Sa57608 one-cell lithium-ion battery protection with over/undercharge and overcurrent protection

INTEGRATED CIRCUITS
SA57608
One-cell Lithium-ion battery protection
with over/undercharge and overcurrent
protection
Philips Semiconductors
Product data
One-cell Lithium-ion battery protection with
over/undercharge and overcurrent protection
GENERAL DESCRIPTION
The SA57608 is a single-cell Li-ion protection IC, and is an improved
version of the NE57600, with different pinout. Its over and under
voltage accuracies are trimmed to within ± 25 mV (5%) over the
entire battery pack operating temperature range. The SA57608 is
available in various over and undervoltage limits.
There is a discharge overcurrent protection circuit which can protectthe battery pack against an accidental short-circuit. The overchargetrip point has a time delay which can be programmed externally. It ispackaged in a space-saving SOT-26A and requires two externalN-channel MOSFETs and a minimum of passive parts.
FEATURES
APPLICATIONS
• Trimmed overvoltage trip point to within ±25 mV • Programmable overvoltage trip time delay • Trimmed undervoltage trip point to within ±25 mV • Very Low undervoltage quiescent sleep current 0.05 mA• Discharge overcurrent cutoff• Low operating current (10 mA)• Very small SOT-26A package SIMPLIFIED SYSTEM DIAGRAM
Figure 1.
Simplified system diagram.
One-cell Lithium-ion battery protection with over/undercharge and overcurrent protection ORDERING INFORMATION
TEMPERATURE
TYPE NUMBER
DESCRIPTION
SA57608XD
small outline plastic surface mount, 6-pin NOTE:
The device has six protection parameter options, indicated by the X on the order code, and defined in the following table.
TYPICAL PROTECTION PARAMETERS
Overcharge
Overcharge detection
Over-discharge
Overcurrent
Part Number
detection voltage (V)
hysteresis voltage (mV)
detection voltage (V)
detection voltage (mV)
Part number marking
PIN CONFIGURATION
Each device is marked with a four letter code. The first three lettersdesignate the product. The fourth letter, represented by ‘x’, is a date Part number
Figure 2.
Pin configuration.
PIN DESCRIPTION
DESCRIPTION
Discharge detection pin. This drives the gate of the discharge N-ch FET Monitor pin. Detects overcurrent and the presence of a charger.
Charge FET pin. This drives the gate of the charge control N-ch FET Charge Time Delay pin. The capacitor connected to this pin sets the delay Positive supply voltage input pin. Connect to positive terminal of the cell.
Ground pin. Connect to negative terminal of the cell MAXIMUM RATINGS
PARAMETER
One-cell Lithium-ion battery protection with over/undercharge and overcurrent protection ELECTRICAL CHARACTERISTICS
Characteristics measured with Tamb = 25 °C, unless otherwise specified.
PARAMETER
CONDITIONS
VCC – GND; Voltage defined as VDD to VM One-cell Lithium-ion battery protection with over/undercharge and overcurrent protection TECHNICAL DISCUSSION
as that provided by the SA57611. This provides two levels ofovercharge protection, with the primary protection of the external Lithium cell safety
charge control circuit and the backup protection from the battery Lithium-ion and lithium-polymer cells have a higher energy density pack’s protection circuit. The charge termination circuit will be set to than that of nickel-cadmium or nickel metal hydride cells and have a stop charging at a level around 50 mV less than the overvoltage much lighter weight. This makes the lithium cells attractive for use in threshold voltage of the battery pack’s own protection circuit.
portable products. However, lithium cells require a protection circuitwithin the battery pack because certain operating conditions can be Lithium cell operating characteristics
hazardous to the battery or the operator, if allowed to continue.
The internal resistance of lithium cells is in the 100 mΩ range,compared to the 5–20 mΩ of the nickel-based batteries. This makes Lithium cells have a porous carbon or graphite anode where lithium the Lithium-ion and polymer cells better for lower battery current ions can lodge themselves in the pores. The lithium ions are applications (less than 1 ampere) as found in cellular and wireless separated, which avoids the hazards of metallic lithium.
telephones, palmtop and laptop computers, etc.
