Si9730
Vishay Siliconix
Dual-Cell Lithium Ion Battery Control IC
FEATURES
D
D
D
D
D
D
Over-Charge Protection
Over-Discharge Protection
Short Circuit Current Limiting
Battery Open-Circuit Center Tap Protection
Cell Voltage Balancing
Undervoltage Lockout
D
D
D
D
D
D
Individual Cell Voltage Monitoring
Low Operating Current (30 A) and Shutdown Current (1 A)
Internal N-Channel MOSFET Driver
High Noise Immunity
Accurate ("1.19%) Over-Charge Voltage Detection
Four Different Cell Types Covered
DESCRIPTION
The Si9730 monitors the charging and discharging of dual-cell
lithium-ion battery packs (carbon or coke chemistry) ensuring
that battery capacity is fully utilized while ensuring safe
operation.
The Si9730 provides protection against
overcharge, over-discharge, and short circuit conditions which
are hazardous to the battery and the environment.
overcharged, an internal cell balancing network “bleeds” off
current at 15 A until both cells are charged to the same
maximum level. Depending on the condition of each cell, the
Si9730 will switch two external source-connected n-channel
MOSFETs on or off to allow the cells to be charged or to
provide current to the load.
Battery voltages of each individual cell are monitored at the
center-tap connection by an internal A/D converter through the
VC pin. If one or both of the cells is determined to be
The Si9730 is available in an 8-pin SOIC package with an
operating temperature range of −25 to 85°C. The Si9730 is
available in both standard and lead (Pb)-free packages.
FUNCTIONAL BLOCK DIAGRAM AND PIN CONFIGURATION
C
VDD
+
VC1
Undervoltage
Lockout
Cell Balancing
Network
−
A/D
Converter
VC
Timer
CDELAY
Time Out
CLK
Control
Logic
OUT
+
VC2
−
Oscillator
SOUT
1.2 VREF
VSS
VSS
DCO
ILIMIT
IS
Document Number: 70658
S-40135—Rev. F, 16-Feb-04
VM
GS Generator
VM
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Si9730
Vishay Siliconix
ABSOLUTE MAXIMUM RATINGS
VM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VDD −15 V to VDD +15 V
Maximum Operating Junction Temperature . . . . . . . . . . . . . . . . . . . . . . 125_C
VDD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VSS −0.3 V to VSS +12 V
VC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VSS −0.3 V to VDD +0.3 V
Power Dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200 mW
IS
Thermal Impedance (PJA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80_C/W
(VSS w VM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . VM −0.3 V to VDD +0.3 V
(VM w VSS ) . . . . . . . . . . . . . . . . . . . . . . . . . . VSS −0.3 V to VDD +0.3 V
Storage Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . −55 to 150_C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of
the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating
conditions for extended periods may affect device reliability.
RECOMMENDED OPERATING RANGE
CVC t10 pF from VC toVDD andVSS , Total
CD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Open to 1.0 F
RIS series resistance to sense resistor . . . . . . . . . . . . . . . . . . . . . . . . t27 k
DCO Load Capacitance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 to 2000 pF
VDD to VSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 V
VDD to VM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 V
Operating Temperature Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . −25 to 85_C
SPECIFICATIONS
Limits
TA = −25 to 85_C
Symbol
Test Condition
Unless Otherwise Specified
IDD_C
VC1 = VC2 = 2.6 V, VDD − VM = 8.4 V
60
IDD
VC1 = VC2 = 4.05 V, VM = VSS
30
IDD_UVL
VM = VDD,VC1 = VC2 = 1.7 V
1
VUVL
Measured at VDD − VSS (Falling)
VC1 = VC2, VDD − VM = 5.5 V
VM Leakage Current
IVM_UVL
