DS2720
Efficient, Addressable Single-Cell
Rechargeable Lithium Protection IC
www.maxim-ic.com
FEATURES
§
Rechargeable Lithium-Ion (Li+) Safety
Circuit
- Overvoltage Protection
- Overcurrent/Short-Circuit Protection
- Undervoltage Protection
- Overtemperature Protection
Controls High-Side N-Channel Power
MOSFETs Driven from 9V Charge Pump
System Power Management and Control
Feature Support
Eight Bytes of Lockable EEPROM
Dallas 1-Wire
®
Interface with Unique 64-Bit
Device Address
8-Pin
mSOP
Package
Low Power Consumption:
- Active Current: 12.5mA typ
- Sleep Current:
1.5mA typ
PIN CONFIGURATION
PLS
PS
DQ
V
SS
1
2
3
4
8
7
6
5
CP
DC
CC
V
DD
§
§
§
§
§
§
DS2720U
mSOP
PIN DESCRIPTION
PLS -
PS
-
DQ -
V
SS
-
V
DD
-
CP -
CC -
DC -
Battery-Pack Positive Terminal Input
Power-Switch Sense Input
Data Input/Output
Device Ground
Power-Supply Input
Reservoir Capacitor
Charge Control Output
Discharge Control Output
DESCRIPTION
The DS2720 single-cell rechargeable Li+ protection IC provides electronic safety functions required for
rechargeable Li+ applications including protecting the battery during charge, protection of the circuit
from damage during periods of excess current flow and maximization of battery life by limiting the level
of cell depletion. Protection is facilitated by electronically disconnecting the charge and discharge
conduction path with switching devices such as low-cost N-channel power MOSFETs.
Since the DS2720 provides high-side drive to external N-channel protection MOSFETs from a 9V charge
pump, superior on-resistance performance results compared to common low-side protector circuits using
the same FETs. The FET on-resistance actually decreases as the battery discharges.
Adding to the uniqueness of the DS2720 is the ability of the system to control the FETs from either the
data interface or a dedicated input thereby eliminating the power-switch control redundancy of
rechargeable Li+ battery systems.
Through its 1-Wire interface, the DS2720 gives the host system read/write access to status and control
registers, instrumentation registers, and general-purpose data storage. Each device has a factory-
programmed 64-bit net address that allows it to be individually addressed by the host system.
1-Wire is a registered trademark of Dallas Semiconductor.
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112602
DS2720
Two types of user-memory are provided on the DS2720 for battery information storage: EEPROM and
lockable EEPROM. EEPROM memory saves important battery data in true nonvolatile (NV) memory
that is unaffected by severe battery depletion, accidental shorts, or ESD events. Lockable EEPROM
becomes ROM when locked to provide additional security for unchanging battery data.
ORDERING INFORMATION
PART
DS2720AU
DS2720AU/T&R
DS2720BU
DS2720BU/T&R
DS2720CU
DS2720CU/T&R
DESCRIPTION
DS2720 in 8-Lead
m
SOP in Bulk with V
OVA
= 4.275V
DS2720 in 8-Lead
m
SOP in Tape-and-Reel with V
OVA
= 4.275V
DS2720 in 8-Lead
m
SOP in Bulk with V
OVB
= 4.35V
DS2720 in 8-Lead
m
SOP in Tape-and-Reel with V
OVB
= 4.35V
DS2720 in 8-Lead
m
SOP in Bulk with V
OVC
= 4.30V
DS2720 in 8-Lead
m
SOP in Tape-and-Reel with V
OVC
= 4.30V
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DS2720
Figure 1. BLOCK DIAGRAM
DQ
PS
1-WIRE INTERFACE
AND CONTROL
TEMP SENSOR
(Tdevice)
64-BIT ROM
LOCKABLE EEPROM
STATUS/CONTROL
+
T
MAX
+
OUTPUT BUFFER
CP
CC
V
DD
V
OV
V
CE
+
+
DELAY
t
OVD
S
R
Q
+ +
Q
V
UV
V
SS
(1)
+ +
DELAY
t
UVD
L
O
G
I
C
S
R
DC
+
R
TST
(2)
V
OC
+
DELAY
t
OCD
+
PLS
V
CH
V
SC
+
+ +
DELAY
t
SCD
1) Normally open, closed to enable test current, I
TST
2) Normally open, closed to enable test current, I
TST
, and recovery charge
(See
Rechargeable Li+ Protection Circuitry
section for more information.)
