L6924D
Battery charger system with integrated
power switch for Li-ION/Li-POLYMER
Features
■
Fully integrated solution, with a power
MOSFET, reverse blocking diode, sense
resistor, and thermal protection
■
Ideal for coke and graphite anode single-cell
LI-ION packs
■
Both linear and quasi-pulse operation
■
Closed loop thermal control
■
USB BUS-compatible
■
Programmable charge current up to 1A
■
Programmable pre-charge current
■
Programmable end-of-charge current
■
Programmable pre-charge voltage threshold
■
Programmable charge timer
■
Programmable output voltage at 4.1V and
4.2V, with ±1% output voltage accuracy
■
PDAs
■
Handheld devices
■
(NTC) or (PTC) thermistor interface for battery
temperature monitoring and protection
■
Cellular phones
■
Digital cameras
■
Flexible charge process termination
■
Standalone chargers
■
Status outputs to drive LEDs or to interface
with a host processor
■
USB-Powered chargers
■
Small VFQFPN 16-leads package (3mm x
3mm)
VFQFPN16
Applications
Table 1. Device summary
June 2007
Order codes
Package
Packaging
L6924D
VFQFPN16
Tube
L6924D013TR
VFQFPN16
Tape & Reel
Rev 7
1/38
www.st.com
38
Contents
L6924D
Contents
1
Device description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2
Pins description and connection diagrams . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1
3
4
Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.1
Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2
Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Electrical specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.1
Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5
Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
6
Operation description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
7
2/38
6.1
Linear mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
6.2
Quasi-pulse mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Applications information: charging process . . . . . . . . . . . . . . . . . . . . . . 17
7.1
Charging process flow chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
7.2
Pre-charge current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
7.3
Pre-charge voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
7.4
Fast charge current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
7.5
End-of-charge current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
7.6
Recharge flow chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
7.7
Recharge threshold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
7.8
Maximum charging time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
7.9
Termination modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
L6924D
8
9
Contents
Application information: monitoring and protection . . . . . . . . . . . . . . . . 24
8.1
NTC thermistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
8.2
Battery absence detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
8.3
Status pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
8.4
Shutdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Additional applications information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
9.1
Selecting input capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
9.1.1
9.2
10
Selecting output capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Layout guidelines and demoboard description . . . . . . . . . . . . . . . . . . . . . . . 30
Application ideas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
10.1
USB battery charger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
11
Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
12
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3/38
Device description
1
L6924D
Device description
The L6924D is a fully monolithic battery charger dedicated to single-cell Li-Ion/Polymer battery
packs. It is the ideal solution for space-limited applications, like PDAs, handheld equipment,
cellular phones, and digital cameras. It is designed with BCD6 technology and integrates all of
the power elements (the Power MOSFET, reverse blocking diode and the sense resistor) in a
small VFQFPN16 3mm x 3mm package. When an external voltage regulated wall adapter is
used, the L6924D works in Linear Mode, and charges the battery in a Constant Current/
Constant Voltage(CC/CV) profile. Moreover, when a current-limited adapter is used, the device
can operate in Quasi-Pulse Mode, dramatically reducing the power dissipation. Regardless of
the charging approach, a closed loop thermal control avoids device overheating. The device
has an operating input voltage ranging from 2.5V to 12V. The L6924D allows the user to
program many parameters, such as pre-charge current, fast-charge current, pre-charge voltage
threshold, end-of-charge current threshold, and charge timer. The L6924D offers two open
collector outputs for diagnostic purposes, which can be used to either drive two external LEDs
or communicate with a host microcontroller. Finally, the L6924D also provides very flexible
control of the charge process termination and Gas Gauge capability, as well as other functions,
such as checking for battery presence, and monitoring and protecting the battery from unsafe
thermal conditions.
4/38
Figure 1.
Minimum application size
Figure 2.
Basis application schematic
L6924D
2
Figure 3.
Pins description and connection diagrams
Pins description and connection diagrams
Pins connection (top view)
IPRE IPRG VPRE IEND
V
VIN
VREF
INSNS
VOUT
ST2
VOSNS
ST1
VOPRG
TPRG GND SD
TH
5/38
Pins description and connection diagrams
2.1
Table 2.
L6924D
Pin description
Pin functions
Pin
I/O
Name
Pin description
1
I
VIN
2
I
VINSNS
3-4
O
5
I
TPRG
Maximum charging time program pin.
It must be connected with a capacitor to GND to fix the maximum charging time,
see Chapter 7.8: Maximum charging time on page 22
6
-
GND
Ground pin.
7
I
SD
Shutdown pin.
When connected to GND enables the device; when floating disables the device.
Temperature monitor pin.
It must be connected to a resistor divider including an NTC or PTC resistor. The
charge process is disabled if the battery temperature (sensed through the NTC or
PTC) is out of the programmable temperature window see Chapter 8.1: NTC
thermistor on page 25 .
Input pin of the power stage.
Supply voltage pin of the signal circuitry.
The operating input voltage range is from 2.5V and 12V, and the start-up
threshold is 4V.
ST2-ST1 Open-collector status pins.
8
I
TH
9
I
VOPRG
Output voltage selection pin.
If is it floating, VOUT = 4.1V. If is it connected to GND, VOUT = 4.2V.
10
I
VOSNS
Output voltage sense pin.
