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Vimicro |
VA7910/VA7920
REV 1.1/Feb 2006
HIGH EFFICIENCY DC-DC STEP UP CONVERT
FEATURES
0.9V start up voltage;
0.9V minimum operating voltage;
Above 95% efficiency;
Low battery voltage detector;
Fixed 3.3V and 5V output or adjustable
output from 2V to 5V;
Internal synchronous rectifier;
Zero shut down current;
Little external elements
Ultra small TSSOP8, MSOP8 package;
APPLICATION
One to three-cell battery powered devices;
PDA and handheld instruments;
Cell phones;
Pagers;
GPS;
Digital cameras;
INTRODUCTION
VA7910/VA7920 series circuits are high
efficiency DC-DC step up converts, with a few
external components to realize the conversion
from the battery voltage to the expect output
voltage. It can be widely used in PDA 、 cell
phones、hand-held devices and so on.
The start up voltage is guaranteed at above
0.9V input and the device keeps working.
With an internal synchronous P-MOS rectifier,
it doesn’t require external diode to rectify.
VA7910FF is completely compatible with
L6920 of ST Corporation. And VA7910DF is
completely compatible with MAX1674/MAX1675
of MAXIM Corporaton.
FUNCTIONAL DIAGRAM
FB
VREF
Zero crossing
comparator
-
Multi-way
selector
+ -+
Voltage
com parator
-
Logic
controller
+
Reference
Voltage
comparator
LBI
Current
limit
circuit
LBO
SHDN
Fig1 Function Diagram
OUT
LX
GND
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© 2003 Vimicro Corporation
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DSC-VA7910/VA7920 -1
ORDERING INFORMATION
Type
VA7910FF
VA7910DF
Package
TSSOP8
MSOP8
VA7910/VA7920
Pin Number
8
8
Print Mark
TBA
TBA
PIN-OUT
FB 1 VA7910FF 8 OUT
LBI 2 VA7910DF 7 LX
LBO 3 Top View 6 GND
REF 4 (Not to scale) 5 SHDN
TSSOP8
MSOP8
Fig2 Pin-Out Diagram
PIN DESCRIPITION
Pin Name
FB
LBI
LBO
REF
SHDN
GND
LX
OUT
Pin Num
VA7910 VA7920
Pin Function
Output voltage selected pin. Connect to Ground for 5V output;
1 1 Connect to OUT for 3.3V output; Connect to a resistor divider for
adjustable output from 2V to 5V.
2
Low battery detector input. Internal detection threshold voltage is
1.15V(VREF).
Low battery detector output. The output goes low when VLBI is lower
3
than the internal threshold voltage, otherwise, the output shown
high impedance. This pin is open drain configuration, it must add an
external pull-up resistor in application.
Reference voltage. Bypass this output to GND with a 0.1μF
4 3 capacitor for filtering high frequency noise.
The maximum current delivered to this pin is 10μA.
Shutdown Pin. The device will shut down when the voltage of this
5 4 pin is below 0.3V; The device is operating when the voltage is
above 0.6V.
6 6 Ground.
7 5 Connect with external inductor.
Power output pin. This pin supplies the power for the internal circuit
8 2 and it must connect to an external about 10uF to 100uF capacitor
for filtering and an about 1uF capacitor for coupling.
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