C11 datasheet(16/72 Pages) AMSOSRAM

16 / 72 page

AS3688

austriami crosyst ems

Datasheet, Confidential

www.austriamicrosystems.com (ptr,tje)

Revision 1.1.1 / 20060707

14 - 70

Note

: Always choose the path with the higher voltage drop as feedback to guarantee adequate supply for the

other (unregulated) path or enable the register bit step_up_fb_auto.

7.2.2 Overvoltage Protection in Current Feedback Mode

The overvoltage protection in current feedback mode (step_up_fb = 01 or 10) works as follows: Only resistor R3

and C10 is soldered and R4 and C11 is omitted. An internal current source (sink) is used to generate a voltage

drop across the resistor R3. If then the voltage on DCDC_FB is above 1.25V, the DCDC is momentarily disabled

to avoid too high voltages on the output of the DCDC converter.

The protection voltage can be calculated according to the following formula:

VPROTECT = 1.25V + IDCDC_FB * R3

Notes:

The voltage on the pin DCDC_FB is limited by an internal protection diode to VBAT + one diode

forward voltage (typ. 0.6V).

If the overvoltage protection is not used in current feedback mode, connect DCDC_FB to ground.

Figure

11 –Step Up DC/DC Converter Block Diagram; Option: Regulated Output Voltage, Feedback is at Pin DCDC_FB

CLK

–

Driver

PWM

Logic

VSS

1.25V

Pulse Skip

Comparator

Error Amplifier

Ramp

Generation

Comparator

Current

Sense

0.5V

Error Amplifier

MUX

24 SENSE_P

23 SENSE_N

19 CURR 1

20 CURR 2

29 DCDC_FB

C10

1.5nF

C11

15nF

100kΩ

1MΩ

Si1304

SOT-323

28 DCDC_GATE

2.2µF

White

LEDs

10µH, 5x5x1.2mm

Coiltronics SD12-100

R2 (RSENSE)

0.1 Ω/5%

Battery

1µF

7.2.3 Voltage Feedback

Setting bit step_up_fb = 00 enables voltage feedback at pin DCDC_FB..

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

configuration)

Ustepup_out = (R3+R4)/R4 x 1.25 + IDCDC_FB x R3

If R4 is not used, the output voltage is by (Bit step_up_res should be set to 0 in this configuration):

Ustepup_out = 1.25 + IDCDC_FB x R3

Where:

Ustepup_out = Step Up DC/DC Converter output voltage.

C11 数据表(PDF) 16 Page - ams-OSRAM AG

C11 数据表(HTML) 16 Page - ams-OSRAM AG

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