It senses the battery voltage to control the voltage regulation loop.
11
O
VOUT
Output pin. (connected to the battery)
12
O
VREF
External reference voltage pin.(reference voltage is 1.8V±2%)
IEND
Charge termination pin.
A resistor connected from this pin to GND fixes the charge termination current
threshold IENDTH: if I < IENDTH, the charger behaves according to the VPRE status
(see Chapter 7.5: End-of-charge current on page 20). The voltage across the
resistor is proportional to the current delivered to the battery (Gas Gauge
function).
13
I/O
Multifunction pin.
A resistor connected to GND allows the user to adjust the pre-charge voltage
threshold VPRETH.
14
I
VPRE
– If the pin is floating, VPRETH = 2.8V. If the voltage on VPRE pin is lower than
0.8V, VPRETH = 2.8V and the charge is not automatically terminated when I <
IENDTH.
– If the voltage on VPRE goes lower than 0.5V (edge sensitive), the maximum
charging time is reset.
15
16
6/38
I
I
IPRG
IPRE
Charge current program pin.
A resistor connected from this pin to GND, fixes the fast charge current value
(ICHG), with an accuracy of 7%.
Pre-charge current program pin.
If the pin is floating IPRETH is equal to 10% of ICHG. If IPRETH has to be
programmed at a different value, the pin has to be connected to GND or VREF,
through a resistor see Chapter 7.2: Pre-charge current on page 18.
L6924D
3
Maximum ratings
Maximum ratings
Stressing the device above the rating listed in the “Absolute Maximum Ratings” table may
cause permanent damage to the device. These are stress ratings only and operation of the
device at these or any other conditions above those indicated in the Operating sections of this
specification is not implied. Exposure to Absolute Maximum Rating conditions for extended
periods may affect device reliability. Refer also to the STMicroelectronics SURE Program and
other relevant quality documents.
3.1
Absolute maximum ratings
Table 3.
Absolute maximum ratings
Symbol
Parameter
Value
Unit
VIN
Input voltage
–0.3 to 16
V
VINSNS, SD
Input voltage
–0.3 to VIN
V
Output voltage
–0.3 to 5
V
Output voltage
–0.3 to 6
V
Output current
30
mA
–0.3 to 4
V
±1.5
kV
±2
kV
Value
Unit
75
°C/W
VOUT, VOSNS
ST1, ST2
VREF, TH, IEND, IPRG,
VPRE, IPRE, VOPRG,
TPRG, GND
ST1 and TH pins
Other pins
3.2
Maximum Withstanding Voltage Range Test Condition:
CDFAEC-Q100-002 (Normal “Human Body Model”
Acceptance Criteria Performance)
Thermal data
Table 4.
Thermal data
Symbol
Parameter
RthJA
Thermal resistance junction to ambient (1)
TSTG
Storage temperature range
–55 to 150
°C
TJ
Junction temperature range
–40 to 125
°C
TBD
W
PTOT
Power dissipation at T= 70°C
1. Device mounted on Demo board
7/38
Electrical specifications
L6924D
4
Electrical specifications
4.1
Electrical characteristics
TJ = 25°C, VIN = 5V, unless otherwise specified
Table 5.
Symbol
VIN(1)
IIN(1)
Electrical characteristics
Parameter
Test condition
Operating input voltage
Min
Typ
2.5
Start up threshold
Supply current
12
V
4.1
V
1.8
2.5
mA
Shutdown mode (RPRG = 24K)
60
80
µA
500
nA
500
nA
Current flowing from VOUT Stand by mode (RPRG = 24K)
(VIN = 2.5V < VBATTERY)
VOPRG at VIN
4.06
4.1
4.14
V
VOPRG at GND
4.16
4.2
4.24
V
RPRG = 24K
450
490
525
mA
RPRG = 12K
905
975
1045
mA
IPRECH
Pre-Charge current
IPRE floating
[default value = 10% ICHG] RPRG = 24K
41
49
56
mA
IPRECH
Pre-Charge current
57
67
78
mA
IPRECH
Pre-Charge current
29.5
35
40.1
mA
VPRETH
Pre-Charge voltage
threshold [default]
VPRE = VPRETHDefault =
Floating
2.7
2.8
2.9
V
VPRETH
Pre-Charge voltage
threshold
RVPRE = 13K; RPRG = 12K
2.87
3.03
3.19
V
VPRETH
Pre-Charge voltage
threshold [default].
Charge termination
disabled
2.7
2.8
2.9
V
IENDTH
Termination current
12
16
20
mA
VOUT(1)
ICHG
TMAXCH
(2)
8/38
Unit
Charging mode (RPRG = 24K)
Shutdown mode (RPRG = 24K)
ISINK
Max
Battery regulated voltage
Charge current
Maximum charging time
RPRE = 62K to GND;
RPRG = 24K
RPRE = 39K to VREF;
RPRG = 24K
REND = 3K3
CTPRG = 10nF
R[IPRG] = 24K
3
hours
L6924D
Electrical specifications
Table 5.
