L6924U STMicroelectronics, L6924U Datasheet - Page 32

• 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

Application idea: dual input management with AC priority
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Application idea: dual input management with AC
priority
In some applications both AC adapter and USB power source may be available.
Figure 26
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 V
The voltage at the V
A correct choice of this diode is important to limit V
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 R
When only the USB power source is available, both Q1 and Q2 switch on and the pin V
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 I
The voltage of the V
The voltage drop across the MOSFETs must be kept as low as possible to avoid reducing
too much the voltage of the V
When both sources are present, this circuit gives the priority to the AC adapter. In fact, for
V
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
in this case because they remove any path between the two power sources.
AC
≥ 5 V, surely both Q1 and Q2 are off and V
shows a possible schematic which provides the possibility to manage two power
IN
IN
pin is:
pin is given by:
V
IN
IN
=
Doc ID 14716 Rev 2
V
pin.
USB
−
V
USB
IN
(
R
DSon
=
(R
V
AC
AC
USB
_
.
Q
IN
−
1
).
+
V
is connected to the AC adapter through
diode
R
diode
DSon
and keeping V
_
Q
2
)
⋅
Figure 26
I
USB
IN
pin through the diode D1.
IN
is particularly useful
as close as
L6924U
IN
is