If the lithium cell is allowed to become overcharged, metallic lithium The average operating voltage of a lithium-ion or polymer cell is plates out onto the surface of the anode and volatile gas is 3.6 V as compared to the 1.2 V of NiCd and NiMH cells. The typical generated within the cell. This creates a rapid-disassembly hazard
discharge curve for Lithium cell is shown in Figure 3.
(the battery ruptures). If the cell is allowed to over-discharge (Vcellless than approximately 2.3 V), then the copper metal from thecathode goes into the electrolyte solution. This shortens the cyclelife of the cell, but presents no safety hazard. If the cell experiences excessive charge or discharge currents, as happens if the wrong charger is used, or if the terminals short circuit, the internal series resistance of the cell creates heating and generates the volatile gas The protection circuit continuously monitors the cell voltage for an overcharged condition or an overdischarged condition. It also
continuously monitors the output for an overcurrent condition. If
any of these conditions are encountered, the protection circuit opens
a series MOSFET switch to terminate the abnormal condition. The
lithium cell protection circuit is placed within the battery pack very Charging control versus battery protection
The battery pack industry does not recommend using the pack’s internal protection circuit to end the charging process. The externalbattery charger should have a charge termination circuit in it, such Figure 3.
Lithium discharge curve.
One-cell Lithium-ion battery protection with over/undercharge and overcurrent protection Charging Lithium cells
SA57608 OPERATION
The lithium cells must be charged with a dedicated charging IC such The SA57608 continuously monitors the terminal voltage and battery as the NE57600. These dedicated charging ICs perform a pack current of a single Li-ion battery pack. Li-ion cells must be current-limited, constant-voltage charge, as shown in Figure 4.
maintained within a set of a very defined operating conditions tooperate safely and with with a long life. If the cell voltage exceeds The charger IC begins charging with a current that is typically the the cell’s full-charge voltage, the charge current is interrupted. If the rating of the cell (1C) or the milliampere rating of the cell. As the cell cell voltage falls below the overdischarge rating of the cell, the approaches its full-charge voltage rating (VOV), the current entering discharge current is interrupted. Also, whenever the discharge the cell decreases, and the charger IC provides a constant voltage.
When the charge current falls below a preset amount, 50 mA for current exceeds the threshold voltage across the RDS(on) of the example, the charge is discontinued.
two MOSFETs, the short-circuit current is interrupted.
If charging is begun below the overdischarged voltage rating of thecell, it is important to slowly raise the cell voltage up to this overdischarged voltage level. This is done by a reconditioning
charge. A small amount of current is provided to the cell (50 mA for
example), and the cell voltage is allowed a period of time to rise tothe overdischarged voltage. If the cell voltage recovers, then anormal charging sequence can begin. If the cell does not reach the overdischarged voltage level, then the cell is too damaged to charge To take advantage of the larger energy density of lithium cells it is important to allow enough time to completely charge the cell . When the charger switches from constant current to constant voltage charge (Point B, Figure 4) the cell only contains about 80 percent of its full capacity. When the cell is 100 mV less than its full rated charge voltage the capacity contained within the cell is 95 percent.
Hence, allowing the cell to slowly complete its charge takesadvantage of the larger capacity of the lithium cells.
Figure 5.
SA57608 block diagram.
Overvoltage condition
When the cell’s terminal voltage exceeds the value of VOV1,
measured from V
CC (pin 5) to GND (pin 6), the overvoltage time delay is initiated. After this time has elapsed, the gate of the chargeMOSFET (CF, pin 3) is driven LOW and the charge current isinterrupted. The terminal voltage of the cell may immediately fall due to the amount of the charge current times the series resistance ofthe Li-ion cell (Ichg × RESR). The charge MOSFET will not turn on again until the cell voltage has fallen below VOV(rel), or when a load is detected across the battery pack terminals. A load is detected
when the VM pin (pin 2) is drawn 0.7 V above the cell’s negative
The timing capacitor CDLY (pin 4) provides a time period between charge MOSFET is turned off. Its timing period is approximately: The variation in timing is approximately ±16 percent.