VC1 = VC2 = 1.7 V, VDD = VM
1
VM Operating Current
IVM
VC1 = VC2 = 2.6 V, VDD − VM = 8.4 V
30
VOH
IOH = −10 A, VC1 = VC2 = 3.3 V
VDD − VM = 6.6 V
Parameter
Mina
Typb
Maxa
Unit
Power Supply
Supply Current, Charging Operation
Supply Current,
Current Normal Operation
Undervoltage Lockout Threshold
3.5
3.7
4.0
A
V
A
Control Logic
DCO Output High Voltage
DCO Rise Time (10% to 80%)
tr
DCO Fall Time (80% to 10%)
tf
DCO Output Low Voltage
VOL
VDD − 0.1
V
7.5
VC1 = 2 V, VC2 = 2.4 V
VDD − VM = 8.4 V CL = 500 pF, DCO to VSS
IOL = 10 A
1
VM = VDD
VC1 = 2 V, VC2 = 2.4 V
VSS +0.4
VM= VSS
VC1 = VC2 = 4.4 V, IS = VDD
VM +0.52
s
V
Analog Section
Current-Limit Comparator Trip Point
VILIMIT
Current-Limit
Comparator Temperature Coefficient
dVILIMIT/dT
Current-Limit
Comparator Response Time
Current Limit Comparator
Input Bias Current
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2
VC1 = VC2 =4.05 V, VM = VSS + 0.25 V
IS Rising, TA = 25_C
25.5
28
32
0.18
tILIMIT
VC1 = VC2 =3.3 V, VM = VSS + 0.25 V
CL = 50 pF, DCO to VSS, See Figure 2
IIS
VC1 = VC2 =3.3 V, VDD = VM, VIS = VSS
%/_C
25
−125
mV
s
nA
Document Number: 70658
S-40135—Rev. F, 16-Feb-04
Si9730
Vishay Siliconix
SPECIFICATIONS
Limits
Parameter
Symbol
Test Condition
Unless Otherwise Specified
TA = −25 to 85_C
Mina
Typb
Maxa
4.20
4.25
Unit
Analog Section (cont’d)
VOC1
Cell 1
A
Suffix
VOC2
Cell 2
VOC1
Cell 1
B
Suffix
VOC2
Cell 2
Over-Charge
Detect Threshold (Rising)
VOC1
Cell 1
C
Suffix
VOC2
Cell 2
VOC1
Cell 1
D
Suffix
VOC2
Cell 2
Over-Charge Threshold Difference
VC2 = 4
4.05
05 V
VDD − VM = 8.6 V
VC1 = 4
4.05
05 V
VDD − VM = 8.6 V
VC2 = 4
4.05
05 V
VDD − VM = 8.6 V
VC1 = 4
4.05
05 V
VDD − VM = 8.6 V
VC2 = 4
4.05
05 V
VDD − VM = 8.6 V
VC1 = 4
4.05
05 V
VDD − VM = 8.6 V
VC2 = 4
4.05
05 V
VDD − VM = 8.6 V
VC1 = 4
4.05
05 V
VDD − VM = 8.6 V
TA = 25_C
4.15
TA = −25_C
4.1
TA = 85_C
4.1
TA = 25_C
4.15
TA = −25_C
4.1
TA = 85_C
4.1
TA = 25_C
4.2
TA = −25_C
4.15
TA = 85_C
4.15
TA = 25_C
4.2
TA = −25_C
4.15
TA = 85_C
4.15
TA = 25_C
4.18
TA = −25_C
4.12
TA = 85_C
4.12
TA = 25_C
4.18
TA = −25_C
4.12
TA = 85_C
4.12
TA = 25_C
4.28
TA = −25_C
4.22
TA = 85_C
4.22
TA = 25_C
4.28
TA = −25_C
4.22
4.40
TA = 85_C
4.22
4.35
4.27
4.27
4.20
4.25
4.27
4.27
4.25
4.30
4.32
4.32
4.25
4.30
4.32
4.32
4.22
4.25
4.30
4.25
4.22
4.25
4.30
4.25
4.32
4.35
4.40
4.35
4.32
4.35
20
ȧVOC1 − VOC2ȧ
Over-Charge Detect Threshold
Hysteresisc
Cell 1
VOC_H1
Cell 2
VOC_H2
Over-Discharge
Detect Threshold (Falling)
Cell 1
VODC1
VC2 = 2.6 V
2.1
2.2
2.3
Cell 2
VODC2
VC1= 2.6 V
2.1
2.2
2.3
Cell 1
IBAL1
VC1= 4.4 V, VC2= 4.05 V
9
15
30
Cell 2
IBAL2
VC2= 4.4 V, VC1= 4.05 V
9
15
30
Cell Balancing Current
VDD − VM = 8.6
86V
VM = VSS
VC2 = 4.05 V
10
VC1 = 4.05 V
10
Timer Charge Current
ITIMER(C)
VC2 = 3.3 V, VM = VSS
VC = VSS, TA = 25_C
Timer Discharge Current
ITIMER(D)
VC1 = VC2 = 3.3 V, VDD = VM
VDD − VC = 6.1 V, TA = 25_C
DL2 Time (Over-Charge)
tDL2OC
VC1 = 4.05 V, VDD − VM = 10 V
CD = 500 pF, TA = 25_C, See Figure 4
27
40
60
tDL2ODC
VC1 = 2.6 V, VM = VSS, CD = 500 pF
TA = 25_C, See Figure 5
27
40
60
IVMSHORT
VC1 = VC2 = 4.4 V, VM = VDD
30
VRTH
VC1 = VC2 = 4.05 V, See Figure 3
42
IVC
VC1 = VC2 = 4.05 V, VM = VDD
−2
tOCC
VC1 = VC2 = 4.4 V, CD = 500 pF
CL = 500 pF, DCO to VSS, See Figure 1
DL2 Time (Over-Discharge)
External Short Circuit Sense Current
Reset Threshold
Center Tap, Average Bias Current
Overcharge Load Detect
Power-Down Charger Detect Threshold
DCO Pulse Width
V
VCHPD
VC1 = 2 V, VC2 = 2.4 V, See Figure 6
tPW
CL = 500 pF, DCO to VSS, See Figure 7
−0.5
1.0
mV
V
A
mA
ms
60
300
A
100
mV
2
A
40
s
1.1
520
V
s
Notes
a. The algebraic convention whereby the most negative value is a minimum and the most positive a maximum.
