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AS3685A Datasheet(PDF) 9 Page - TEXAS ADVANCED OPTOELECTRONIC SOLUTIONS

Part No. AS3685A
Description  Ultra Small High Efficiency 1000mA Charge Pump
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Maker  TAOS [TEXAS ADVANCED OPTOELECTRONIC SOLUTIONS]
Homepage  http://www.taosinc.com
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AS3685A Datasheet(HTML) 9 Page - TEXAS ADVANCED OPTOELECTRONIC SOLUTIONS

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AS3685A/AS3685B
Datasheet
www.austriamicrosystems.com/
AS3685
(ptr)
Revision 2.2
8 - 24
7
Detailed Functional Description
Figure 12 – Internal Circuit Diagram of AS3685A/AS3685B
7.1 Low Noise Charge Pump
The AS3685 charge pump uses two external flying capacitors to generate output voltages higher than the battery
voltage. The charge pump can operate in three different modes:
1:1 Bypass Mode or Off Mode
Battery input and output are connected by a low-impedance switch
Battery current = output current
1:1.5 Mode
The output voltage is 1.5 times the battery voltage (without load)
Battery current = 1.5 times output current
1:2 Mode
The output voltage is 2 times the battery voltage (without load)
Battery current = 2 times output current
The flying capacitors are switched at the fixed frequency fclk.
7.1.1 Mode Switching
The AS3685 monitors the voltage at the current sink V(ILED) and if this voltage falls below VSWITCH, for a time
longer than the debounce time, the charge pump automatically switches into a higher mode. The debounce time
is set to tUP_DEB_LONG at enabling of the charge pump or immediately after a 1:1 to 1:1.5 mode change. Afterwards
the debounce time is reduced to tUP_DEB. (This allows the LED current to settle properly on startup or after a
mode change)
The charge pump enters always 1:1 mode in off mode or in case of overtemperature.
It is possible to avoid the 1:2 mode (factory programmable) to limit the battery current to 1.5 times the output
(=LED) current.
C1+
C1-
C2+
C2-
VCP
ILED
ISET
VBAT
EN1
EN2
VBAT
EN1
EN2
TXMask
Low Noise
Charge Pump
1:1, 1:1.5, 1:2 Modes
Digital
Control
1.3V
Vswitch
5.3V
soft_limit
AS3685
Different Control Logic
for AS3685A and AS3685B
1MHz
Overtemp
Detect
VSS


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