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PDF VA7205 Data sheet ( Hoja de datos )
| Número de pieza | VA7205 | |
| Descripción | Advanced Linear Charger IC | |
| Fabricantes | Vimicro | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de VA7205 (archivo pdf) en la parte inferior de esta página. Total 14 Páginas | ||
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VA7205_100-1.3_En
ADVANCED LINEAR CHARGER IC
For LITHIUM-ION AND LITHIUM-POLYMER Battery
FEATURES
• Ideal for Single (4.2V) Li-ion or Li-Polymer
Packs
• Better Than ±1% Voltage Regulation Accuracy
With Preset Voltage
www.DataSheet4U.com
• Adjustable precharge current with an external
resistor
• Adjustable Charging Current During Constant
Current Charging Stage
• Constant Voltage Charging
• Automatic Battery-Recharge Feature
• Cell-Temperature Monitoring Before and During
Charge
• Dynamic compensation of Battery Pack’s
Internal Impedance to Reduce Charge Time
• Charge Status Output for Dual Led
• Cell Condition Monitoring
• Automatic Low-Power Sleep Mode When Vcc is
Removed or When Voltage Supply is Lower
than battery voltage
• Requires Small Number of External
Components
• Packaging: 8-Pin SOP or MSOP
DESCRIPTION
The VA7205 series advanced Lithium-Ion (Li-Ion)
and Lithium-Polymer (Li-Pol) Linear Charger ICs
are designed for cost-sensitive and compact
portable electronics.
They combine
high-accuracy current and voltage regulation,
battery condition monitoring, temperature
monitoring, charge termination, charge-status
indication, and internal impedance compensation
in a single 8-pin IC. It is the best suitable device
to be used in the PDA, mobile phones, and other
portable devices.
The VA7205 monitors the battery charging status
by detecting the battery voltage level. The
VA7205 charges the battery in three phases:
conditioning, constant current, and constant
voltage.If the battery voltage is below the
low-voltage threshold, Vmin (normally at 3V), the
VA7205 precharges using a low current to
FUNCTION BLOCK DIAGRAM
condition the battery. The conditioning charge
rate can be adjusted with an external resistor.
After the battery is precharged to Vmin, the
VA7205 applies a constant current to the battery.
An external sense-resistor sets the current.
The constant-current phase continues until the
battery reaches the charge-regulation voltage
(normally at 4.2V) and then the VA7205 begins
the constant-voltage phase. The accuracy of the
voltage regulation is better than ±1% over the
operating-temperature and supply-voltage
ranges. Under this stage the charging current
will gradually decrease. Charge stops when the
current tapers to the charge termination
threshold, ITERM. The VA7205 will continue
monitoring the battery voltage level and entering
a new cycle of charging if the battery’s voltage
level has fell below VRECHG (normally at VREG -
125mV).
During the charging process, for the safety
concern, the VA7205 continuously measures
battery temperature using the battery’s internal
heat sensitive resistor and an external resistors.
If the temperature of the battery exceeds the
pre-set temperature range, the charging process
will come to a halt after 0.5 seconds; After the
temperature fell back into the pre-set
temperature range, the charging will continue
again after 0.5 seconds. The VA7205 can also
dynamically compensate the battery pack’s
internal impedance to reduce the charge time.
LED
S
T
S
VSS
1
2
3
BAT 4
VA7205CF
Top
View
(Not to
Scale)
8 VCC
7 CS2/LEDT
6 CS1
5
DRIV
E
Figure 1 VA7205CF 8-Pin SOP
Vimicro Copyright© 1999-2005
1
1 page  
VA7205_100-1.3_En
www.DataSheet4U.com
Figure 3 Li-ion/Li-Pol Charger Using a PNP Pass Transistor
Regulation
Current
Preconditioning
Phase
Current
Regulation
Phase
Voltage Regulation
and charge
Termination Phase
IREG
Regulation
Voltage
Regulation
Voltage
VREG
Regulation
Current
IPRECHG
ITERM
t<tFAIL
Figure 4 Typical Charge Profile
VMIN
VBSC
5
5 Page 
has the largest power dissipation and the
source-drain voltage is:
VDS＝VCC－VD1－VR1－VBAT
＝6.5－0.7－0.15－3.0＝2.65V；
Drain current ID＝IREG＝0.5A
Therefore PMOS transistor’s power dissipation
PD is:
PD＝VDS×ID .............................................. （11）
＝2.65×0.5＝1.325W
www.DataSheet4U.comc) SelectingθJA
The maximum allowed thetaθJAMAX for PMOS
transistor is:
θJAMAX＝(TJMAX－TA)/ PD
＝(150℃－40℃)/1.325W＝83℃/W
Therefore, it’s ample to select a PMOS
transistor with TSSOP-8 package that has a
thetaθJA of 70℃/W.
d) Selecting maximum allowed current ID
The maximum allowed current for PMOS is
same as using PNP transistor: ID＝ 0.75A
e) Gate-source driving voltage VGS
Referencing Fig. 5, we can conclude that the
voltage across gate-source of the PMOS is:
VGS＝VCC－(VD1＋VR1＋VDRIVE)
When DRIVE terminal of VA7205 outputs low
voltage VOL（~ 1.0V）, PMOS transistor is turned
on. At same time, at constant-current charging
state, VR1 is at maximum so VGS is at minimum:
VGSMIN ＝VCC－(VD1＋VR1＋VOL) ............. （12）
＝6.5－(0.7＋0.1＋1.0)＝4.65V
We need to make sure we choose a PMOS
VA7205_100-1.3_En
whose VGS at IREG is smaller than VGSMIN, of
course, the PMOS’s threshold voltage must be
smaller than VGSMIN.
Likewise, following steps a～e above, we can
determine the type of PMOS to choose.
5. Blocking Diode D1
The main purpose of this blocking diode D1 is
to prevent battery reversing discharging at the
circumstance when power supply voltage VCC is
lower than battery voltage VBAT. In actual
application, customer can decide whether the
diode D1 is required in the specific situation.
In an actual charger power supply, if diode
rectifying is used (half wave or full wave), its
reversing resistance is huge and battery
discharging current will be very small even if
VCC is zero; if switch power supply is used, in
general, there is a ~3.8V Zener diode at the
negative electrode of the power supply,
combining with circuit resistance, the discharging
current should be small as well.
Therefore, customer can choose whether to
use the blocking diode based on actual
application circuit and its specific requirement.
6. PCB layout
When layout PCB, R1 should be put between
VCC and VA7205’s CS1 pin and the connection
line to R1 from both sides should be as short as
possible. C1 should be placed tightly with R1 and
C2 should be placed tightly with VA7205. Every
effort should be made to ensure the lines
between C1, R1, Q1, C2 and VA7205 as short
and wide as possible.
For best performance, it is suggested to
minimize the area of PCB. Of course, this is also
required for small form factor, reducing
manufacturing cost.
11
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| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet VA7205.PDF ] | |
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