severely depleted cells
are pre-conditioned before entering full charge mode.
The DS2715 terminates full charge using the dT/dt
technique. It requires an external thermistor for dT/dt
detection. Over-temperature, under-temperature, and
over-voltage detection prevents charging under
unsafe environmental conditions. A user selectable
charge timer allows charge rates from 0.15C to 2C.
Fast-charge, top-off and charge done modes are
included for highly reliable, safe charging of NiMH
cells. Discharge mode allows the DS2715 to enter a
low power sleep state while the cell pack is being
discharged.
FEATURES
§
§
§
§
§
§
§
§
§
Charges 1 to 10 NiMH Cells
Fast Charges up to a 2C Rate
Pre-Charge and Top-Off Charge Modes Help Cell
Conditioning
Load Detection Allows the DS2715 to Enter Low
Power Sleep Mode (Less than 10µA) while the
Cell Pack is Discharged
dT/dt Charge Termination Eliminates Cell Charge
Stress
Monitors Voltage, Temperature, and Time for
Safety and Secondary Termination
Regulates Current through Either Linear Control
or Switch-Mode Control
LED Outputs Display Charge State
Small 16-Pin SO Package
CBIAS
CC1
VCH
CC2
VSS
LED1
LED1
VSS
LED2
LED2
VSS
CSOUT
CTG
VN1
1
16
VVP2
BATT
2
15
THM
VP1
3
14
RTHM2
T
4
13
VTHM1
DD
5
12
SNSVDD
6
11
SNS+
TMR
7
10
DIV
CTST
CTG
VN0
8
9
MODE
DMSEL
16 SO
See Table 1 for Ordering Information.
Table 1. ORDERING INFORMATION
PART
DS2715Z+
DS2715Z+T&R
MARKING
DS2715+
DS2715+
PIN-PACKAGE
16 SO
16 SO Tape-and-Reel
+ Denotes lead-free package.
OPERATIONAL DIAGRAM
CHARGE
SOURCE/LOAD
Vch
Vdd
Vbatt
Divide by n
DS2715
THM
+
GROUND
-
n Cells
Sense
APPLICATIONS
Portable DVD Players
Portable Television Sets
Handheld Gaming
Test Equipment
Handheld POS Terminals
Note: Some revisions of this device may incorporate deviations from published specifications known as errata. Multiple revisions of any device
may be simultaneously available through various sales channels. For information about device errata, click here: www.maxim-ic.com/errata.
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042605
DS2715: NiMH Cell Pack Charge Controller
ABSOLUTE MAXIMUM RATINGS*
Voltage on VDD and VCH Pins with Respect to VSS
Voltage on LED1 and LED2 Pins
Voltage on SNSVoltage on CBIAS
Voltage on all Other Pins
Continuous Sink Current VCH, LED1, and LED2
Operating Temperature Range
Storage Temperature Range
Soldering Temperature
-0.3V to +18V
-0.3V to +18V
-0.3V to +0.3V
-0.3V to 6V
-0.3V to VCbias
28mA
-20°C to +85°C
-55°C to +125°C
See IPC/JEDECJ-STD-020
*This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operation
sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability.
RECOMMENDED DC OPERATING CONDITIONS
PARAMETER
SYMBOL
CONDITIONS
(4.5V £ VDD £ 16.5V; TA = 0°C to +70°C.)
MIN
TYP
MAX
UNITS
Supply Voltage
VDD
(Note 1)
4.5
16.5
V
LED1, LED2 Voltage
VLED
(Note 1)
0.0
16.5
V
Mode Voltage
VMODE
(Note 1)
0.0
VCbias
V
VCH Voltage
VVCH
(Note 1)
0.0
16.5
V
CBIAS Capacitor Range
CCbias
.02
.15
µF
RRt
20
240
KΩ
RT Resistor Range
DC ELECTRICAL CHARACTERISTICS
PARAMETER
SYMBOL
(4.5V £ VDD £ 16.5V, TA = 0°C to +70°C, unless otherwise noted.)
