LM5069 datasheet(18/22 Pages) NSC

18 / 22 page

Application Information

(Refer to Figure 1) (Continued)

The four resistor values are calculated as follows:

- Choose the upper and lower UVLO thresholds (V

UVH)

and (V

UVL).

-Choose the upper and lower OVLO threshold (V

OVH) and

OVL).

As an example, assume the application requires the follow-

ing thresholds: V

UVH = 22V, VUVL = 17V, VOVH = 60V, and

OVL = 58V. Therefore VUV(HYS) = 5V, and VOV(HYS) =2V.

The resistor values are:

R1 = 238 k

Ω,R2=41kΩ

R3 = 95.2 k

Ω, R4 = 4.14 kΩ

Where the R1-R4 resistor values are known, the threshold

voltages and hysteresis are calculated from the following:

UV(HYS) =R1x21µA

OV(HYS) =R3x21µA

Option C: The minimum UVLO level is obtained by connect-

ing the UVLO pin to VIN as shown in Figure 14. Q1 is

switched on when the VIN voltage reaches the POR

threshold ()8.8V). An external transistor can be connected

to UVLO to provide remote shutdown control, and to restart

the LM5069-1 after a fault detection. The OVLO thresholds

are set using R3, R4. Their values are calculated using the

procedure in Option B.

20197241

FIGURE 13. Programming the Four Thresholds

20197250

FIGURE 14. UVLO = POR

EN with Shutdown/Restart Control

LM5069 Datasheet(PDF) 18 Page - National Semiconductor (TI)