L6924U
USB compatible battery charger system
with integrated power switch for Li-Ion/Li-Polymer
Datasheet - production data
Applications
• GPS and MP3 players
• USB-powered devices
• Digital still cameras
• Standalone chargers
• Wireless appliances
VFQFPN16
Features
• Fully integrated solution, with power MOSFET,
reverse blocking diode, sense resistor, and
thermal protection
• Charges single-cell Li-Ion batteries from
selectable AC adapter or USB input
Table 1. Device summary
Order code
Package
Packing
L6924UTR
VFQFPN16
Tape and reel
• Programmable charge current up to 1 A in AC
adapter mode
• Programmable charging current in USB mode
for both high-power and low-power inputs
• 4.2 V output voltage with ± 1% accuracy
• Linear or quasi-pulse operating mode
• Closed-loop thermal control
• Programmable end-of-charge current
• Programmable charge timer
• (NTC) or (PTC) thermistor interface for battery
temperature monitoring and protection
• Status outputs to drive LEDs or to interface
with a host processor
• Small VFQFPN 16-lead package (3 x3 mm)
February 2022
This is information on a product in full production.
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www.st.com
Contents
L6924U
Contents
1
Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2
Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1
Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3
Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4
Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5
Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
6
Operation description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
7
8
9
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6.1
Linear mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.2
Quasi-pulse mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Application information: charging process . . . . . . . . . . . . . . . . . . . . . 17
7.1
Pre-charge phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
7.2
AC or USB mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
7.3
Fast charge phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
7.4
End-of-charge current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
7.5
Recharge flow chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
7.6
Recharge threshold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
7.7
Maximum charging time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Application information: monitoring and protection . . . . . . . . . . . . . . 23
8.1
NTC thermistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
8.2
Battery absence detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
8.3
Status pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
8.4
Shutdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Additional application information . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
9.1
Selecting the input capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
9.2
Selecting the output capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
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Contents
9.3
Battery floating voltage setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
9.3.1
9.4
Battery floating voltage: VFLOAT
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Layout guidelines and demonstration board . . . . . . . . . . . . . . . . . . . . . . 32
10
Application idea: dual input management with AC priority . . . . . . . . 36
11
Package information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
11.1
12
VFQFPN16 package information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
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Description
1
L6924U
Description
The L6924U is a fully monolithic battery charger that safely charges single-cell LiIon/Polymer battery from either a USB power source or an AC adapter. In USB mode, the
L6924U supports both low-power and high-power mode. Alternatively the device can charge
from an AC wall adapter. The ideal solution for space-limited portable products integrates
the power MOSFET, reverse blocking diode, sense resistor and thermal protection into a
compact VFQFPN16 package. When an external voltage regulated adapter or USB port is
used, the L6924U 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 2.5 V to 12 V and it
allows the user to program many parameters, such as fast-charge current, end-of-charge
current threshold, and charge timer. The L6924U 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 L6924U also provides other features like gas gauge
function, checks for battery presence, and monitors and protects the battery from unsafe
thermal conditions.
Figure 1. Minimum size application board
Figure 2. Basic application schematic
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L6924U
2
Pin description
Pin description
Figure 3. Pin connections (top view)
2.1
Pin description
Table 2. Pin functions
Pin
I/O
Name
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 Section 7.7: Maximum charging time.
6
-
GND
Ground pin.
7
I
SD
Shutdown pin.
When connected to GND enables the device; when floating
disables the device.
TH
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 Section 8.1: NTC thermistor.
8
I
Pin description
Input pin of the power stage.
Supply voltage pin of the signal circuitry.
The operating input voltage ranges from 2.5 V to 12 V, and the
start-up threshold is 4 V.
ST2-ST1 Open-collector status pins.
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Pin description
L6924U
Table 2. Pin functions (continued)
Pin
Name
Pin description
9
I
ISEL
Switches between high power USB (IUSB up to 500 mA) and low
power USB (IUSB/5) in USB mode. A low level sets the L6924U in
low power mode and a high level sets the L6924U in high power
mode. When the AC mode is selected, the ISEL pin must be
connected to ground or left floating.
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 1.8 V ± 2%)
IEND
Charge termination pin.
A resistor connected from this pin to GND sets the charge
termination current threshold IENDTH: if ICHG < IENDTH, the charge
process ends. The voltage across the resistor is proportional to the
current delivered to the battery (gas gauge function).