Symbol
TMAXCH
(2)
SDTH
Electrical characteristics (continued)
Parameter
Maximum charging time
accuracy
Test condition
Min
CTPRG = 5.6nF
Typ
Unit
2
V
10%
RPRG = 24K
Shutdown threshold high
Shutdown threshold low
Max
0.4
V
ST1,2
Output status sink current Status on
10
RDS(on)
Power MOSFET
resistance
280
380
mΩ
RDS(on)@ICHG = 500mA
mA
NTC pin hot threshold
voltage
10
12.5
15
%VREF
NTC pin cold threshold
voltage
40
50
60
%VREF
TH
1. TJ from –40°C to 125°C.
2. Guaranteed by design.
9/38
Block diagram
5
Figure 4.
10/38
Block diagram
Block diagram
L6924D
L6924D
6
Operation description
Operation description
The L6924D is a fully integrated battery charger that allows a very compact battery
management system for space limited applications. It integrates in a small package, all the
power elements: power MOSFET, reverse blocking diode and the sense resistor.
It normally works as a linear charger when powered from an external voltage regulated adapter.
However, thanks to its very low minimum input voltage (down to 2.5V) the L6924D can also
work as a Quasi-Pulse charger when powered from a current limited adapter. To work in this
condition, is enough to set the device’s charging current higher than the adapter one
(Chapter 7.4 on page 19). The advantage of the linear charging approach is that the device has
a direct control of the charging current and so the designer needn’t to rely on the upstream
adapter. However, the advantage of the Quasi-Pulse approach is that the power dissipated
inside the portable equipment is dramatically reduced.
Regards the charging approach, the L6924D charges the battery in three phases:
●
Pre-Charge constant current: in this phase (active when the battery is deeply
discharged) the battery is charged with a low current.
●
Fast-Charge constant current: in this phase the device charges the battery with the
maximum current.
●
Constant Voltage: when the battery voltage is closed to the selected output voltage, the
device starts to reduce the current, until the charge termination is done.
The full flexibility is provided by:
●
Programmable pre-charging current and voltage thresholds (IPRETH and VPRETH)
(Chapter 7.2 on page 18, Chapter 7.3 on page 19).
●
Programmable fast-charging current (ICHG) (Chapter 7.4 on page 19).
●
Programmable end of charge current threshold (IENDTH) (Chapter 7.5 on page 20).
●
Programmable end of charge timer (TMAXCH) (Chapter 7.8 on page 22).
If the full flexibility is not required and a smaller number of external components is preferred,
default values of IPRETH and VPRETH are available leaving the respective pins floating.
●
If a PTC or NTC resistor is used, the device can monitor the battery temperature in order
to protect the battery from operating in unsafe thermal conditions.
●
Beside the good thermal behavior guaranteed by low thermal resistance of the package,
additional safety is provided by the built-in temperature control loop. The IC monitors
continuously its junction temperature. When the temperature reaches approximately
120°C, the thermal control loop starts working, and reduces the charging current, in order
to keep the IC junction temperature at 120°C.
●
Two open collector outputs are available for diagnostic purpose (status pins ST1 and ST2).
They can be also used to drive external LEDs or to interface with a microcontroller.
●
The voltage across the resistor connected between IEND and GND gives information about
the actual charging current (working as a Gas Gauge), and it can be easily fed into a µC
ADC.
11/38
Operation description
L6924D
When the VPRE pin is not used to program the Pre-Charge voltage threshold, it has two
different functions:
●
If the voltage across VPRE pin is lower than 0.8V, when I < IENDTH, the end of charge in
notified by the status pin, but the charging process is not disabled. The charge process
ends when the maximum charging time expires.
●
If pin VPRE goes lower than 0.5V the timer is reset on the falling edge.
Battery disconnection control is provided thanks to the differentiated sensing and forcing output
pins. A small current is sunk and forced through VOUT. If VOSNS doesn’t detect the battery, the
IC goes into a standby mode.
Figure 5 shown the real charging profile of a Li-Ion battery, with a Fast Charge current of
450mA (RPRG = 26KΩ),
Figure 5.
Li-Ion charging profile
C harging profile
0.50 0
4.50 0
0.45 0
4.00 0
0.40 0
3.50 0
0.35 0
Ichg
2.50 0
0.25 0
2.00 0
0.20 0
1.50 0
0.15 0
1.00 0
0.10 0
0.50 0
0.05 0
0.00 0
0.00 0
0
2 00
400
60 0
Charging tim e (sec )
12/38
8 00
10 00
1 200
Vbatt (V)
Ichg (A)
3.00 0
Vb att
0.30 0
L6924D
6.1
Operation description
Linear mode
When operating in Linear Mode, the device works in a way similar to a linear regulator with a
constant current limit protection.
It charges the battery in three phases:
●
Pre-charging current ("Pre-Charge" phase).
●
Constant current ("Fast-Charge" phase).
●
Constant voltage ("Voltage Regulation" phase).
VADP is the output voltage of the upstream AC-DC adapter that is, in turn, the input voltage of
the L6924D. If the battery voltage is lower than a set pre-charge voltage (VPRETH), the precharge phase takes place. The battery is pre-charged with a low current IPRE (Chapter 7.2 on
page 18).
When the battery voltage goes higher than VPRETH, the battery is charged with the Fast Charge
current ICHG, set with an external resistor (Chapter 7.4 on page 19).
Finally, when the battery voltage is close to the regulated output voltage VOPRGTH (4.1V or
4.2V), the voltage regulation phase takes place and the charging current is reduced. The
charging process usually is terminated when the charging current reaches a set value or when
a charging timer expires (Chapter 7.9 on page 23).