b. Typical values are for DESIGN AID ONLY, not guaranteed nor subject to production testing.
c. Guaranteed by design, not subject to production test.
Document Number: 70658
S-40135—Rev. F, 16-Feb-04
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Si9730
Vishay Siliconix
TIMING DIAGRAMS
VM Waveform
200 mV
50%
tr x 100 nS
VSS
High
DCO Waveform
50%
VSS
tOCC
FIGURE 1. OC Load Detect
60 mV
IS Input
50%
VSS
VDD
VM Waveform
(After Short is
Removed)
tr x 100 nS
VDD
DCO Waveform
VRTH
VSS
tILIMIT
VDD
DCO Waveform
50%
VSS
VSS
VRTH = VM − VSS at DCO Transition
FIGURE 2. Current-Limit Comparator Response Time
4.4 V
VC2 Waveform
4.0 V
FIGURE 3. Reset Threshold
2.6 V
VC2 Waveform
2.0 V
t30
t30
C Waveform
C Waveform
VSS
1
32
t DL20C +
30
VSS
31
32
t DL20DC +
30
t 30
FIGURE 4. DL2 Time (Over-Charge)
VSS
VM Waveform
VCHPD
1
31
t 30
FIGURE 5. DL2 Time (Over-Discharge)
+
−
High
VM Waveform
VSS
^VRTH
DCO Waveform
Low
VCHPD = VSS − VM at DCO Transition
FIGURE 6. Power-Down Charger Detect Threshold
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VDD
DCO Waveform
tpw
VSS
FIGURE 7. Load Detection in Overcharge Mode
Document Number: 70658
S-40135—Rev. F, 16-Feb-04
Si9730
Vishay Siliconix
TYPICAL CHARACTERISTICS (25_C UNLESS NOTED)
100.0
DL2 Period (Over Charge) vs. Capacitance
100.0
DL2 Period (Over Discharge) vs. Capacitance
25_C
10.0
t DL20DC− Time (s)
t DL20C − Time (s)
25_C
TA = 85_C
−25_C
1.0
0.1
10.0
1.0
0.1
0.01
0.1
1
0.01
0.1
CD - Capacitance (F)
1.08
100
1.06
V RTH − Threshold (Normalized)
t ILIMIT ( S)
Reset Threshold vs. Temperature
120
80
60
40
20
0
20
40
60
80
1.04
1.02
1.00
0.98
0.96
0.94
−25
100
VIS − VSS (mV)
OCC (V)
Overcharge Threshold V
t OCC ( s)
5.0
4.5
4.0
3.5
125
150
VM − VSS (mV)
Document Number: 70658
S-40135—Rev. F, 16-Feb-04
50
75
100
4.2050
5.5
100
25
Overcharge Threshold
vs. Opposing Cell Voltage
6.0
75
0
Temperature (_C)
Load Detect Time vs. VM − VSS
50
1
CD - Capacitance (F)
Over Current Sense Voltage
vs. Current Sense Time
6.5
−25_C
TA = 85_C
175
200
4.2025
4.2000
4.1975
4.1950
2.5
3.0
3.5
4.0
Opposing Cell Voltage (V)
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Si9730
Vishay Siliconix
TYPICAL CHARACTERISTICS (25_C UNLESS NOTED)
1000.00
DCO Rise and Fall Times vs. Capacitance
100.00
Time ( s)
10.00
1.00
Rise
Fall
TA = 85_C
0.10
TA = −25_C
0.01
100
1000
10000
DCO Capacitance (pF))
PIN CONFIGURATION
SO-8
ORDERING INFORMATION
VM
1
8
DCO
NC
2
7
VSS
Si9730ABY-T1
Si9730ABY-T1—E3 (Lead Free)
Si9730BBY-T1
VDD
3
6
IS
CD
4
5
VC
Part Number
VOC1/2 Typ. Temp Range
Si9730BBY-T1—E3 (Lead Free)
Si9730CBY-T1
Top View
Si9730CBY-T1—E3 (Lead Free)
Si9730DBY-T1
Si9730DBY-T1—E3 (Lead Free)
4 20 V
4.20
4 25 V
4.25
−25_ to 85_C
4 22 V
4.22
4 32 V
4.32
PIN DESCRIPTION
Pin
Number
Symbol
1
VM
Negative Battery Pack Terminal - connection for external negative terminal of the battery pack.