MODE
Selects pin AC adapter or USB port input modes. A high level sets
the L6924U in USB mode while a low level sets the L6924U in the
AC adapter mode. When the AC adapter input is selected, the ISEL
pin status does not affect the current set.
13
14
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I/O
I/O
I
15
I
IUSB
Charge current program pin in USB mode: a resistor connected
from this pin to ground sets the fast charge current value (IUSB up
to 500 mA) with an accuracy of 7%. The USB high power/low
power mode is selected with the ISEL pin.
16
I
IAC
Charge current program pin in AC mode: a resistor connected from
this pin to GND sets the fast charge current value (IAC up to 1 A)
with an accuracy of 7%.
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L6924U
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.
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
VOUT, VOSNS
Output voltage
-0.3 to 5
V
ISEL, MODE
Input voltage
-0.3 to 6
V
Output voltage
-0.3 to VIN
V
Output current
30
mA
-0.3 to 4
V
±2
kV
Value
Unit
75
°C/W
ST1, ST2
VREF, TH, IEND,
IAC, IUSB, TPRG,
GND
All pins
Maximum withstanding voltage range test condition:
CDFAEC-Q100-002- “human body model”
acceptance criteria: “normal performance’
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
0.67
W
PTOT
Power dissipation at T = 70 °C
1. Device mounted on demonstration board
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Electrical characteristics
4
L6924U
Electrical characteristics
TJ = 25 °C, VIN = 5 V, unless otherwise specified.
Table 5. Electrical characteristics
Symbol
VIN (1)
IIN (1)
Parameter
Test conditions
Operating input voltage
Min.
Typ.
2.5
Start up threshold
Supply current
ISINK
Current flowing from VOUT
VOUT (1)
Battery regulated voltage
Max.
Unit
12
V
4.1
V
Charging mode (RPRG = 24 kΩ)
1.8
2.5
mA
Shutdown mode (RPRG = 24 kΩ)
60
90
µA
Shutdown mode (RPRG = 24 kΩ)
500
nA
Stand by mode (RPRG = 24 kΩ)
(VIN = 2.5 V < VBATTERY)
500
nA
4.16
4.2
4.24
V
MODE at GND, RPRG = 24 kΩ
450
490
525
mA
MODE at GND, RPRG = 12 kΩ
905
975
1045
mA
MODE at HIGH, ISEL at HIGH,
RPRG-USB = 24 kΩ
450
490
525
MODE at HIGH, ISEL at LOW,
RPRG-USB = 2 4 kΩ
86
96
105
MODE at GND,
RAC = 24 kΩ
41
49
56
mA
Pre-charge current with USB MODE at HIGH, ISEL at HIGH
input (high power mode)
RUSB = 24 kΩ
41
49
56
mA
Pre-charge current with USB MODE at HIGH, ISEL at LOW
input (low power mode)
RUSB = 24 kΩ
7.6
9.6
11.4
mA
VPRETH
Pre-charge voltage threshold
2.9
3.0
3.1
V
IENDTH
Termination current
12
16
20
mA
IAC
IUSB
IPRE_AC
IPRE_USB
Charge current with AC
adapter input
Charge current with USB
input
Pre-charge current with AC
input
REND = 3.3 kΩ
mA
TMAXCH (2) Maximum charging time
CTPRG = 10 nF
R[IPRG] = 24 kΩ
3
hours
Maximum charging time
accuracy
CTPRG = 5.6n F
RPRG = 24 kΩ
10
%
TMAXCH (2)
SDTH
ST1,2
MODETH
ISELTH
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Shutdown threshold high
2
Shutdown threshold low
Output status sink current
0.4
Status on
V
10
MODE threshold high
mA
1.3
MODE threshold low
0.4
ISEL threshold high
0.4
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V
V
1.3
ISEL threshold low
V
V
V
L6924U
Electrical characteristics
Table 5. Electrical characteristics (continued)
Symbol
RDS(on)
TH
Parameter
Power MOSFET resistance
(3)
Test condition
Min.
Charge current = 500 mA
Typ.
Max.
Unit
280
380
mΩ
NTC pin hot threshold
voltage
10
12.5
15
%VREF
NTC pin cold threshold
voltage
40
50
60
%VREF
1. TJ from -40 °C to 125 °C
2. Guaranteed by design
3. Device working in quasi pulse mode
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Block diagram
5
L6924U
Block diagram
Figure 4. Block diagram
Logic
Logic
I FAULT
I DETECT
VIN
VOUT
POWER MOS
VINS
Logic
UVLO
Gas Gauge
BODY
CONTROL
SD
Mos
Driver
Logic
ANALOG
PRE.