Figure 6 shows the different phases.
Figure 6.
Typical charge curves in linear mode
Pre-Charge
Phase
V ADP
V OPRGTH
Fast-Charge
Phase
Voltage-Regulation
Phase
End
Charge
Adapter Voltage
Battery Voltage
V PRETH
I CHG
Charge Current
I PRETH
Power dissipation
13/38
Operation description
L6924D
The worst case in power dissipation occurs when the device starts the Fast-Charge Phase. In
fact, the battery voltage is at its minimum value. In this case, this is the maximum difference
between the adapter voltage and battery voltage, and the charge current is at its maximum
value.
The power dissipated is given by the following formula:
PDIS = (VADP − VBAT ) × I CHG
Eq. 7-1
The higher the adapter voltage is, the higher the power dissipated. The maximum power
dissipated depends on the thermal impedance of the device mounted on board.
6.2
Quasi-pulse mode
The Quasi-Pulse Mode can be used when the system can rely on the current limit of the
upstream adapter to charge the battery. In this case, ICHG must be set higher than the current
limit of the adapter. In this mode, the L6924D charges the battery with the same three phases
as in Linear Mode, but the power dissipation is greatly reduced as shown in Figure 7.
Figure 7.
Typical charge curves in quasi pulse mode
Pre-Charge
Phase
Fast-Charge
Phase
Adapter Voltage
V ADP
V O PRGTH
V PRETH
Voltage Regulation
Phase
Battery Voltage
Ilim x Rdson
I CHG
I LIM
Charge Current
I PRETH
Power dissipation
14/38
End
Charge
L6924D
Operation description
The big difference is due to the fact that ICHG is higher than the current limit of the adapter.
During the Fast-Charge Phase, the output voltage of the adapter drops and goes down to the
battery voltage plus the voltage drop across the power MOSFET of the charger, as shown in
the following equation:
VIN = VADP = VBAT + ∆VMOS
Eq. 7-2
Where ∆VMOS is given by:
∆V
MOS
= R DS ( ON ) × I LIM
Eq. 7-3
Where,
ILIM = current limit of the wall adapter, and RDS(on) = resistance of the power MOSFET.
The difference between the set charge current and the adapter limit should be high enough to
minimize the RDS(on) value (and the power dissipation). This makes the control loop completely
unbalanced and the power element is fully turned on.
Figure 8 shows the RDS(on) values for different output voltage and charging currents for an
adapter current limit of 500mA.
Figure 8.
rDS(on) curves vs charging current and output voltage
15/38
Operation description
L6924D
Neglecting the voltage drop across the charger (∆VMOS) when the device operates in this
condition, its input voltage is equal to the battery one, and so a very low operating input voltage
(down to 2.5V) is required. The power dissipated by the device during this phase is:
PCH = RDS ( on ) × I LIM
2
Eq: 7-4
When the battery voltage approaches the final value, the charger gets back the control of the
current, reducing it. Due to this, the upstream adapter exits the current limit condition and its
output goes up to the regulated voltage VADP. This is the worst case in power dissipation:
PDIS = (VADP − VBAT ) × I LIM Eq: 7-5
In conclusion, the advantage of the linear charging approach is that the designer has the direct
control of the charge current, and consequently the application can be very simple. The
drawback is the high power dissipation.
The advantage of the Quasi-Pulse charging method is that the power dissipated is dramatically
reduced. The drawback is that a dedicated upstream adapter is required.
16/38
L6924D
Applications information: charging process
7
Applications information: charging process
7.1
Charging process flow chart
Figure 9.
Charging process flow chart
17/38
Applications information: charging process
7.2
L6924D
Pre-charge current
The L6924D allows pre-charging the battery with a low current when the battery voltage is
lower than a specified threshold (VPRETH). The Pre-charge current has a default value equal to
10% of the fast-charge current (see Chapter 7.2: Pre-charge current on page 18). However it
can be adjusted by connecting a resistor from the IPRE pin to GND or VREF Figure 10. When the
resistor is connected from IPRE pin and GND, the current is higher than the default value. The
RPRE value is given by:
RPRE =
VBG
I PRECH VBG Eq: 8-1
−
K PRE RPRG
Figure 10. IPRE pin connection
IPRE
L6924D
When RPRE is connected to VREF, the current is lower than the default value. VREF is the
external reference equal to 1.8V, VBG is the internal reference equal to 1.23V and KPRE is a
constant equal to 950.Figure 11
The relationship is shown in the equation 8.2:
RPRE =
VREF − VBG
VBG I PRECH
−
RPRG KPRE
Eq: 8-2
Figure 11. IPRE pin connection
VREF
IPRE
L6924D
18/38
L6924D
7.3
Applications information: charging process
Pre-charge voltage
If the VPRE pin is floating, a default value of VPRETH is set, equal to 2.8V (VPRETHDefault).
Otherwise, the device offers the possibility to program this value, with a resistor connected
between the VPRE pin and GND Figure 12. In this case, the RVPRE is given by the equation 8.3:
⎛ VPRETH
RVPRE = RPRG × ⎜
⎜V
⎝ PRETHDefault
⎞
⎟ Eq: 8-3
⎟
⎠
Figure 12. VPRE pin connection
VPRE
L6924D
RPRE
Where RVPRE is the resistor between VPRE and GND, and RPRG is the resistor used to set the
charge current (see Section 7.4: Fast charge current), and VPRETH is the selected threshold.