CONDITIONS
MIN
TYP
MAX
UNITS
Operating Current
(Note 2)
Linear Mode, VDD = 16.5V
1.3
1.6
mA
IDDA
Comparator Mode,
VDD = 16.5V
150
250
µA
Idle Current
IDDS
VDD < VUVLO
10
µA
Discharge Current
IDDD
Discharge latch set (Note 2)
200
µA
4.0
V
UVLO Threshold
VUVLO
UVLO Hysteresis
VUVLO-HYS
VDD Falling
VCH Sink Current
IOL-Vch
VOL = 1.5V
20
mA
LED1, LED2 Sink Current
IOL-LED
VOL = 1.0V
20
mA
Pin inactive or Device Idle
-1
+1
µA
ILKG-THM
-1
+1
µA
ILKG-Vbatt
-50
+50
nA
4.3
V
500
uA
7.5
Ω
-1
Ω
-1
Leakage Current, VCH,
LED1, LED2
THM Pin Leakage
Current
VBATT Pin Leakage
Current
CBIAS Voltage
DIV Pin Load Current
Current Sense Amplifier
Gain
Current Sense
Comparator Gain
ILKG
VCbias
VDD Rising (Note 3)
3.8
3.9
35
0 < ICbias < 0.4ma
3.9
4.0
IDiv
GERR
100µA < I Vch < 20mA
GCOMP
(Note 7)
5
10
2 of 12
6.25
mV
DS2715: NiMH Cell Pack Charge Controller
AC ELECTRICAL CHARACTERISTICS
PARAMETER
SYMBOL
UVLO Debounce Time
tUVLO
Current Sense
Comparator Propagation
Delay
tCOMP
(4.5V £ VDD £ 16.5V, TA = 0°C to +70°C, unless otherwise noted.)
CONDITIONS
MIN
TYP
MAX
UNITS
10
µs
(Note 7)
250
ns
Discharge Detect
Propagation Delay
tDD
From detection of current
reversal
1
µs
Return To Normal
Function (Op-Amp or
Comparator Mode)
tRNF
Time from reset of
discharge latch
1
µs
RT Timing Accuracy
tRt
-10
+10
%
-10
+10
%
Internal Clock Accuracy
(Note 4)
tBASE
ELECTRICAL CHARACTERISTICS: CHARGING
PARAMETER
Fast Charge Comparator
Threshold
Fast Charge Comparator
Hysteresis
Top-off and Pre-Charge
Comparator Threshold
Top-off and Pre-Charge
Comparator Hysteresis
Discharge Latch Reset
Threshold
Discharge Latch Set
Threshold
Low Battery Detect
Threshold
SYMBOL
(4.5V £ VDD £ 16.5V, TA = 0°C to +70°C, unless otherwise noted.)
CONDITIONS
MIN
TYP
MAX
UNITS
VFC
Fast charge
-127
-121
-115
mV
VHYS-FC
Fast charge
-31
-28
-25
mV
VTO
Top-off and pre-charge
-38
-33
-28
mV
VHYS-TO
Top-off and pre-charge
-10
-8
-6
mV
-15
-10
-5
mV
5
10
15
mV
0.95
1.0
1.05
V
VDCHG-RST
VDCHG-SET
VLB
Reverse current through
sense resistor
From presence detect into
pre-charge
Cell Detect Threshold
VDET
1.50
1.55
1.60
V
No Cell Detect Threshold
VOPEN
1.60
1.65
1.70
V
Presence Detect
Threshold Hysteresis
VHYS-PD
90
100
110
mV
Minimum Charge Temp
VTHM-MIN
(Note 5, 6)
2.88
2.96
Maximum Charge Temp
VTHM-MAX
(Note 5, 6)
Over Temp
VTHM-STOP
(Note 5, 6)
2.92
0
1.32
45
1.16
50
V
ºC
V
ºC
V
ºC
dT/dt Detect
TTERM
0.425
0.5
0.575
ºC/min
dT/dt Blanking Time
tBLANK
3.85
4.3
4.75
Min
tFC
0.5
6
Hours
Fast Charge Timer
Range
Top-Off to Fast Charge
Duration Ratio
1.28
1.12
1:2
3 of 12
1.36
1.20
DS2715: NiMH Cell Pack Charge Controller
Note 1:
Note 2:
Note 3:
Note 4:
Note 5:
Note 6:
Note 7:
Voltages relative to VSS.