IEND
VDD
VDD
VOSNS
Logic
VBG
VREF
Charge
Control
BG
Logic
4.2V
CA-VA-TA
REG
THERMAL
CONTROL
ISEL
MODE
VREF
IAC
VPRE
IUSB
LOGIC
VDD
VREF
NTC/PTC
MANAG.
OSC
TPRG
10/41
ST2
ST1
GND
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VDD
TH
L6924U
6
Operation description
Operation description
The L6924U 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 or USB port.
However, thanks to its very low minimum input voltage (down to 2.5 V) the L6924U can also
work as a quasi-pulse charger when powered from a current limited adapter. To work in this
condition, it is enough to set the device’s charging current higher than the adapter’s one
(Section 6.2: Quasi-pulse mode). 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
power source. However, the advantage of the quasi-pulse approach is that the power
dissipated inside the portable equipment is dramatically reduced.
The L6924U 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 (internally set to 10 % of the fastcharge current).
•
Fast-charge constant current: in this phase the device charges the battery with the
maximum current (IAC for AC adapter mode, IUSB for USB mode).
•
Constant voltage: when the battery voltage reaches the selected output voltage, the
device starts to reduce the current, until the charge termination is done.
The full flexibility is provided by:
•
Programmable fast-charging current (IAC or IUSB) (Section 7.3: Fast charge phase).
•
Programmable end of charge current threshold (IENDTH) (Section 7.4: End-of-charge
current).
•
Programmable end of charge timer (TMAXCH) (Section 7.7: Maximum charging time).
If a PTC or NTC resistor is used, the device can monitor the battery temperature in order to
protect the battery from operating under 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
microcontroller ADC.
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 on page 12 shows the real charging profile of a Li-Ion battery, with a fast charge
current of 450 mA (R1 or R2 = 26 kΩ).
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Operation description
L6924U
Figure 5. Li-Ion charging profile
0.500
4.500
0.450
4.000
0.400
Ichg (A)
Ichg
3.000
Vbatt
0.300
2.500
Vbatt (V)
3.500
0.350
0.250
2.000
0.200
1.500
0.150
1.000
0.100
0.500
0.050
0.000
0.000
0
200
400
600
800
1000
1200
Charging time (sec)
6.1
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 L6924U. If the battery voltage is lower than the default pre-charge voltage (VPRETH),
the pre-charge phase takes place. The battery is pre-charged with a low current, internally
set to 10 % of the fast charge current.
When the battery voltage goes higher than VPRETH, the battery is charged with the fast
charge current (IUSB or IAC according to the selection of the MODE pin).
Finally, when the battery voltage is close to the regulated output voltage (4.2 V), the voltage
regulation phase takes place and the charging current is reduced. The charging process
ends when the charging current reaches the programmed value (IENDTH) or when the
charging timer expires.
Figure 6 shows the different phases.
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Operation description
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
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, there 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 equation:
Equation 1
PDIS = (VADP − VBAT ) × I CHG
The higher the adapter voltage is, the higher the power dissipated is. The maximum power
dissipated depends on the thermal impedance of the device mounted on board.
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Operation description
6.2
L6924U
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, the fast charge current must be set
higher than the current limit of the adapter. In this mode, the L6924U 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
Voltage Regulation
Phase
End
Charge
Adapter Voltage
V ADP
V OPRGTH
V PRETH
Battery Voltage
Ilim x Rdson
I CHG
I LIM
Charge Current
I PRETH
Pow er dissipation
The big difference is due to the fact that the charge current 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:
Equation 2
VIN = VADP = VBAT + ∆VMOS
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Operation description
Where ∆VMOS is given by:
Equation 3
∆V
MOS
=
R
DS( ON)
×
I
LIM
Where,
ILIM = current limit of the wall adapter, and RDS(on) = resistance of the power MOSFET.
The difference between the programmed 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 voltages and charging currents for an
adapter current limit of 500 mA.
Figure 8. RDS(on) curves vs. charging current and output voltage
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 2.5 V) is required. The power dissipated by the device during this phase is:
Equation 4
PCH = RDS(on) × ILIM 2
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Operation description
L6924U
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:
Equation 5
PDIS = (VADP − VBAT ) × ILIM
In conclusion, the advantage of the linear charging approach is that the designer has 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.