A safety timer is also present. If the battery voltage doesn't rise over VPRETH, before this time is
expired, a fault is given (see Section 7.8: Maximum charging time). If at the beginning of the
charge process, the battery voltage is higher than the VPRETH, the Pre-Charge phase is
skipped.
7.4
Fast charge current
When the battery voltage reaches the Pre-charge voltage threshold (VPRETH), the L6924D
starts the Fast-charge Phase. In this phase, the device charges the battery with a constant
current, ICHG, programmable by an external resistor that sets the charge current with an
accuracy of 7% Figure 13. The formula used to select the RPRG as follows:
⎛ KPRG ⎞
⎟⎟ Eq: 8-4
RPRG = VBG × ⎜⎜
⎝ I CHG ⎠
Figure 13. IPRG pin connection
Where KPRG is a constant, equal to 9500.
During this phase, the battery voltage increases until it reaches the programmed output
voltage. A safety timer is also present. If this time expires, a fault is given (Section 7.8:
Maximum charging time).
19/38
Applications information: charging process
7.5
L6924D
End-of-charge current
When the charge voltage approaches the selected value (4.1V or 4.2V), the Voltage Regulation
phase takes place. The charge current starts to decrease until it goes lower than a
programmable end value, IENDTH, depending on an external resistor connected between the
IEND pin and GND Figure 14. The formula that describes this relation as follows:
⎛ KEND
REND = VMIN × ⎜⎜
⎝ I ENDTH
⎞ Eq: 8-5
⎟⎟
⎠
Figure 14. IEND pin connection
Where KEND is 1050; and VMIN is 50mV.
Typically, this current level is used to terminate the charge process. However, it is also possible
to disable the charge termination process based on this current level (Chapter 7.9 on page 23).
This pin is also used to monitor the charge current, because the current injected in REND is
proportional to ICHG. The voltage across REND can be used by a microcontroller to check the
charge status like a gas gauge.
20/38
L6924D
7.6
Applications information: charging process
Recharge flow chart
Figure 15. Recharge flow chart
FROM CHARGING PROCESS FLOW CHART
FAULT
END of CHARGE
IND FAULT
YES
VBAT
>
VRCH
NO
VBAT
>
VRCH
YES
NO
Detect High Fault
Detect Low
VBAT
<
VABS
VBAT
>
VPRETH
YES
YES
FAST CHARGE
NO
NO
Detect Low Fault
YES
DETECT LOW = a ISINK is sunk for a TDET from the battery
DETECT HIGH = a IINJ is injected for a TDET in the battery
DETECT LOW FAULT = a ISINK is sunk for a TDET from the battery
DETECT HIGH FAULT = a IINJ is injected for a TDET in the battery
VABS = VOPRG – 50mV
VRCH = VOPRG – 150mV
TDET = 100ms (Typ.)
ISINK = IINJ = 1mA (Typ.)
VBAT
>
VRCH
VBAT
>
VPRETH
RETURN TO CHARGING PROCESS
FLOW CHART
Detect High
YES
PRE CHARGE
NO
NO
BATTERY
ABSENT
BATTERY
ABSENT
GO TO BATTERY ABSENT
FLOW CHART
7.7
Recharge threshold
When, from an End-of-Charge condition, the battery voltage goes lower than the recharging
threshold (VRCH), the device goes back in charging state. The value of the recharge threshold
is VOPRG–150mV.
21/38
Applications information: charging process
7.8
L6924D
Maximum charging time
To avoid the charging of a dead battery for a long time, the L6924D has the possibility can be
set a maximum charging time starting from the beginning of the Fast-Charge Phase. This timer
can be set with a capacitor, connected between the TPRG pin and GND. The CTPRG is the
external capacitor (in nF) and is given by the following formula:
C TPRG
Note:
⎛ T MAXCH V BG
⎜
×
R PRG
⎜ KT
=
⎜
V REF
⎜
⎝
⎞
⎟
⎟
× 10 9
⎟
⎟
⎠
Eq: 8-6
The maximum recommended CTPRG value must be less than 50 nF.
Figure 16. TPRG pin connection
TPRG
L6924D
CTPRG
Where,
VREF = 1.8V,
KT = 279 x 105,
VBG = 1.23V, and
TMAXCH is the charging time given in seconds.
If the battery does not reach the End-of-Charge condition before the time expires, a fault is
issued.
Also during the Pre-Charge Phase there is a safety timer, given by:
1
TMAXPRECH = × TMAXCH Eq: 8-7
8
If this timer expires and the battery voltage is still lower than VPRETH, a fault signal is generated,
and the charge process is terminated.
22/38
L6924D
7.9
Applications information: charging process
Termination modes
Figure 17. Charge termination flow chart
As shown in Figure 17, it is possible to set an end of charge current IENDTH connecting a
resistor between the IEND pin and GND. When the charge current goes down to this value, after
de-glitch time, the status pins notify that the charge process is complete. This de-glitch time
expressed as:
TDEGLITCH =
TMAXCH
220
Eq: 8-9
However, the termination of the charger process depends on the status of the VPRE pin:
●
If the voltage at the VPRE pin is higher than 0.8V, the charger process is actually
terminated when the charge current reaches IENDTH.
