AS3608 datasheet(19/68 Pages) AMSCO

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AS3608 2v2

Data Sheet - D e t a i l e d D e s c r i p t i o n - P o w e r M anage ment F uncti ons

8.3 30V Step-Up DCDC Converter

The integrated Step-Up DC/DC Converter is a high efficiency current-mode PWM regulator, providing an output voltage up to 30V. A constant

switching-frequency results in a low noise on supply and output voltages.

It has two programmable high voltage current sinks (0 to 38.25mA) for driving e.g. white LEDs as back-light. It can drive also unbalanced strings

due to the internal automatic feedback selection.

A voltage feedback mode allows generating constant supply voltages for e.g. OLEDs. The output voltage is set by an external resistor divider

and an internal current sink.

An internal protection circuit will shut down the regulator if the voltage on FBSU exceeds the over voltage threshold. No more external protection

has to be used to avoid an exceeding of the operation conditions in a no load situation.

Figure 9. DCDC15 Block Diagram

8.3.1 Voltage Feedback and OV Protection

8.3.2 Voltage Feedback

Setting bit SU_CURR_FB = 0 enables voltage feedback at pin FBSU.

The output voltage is regulated to a constant value, given by (Bit SU_GAIN should be set to 1 in this configuration)

UStep up_out = (R1+R2)/R2 *1.25 + IFB * R1

(EQ 1)

If R2 is not used, the output voltage is by (Bit SU_GAIN should be set to 0 in this configuration)

UStep up_out = 1.25 + IFB * R1

(EQ 2)

Where:

UStep up_out = Step Up DC/DC Converter output voltage

R1 = Feedback resistor R1

R2 = Feedback resistor R2

IFB = Tuning current at pin FBSU; 0 to 31µA

AS3608 数据表(PDF) 19 Page - ams AG