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7
Application information: charging process
Application information: charging process
Figure 9. Charging process flow chart
7.1
Pre-charge phase
The L6924U allows pre-charging the battery with a low current when the battery is deeply
discharged.
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Application information: charging process
L6924U
The battery is considered deeply discharged when its voltage is lower than a threshold
(VPRETH), internally set to 3 V.
During the pre-charge phase, the current (IPRECH) has a default value equal to 10 % of the
fast-charge current.
A safety timer is also present. If the battery voltage does not rise over VPRETH within this
time, a fault is given (Section 7.7: 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.
7.2
AC or USB mode
The L6924U can charge batteries from both an AC adapter and USB inputs.
The power supply type can be chosen by driving the MODE pin.
A low level sets the L6924U in AC mode. The fast charge current is determined by the
resistor connected to the IAC pin (Section 7.3: Fast charge phase), regardless of the resistor
connected to IUSB.
On the other hand, a high level at the MODE pin sets the L6924U in USB mode. The fast
charge current is determined by the resistor connected to the IUSB pin (Section 7.3: Fast
charge phase), regardless of the resistor connected to IAC.
Figure 10. MODE pin selection
Sets the fast charge current
Sets the fast charge current
IUSB
IUSB
L6924U
L6924U
IAC
MODE
IAC
RAC
RUSB
RAC
MODE
RUSB
VIN
AC adapter mode
7.3
USB mode
Fast charge phase
When the battery voltage reaches the pre-charge voltage threshold (VPRETH), the L6924U
enters the fast-charge phase.
In this phase the device charges the battery with a constant current, whose value can be set
by external resistors connected to IAC pin (AC adapter mode selected) or to IUSB pin (USB
mode) with an accuracy of 7%.
In AC adapter mode (MODE pin low), the resistor RAC can be calculated as:
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Application information: charging process
Equation 6
V
R AC = BG ⋅ KPRG
IAC
Where VBG is the internal reference equal to 1.23 V, whereas KPRG is a constant equal to
9500.
Figure 11. IAC pin connection
In USB mode (MODE pin high), the RUSB resistor can be selected as:
Equation 7
V
RUSB = BG ⋅ KPRG
IUSB
Where VBG and KPRG have the same meaning and value above mentioned.
The charge current in USB mode depends on RUSB as well as the state of the ISEL pin.
When this pin is high, the “high-power” USB mode is selected and the charge current is
determined by the equation 7.
The charge current in USB mode should be set in accordance with the typical USB current
capability (up to 500 mA). If ISEL is low, the “low-power” USB mode is selected and the
charge current is a fifth of the high-power USB mode charge current (up to 100 mA)
During low power USB mode operation, since the charge current is reduced by one fifth, the
maximum charging time is proportionally increased (Section 7.7: Maximum charging time).
Figure 12. IUSB pin connection
Regardless of the operation mode (AC adapter or USB), during the fast-charge phase the
battery voltage increases until it reaches the programmed output voltage (4.2 V). A safety
timer is also present. If the Fast-charge phase does not finish within the programmed time
(see Chapter 7.7: Maximum charging time on page 22), a fault is given.
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Application information: charging process
7.4
L6924U
End-of-charge current
When the charge voltage approaches the battery regulated voltage (internally set to 4.2 V),
the voltage regulation phase takes place. The charge current starts to decrease until it goes
below a programmable termination current, IENDTH. This current can be selected by an
external resistor connected between the IEND pin and GND Figure 13, whose value can be
calculated as:
Equation 8
KEND
REND = VMIN ×
I ENDTH
Eq: 8-5
Figure 13. IEND pin connection
Where KEND is 1050 and VMIN is 50 mV.
When the charge current goes below IENDTH, after a deglitch time, the status pins notify the
end of charge and the charge process ends.
This de-glitch time is expressed as:
Equation 9
TDEGLITCH =
TMAXCH
220
where TMAXCH is the maximum charging time. (Chapter 7.7 on page 22)
IEND pin is also used to monitor the charge current, because the current injected in REND is
proportional to the charge current. The voltage across REND can be used by a
microcontroller to check the charge status like a gas gauge.
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7.5
Application information: charging process
Recharge flow chart
Figure 14. Recharge flow chart
7.6
Recharge threshold
When, from an end-of-charge condition, the battery voltage goes below the recharging
threshold (VRCH), the device goes back in charging state. The value of the recharge
threshold is 4.05 V.