2
NC
No Connection, do not connect this pin.
3
VDD
Dual Cell Positive Terminal - connection for positive terminal of dual series connected LiI+ cells.
4
CD
Delay Capacitor Connection - an external capactior connected across CD and Vss allows additional charge time (DL2, see
Detailed Description ) after a charge error has occured. Suggested capacitor values are shown in DL2 Period vs. Capacitance
Curves.
5
VC
Dual Cell Center Tap Connection - monitors individual battery voltages for overcharge and overdischarge errors.
6
Is
Current Sense Comparator Input - monitors load current for short circuit conditions . If VILIMIT is exceeded, then DCO opens the
low-side switch, disconnecting the cells.
7
VSS
Dual Cell Negative Terminal - connection for negative terminal of dual series connected LiI+ cells.
8
DCO
Low-side Switch Gate Driver Output - drives the gate of two external source connected n-channel MOSFETs. DCO swings
from VOL to VDD.
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Description
Document Number: 70658
S-40135—Rev. F, 16-Feb-04
Si9730
Vishay Siliconix
DETAILED DESCRIPTION
Overview
The purpose of the Si9730 is to safely and reliably control the
charging and discharging of a two-cell lithium-ion battery
(carbon or coke chemistry). It provides protection against all
possible fault conditions, including:
D external short circuits
D reversed charger
D overcharged cell or cells
D undervoltage
D battery open center-tap
General Concepts
The Si9730 operates by connecting or disconnecting the
negative terminal of the battery to the negative side of the load
and/or charger (see Figure 8); that is, it does ground side
switching. It is important to bear the distinction between these
two “grounds” in mind in order to understand the operation of
the Si9730. The switching is accomplished by controlling two
“back-to-back” MOSFETs: having the two MOSFETs in this
arrangement is mandatory to ensure that current cannot flow
in either direction when the MOSFETs are off. To turn the
switch on, the Si9730 applies a gate-source voltage to both
MOSFETs (from the DCO pin) that is high with respect to the
sources. The Si9730 DCO signal is referenced to the VM pin
while the battery is being charged, and to the Vss pin while the
battery is being discharged. The Si9730 causes the DCO to be
referenced to the lower of the two voltages. This prevents the
switch from turning on or off unintentionally.
The Si9730 is designed to operate only with a current-limited
lithium-ion battery charger. Specifically, the battery charger
must have an open-circuit voltage that does not exceed the
absolute maximum IC voltage, and it must have a limited
short-circuit current that does not exceed the allowed charging
current of the battery.
The following descriptions cover all the common operational
scenarios; additional information on unusual battery
conditions can be found in the state transition table.
(VOC ~ 4.2 V); and c) the center tap is connected to the VC pin.
When a charger is present in these conditions, the switch will
be on, charging the cells at the current limit of the charger.
Normal Discharging
The cells are in normal discharging conditions if a, b, and c
above are satisfied, and if in addition d) the load current is less
than the discharge current limit. With no charger present, the
switch will be on, discharging the cells and powering the load.
Overcharged Cell(s) Charging
The most destructive condition that a LiI+ cell can experience
is overcharging. If the cell becomes overcharged beyond its
recommended limits, it can become permanently disabled.
If one or both cells rise above the over-charge detect threshold
(VOC1 and VOC2), and a charger is present, the Si9730 will
open the switch (to prevent further charging) and begin
bleeding off charge (15-A typical) from the overcharged cell
or cells.
The details of this operation depend on the fact that the voltage
level of lithium-ion batteries drops for a short time after
charging ceases (due to momentary changes in battery
chemistry, ESR, etc.). Because of this recovery, the Si9730
allows the battery to continue charging for a short time (the
overcharge time, tDL2OC). This additional charge time only
occurs if the overcharge condition persists for more than
8 msec (two periods of an internal 4msec oscillator). TDL2OC
is determined by the capacitor attached to the CD pin, see
Figure 8.