Does not include current through VCH, RT, and DIV pins.
Below this voltage no I/O pins are active.
Does not include tolerance of RT resistor.
VBIAS and resistor tolerances must be added to determine actual threshold.
Specified temperature thresholds are only valid if recommended thermistor types are used.
Specification is guaranteed by design.
DETAILED PIN DESCRIPTION
PIN
1
2
3
4
5
6
7
8
NAME
CBIAS
VCH
VSS
LED1
LED2
VSS
CTG
CTG
9
MODE
10
DIV
11
12
13
14
SNS+
SNSVDD
RT
15
THM
16
VBATT
DESCRIPTION
Bypass for Internal Voltage Regulator
Cell Stack Charge Control Output
Ground Reference and Chip Supply Return
Charging Indicator Output
Done Indicator Output
Ground Reference and Chip Supply Return
Connect to Ground
Connect to Ground
Mode Select. Connect to VSS for linear mode of operation or CBIAS for comparator
mode of operation.
Thermistor Divider. Stable output to form a resistor divider for measuring
temperature on THM.
Positive Current Sense. Connect to the pack side of the sense resistor.
Negative Current Sense. Connect to the cell stack side of the sense resistor.
Chip Supply Input: +4.0V to +5.5V range.
Failsafe Timeout. Timeout is selected by an external resistor from RT to VSS.
Thermistor Input. Connect to a thermistor located in the cell pack and a divider
resistor from the Div pin.
Battery Voltage Sense Input. Connect to a divider from the positive terminal of the
cell stack to measure the voltage of a single cell.
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DS2715: NiMH Cell Pack Charge Controller
Figure 1. BLOCK DIAGRAM
DS2715
Cbias
VDD
Pwr
HV
VUVLO
Disable during
discharge
Div
R
E
F
Regulator
Ref
LED2
A
D
C
Fast Charge
Exit on Full
Or Timeout
HV
THM
State Machine
Pre-Charge
Low Cells
HV
Th
UVLO
Oscillator
LED1
Vbatt
M
U
X
Disch. Detect
@-0.01V
+
-
Ref
SNS+
Mode
Pwr
25% Top-Off Charge
(Set by Timer)
Rt
Charge
Timer
AMP
or
Comp
Vsns
Ref
Rt start-up test
Rt
Ref
Done, Waiting for event
to start charging
121mV,
33mV,
10mV
R
+
+
SNS+
SNSVch
RS Latch
VSS
Latch is set until
Vsns negative WRT Vss
5 of 12
VSS
DS2715: NiMH Cell Pack Charge Controller
Figure 2. STATE DIAGRAM
DS2715 State Diagram
Discharge
Latch Set
VDD < V UVLO-VUVLO-HYS
(asynchronously from
anywhere)
Reset
Vch = Hi-Z
LED Hi-Z= No Battery
Vbatt>1.65
Vref = 0.033V
LED1 = Charging
30 min PCtimeout
Vbatt < 1V
Vbatt < 1.55V
AND
0C < T < 45C
Vbatt > 1.65V
OR
T < 0C
OR
T > 45C
Di
sc
ha
rg
e
Discharge
Latch
Still Set?