●
If the voltage at VPRE pin goes lower than 0.8V, the charge process does not terminate,
and the charge current can go lower than IENDTH. The status pins notify the End-of-Charge
as a fault condition, but the device continues the charge. When the TMAXCH is elapsed, the
charge process ends, and a fault condition is issued.
●
If the voltage on VPRE pin is lower than 0.8V during the Pre-charge Phase, the device sets
the VPRETHDefault automatically.
●
If the voltage at the VPRE pin goes lower than 0.5V (edge sensitive), the timer is reset, both
in Pre-Charge and in Fast-Charge Phase.
23/38
Application information: monitoring and protection
8
L6924D
Application information: monitoring and protection
The L6924D uses a VFQFPN 3mm x 3mm 16-pin package with an exposed pad that allows the
user to have a compact application and good thermal behavior at the same time. The L6924D
has a low thermal resistance because of the exposed pad (approximately 75°C/W, depending
on the board characteristics). Moreover, a built-in thermal protection feature prevents the
L6924D from having thermal issues typically present in a linear charger.
Thermal Control is implemented with a thermal loop that reduces the charge current
automatically when the junction temperature reaches approximately 120°C. This avoids further
temperature rise and keeps the junction temperature constant. This simplifies the thermal
design of the application as well as protects the device against over-temperature damage.
The figure above shows how the thermal loop acts (with the dotted lines), when the junction
temperature reaches 120°C..
Figure 18. Power dissipation both linear and quasi pulse mode with thermal loop
24/38
L6924D
8.1
Application information: monitoring and protection
NTC thermistor
The device allows designers to monitor the battery temperature by measuring the voltage
across an NTC or PTC resistor. Li-Ion batteries have a narrow range of operating temperature,
usually from 0°C to 50°C. This window is programmable by an external divider which is
comprised of an NTC thermistor connected to GND and a resistor connected to VREF. When
the voltage on the TH pin exceeds the minimum or maximum voltage threshold (internal
window comparator), the device stops the charge process, and indicates a fault condition
through the status pin.
When the voltage (and thus, the temperature), returns to the window range, the device re-starts
the charging process. Moreover, there is a hysteresis for both the upper and lower thresholds,
as shown in Figure 20
Figure 19. Battery temperature control flow chart
Note:
TBAT = OK when the Battery temperature between 0°C and 50°C
25/38
Application information: monitoring and protection
L6924D
Figure 20. Voltage window with hysteresis On TH
VMINTH
VMINTH_HYS
900mV
780mV
Voltage
Variation on TH pin
Charge disable
Charge enable
VMAXTH_HYS
248mV
VMAXTH
225mV
Figure 21. Pin connection
VREF
TH
L6924D
NTC
When the TH pin voltage rises and exceeds the VMINTH = 50% of VREF (900mV typ), the
L6924D stops the charge, and indicates a fault by the status pins. The device re-starts to
charge the battery, only when the voltage at the TH pin goes under VMINTH_HYS = 780mV (typ).
For what concerns the high temperature limit, when the TH pin voltage falls under the VMAXTH =
12.5% of VREF (225mV Typ.), the L6924D stops the charge until the TH pin voltage rises at the
VMAXTH_HYS = 248mV (Typ.).
When the battery is at the low temperature limit, the TH pin voltage is 900mV. The correct
resistance ratio to set the low temperature limit at 0°C can be found with the following formula:
VMINTH = VREF ×
RNTC 0°C
RUP + RNTC 0°C
Eq: 9-1
Where RUP is the pull-up resistor, VREF is equal to 1.8V, and RNTC0°C is the value of the NTC
at 0°C. Since at the low temperature limit VMINTH = 900mV:
0.9 = 1.8 ×
RNTC 0°C
RUP + RNTC 0°C
Eq: 9-2
It follows that:
RNTC 0°C = RUP Eq: 9-3
26/38
L6924D
Application information: monitoring and protection
Similarly, when the battery is at the high temperature limit, the TH pin voltage is 225mV. The
correct resistance ratio to set the high temperature limit at 50°C can be found with the following
formula:
VMAXTH = VREF ×
RNTC 50°C
RUP + RNTC 50°C
Eq: 9-4
Where RNTC50°C is the value of the NTC at 50°C. Considering VMAXTH = 225mV it follows that:
0.225 = 1.8 ×
RNTC 50°C
RUP + RNTC 50°C
Eq: 9-5
Consequently:
RNTC 50°C =
RUP
7
Eq: 9-6
Based on equations 9-3 and 9-6, it derives that:
RNTC 0°C
=7
RNTC 50°C
Eq: 9-7
The temperature hysteresis can be estimated by the formula:
THYS =
VTH − VTH _ HYS
VTH × NTCT
Eq: 9-8
Where VTH is the pin voltage threshold on the rising edge, VTH_HYS is the pin voltage threshold
on the falling edge, and NTCT (- %/°C) is the negative temperature coefficient of the NTC at
temperature (T) expressed in % resistance change per °C. For NTCT values, see the
characteristics of the NTC manufacturers (e.g. the 2322615 series by VISHAY). At the low
temperature, the hysteresis is approximately:
THYS 0°C =
900mV − 780mV
900mV × NTC 0°C
Eq: 9-9
Obviously at the high temperature hysteresis is:
THYS 50°C =
225mV − 248mV
225mV × NTC 50°C
Eq: 9-10
Considering typical values for NTC0°C and NTC50°C, the hysteresis is:
THYS 0°C =
900mV − 780mV
≅ 2.5o C
900mV × 0.051
Eq: 9-11
And:
THYS 50°C =
225mV − 248mV
≅ −2.5o C
225mV × 0.039
Eq: 9-12
27/38
Application information: monitoring and protection
L6924D
If a PTC connected to GND is used, the selection is the same as above, the only difference is
when the battery temperature increases, the voltage on the TH pin increases, and vice versa.