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Application information: charging process
7.7
L6924U
Maximum charging time
To avoid the charging of a dead battery for a long time, the L6924U has the possibility to set
a maximum charging time starting from the beginning of the fast-charge phase. This timer
can be set through a capacitor, connected between the TPRG pin and GND. CTPRG is the
external capacitor (in nF) and is given by the following equation:
Equation 10
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 15. TPRG pin connection
Where,
RPRG = resistor which sets the current (RUSB or RAC)
VREF = 1.8 V,
KT = 279 x 105,
VBG = 1.23 V, and
TMAXCH is the charging time given in seconds.
If the battery does not reach the end-of-charge condition before the timer expires, a fault is
issued.
Also during the pre-charge phase there is a safety timer, given by:
Equation 11
1
TMAXPRECH = × TMAXCH
8
If this timer expires and the battery voltage is still lower than VPRETH, a fault signal is
generated, and the charge process finishes.
Note:
22/41
When the device is charged in low power USB mode, in order to take into account the
reduced charge current, the maximum charging time is proportionally increased (five times
the maximum charging time calculated with RUSB).
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8
Application information: monitoring and protection
Application information: monitoring and protection
The L6924U uses a VFQFPN (3 x 3 mm) 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
L6924U 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 L6924U 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.
Figure 16 shows how the thermal loop acts (dotted lines), when the junction temperature
reaches 120 °C.
Figure 16. Power dissipation in both linear and quasi pulse modes with thermal loop
8.1
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
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Application information: monitoring and protection
L6924U
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 restarts the charging process. Moreover, there is a hysteresis for both the upper and lower
thresholds, as shown in Figure 18.
Figure 17. Battery temperature control flow chart
Note:
TBAT = OK when the battery temperature is between 0 °C and 50 °C
Figure 18. 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 19. Pin connection
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Application information: monitoring and protection
When the TH pin voltage rises and exceeds the VMINTH = 50% of VREF (900 mV typ.), the
L6924U 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 = 780 mV
(typ).
For what concerns the high temperature limit, when the TH pin voltage falls under the
VMAXTH = 12.5% of VREF (225 mV typ.), the L6924U stops the charge until the TH pin
voltage reaches the VMAXTH_HYS = 248 mV (typ.).
When the battery is at the low temperature limit, the TH pin voltage is 900 mV. The correct
resistance ratio to set the low temperature limit at 0 °C can be found with the following
equation:
Equation 12
VMINTH = VREF ×
RNTC 0°C
RUP + RNTC 0°C
Where RUP is the pull-up resistor, VREF is equal to 1.8 V, and RNTC0°C is the value of the
NTC at 0 °C. Since at the low temperature limit VMINTH = 900 mV:
Equation 13
0.9 = 1.8 ×
RNTC 0°C
RUP + RNTC 0°C
It follows that:
Equation 14
RNTC 0°C = RUP
Similarly, when the battery is at the high temperature limit, the TH pin voltage is 225 mV.
The correct resistance ratio to set the high temperature limit at 50 °C can be found with the
following equation:
Equation 15
VMAXTH = VREF ×
RNTC 50°C
RUP + RNTC 50°C
Where RNTC50°C is the value of the NTC at 50 °C. Considering VMAXTH = 225 mV it follows
that:
Equation 16
0.225 = 1.8 ×
RNTC 50°C
RUP + RNTC 50°C
Consequently:
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Application information: monitoring and protection
L6924U
Equation 17
RNTC 50°C =
RUP
7
Based on Equation 14 and Equation 17, it derives that:
Equation 18
RNTC 0°C
=7
RNTC 50°C
The temperature hysteresis can be estimated by the equation:
Equation 19
THYS =
VTH − VTH _ HYS
VTH × NTCT
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 low
temperature, the hysteresis is approximately:
Equation 20
THYS 0°C =
900mV − 780mV
900mV × NTC 0°C
Obviously at high temperature hysteresis is:
Equation 21
THYS 50°C =
225mV − 248mV
225mV × NTC 50°C
Considering typical values for NTC0°C and NTC50°C, the hysteresis is:
Equation 22
THYS 0°C =
900mV − 780mV
≅ 2.5o C
900mV × 0.051
THYS 50°C =
225mV − 248mV
≅ −2.5o C
225mV × 0.039
And:
Equation 23
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Application information: monitoring and protection
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 the de-glitch time, a detection current IDETECT, equal to 1 mA, 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 VRCH (4.05 V). If the battery
voltage changes from VPRETH to VRCH and vice versa in a TDETECT time, it means that no
battery is connected to the charger. The TDETECT is expressed by:
Equation 24
TDETECT =
TMAXCH
54× 103
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Application information: monitoring and protection
L6924U
Figure 20. Battery absence 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
8.3
VBAT
>
VRCH
NO
PRE CHARGE
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.
