L6983 datasheet(30/63 Pages) STMICROELECTRONICS

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The device turns on when the average of the signal applied is higher than VEN rising (refer to Table 6. Electrical

characteristics). The device turns off when the average of the signal should be lower than VEN falling (refer to

Table 6. Electrical characteristics).

Considering, for example, a clock source with VPP = 5.0 V, the minimum duty cycle to guarantee the power-up is

given by:

Dutymin =VEN, Rising

VPP =0.24

(30)

The maximum duty cycle to guarantee the turn-off is given by:

DutyMAX, =VEN, Falling

VPP =0.2

(31)

The device allows also the AC coupling.

Figure 28. External synchronization. AC coupling

VIN

VINLDO

EN/CLKIN(*)

FSW

VCC

AGND

GND

VIN

RFSW

CVCC

CIN

Clock

Source

VPP

EXT. Clock(t)

CFILT

RFILT

CEN

REN H

REN L

The AC-coupling allows the device to keep the power-up and down thresholds defined by the partition connected

to EN/CLKIN pin and described on Section 8.1 Programmable power up threshold.

The following table resumes the minimum pulse duration for the external signal and maximum duty cycle that

allows the synchronization by keeping the selected power-up and down thresholds.

Table 8. External synchronization AC coupling suggested operation range

VPP [V]

TON, MIN, EXTClock [ns]

DMAX, EXTClock [%]

2.3

3.3

The minimum amplitude for the external clock signal is, for both the configurations, equal to 2.3 V.

The network given by CEN and RENL sets a high-pass filter. Considering a resistor in the order of 220 kΩ, a

capacitor equal to 1 nF is a correct choice.

8.3

Output voltage adjustment

The error amplifier reference voltage is 0.85 V typical (refer to Table 6. Electrical characteristics). The output

voltage is adjustable as per the following equation:

VOUT=0.85V∙ 1+R1R2

(32)

L6983

Output voltage adjustment

DS13116 - Rev 1

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