La
tc h
se
t
D
i sc
ha
rg
e
LEDs = OFF
Vch = LOW
se
t
PreCHG
AND
Discharge
Mode
Pwr=Low
4 Sec
Delay
ch
t < PCTimeout
la
t
Latch
Reset
Presence
TEST
V DD > V UVLO
Standby power
Check Rt, set mode
Vch = Hi-Z
LEDx = Hi-Z
t < Fast Timeout
t > PCTimeout
OR
T > 50
Vbatt>1V
AND
T < PCTimeout
AND
T < 50C
Fast
CHARGE
Overtemp, Overvoltage Detect
FAULT
Vch = Hi-Z
LED2 = Fault
Flash until Vbatt>1.65
Vbatt > 1.65
Vref = 0.121V
LED1 = Charging
Discharge latch set
T > 50
dT/dt OR
t > Fast Timeout
Vbatt > 1.65
or
Vbatt < 1.0
t < Topoff Timeout
Topoff
CHARGE
T > 50
OR
t > Topoff Timeout
Vref= 0033V
LED1 = Charging
Discharge latch set
Vbatt > 1.65
Discharge latch set
6 of 12
DONE
Vch = Hi-Z
LED2 = DONE
DS2715: NiMH Cell Pack Charge Controller
DETAILED DESCRIPTION
Charge Cycle Overview
The DS2715 regulates the charge of up to 10 NiMH cells in a series configuration. With the mode select pin the
DS2715 can be configured to regulate either as an error amplifier in linear mode or as a comparator in switched
mode. A charge cycle begins in one of two ways: with the application of power to the DS2715 with cell pack already
inserted or with the detection of cell insertion after power-up.
The charge cycle begins with pre-charge qualification to prevent fast charging of deeply depleted cells or charging
under extreme temperature conditions. Pre-charging is performed at a reduced rate until each cell reaches 1V. The
algorithm proceeds to a fast-charge phase. Fast charging continues as long as the cell pack temperature is less
than 50°C based on the THM voltage, the cell voltage as measured by the VBATT pin remains below 1.65V
indicating the cell pack is still present. Fast charging terminates by measuring the cell pack’s thermal rate of
change dT/dt. When the cell pack’s thermal rate of change exceeds 0.5°C per minute the DS2715 enters top-off.
The DS2715 has an internal charge timer as secondary overcharge protection if the charge is not terminated by the
dT/dt method. The charge termination timer duration is user selectable from 30 minutes up to 6 hours by an
external resistor on the RT pin.
The DS2715 remains in top-off for one-half of the period of the fast charge timer duration as selected by the
external resistor on RT. After the top-off charge timer expires, the done phase continues indefinitely until the cell
pack is removed from the charger or a load is attached. When a load attached to the cell pack, the DS2715
switches to discharge mode. All charge functions are disabled and the regulation FET is driven on to allow the cell
pack to discharge. Two LED indicators display the charge status to the user.
Undervoltage Lockout (Reset)
The UVLO circuit serves as a power-up and brownout detector by monitoring VDD to prevent charging until VDD
rises above VUVLO, or when VDD drops below VUVLO - VUVLO-HYS. If UVLO is active, charging is prevented, the state
machine is forced to the RESET state, and all charge timers are reset. A 10ms deglitch circuit provides noise
immunity. Once VDD reaches an acceptable operating voltage the DS2715 enters the PRESENCE state.
Presence
The DS2715 enters the PRESENCE state whenever VDD > VUVLO and VBATT > VOPEN indicating that the charge
source is present, but no cell is available to charge. The DS2715 will remain in the presence state until a cell is
inserted into the circuit causing the voltage on VBATT to fall below 1.55V (VDET) and the cell temperature is inside a
valid charging range between 0°C and 45°C (TTHM-MIN and TTHM-MAX). If both these conditions are met the DS2715
will enter pre-charge. If cells are inserted, but the temperature is outside the valid charging range the DS2715 will
remain in the PRESENCE state until the cell temperature falls within the valid charging range.
