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AS3542 3v2
Data Sheet, Strictly Confidential - D e ta i l e d D e s c r i p t i o n - P o w e r M a n a g e m e n t F u n c t i o n s
9.3
15V Step-Up DCDC Converter
9.3.1 General
The integrated Step-Up DC/DC Converter is a high efficiency current-mode PWM regulator, providing an output volt-
age up to 15V. A constant switching-frequency results in a low noise on supply and output voltages.
It has a programable high voltage current sinks (1.2 to 37.2mA) for driving e.g. white LEDs as back-light. A voltage
feedback mode allows generating constant supply voltages for e.g. OLEDs by using an external Zener diode. To bias
the diode ISINK is sinking about 50uA in this voltage feedback mode.
An internal protection circuit will shut down the regulator if the voltage on SW15 exceeds 15V. No more external pro-
tection has to be used to avoid an exceeding of the operation conditions in a no load situation.
9.3.2 Dimming
The DCDC boster together with the current sinks has an adjustable automatic logarithmic dimming for a smooth ON/
OFF transition. It is also possible to control the dimming with an external signal via a GPIO pin. PWGD, Q24M or Q32K
pin can be selected as input for the external dimming signal.
9.3.3 Current Sink Only Mode
The current sinks are normally only working when the DCDC booster is swichted on, but can also be activated sepa-
rtely. To do so reg. 1Bh-1 has to be set to 08h (select external dimming), and reg. 1Ah-4 has to be set to xxxx xx00b
(no ext. dimming source selected).
Figure 25. DCDC15 Block Diagram
9.3.4 Parameter
BVDD=3.6V, T
A
= 25
o
C, unless otherwise mentioned
Table 23. DCDC Parameter
Symbol
Parameter
Condition
Min
Typ
Max
Unit
V
SW
High Voltage Pin
Pin SW15
0
15
V
I
VDD
Quiescent Current
Pulse Skipping mode
140
µA
V
FB
Feedback Voltage, Transient
Pin ISINK
0
5.5
V
V
FB
Feedback Voltage, during
Regulation
Pin ISINK
0.63
V