Once the overcharge time has ended, the switch is opened,
preventing the battery from further overcharging. Now, the
Si9730 begins bleeding current off the overcharged cell or
cells (IBAL1 and IBAL2), as long as a charger is present.
Eventually, the cell(s) will return into their normal range, and
charging will begin, starting the whole cycle over again.
Overcharged Cell(s) Discharging
If one or more cells is overcharged, and a load is connected,
the switch is turned on, permitting the battery to power the
load.
Normal Charging
Over-Discharged Cell(s) Discharging
The cells are in normal charging conditions if a) both cells are
above the Over-Discharge Detect Threshold (VODC ~ 2.2 V);
b) both cells are under the Over-Charge Detect Threshold
Document Number: 70658
S-40135—Rev. F, 16-Feb-04
Repeated over-discharging of LiI+ cells can cause irreversible
reactions in the cells which lead to decreased cycle life.
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Si9730
Vishay Siliconix
To avoid this, if one or both cells becomes over-discharged
(VCELL < VODC) and no charger is present, the Si9730 opens
the switch to prevent further discharging, and goes into a
shutdown mode in which it draws minute power from the
battery (IDD_UVL < 1 A).
Over-Discharged Cell(s) Charging
If one or both cells is over-discharged, and a charger is
present, charging can begin, and so the Si9730 closes the
switch. However, removal of the charger in this condition could
potentially damage the battery if the removal is not recognized
and the cells are discharged. Since the voltage drop across
the switch is small, the Si9730 actually cycles the switch at a
7/8 duty cycle; during the 1/8 time when the switch is open, the
IC checks that the charger is still present.
Once both cells are back into the normal operating range,
normal charging resumes.
Undervoltage Charging
If for some reason the battery drops below about 3.7 V (VUVL),
there is insufficient voltage for the Si9730 to properly monitor
fault conditions. Of course, the switch is already open, since
VUVL < VODC x 2. However, when a charger is detected, the
Si9730 recovers and goes into an undervoltage mode. (A
charger is detected if the VS pin is higher than the VM pin by
at least VCHPD = 1.1 V, see Figure 6). In this undervoltage
mode, the switch is on at a 1/8 duty cycle, to limit the power
dissipation across the switch, and, again, to detect the
continuing presence of the charger.
Once the battery voltage is above VUVL, the charging
continues in the over-discharged state.
Output Short
If too much current is drawn from the battery due to a load
short, the switch must be opened quickly to prevent damage
to the battery. The Si9730 monitors the load current by looking
at the voltage across an external sense resistor (see Figure 8).
If the voltage across the sense resistor exceeds VILIMIT ~ 28
mV, the switch is opened. The Si9730 leaves the switch open
until the load is completely removed.
Of course, the IC must have some way of detecting that the
load has been removed. For this purpose, a small current
(IVMSHORT) passes through the Si9730, from pin VM to pin VSS
once the short is detected and the switch is turned off. The
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IVMSHORT current causes the voltage on the VM pin to equal the
voltage on the VDD pin while the short is present, or the voltage
on the VM pin to equal the voltage on the VSS pin if the short
is removed. If the short is not removed, IVMSHORT current will
continue to flow until the battery voltage becomes
overdischarged. Once the short is removed, the IC is allowed
to turn the switch back on.
The current limit threshold has a temperature coefficient of
0.18%/_C. This can partially compensate for a copper circuit
board trace being used as the sense resistor.
Open Center Tap
An open center tap is a mechanical failure of the battery pack
such that the Si9730’s VC pin is disconnected from the center
point of the two-cell battery. If this connection is open, the IC
opens the switch, as it cannot measure the cell voltages in this
condition. The switch is left open until connection is
re-established. If the battery is under-voltaged and the
charger is present in this case, the battery is allowed to charge
even with the center tap open. In this state, batteries are
almost impossible to damage by 1/8 duty cycle charging.
Once the battery voltage reaches the over-discharged
voltage, the switch is turned off.
State Transition Table
The number of different states of the Si9730 can seem
overwhelming at first. This state transition table will help to
organize thinking about the different operational conditions of
the IC, by listing each possible transition from one condition to
another.