Pre-Charge
The DS2715 enters the PRE-CHARGE state when a valid cell voltage is applied to VBATT and the cell temperature
as measured by the DS2715 is within the valid charging range. Pre-charge has a 4 second filter to suppress noise
on VBATT caused by cell insertion. The DS2715 pre-charges the cell by regulating the voltage drop across the sense
resistor to -33mV (VTO) in linear mode or -29mV (VTO - 0.5 x VHYS-TO) in comparator mode. Pre-charge will last until
the cell voltage measured by VBATT exceeds 1.0V (VBATT > VLB) at which time the DS2715 will enter FAST CHARGE
state. If the cell voltage does not exceed VLB within 30 minutes or if the cell temperature exceeds 50°C at any time
during pre-charge, the DS2715 enters the FAULT state. If at any time during pre-charge the voltage on VBATT
exceeds 1.65V (VOPEN), the DS2715 determines that the cell pack has been removed and returns to the
PRESENCE state.
Fast Charge
In fast charge mode, the DS2715 regulates the voltage across the sense resistor to -121mV (VFC) in linear mode or
-107mV (VFC - 0.5 x VHYS-FC) in comparator mode. LED1 indicates the cell pack is being charged. During fast
charge the DS2715 constantly measures the rate of change of the cell temperature (dT/dt). When the cell pack’s
dT/dt exceeds 0.5°C per minute (TTERM) the DS2715 enters the TOP-OFF state. The DS2715 ignores changes in
the cell temperature caused by charge initiation for the first 4.3 minutes (tBLANK). As secondary overcharge
protection, the DS2715 will terminate fast charge and enter top-off based on a time delay set by the external
resistor on the RT pin. This resistor value can set the secondary charge termination delay to anywhere from 30
minutes up to 6 hours. If the cell temperature exceeds 50°C at any time during fast charge, the DS2715 enters the
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DS2715: NiMH Cell Pack Charge Controller
DONE state. If at any time during fast charge the voltage on VBATT exceeds 1.65V (VOPEN), the DS2715 determines
that the cell pack has been removed and returns to the PRESENCE state.
Top-Off
In top-off mode, the DS2715 regulates the voltage across the sense resistor to -33mV (VTO) in linear mode or 29mV (VTO - 0.5 x VHYS-TO) in comparator mode. LED1 indicates the cell pack is being charged. The charge timer is
reset and restarted with a time-out period of one half the fast-charge duration. When the charge timer expires or if
the measured temperature exceeds 50°C, the charger enters the DONE state.
DONE/Maintenance
The DS2715 enters the DONE state whenever the charge completes normally or if the measured cell temperature
exceeds 50°C during the charge. While in the done state VCH is driven to high impedance to prevent further
charging of the cell pack and LED is driven on to indicate charge completion. A maintenance charge can be
applied to the cells by providing a resistive path from the cell pack to the charge source bypassing the regulator.
See the example circuit in Figure 3. The DS2715 remains in DONE until a cell voltage greater than 1.65V (VOPEN) is
detected on VBATT indicating the cell pack has been removed. The DS2715 then enters the PRESENCE state and
waits for the next cell insertion.
FAULT
The DS2715 enters FAULT if pre-charge is unable to charge the cell above 1.0V (VLB) before the 30 minute precharge timeout of if the cell temperature exceeds 50°C during pre-charge. In the fault state VCH is driven to high
impedance and LED2 blinks to indicate the fault condition. The DS2715 remains in FAULT until a cell voltage
greater than 1.65V (VOPEN) is detected on VBATT indicating the cell pack has been removed. The DS2715 then
enters the PRESENCE state and waits for the next cell insertion.
Discharge Mode
When the DS2715 detects a discharge current voltage drop of VDCHG-SET or greater across the sense resistor,
charging is terminated and the DS2715 enters the DISCHARGE state. While in this mode, voltage sensing, thermal
sensing, and LED outputs are disabled. The VCH pin is driven low to allow the pack to be discharged. Current drain
of the DS2715 drops to IDDD. The DS2715 remains in discharge mode until a charge current of at least VDCHG-RST is
detected. When this occurs the DS2715 enters the presence detect state to begin a new charge cycle.