For applications that do not need a monitor of the battery temperature, the NTC can be
replaced with a simple resistor whose value is one half of the pull-up resistor RUP.
In this case, the voltage at the TH pin is always inside the voltage window, and the charge is
always enabled.
8.2
Battery absence detection
This feature provides a battery absent detection scheme to detect the removal or the insertion
of the battery. If the battery is removed, the charge current falls below the IENDTH. At the end of
de-glitch time, a detection current IDETECT, equal to 1mA, is sunk from the output for a time of
TDETECT. The device checks the voltage at the output. If it is below the VPRETH, a current equal
to IDETECT is injected in the output capacitor for a TDETECT, and it is checked to see if the
voltage on the output goes higher than VABS (the value is VOPRGTH-50mV). If the battery
voltage changes from VPRETH to VABS and vice versa in a TDETECT time, it means that no
battery is connected to the charger. The TDETECT is expressed by::
TDETECT =
TMAXCH
54× 103
Eq: 9-13
Figure 22. Battery absent detection flow chart
DETECT LOW ABSENT = a ISINK is sunk for a TDET from the battery
DETECT HIGH ABSENT = a IINJ is injected for a TDET in the battery
TDET = 100ms (Typ.)
ISINK = IINJ = 1mA (Typ.)
BATTERY
ABSENT
Detect Low Absent
YES
VBAT
>
VPRETH
FAST CHARGE
NO
Detect High Absent
YES
28/38
VBAT
>
VRCH
NO
PRE CHARGE
L6924D
8.3
Application information: monitoring and protection
Status pins
To indicate various charger status conditions, there are two open-collector output pins, ST1 and
ST2. These status pins can be used either to drive status LEDs, connected with an external
power source, by a resistor, or to communicate to a host processor. These pins must never be
connected to the VIN when it overcomes their absolute value (6V).
Figure 23. ST1 and ST2 connection with LEDs Or µC
Table 6.
Status LEDs Indications
Charge condition
ST1
ST2
When the device is in Pre-Charge or fastCharge status
ON
OFF
When the charging current goes lower
than the IENDTH
OFF
ON
Stand By mode
When the input voltage goes under VBAT50mV
OFF
OFF
Bad battery temperature
When the voltage on the TH pin is out of
the programmable window, in accordance
with the NTC or PTC thermistor
ON
ON
When the battery pack is removed
ON
ON
When TMAXCH or TMAXPRECH is expired
ON
ON
Charge in progress
Charge done
Battery absent
Over time
8.4
Description
Shutdown
The L6924D has a shutdown pin; when the pin is connected to GND, the device is operating.
When the pin is left floating, the device enters in shutdown mode, the consumption from the
input is dramatically reduced to 60µA (typ.). In this condition, VREF is turned OFF.
29/38
Additional applications information
L6924D
9
Additional applications information
9.1
Selecting input capacitor
In most applications, a 1µF ceramic capacitor, placed close to the VIN and VINSN pins can be
used to filter the high frequency noise.
9.1.1
Selecting output capacitor
Typically, 1µF ceramic capacitor placed close to the VOUT and VOUTSN pin is enough to keep
voltage control loop stable. This ensures proper operation of battery absent detection in
removable battery pack applications.
9.2
Layout guidelines and demoboard description
The thermal loop keeps the device at a constant temperature of approximately 120°C which in
turn, reduces ICHG. However, in order to maximize the current capability, it is important to
ensure a good thermal path. Therefore, the exposed pad must be properly soldered to the
board and connected to the other layer through thermal vias. The recommended copper
thickness of the layers is 70µm or more.
The exposed pad must be electrically connected to GND. Figure 24 shows the thermal image of
the board with the power dissipation of 1W. In this instance, the temperature of the case is
89°C, but the junction temperature of the device is given by the following formula:
TJ = RTHJ − A × PDISS + TAMB
Eq: 10-1
Where the RTH J-A of the device mounted on board is 75°C/W, the power dissipated is 1W, and
the ambient temperature is 25°C.
In this case the junction temperature is:
TJ = 75 ×1 + 25 = 100o C Eq: 10-2
30/38
L6924D
Additional applications information
Figure 24. Thermal image of the demo board
The VOSNS pin can be used as a remote sense; so, it should be connected as closely as
possible to the battery. The demo board layout and schematic are shown in Figure 25 and
Figure 26.