Reading the table is straightforward. There are two cells
constituting the battery, one with its positive terminal
connected to VDD and its negative terminal connected to VC,
referred to as the high cell (see Figure 8); and one cell with its
positive terminal connected to VC and its negative terminal
connected to VSS, referred to as the low cell. Each cell can be
in one of three voltages:
D Over-discharge (ODC), where VCELL < VODC;
D Normal Operation (NO), where
VODC < VCELL < VOC;
or
D Overcharge (OC), where VOC < VCELL.
Document Number: 70658
S-40135—Rev. F, 16-Feb-04
Si9730
Vishay Siliconix
Additionally, the battery as a whole can be undervoltage (UV),
where VBATTERY < VUVL. Note that this final condition is not
necessarily (though normally) mutually exclusive with the
other cell conditions: if one cell were at 0V, the other cell could
be in NO, and the battery could still be in UV.
The charger can be either present (ON) or not present (OFF);
the “X” in the table means the condition is true regardless of the
state of the charger. The load current can be either 0, normal
(0 < ILOAD < IILIMIT) or a short (IILIMIT< ILOAD) where IILIMIT is
set by VILIMIT/RSENSE; the “X” in the table refers to a load
current that can be either 0 or normal. Finally, the switch can
be either ON, OFF, or cycling at either 1/8 or 7/8 duty cycle,
where the duty cycle refers to the portion of the period when
the switch is on; the notation On−>On simply means that the
switch does not change state, it remains on; the notation −>Off
means that the switch turns off regardless of its previous state.
STATE TRANSITION TABLE
High-Cell Voltage
Low-Cell Voltage
Charger On/Off
Load Current
Switch State
NO
NO
Off>On
X
On−>On
NO−>OC
NO
Off
0
On−>Off
NO
NO−>OC
Off
0
On−>Off
NO−>OC
NO
Off
Normal
Cycles at very high duty cycle
NO
NO−>OC
Off
Normal
Cycles at very high duty cycle
OC
NO
Off−>On
X
Off−>Off
NO
OC
Off−>On
X
Off−>Off
OC
OC
Off−>On
X
Off−>Off
NO
NO
Off
Normal−>Short
On−>Off
OC
NO
Off
Normal−>Short
On−>Off
NO
OC
Off
Normal−>Short
On−>Off
NO−>ODC
NO
Off
0
On−>Off
NO
NO−>ODC
Off
0
On−>Off
NO−>ODC
NO
Off
Normal
On−>Off
NO
NO−>ODC
Off
Normal
On−>Off
ODC
NO
Off−>On
X
Off−>Cycle at 7/8 duty cycle
NO
ODC
Off−>On
X
Off−>Cycle at 7/8 duty cycle
ODC
ODC
Off−>On
X
Off−>Cycle at 7/8 duty cycle
Off−>On
X
Off−>Cycle at 1/8 duty cycle
UV
NO−>ODC
OC
Off
0
Cycle−>Off
OC
NO−>OC
Off
0
Off
NO
NO
V<0
X
Off
On
Center Tap−>Open
Cycle at 1/8 duty cycle
UV
ODC
ODC
X
Center Tap−>Open
−.>Off
NO
ODC
X
Center Tap−>Open
−.>Off
ODC
NO
X
Center Tap−>Open
−.>Off
NO
NO
X
Center Tap−>Open
−.>Off
OC
OC
X
Center Tap−>Open
−.>Off
Document Number: 70658
S-40135—Rev. F, 16-Feb-04
www.vishay.com
9
Si9730
Vishay Siliconix
APPLICATION CIRCUIT
10 F
Si9730
100 VDD
+
C
4
3
CD
Cell 1
VC1
C1
0.1 F
100 VC
5
Cell 2
VC2
A/D
Converter
Timer
CDELAY
Time Out
CLK
Control
Logic
OUT
Load
Chgr.
8.4 V
1A
Oscillator
100 Current
Sense
14 M
Undervoltage
Lockout
Cell Balancing
Network
VSS
7
SOUT
1.2 VREF
VSS
GS Gen.
Comparator
C2
0.47 F
VM
ILIMIT
Filter
IS
6
8
RIS
47 k
1
VM
DCO
Si9936DY
FIGURE 8. Typical 2 -Cell Circuit
General Considerations
Figure 8 shows a typical application of the Si9730, controlling
a 2-cell lithium-ion battery (carbon or coke chemistry).
Specifics of the selection of MOSFETs, current sensing
resistor, and output capacitor are detailed below. In addition,
there are several typical features of this circuit to be observed.