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DS2720
Table 1. DETAILED PIN DESCRIPTION
SYMBOL
PLS
DESCRIPTION
Battery-Pack Positive Terminal Input.
The device monitors the state of the battery
pack’s positive terminal through this pin in order to detect events such as the attachment
of a charger or the removal of a short circuit. Connect PLS to the pack positive terminal
through a 100W resistor.
Power-Switch Sense Input.
The device wakes up from sleep mode when it senses the
closure of a switch to V
SS
on this pin.
PS
has a high-impedance internal pullup.
Data Input/Out.
1-Wire data line. Open-drain output driver. Connect this pin to the
DATA terminal of the battery pack. DQ has an internal 0.5mA pull-down.
Device Ground.
Connect directly to the negative terminal of the battery cell.
Power Supply Input.
Connect V
DD
to the positive terminal of the battery cell through a
decoupling network.
Charge Pump Output.
The internal charge pump regulates CP to 9V which supplies
the ON state drive to the protection FETs. Connect a 0.1mF reservoir capacitor from CP
to V
SS
.
Charge Protection Control Output.
Controls an external N-channel high-side charge
protection FET.
Discharge Protection Control Output.
Controls an external N-channel high-side
discharge protection FET.
PS
DQ
V
SS
V
DD
CP
CC
DC
Figure 2. APPLICATION EXAMPLE
102
102
PACK+
100
102
1k
1k
DS2720
330
PLS
PS
DQ
330
VSS
CP
DC
CC
VDD
104
104
10
PS
DATA
1-CELL Li+
PACK-
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DS2720
POWER MODES
The DS2720 has two power modes: active and sleep. While in active mode, the DS2720 continuously
performs safety monitoring. In sleep mode, the DS2720 ceases monitoring activities and drives both the
charge and discharge protection FETs to an “off state”. Upon returning to the active mode from the sleep
mode, DS2720 resumes safety monitoring and conditionally turns on the protection FETs.
Table 2. POWER MODE TRANSITION CONDITIONS
Active
®
Sleep
V
DD
< V
UV
Sleep
®
Active
(1)
PS
pulled to V
SS
or
V
PLS
> V
DD
+ V
CH
(1) DS2720 does not transition to Active Mode if V
DD
< V
SC
.
RECHARGEABLE Li+ PROTECTION CIRCUITRY
During active mode, the DS2720 constantly monitors cell voltage and voltage drop across the FETs to
protect the battery from overcharge (overvoltage), overdischarge (undervoltage), and excessive discharge
currents (overcurrent, short circuit). Conditions and DS2720 responses are described in the sections
below and summarized in Table 3 and Figure 3.
Table 3. PROTECTION CONDITIONS AND DS2720 RESPONSES
CONDITION
NAME
Overvoltage
Undervoltage
ACTIVATION
THRESHOLD
DELAY
RESPONSE
V
DD
> V
OV
V
SC
< V
DD
< V
UV
V
DD
< V
SC
or
(while in active
mode) V
DD
< V
CE
V
DD
- V
PLS
> V
OC
V
DD
< V
SC
T
device
> T
MAX
t
OCD
t
SCD
t
OVD(1)
t
UVD
CC = V
OLCC
CC = V
OLCC
DC = V
OLDC
R
TST
enabled
(2)
CC = V
OLCC
DC = V
OLCC
CC = V
OLCC
DC = V
OLDC
CC = V
OLCC
DC = V
OLDC
RELEASE
THRESHOLD
V
DD
< V
CE
or
V
DD
- V
PLS
> V
OC
V
PLS
> V
DD
+ V
CH
and
V
DD
> V
UV
(charger connected)
V
DD
³
V
CE
V
PLS
> V
DD
- V
OC(3)
V
PLS
> V
DD
- V
OC(3)
T
device
< T
MAX
Recovery Charge
Overcurrent
Short Circuit
Overtemperature
All voltages are with respect to V
SS
.
(1) During transition from sleep to active, t
OVD
= 0.
(2) Recovery charge current is limited by R
TST
and forward voltage of blocking diode, which prevents discharging through
R
TST
when recovery charge enabled.
(3) With test current I
TST
flowing from V
DD
to PLS (pullup on PLS).
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