Application Circuit
Figure 3 shows a typical application circuit for charging a 3-cell stack. The mode pin is tied to VSS for linear
operation. A 75mΩ sense resistor (R10) sets the charge current at 1.6A. The DS2715 regulates the current through
Q1. 68kΩ on RT (R6) sets the fast charge timeout to 102 minutes. R5 and R8 form a 1:3 voltage divider to allow
VBATT to measure the voltage of a single cell. The charge source is isolated with diode CR1 to prevent discharge
through the source connection. R1 and CR2 form a maintenance charge path to supply the cell pack with ~40mA
constant current after the charge completes. Lastly VR1 and R4 create a current leakage path to bias the regulator
circuit and prevent an in-rush current spike when the cell stack is connected to the powered circuit.
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DS2715: NiMH Cell Pack Charge Controller
Figure 3. TYPICAL APPLICATION CIRCUIT FOR A 3-CELL STACK
LOAD
CR2
R1
LED2 LED1
CR1
+9VDC
C1 10 uF
R2 470
R3 1K
R12 1K
C3
10 uF
R9
47
100
Q1
IRF9Z24
LED1 Vch
LED2
Vbatt
C4
0.1 uF
Div
Mode
SNS+
Cbias
5.6V
R4
100
U1
DS2715
Vdd
Rt
R6 68K
VR1
R7
10K
R5
200K
R8
100K
VSS
THM
VSS CTG SNSR11
47
R10 0.075
9 of 12
THM1
10K
C2
47 uF
DS2715: NiMH Cell Pack Charge Controller
CURRENT REGULATION
Three basic modes of charging operation are supported by the DS2715: Offline switching through an optocoupler,
linear regulation, and DC input switched mode. The DC Switched method requires a currrent-limited power source.
Mode of operation is selected through the Mode pin. Connecting the Mode pin to VSS configures the analog block
as a transconductance amplifier for linear mode of operation. Connecting the Mode pin to the Cbias pin configures
the DS2715 as a comparator for switched mode of operation.
Current-Sense Amplifier Mode
An error amplifier block provides several options to regulate the charge current. The 20mA open-drain output can
drive a PMOS or PNP pass element for linear regulation, or the output can drive an optocoupler for isolated
feedback to a primary-side PWM controller. The SNS- pin is a remote-sense return and should be connected to the
grounded side of the sense resistor using a separate, insulated conductor. During fast charge, an error signal
between the current-sense signal (across the sense resistor) and the internal reference is produced so the voltage
across the sense resistor is maintained at VFC in a closed-loop circuit. During top-off the voltage across the sense
resistor is maintained at VTO.
Current-Sense Comparator Mode
The comparator in the DS2715 switches between ON and OFF and is capable of driving a PNP bipolar or a PMOS
transistor, enabling the use of a switched-mode power stage. Hysteresis on the comparator input provides noise
rejection. In a closed-loop regulation circuit, the comparator regulates voltage across the sense resistor to a DC
average of:
VRSNS = VFC - 0.5 x VHYS-FC = -0.107V during fast charge
VRSNS = VTO - 0.5 x VHYS-TO = -0.029V during top-off
Charge Rate Selection
The charge rate is determined by an external sense resistor connected between the SNS+ and SNS- pins. The
DS2715 will regulate the charge current to maintain a voltage drop of VFC (VFC - 0.5 x VHYS-FC in comparator mode)
across the sense resistor during fast charge. The sense resistor can therefore be selected by:
Linear Mode:
R = VFC / Desired Fast Charge Current
Comparator Mode:
R = (VFC - 0.5 x VHYS-FC) / Desired Fast Charge Current
Charge Time and Top-Off Time Selection
Pre-charge has a fixed 30 minute limit generated by an internal oscillator. Charge time and top-off time are
controlled by an external resistor from the RT pin to VSS. Resistors can be selected to support fast-charge time-out
periods of 0.5 to 6 hours and top-off charge time-out periods of 0.25 to 3 hours. If the timer expires in fast-charge,
the timer count is reset and charging proceeds to the top-off charge phase. The top-off time-out period is half of the
fast charge time-out period. If the timer expires in top-off, the DS2715 enters the DONE state. The programmed
charge time approximately follows the equation:
t = 1.5 x R / 1000
(time in minutes)
10 of 12
DS2715: NiMH Cell Pack Charge Controller
TEMPERATURE SENSE
Accurate temperature sensing is needed to determine end of charge by dT/dt and to detect over temperature fault
conditions. Connecting an external 10kW NTC thermistor between THM and VSS, and a 10kW bias resistor between
Div and THM allows the DS2715 to sense temperature. To sense the temperature of the cell pack, locate the
thermistor close to the body of a cell, preferably in the middle of the cell pack. Several recommended 10kW
thermistors are shown in Table 2.
