L6924U STMicroelectronics, L6924U Datasheet - Page 11

• Manufacturer Part Number: L6924U
• Description: Battery Management USB Battery Charger System w/integra
• Manufacturer: STMicroelectronics

Specifications of L6924U

• Product: Charge Management
• Battery Type: Li-Ion
• Output Voltage: 4.2 V
• Output Current: 30 mA
• Maximum Operating Temperature: + 125 C
• Minimum Operating Temperature: - 40 C
• Package / Case: VFQFPN
• Mounting Style: SMD/SMT
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

L6924U
6
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
(Chapter 6.2: Quasi-pulse mode on page
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:
●
●
●
The full flexibility is provided by:
●
●
●
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 I
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 V
battery, the IC goes into a standby mode.
Figure 5 on page 12
current of 450 mA (R
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 fast-
charge current).
Fast-charge constant current: in this phase the device charges the battery with the
maximum current (I
Constant voltage: when the battery voltage reaches the selected output voltage, the
device starts to reduce the current, until the charge termination is done.
Programmable fast-charging current (I
Programmable end of charge current threshold (I
Programmable end of charge timer (T
shows the real charging profile of a Li-Ion battery, with a fast charge
1
or R
AC
2
for AC adapter mode, I
= 26 kΩ).
Doc ID 14716 Rev 2
14). The advantage of the linear charging
MAXCH
AC
or I
END
)
USB
USB
(Chapter 7.7 on page
and GND gives information about the
)
ENDTH
(Chapter 7.3 on page
for USB mode).
OUT
)
. If V
(Chapter 7.4 on page
OSNS
Operation description
doesn’t detect the
21).
18).
20).
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