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t

3.3

C

SS

I

SSDIS

(s)

(31)

UVLO Programming

5

UVLO

1.33 V

+

TPS40100

UDG−04139

10

µA

UVLO

R

V

HYST

I

UVLO

W

(32)

R

V

UVLO

R

1

V

I

UVLO

W

(33)

TPS40101

SLUS726 – SEPTEMBER 2006

APPLICATION INFORMATION (continued)

MOSFET and the low-side MOSFET. The soft-start capacitor is then discharged at 25% of the charge rate

during an overcurrent condition and the converter remains idle until the soft start pin reaches 200 mV, at which

point the soft-start circuit starts charging again and the converter attempts to restart. In normal operation, the

soft-start capacitor is charged to approximately 3.5 V when an initial fault is applied to the output. This means

that the minimum time before the first restart attempt is:

where

• t

• C

• I

If the output fault is persistent, and an overcurrent is declared on the restart, both of the MOSFETs are turned

off and the soft-start capacitor continues to charge to 3.5 V and then discharge to 200 mV before another restart

is attempted.

The TPS40101 provides the user with programmable UVLO level and programmable hysteresis. The UVLO

detection circuit schematic is described in Figure 37 from a functional perspective.

Figure 37. UVLO Circuit Functional Diagram

To program this circuit, first select the amount of hysteresis (the difference between the startup voltage and the

shutdown voltage) desired:

where

• V

• I

• V

26

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