Min, Max Temperature Compare
The voltage thresholds of the THM input (VTHM-MIN, VTHM-MAX) are set to allow charging to start if 0°C < TCELL < 45°C
when using the recommended 10kW bias and 10kW thermistor. If pre-charging is in progress, and the voltage on
THM reaches VTHM-STOP, pre-charging stops and a fault condition is generated. If the voltage on THM reaches VTHMSTOP during fast charge or top-off, charging stops and the DS2715 enters the DONE state. Fast charging will
complete normally and top-off will begin if the voltage change on THM exceeds TTERM ºC per minute (dT/dt charge
termination).
Table 2. THM1, THM2 THRESHOLDS
TEMPERATURE (°C)
THM
THRESHOLD
RATIO
OF VCBIAS
THERMISTOR
RESISTANCE
(W)
Semitec
103AT-2
MIN
MAX
STOP
0.73
0.33
0.29
27.04k
4.925k
4.085k
0°C
45°C
50°C
Fenwal
197-103LAG-A01
173-103LAF-301
4°C
42°C
47°C
Used with a 10k resistor the Semitec 103AT-2 provides about 0.9% full scale per degree sensitivity. This linearity is
shown in the curve in Figure 4. The left axis is the ratio of the sensed voltage to the divider’s input voltage (VCbias).
Figure 4. RATIO OF THM PIN TO CBIAS PIN OVER TEMPERATURE
Divider Output
0.75
0.70
Voltage Ratio
0.65
0.60
0.55
0.50
0.45
0.40
0.35
0.30
0
10
20
30
Degrees Centigrade
11 of 12
40
50
DS2715: NiMH Cell Pack Charge Controller
LED1 and LED2 Outputs
Open-drain outputs LED1 and LED2 pull low to indicate charge status. When inactive, the outputs are high
impedance. LED1 displays the state of charge and LED2 displays the charge results. The LED1 pin drives low in a
1Hz, 50% duty cycle “blink” pattern to indicate cells are charging. LED2 drives low with 100% duty cycle to signal a
successful charge completion or blinks at 4Hz, 50% duty cycle to signal a charging fault has occurred. Both LED
pins remain in a high-impedance state when no cells are present or the discharge latch is set. LED pins can be tied
together if only one LED display is desired. Table 3 summarizes the LED operation for each charge condition.
Table 3. LED DISPLAY PATTERNS BASED ON CHARGE STATE
CHARGE STATE
NO
BATTERY
CHARGING
DONE
FAULT
DISCHARGE
MODE
LED1
High-Z
Blinks at 1HZ,
50% duty cycle
High-Z
High-Z
High-Z
LED2
High-Z
High-Z
Low
Blinks at 4Hz,
50% duty cycle
High-Z
LED1 +
LED2
High-Z
Blinks at 1HZ,
50% duty cycle
Low
Blinks at 4Hz,
50% duty cycle
High-Z
High-Z = High Impedance
Package Information
For the latest package outline information, go to www.maxim-ic.com/DallasPackInfo.
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