4.8

Fast output discharge

To assure a quick discharge of the external capacitor tied to the output pin down to around 1.3 V the L99VR01

uses an internal pulldown circuit. Activated each time the EN pin goes low, during thermal shut down and during

undervoltage lockout, the output current will flow through the pulldown resistor of the fast output discharge circuit

to ground. The fast output discharge feature is available for the output voltages Vo= 2.5 V (SELx = [1;0;0]) Vo=

2.8 V (SELx = [1;0;1]) Vo= 3.3 V (SELx = [1;1;0]) and Vo= 5 V (SELx = [1;1;1]).

4.9

Undervoltage lockout UVLO

The undervoltage lockout (UVLO) circuit allows a fast regulating element to turn off (activating the internal Fast

Output Discharge circuit) if the input voltage drops below the threshold, VUVLO_fall, avoiding undesired unknown

output state during low input voltage. When the input voltage is above the VUVLO_rise threshold, the regulating

element is again turned on.

Figure 37. Undervoltage lockout on output voltage

VS

VO

VUVLO_rise

VUVLO_fall

4.10

Functional safety management

Even if not designed as safety HW element, the device contains some features that can be used to support

application that need to fulfill functional safety requirements. Analysis of the IC’s capability to reach the required

safety level, should be made at system level under user's responsibility.

The following device safety requirements have been considered for a typical application:

Table 12. Safety requirement

ID

Description

SR-001

Operation of the voltage regulator(s) is allowed till over temperature limit.

SR-002

Operation of voltage regulator(s) is enabled until programmed current limit is

reached.

SR-003

Output voltage of regulator(s) shall remain within programmed range when RST pin

is not asserted.

SR-004

Output voltage of regulator(s) shall remain within programmed range when square

wave at TW pin is not generated.

Based on the above requirements list the following safety mechanism has been implemented:

L99VR01

Application information

DS13649 - Rev 4

page 21/40