Figure 4.
Lithium Cell charging Curves
One-cell Lithium-ion battery protection with over/undercharge and overcurrent protection Undervoltage condition
If the battery pack is being charged, and the cell’s voltage exceeds When the cell voltage falls below the overdischarge threshold, the overvoltage threshold, then the charge MOSFET is turned OFF (FET towards the pack’s external terminal). The cell’s voltage must UV1), as measured between VCC (pin 5) and GND (pin 6), the gate of the discharge MOSFET (DF, pin 1) is brought LOW (OFF) after an fall lower than the overvoltage hysteresis voltage (VOV(Hyst)) before internal time delay. The SA57608 then assumes a sleep condition the charge MOSFET is again turned ON.
where its ICC assumes a very low state (ICC(SLP)) The gate is then If the battery pack is being discharged and the undervoltage brought HIGH (ON) when a charge current is detected, or when the threshold (VUV(Th)) is exceeded, then the discharge MOSFET is VM pin (pin 2) is brought to 0.7 V higher than the negative terminal turned OFF. It will not run back ON until a charger is applied to the of the cell (GND, pin 6) or when the cell voltage is higher than the pack’s external terminals and the cell’s voltage rises above the
undervoltage hysteresis voltage (VUV(Hyst)).
Discharge overcurrent condition
When the battery pack is being discharged, the load current causes If a discharge overcurrent condition is experienced as seen when a the voltage across the discharge MOSFET to increase past the short-circuit is experienced across the battery terminals, the overcurrent threshold voltage (VOC(TH)), then the discharge SA57608 views a high voltage across the MOSFET’s RDS(on). If this MOSFET is turned OFF after a fixed 7–18 ms delay. If short-circuit voltage exceeds the threshold voltage (VSC), the discharge gate is is placed across the pack’s terminals, then the discharge MOSFET brought to a LOW condition (OFF) after an internally set of time is turned OFF after a 100–300 µs time delay to avoid damaging the delays are exceeded. If the overcurrent is LOW, then the tSC1 is enacted. If the the overcurrent is higher, as experienced in a hardshort-circuit, the time delay is less than 400 ns. This prevents the The R-C filter on the VCC pin
MOSFETs from failing from an FBSOA failure.
One needs to place an R-C filters on the VCC pin. It is to primarilyshield the IC from electrostatic occurrences and spikes on the The gate of the discharge MOSFET is turned on again only when terminals of the battery pack. A secondary need is during the the voltage of the VM pin is allowed to fall within the 0.7 volts of the occurrence of a short-circuit across the battery pack terminals. Here, negative terminal of the cell (GND, Pin 6). If the short-circuit the Li-ion cell voltage could collapse and cause the IC to enter an persists, the gate of the discharge MOSFET is immediately brought unpowered state. The R-Cs then provide power during the first LOW (OFF) again until the short-circuit condition is again removed.
instant of the short circuit and allow the IC to turn OFF the dischargeMOSFET. The IC can then enter an unpowered state. Lastly, theR-C filter filters any noise voltage caused by noisy load current.
APPLICATION INFORMATION
The typical single-cell lithium-ion or polymer protection circuit based
The values shown in Figure 6 are good for these purposes.
upon the SA57608 is seen in Figure 6.
Selecting the Optimum MOSFETs:
For a single-cell battery pack, a logic-level MOSFET should be
used. These MOSFETs have turn-on thresholds of 0.9 V and are
considered full-ON at 4.5 V VGS. Some problem may be encountered in not having enough gate voltage to fully turn-ON the series MOSFETs over the battery pack’s entire operating voltage. If one deliberately selects an N-Channel MOSFET with a much The MOSFETs should have a voltage rating greater than 20 V and should have a high avalanche rating to survive any spikes generated across the battery pack terminals.
