L99VR02XP datasheet(31/50 Pages) STMICROELECTRONICS

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4.10

Fast output discharge

To assure a quick discharge of the external capacitors tied on the output pins down to around 1.3 V the

L99VR02XP uses two internal pull-down circuits. When the EN_LDO1,2 pins go low, during thermal shut-down

and during undervoltage lockout, the output currents flow through the pull-down resistors of the fast output

discharge circuit to the ground. The fast output discharge feature is available for the output voltages VO_LDO1,2 =

2.5 V (SELx = [1;0;0]) VO_LDO1,2 = 2.8 V (SELx = [1;0;1]) VO_LDO1,2 = 3.3 V (SELx = [1;1;0]) and VO_LDO1,2 = 5 V

(SELx = [1;1;1]).

4.11

Automatic voltage (de)tracking of LDO1 or tracking of an external LDO

Voltage (de)tracking is a solution adopted when long cable supplies off-board loads with voltage regulators

located on the main module. Under that operative condition short to GND and short to battery protection have to

be granted to contrast electrical failures caused by damaging of the cable. Moreover, to guarantee high accuracy

of data acquisition by microcontrollers, a very low discrepancy between the rails on-board and off-board is

assured.

In L99VR02XP, LDO2 can be a tracker of LDO1 or an external voltage regulator.

This function is enabled by TRK_MODE pin, IN_TRK pin and TRK_STAT, according to the following table:

Table 19. Tracking mode configuration

Function

TRK_MODE = GND

IN_TRK = LDO1

TRK_STAT = High

LDO2 automatically trackers LDO1 if SELx_LDO1 = SELx_LDO2 in case of SELx_LDO1 ≠

SELx_LDO2, LDO2 becomes a fully independent regulator.

TRK_MODE = VS

IN_TRK = external LDO

TRK_STAT = High

LDO2 trackers of an external voltage regulator output. The user MUST guarantee the same rails for

the external output voltage regulator and LDO2. Also, if SELx_LDO1 = SELx_LDO2 such internal

voltage regulators (LDO1 and LDO2) are always untied.

TRK_MODE = VS

IN_TRK = GND

TRK_STAT = Low

LDO2 works as a fully independent regulator.

The TRK_STAT pin is required to communicate to the MCU, if LDO2 is in tracking mode or working as an

independent regulator.

During the startup phase (soft-start), if the tracking mode is disabled or LDO2 is in UV/OV the TRK_STAT pin is

set low.

After startup, without UV/OV faults, when the tracking mode is activated the TRK_STAT pin goes high.

If the device is configured with LDO2 tracker of LDO1 and the soft start signal of LDO1 is high (soft start phase in

progress), the tracking comparators are ignored to avoid unwanted transient effects during standard startup in the

tracking with LDO1.

Tracking mode = 1 → If V(IN_TRK) and all other conditions are correct when LDO2 is enabled, tracking mode is

enabled otherwise it is disabled during all the LDO2 soft start.

L99VR02XP

Application information

DS14686 - Rev 1

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