First, each connection from a cell to the IC has a 100- resistor
in series with it. The purpose of the resistor is to ensure that in
the unlikely event of the IC shorting, the cells themselves will
not see a short. The maximum size of this resistance is set by
the current drain of the IC; for example, the VDD pin draws a
maximum of 60 A, which will drop V = 60 A * 100 = 6 mV
www.vishay.com
10
across the resistor. This drop constitutes an error in the
measured cell voltage, and so the resistor must be small
enough that the error voltage is acceptable.
A second typical feature demonstrated in Figure 8 is the
current sense filter formed by RIS and C2. This provides a
noise filter, to prevent the Si9730 from opening the connection
to the battery if there is noise on its current sense pin. It also
causes a delay in the response of the IC to a genuine
overcurrent, the amount of the delay being inversely
proportional to the amount of overcurrent, since the Is pin
senses a voltage. Increasing this filter’s time constant could be
used to allow short-time surges of current out of the battery
without compromising its ability to protect the battery.
Document Number: 70658
S-40135—Rev. F, 16-Feb-04
Si9730
Vishay Siliconix
Output Capacitor
Depending on the MOSFET selected, the Si9730 can open the
switch quite rapidly, in a matter of a few microseconds.
However, the various monitoring operations take 10-100 times
longer than this, and the basic period of the Si9730’s oscillator
is 4 msec. In order to prevent false readings by the Si9730, it
is necessary to attach a capacitor across the output of the
battery charger/load (this is not in parallel with the battery,
because of the switch). A 10-F capacitor is recommended for
this purpose; see Figure 8.
Selecting a Current Sense Resistor
The current sense resistor should be selected based on the
maximum current the battery can source or charge at; above
this current, the Si9730 will open the switch, disconnecting the
battery from its load or charger.
Rsense = VILIMIT/IILIMIT 28 mV/IILIMIT
Of course, the resistor must be rated to take the power
dissipated in it as well:
PRSENSE = IILIMIT* VILIMIT 28 mV * IILIMIT
For example, suppose that the maximum current the battery
will see is 1.8 A. Then, ILIMIT might be chosen to be 2 A. We
would then select a resistor of
RSENSE = 28 mV/2 A = 14 m.
The power dissipation in this resistor is
PRSENSE = 28 mV * 2 A = 56 mW
For example, to get a 14-m. resistor, we need length/width
= 28; with a trace width of 0.01”, the length of the trace should
be 0.28”.
MOSFET Selection
Two MOSFETs in series, with their sources and gates
connected together, are used as the switch. This prevents
current from flowing in either direction when the gate is low; if
only one MOSFET were used, the body diode could conduct
current in the opposing direction.
LITTLE FOOT MOSFETs are recommended for this
application, because of their size, performance and cost
benefits. SO-8 and TSSOP-8 MOSFETs allow for space
efficient designs with performance equal to or better than their
DPAK and TO-220 predecessors. Further, their availability
from multiple sources permits a cost effective solution.
There are two important parameters to consider in MOSFET
selection: gate threshold voltage; and on-resistance, which
determines power dissipation.
Even when the DCO pin of the Si9730 is low, the specification
allows its value to be as high as 0.4 V. If this voltage were close
to the gate threshold voltage, leakage current through the
MOSFETs could be hundreds of microamps, which would
result in the battery quickly becoming discharged. To ensure
that leakage is minimized, n-channel MOSFETs with a
minimum gate threshold voltage of 0.8 V should be chosen.
On resistance of the MOSFETs needs to be selected to limit
power dissipation into the MOSFETs’ package. For example,
a dual MOSFET SO-8 package is rated at 2 W, and a dual
MOSFET TSSOP-8 package is rated at 1 W (both at 25_C; if
the ambient temperature is higher, the allowable power
dissipation in these packages is less). For example, if the
maximum current is 2 A, and a dual MOSFET SO-8 package
is being used, the maximum on-resistance of the two
MOSFETs in series must not exceed
and so a 100mW surface mount resistor would be suitable.
Another possibility is to use a thin copper trace as the sense
resistor. The copper has a temperature coefficient of
0.39%/_C, but this is partially compensated for by the
temperature coefficient of the current limit comparator in the
Si9730, which is 0.18%/_C. A simple formula for selecting a
trace to act as a current sensor is:
R + 0.5 m
Document Number: 70658
S-40135—Rev. F, 16-Feb-04
length ǒ
1 oz. CopperǓ
width
1 W = (2 A)2 * RON
or RON = 0.25 ; each MOSFET can be allotted half of this,
RON = 125 m. Account must also be taken of the fact that
MOSFETs’ on-resistance is a function of temperature; a
conservative approach would give a discount of 1/3, RON =
125 m m per MOSFET.
