APW8811 datasheet(14/23 Pages) ANPEC

14 / 23 page

Rev. A.3 - Sep., 2012

APW8811

www.anpec.com.tw

Current-Limit (PWMs) (Cont.)

Function Description (Cont.)

an external resistor. The ILIMx pin adjustment range is

from 515mV to 2V. In the adjustable mode, the current-

limit threshold voltage is 1/10th the voltage at ILIM pin. As

shown in Figure 2, The ILIM pin can source 10

µA. The

voltage at ILIM pin is equal to 10

µA x R

ILIM. Connect ILIM to

REF for a fixed 200mV threshold. The logic current-limit

threshold is default to 250mV value if ILIM is 5V. The

relationship between the sampled voltage V

ILIM and the

current-limit threshold I

LIMIT is given by:

Where V

ILIM is the voltage at the ILIM pin. RDS(ON) is the low

side MOSFETs conducive resistance. I

LIMIT is the setting

current-limit threshold. I

LIMIT can be expressed as IOUT mi-

nus half of peak-to-peak inductor current.

The PCB layout guidelines should ensure that noise and

DC errors do not corrupt the current-sense signals at

PHASE. Place the hottest power MOSEFTs as close to

the IC as possible for best thermal coupling. When com-

bined with the under-voltage protection circuit, this cur-

rent-limit method is effective in almost every circumstance.

)

(

LIMIT

ILIM

Figure 2. Current-Limit Setting Block Diagram

VCC

10µA

TO CURRENT

LIMIT LOGIC

ILIM

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