The current rating of the MOSFETs should be greater than fourtimes the maximum “C-rating” of the cells. The current rating, though, is more defined by the total series resistance of the battery pack. The total resistance of the battery pack is given by Equation 2.
The total pack resistance is typically determined by the system requirements. The total pack resistance directly determines howmuch voltage droop will occur during pulses in load current.
Figure 6.
Typical protection circuit
Another consideration is the forward-biased safe operating area ofthe MOSFET. During a short-circuit, the discharge current can easily The SA57608 drives the series N-Channel MOSFETs to states reach 10–15 times the “C-rating” of the cells. The MOSFET must determined by the cell’s voltage and the battery pack load current.
survive this current prior to the discharge MOSFET can be turned During normal periods of operation, both the discharge and charge OFF. So having an FBSOA envelope that exceeds 20 amperes for MOSFETs are in the ON state, thus allowing bidirectional current One-cell Lithium-ion battery protection with over/undercharge and overcurrent protection PACKING METHOD
TAPE DETAIL
One-cell Lithium-ion battery protection with over/undercharge and overcurrent protection SOT-26A: plastic small outline package; 6 leads; body width 1.8 mm
One-cell Lithium-ion battery protection with over/undercharge and overcurrent protection Data sheet status
Definitions
Data sheet status [1]
status [2]
This data sheet contains data from the objective specification for product development.
Philips Semiconductors reserves the right to change the specification in any manner without notice.
This data sheet contains data from the preliminary specification. Supplementary data will bepublished at a later date. Philips Semiconductors reserves the right to change the specificationwithout notice, in order to improve the design and supply the best possible product.
This data sheet contains data from the product specification. Philips Semiconductors reserves theright to make changes at any time in order to improve the design, manufacturing and supply.
Changes will be communicated according to the Customer Product/Process Change Notification(CPCN) procedure SNW-SQ-650A.
[1] Please consult the most recently issued data sheet before initiating or completing a design.
[2] The product status of the device(s) described in this data sheet may have changed since this data sheet was published. The latest information is available on the Internet at URL http://www.semiconductors.philips.com.
Definitions
Short-form specification — The data in a short-form specification is extracted from a full data sheet with the same type number and title. For
detailed information see the relevant data sheet or data handbook.
Limiting values definition — Limiting values given are in accordance with the Absolute Maximum Rating System (IEC 60134). Stress above one
or more of the limiting values may cause permanent damage to the device. These are stress ratings only and operation of the device at these or
at any other conditions above those given in the Characteristics sections of the specification is not implied. Exposure to limiting values for extended
periods may affect device reliability.
Application information — Applications that are described herein for any of these products are for illustrative purposes only. Philips
Semiconductors make no representation or warranty that such applications will be suitable for the specified use without further testing or
modification.
Disclaimers
Life support — These products are not designed for use in life support appliances, devices or systems where malfunction of these products can
reasonably be expected to result in personal injury. Philips Semiconductors customers using or selling these products for use in such applications
do so at their own risk and agree to fully indemnify Philips Semiconductors for any damages resulting from such application.
Right to make changes — Philips Semiconductors reserves the right to make changes, without notice, in the products, including circuits, standard
cells, and/or software, described or contained herein in order to improve design and/or performance. Philips Semiconductors assumes no
responsibility or liability for the use of any of these products, conveys no license or title under any patent, copyright, or mask work right to these
products, and makes no representations or warranties that these products are free from patent, copyright, or mask work right infringement, unless
otherwise specified.
Contact information
 Koninklijke Philips Electronics N.V. 2001 All rights reserved. Printed in U.S.A.
http://www.semiconductors.philips.com.
Fax: +31 40 27 24825
For sales offices addresses send e-mail to:
[email protected].

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