Figure 21. ST1 and ST2 connection with LEDs or microcontroller
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Application information: monitoring and protection
Table 6. Status LEDs Indications
Charge condition
Charge in progress
Charge done
Stand by mode
Bad battery temperature
Battery absent
Over time
8.4
Description
ST1
ST2
When the device is in pre-charge or fastcharge status
ON
OFF
When the charging current goes below the
IENDTH
OFF
ON
When the input voltage goes under
VBAT + 50 mV
OFF
OFF
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 expires
ON
ON
Shutdown
The L6924U has a shutdown pin; when the pin is connected to GND, the device is
operating. When the pin is left floating, the device enters the shutdown mode, the
consumption from the input is dramatically reduced to 60 µA (typ.). In this condition, VREF is
turned OFF.
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Additional application information
L6924U
9
Additional application information
9.1
Selecting the input capacitor
In most applications, a 1 µF ceramic capacitor, placed close to the VIN and VINSN pins can
be used to filter the high frequency noise.
9.2
Selecting the output capacitor
Typically, a 4.7 µF 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.
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9.3
Additional application information
Battery floating voltage setup
The L6924U has been evaluated with the following application schematic.
Figure 22. Application schematic
Table 7. External component values for the L6924U
Name
Value
Description
R6, R5
1 kΩ
Pull-up resistor
C1
1 µF
Input supply voltage capacitor
C3
10 nF
Maximum charging time capacitor
Rosns
7500 Ω
C2
1 µF
Output battery capacitor
R4
1 kΩ
NTC supply resistor
RT1
470 Ω
C4
1 µF
R1
12 kΩ
R2
R3
Note
VFLOAT programming resistor
NTC tuning parallel resistor
VREF filter capacitor
Fast-charge current programming resistor AC mode
IFAST = 975 mA
48.6 kΩ
Fast-charge current programming resistor USB mode
IFAST = 240 mA
2.2 kΩ
Set standard IEND = 10% IFAST
IEND ~ 24 mA
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Additional application information
9.3.1
L6924U
Battery floating voltage: VFLOAT
The battery floating voltage can be set to a value higher than 4.2 V by using the following
formula:
VFLOAT = 4.2 V + Rosns * 19.5 µA = 4.346 V
As an example, with Rosns = 7.5 kΩ the battery floating voltage (VFLOAT) is set to be
VFLOAT = 4.346 V.
Figure 23. VFLOAT vs. Rosns
The L6924U works with the selected external components. The test results confirm that their
behavior is in line with the design.
9.4
Layout guidelines and demonstration board
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 70 µm 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 1 W. In this instance, the temperature of the
case is 89 °C, but the junction temperature of the device is given by the following equation:
Equation 25
TJ = RTHJ − A × PDISS + TAMB
Where the RthJA of the device mounted on board is 75 °C/W, the power dissipated is 1 W,
and the ambient temperature is 25 °C.
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Additional application information
In this case the junction temperature is:
Equation 26
TJ = 75 × 1 + 25 = 100o C
Figure 24. Thermal image of the demonstration board
The VOSNS pin can be used as a remote sense; it should be therefore connected as closely
as possible to the battery. The demonstration board layout and schematic are shown in
Figure 25, Figure 26 and Figure 27.