A list of recommended MOSFETs, which Vishay Silicoix
supplies, follows.
www.vishay.com
11
Si9730
Vishay Siliconix
N-CHANNEL MOSFET SELECTION GUIDE
Recommended
Application Current
(A) @ 25_C
Part
Number
rDS (on)() @
VGS = 10 V
rDS(on)() @
VGS = 4.5 V
ID(A)
VGS(th) (V)
Config.
Package
Si4410DY
0.0135
0.020
10
1.0
Single
SO-8
9
Si4412DY
0.028
0.042
7
1.0
Single
SO-8
6.3
Si6434DQ
0.028
0.042
5.6
1.0
Single
TSSOP-8
4.9
Si4936DY
0.037
0.055
5.8
1.0
Dual
SO-8
3.5
Si9936DY
0.050
0.080
5
1.0
Dual
SO-8
2.9
Si6954DQ
0.065
0.095
3.9
1.0
Dual
TSSOP-8
1.9
V+
100 Si9730
1 VM
DCO
2 NC
3 VDD
100 8
VSS 7
4 CD
IS 6
VC
5
10 nF
100 +
15 M
470 nF
47 k
100 F
Si9936
100 Si9730
1 VM
DCO
2 NC
100 100 F
VSS 7
3 VDD
4 CD
+
8
IS 6
VC
5
470 nF
10 nF
100 47 k
15 M
V−
Si9936
FIGURE 9.
www.vishay.com
12
4-Cell Battery Circuit
Document Number: 70658
S-40135—Rev. F, 16-Feb-04
Si9730
Vishay Siliconix
resistor. A tradeoff can be made here between the power rating
of the zener, which can be decreased by increasing the
resistor value, and the accuracy of the voltage measurement
by the Si9730, which can be increased by decreasing the
resistor value.
Four Cell Application
Figure 9 shows a method for using the Si9730 in a 4-cell
application. Basically, this is two complete 2-cell circuits
stacked in series. Each half of the complete circuit monitors its
own 2-cell portion of the battery, and opens its own MOSFET
switch under any of the appropriate conditions. Observe that
the total percent power loss in this circuit is identical to that in
the 2-cell application; although there are now two sets of
MOSFETs in series, there is also double the battery voltage,
and so total efficiency is the same.
Reset from Shutdown
There are two specialized conditions that can place the Si9730
in shutdown mode. The first condition can occur when the
circuit is first attached to a battery in the factory. When the IC
comes up, it will be in the undervoltage shutdown mode. The
Si9730 may also enter this mode when the ambient
temperature drops and the battery is nearly in UV. When the
temperature drops, the battery pack voltage will drop and the
IC may enter the shutdown mode. In either case, the Si9730
must be reset by raising the VSS pin higher than the VM pin by
VCPHD. Figure 10 shows a circuit that resets the circuit once
it has entered the shutdown mode.
One novel feature of this 4-cell circuit is the increase in the size
of the bypass capacitors. Each half of the circuit retains its own
output cap, to reduce noise seen by the circuit. Since the two
halves interact with each other (when one opens its switch, the
other one is also opened), there can be additional noise, which
must be rejected for proper operation. The capacitors have
been increased to 100 F for this reason; remember that they
must be rated to take the full maximum voltage rating of the
charger, not half of it, since if one switch is closed and the other
open, the charger (minus two cells’ voltage drop, which might
be zero) is applied across the other capacitor.
The circuit works by initially connecting the 0.1-F capacitor to
the battery’s center tap and placing the switch in position #1.
Although the MOSFETs are open, the 1-m resistor is
sufficient to allow the capacitor to charge up in about
300-400 msec. Once the capacitor is charged, the switch is
placed in position #2, momentarily making VSS higher than VM,
thus placing the Si9730 in the normal operating mode. The
entire circuit provides a leakage of only a few microamps,
which is much lower than the self discharge current of the LiIon
battery.
A second addition on this circuit is the (optional) two zeners,
one each for each Si9730, placed from VDD to VM. These are
necessary only if the charger voltage is higher than the 15-V
absolute maximum of the IC plus two cells’ voltage drop. Just
as with the capacitor, if one switch is open and the other
closed, the IC will see this charger voltage, and must be
protected. The power rating of the zener can be inferred by
observing that the current through it is limited by the 100-
Si9730
1 VM
2 NC
3 VDD
4 CD
DCO
8
VSS 7
IS 6
VC
#2
#1
SPDT
5
15 M
1 M
0.1 F
FIGURE 10. Factory Startup Circuit
Document Number: 70658
S-40135—Rev. F, 16-Feb-04
www.vishay.com
13