Figure 25. Demoboard layout, top side
Figure 26. Demoboard layout, bottom side
31/38
Additional applications information
L6924D
Figure 27. Demoboard schematic
R9
R3
C4
CHARGER
VIN
VREF
NTC
TH
VOUT
VINSNS
R1
BATTERY
VOSNS
C1
IEND
R2
C2
LD1
TPRG
IPRG
L6924D
C3
LD2
J2
R4
ST2
VPRE
ST1
J1
R5
J5
SHDN GND VOPRG
J3
IPRE
J4
R6
R10
µC
Vref
R7
Table 7.
32/38
R8
Demo board components description
Name
Value
Description
R1
1K
Pull up resistor. To be used when the ST1 is connected with a LED.
R2
1K
Pull up resistor. To be used when the ST1 is connected with a LED.
R3
1K
Pull up resistor. Connected between VREF and TH pin.
R4
3K3
End of Charge current resistor. Used to set the termination current and, as a
“Gas Gauge” when measuring the voltage across on it.
R5
24K
Fast-charge current resistor. Used to set the charging current.
R6
N.M.
VPRETH resistor. Used to set programmable pre-charge voltage threshold. If
not mounted, the VPRETHDefault, equal to 2.8V, is set.
R7
N.M.
IPRETH resistor. Used to set the programmable pre-charge current threshold
below the default one. If not mounted, the IPRETHDefault is set.
R8
68K
IPRETH resistor. Used to set the programmable pre-charge current threshold
above the default one. If not mounted, the IPRETHDefault is set.
R9
470R
If a NTC is not used, a half value of R3 must be mounted to keep the TH
voltage in the correct window.
R10
N.M.
It has the same function of R6. Moreover, if it is replaced with a short-circuit,
when J5 is closed, the timer is reset (falling edge).
C1
1uF
Input capacitor.
C2
10nF
TMAX capacitor. Used to set the maximum charging time.
C3
4.7uF
Output capacitor.
C4
1nF
LD1
GREEN
VREF filter capacitor.
ST1 LED.
L6924D
Additional applications information
Table 7.
Demo board components description (continued)
Name
Value
LD2
RED
Description
ST2 LED.
J1
ST1 jumper. Using to select the LED or the external µC.
J2
ST2 jumper. Using to select the LED or the external µC.
J3
SD jumper. If open, the device is in SD mode; when closed, the device starts
to work.
J4
VOPRG jumper. If closed, the 4.2V output voltage is set; if open, the 4.1V is
set.
J5
VPRE jumper. If closed with R10 in short-circuit with GND, reset the timer.
33/38
Application ideas
L6924D
10
Application ideas
10.1
USB battery charger
With a voltage range between 4.75V and 5.25V, and a maximum current up to 500mA, the USB
power bus is an ideal source for charging a single-cell Li-Ion battery. Since it is not possible to
rely on the USB current limit to charge the battery, a linear approach must be adopted.
Therefore, it is only necessary to set the ICHG with a maximum value lower than 500mA, and
the device will charge the battery in Linear mode.
Figure 28 shows an example of USB charger application schematic.
Figure 28. USB charger application
R1
C4
VBUS
GND
VIN
VOUT
C1
SYSTEM
AND
PACK
VOSNS
VINSNS
D- D+
BATTERY
TH
VREF
IEND
C3
TPRG
C2
L6924D
IPRG
R2
VPRE
ST1
ST2 SD GND V
IPRE
OPRG
USB
CONTROLLER
R4
34/38
R5
R3
L6924D
11
Package mechanical data
Package mechanical data
In order to meet environmental requirements, ST offers these devices in ECOPACK® packages.
These packages have a Lead-free second level interconnect . The category of second Level
Interconnect is marked on the package and on the inner box label, in compliance with JEDEC
Standard JESD97. The maximum ratings related to soldering conditions are also marked on
the inner box label. ECOPACK is an ST trademark. ECOPACK specifications are available at:
www.st.com.
35/38
Package mechanical data
Table 8.
L6924D
VFQFPN16 (3mm x 3mm) mechanical data
Dimensions
mm.
inch
Dim.
Min.
Typ.
Max.
Min.
Typ.
Max.
0.800
0.900
1.000
0.031
0.035
0.039
A1
0.020
0.050
0.001
0.002
A2
0.650
1.000
0.025
0.039
A3
0.250
A
0.010
b
0.180
0.230
0.300
0.007
0.010
0.012
D
2.875
3.000
3.125
0.113
0.120
0.123
D2
0.250
0.700
1.250
0.009
0.027
0.050
E
2.875
3.000
3.125
0.113
0.118
0.123
E2
0.250
0.700
1.250
0.009
0.027
0.049
e
0.450
0.500
0.550
0.017
0.019
0.021
L
0.300
0.400
0.500
0.011
0.015
0.019
ddd
0.080
0.003
Figure 29. Package dimensions
E
E2
A
K
A1
e
D2
D
b
A3
K
L
r
This drawing is not to scale
36/38
L6924D
12
Revision history
Revision history
Table 9.
Revision history
Date
Revision
Changes
16-Dec-2005
1
First draft
20-Dec-2005
2
Package dimensions updated
10-Jan-2006
3
Few updates
14-Feb-2006
4
Part number updated
03-Jul-2006
5
Updates to formula in page 22, updated block diagram Figure 4.
07-Sep-2006
6
Added Note: on page 22, updated value CTPRG page 8
29-Jun-2007
7
Updated capacitor values C2, C3 in Table 7 on page 32
37/38
L6924D
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38/38