Figure 25. Demonstration board layout, top side
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Additional application information
L6924U
Figure 26. Demonstration board layout, bottom side
Figure 27. Demonstration board schematic
Table 8. Demonstration board components description
34/41
Name
Value
Description
R1
24 kΩ
AC mode fast-charge current resistor. Used to set the charging current in AC mode
R2
24 kΩ
USB mode fast-charge current resistor. Used to set the charging current in USB
mode
R3
3.3 kΩ
End of Charge current resistor. Used to set the termination current and, as a “gas
gauge” when measuring the voltage across on it
R4
1 kΩ
Pull up resistor. Connected between VREF and TH pin
R5
1 kΩ
Pull up resistor. To be used when the ST1 is connected to a LED
R6
1 kΩ
Pull up resistor. To be used when the ST2 is connected to a LED
RT1
470 Ω
C1
1 µF
C2
4.7 µF
Output capacitor
C3
10 nF
TMAX capacitor. Used to set the maximum charging time
If a NTC is not used, a half value of R4 must be mounted to keep the TH voltage in
the correct window
Input capacitor
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L6924U
Additional application information
Table 8. Demonstration board components description
C4
D1
D2
1 nF
VREF filter capacitor
GREEN ST1 LED
RED
ST2 LED
J1
ST2 jumper. Using to select the LED or the external microcontroller
J2
ST1 jumper. Using to select the LED or the external microcontroller
J3
SD jumper. If open, the device is in shutdown mode; when closed, the device starts
to work
J4
Low power/ high power USB mode selection jumper
J5
AC/USB mode selection jumper
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Application idea: dual input management with AC priority
10
L6924U
Application idea: dual input management with AC
priority
In some applications both AC adapter and USB power source may be available.
Figure 28 shows a possible schematic which provides the possibility to manage two power
sources (AC/USB) and gives the priority to AC adapter in case both sources are available at
the same time.
For simplicity, only the relevant pins of the L6924U for this application have been indicated.
If only the AC adapter is available, since the gates of Q1 and Q2 are connected to AC, both
MOSFETs are off. The AC adapter voltage is provided to the VIN pin through the diode D1.
The voltage at the VIN pin is:
VIN = VAC − Vdiode
A correct choice of this diode is important to limit Vdiode and keeping VIN as close as
possible to AC.
In this condition the MODE pin is low. This sets the L6924U in AC mode and the battery is
charged with the current programmed by RAC.
When only the USB power source is available, both Q1 and Q2 switch on and the pin VIN is
connected to USB.
The MODE pin is connected to the drains of Q1 and Q2 and is high. Therefore the USB
mode for the L6924U is selected and the battery is charged with a current in accordance
with the resistor connected to the pin IUSB (RUSB).
The voltage of the VIN pin is given by:
VIN = VUSB − (RDSon _ Q1 + RDSon _ Q2 ) ⋅ IUSB
The voltage drop across the MOSFETs must be kept as low as possible to avoid reducing
too much the voltage of the VIN pin.
When both sources are present, this circuit gives the priority to the AC adapter. In fact, for
VAC ≥ 5 V, surely both Q1 and Q2 are off and VIN is connected to the AC adapter through
D1. The MODE pin is kept low and L6924U is set to AC mode.
The use of two P-channel MOSFETs connected as shown in Figure 28 is particularly useful
in this case because they remove any path between the two power sources.
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L6924U
Application idea: dual input management with AC priority
Figure 28. Dual input management
VOUT
D1
AC
Li-Ion
battery
Q1
Q2
VIN
USB
L6924U
IUSB
IAC
MODE
RG
RAC
RUSB
RM
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41
Package information
11
L6924U
Package information
In order to meet environmental requirements, ST offers these devices in different grades of
ECOPACK packages, depending on their level of environmental compliance. ECOPACK
specifications, grade definitions and product status are available at: www.st.com.
ECOPACK is an ST trademark.
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11.1
Package information
VFQFPN16 package information
Figure 29. VFQFPN16 (3x3 mm) package outline
Table 9. VFQFPN16 (3x3 mm) mechanical data
mm
Dim.
Min.
Typ.
Max.
0.80
0.90
1.00
A1
0.02
0.05
A2
0.65
1.00
A
A3
b
0.20
0.18
0.25
0.30
D
2.85
3.00
3.15
D2
1.45
1.60
1.75
E
2.85
3.00
3.15
E2
1.45
1.60
1.75
e
0.45
0.50
0.55
L
0.30
0.40
0.50
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Revision history
12
L6924U
Revision history
Table 10. Document revision history
40/41
Date
Revision
Changes
20-May-2008
1
First release
22-Sep-2010
2
Modified: Table 9 and Figure 29 on page 39. Minor changes.
25-Sep-2017
3
Updated Applications and Table 1: Device summary
Added Section 9.3: Battery floating voltage setup
18-Jan-2019
4
Updated Figure 22.
22-Feb-2022
5
Updated supply current in shutdown mode Max value in Table 5.
DocID14716 Rev 5
L6924U
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