LM5069 datasheet(17/22 Pages) NSC

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Application Information

(Refer to Figure 1) (Continued)

seven additional charge/discharge cycles between 1.25V

and 4.0V as shown in Figure 6. The restart time ends when

the TIMER pin voltage reaches 0.3V during the final high-to-

low ramp. The restart time, after the Fault Timeout Period, is

equal to:

T x9.4x10

For example, if C

T = 0.33 µF, tRESTART = 3.1 seconds. At the

end of the restart time, Q1 is switched on. If the fault is still

present, the fault timeout and restart sequence repeats. The

on-time duty cycle of Q1 is approximately 0.5% in this mode.

UVLO, OVLO

By programming the UVLO and OVLO thresholds the

LM5069 enables the series pass device (Q1) when the input

supply voltage (V

SYS)

is within the desired operational

range. If V

SYS is below the UVLO threshold, or above the

OVLO threshold, Q1 is switched off, denying power to the

load. Hysteresis is provided for each threshold.

Option A: The configuration shown in Figure 12 requires

three resistors (R1-R3) to set the thresholds.

The procedure to calculate the resistor values is as follows:

- Choose the upper UVLO threshold (V

UVH), and the

lower UVLO threshold (V

UVL).

- Choose the upper OVLO threshold (V

OVH).

- The lower OVLO threshold (V

OVL) cannot be chosen in

advance in this case, but is determined after the values for

R1-R3 are determined. If V

OVL must be accurately defined in

addition to the other three thresholds, see Option B below.

The resistors are calculated as follows:

The lower OVLO threshold is calculated from:

As an example, assume the application requires the follow-

ing thresholds: V

UVH = 36V, VUVL = 32V, VOVH = 60V.

The lower OVLO threshold calculates to 55.8V, and the

OVLO hysteresis is 4.2V. Note that the OVLO hysteresis is

always slightly greater than the UVLO hysteresis in this

configuration. When the R1-R3 resistor values are known,

the threshold voltages and hysteresis are calculated from

the following:

UV(HYS) =R1x21µA

OV(HYS) =(R1+R2)x21µA

Option B: If all four thresholds must be accurately defined,

the configuration in Figure 13 can be used.

20197229

FIGURE 12. UVLO and OVLO Thresholds Set By R1-R3

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