7.3.4 Enable (EN Pin) and UVLO

System UVLO by EN and V_{CC_UVLO} voltage on the EN pin (V_EN) controls the ON/OFF functionality of the LM76002/LM76003. Applying a voltage less than 0.3 V to the EN input shuts down the operation of the LM76002/LM76003. In shutdown mode the quiescent current drops to typically 1.2 µA at V_IN = 24 V.

The internal LDO output voltage V_CC is turned on when V_{EN_VOUT_H} is higher than 1.15 V. The LM76002/LM76003 switching action and output regulation are enabled when V_EN is greater than 1.204 V (typical). The LM76002/LM76003 supplies regulated output voltage when enabled and output current up to 2.5 A/3.5 A. The EN pin is an input and cannot be open circuit or floating. The simplest way to enable the operation of the LM76002/LM76003 is to connect the EN pin to PVIN pins directly. This allows self-start-up of the LM76002/LM76003 when V_IN is within the operation range.

Many applications may benefit from the employment of an enable divider R_ENT and R_ENB (see Figure 12) to establish a precision system UVLO level for the stage. System UVLO can be used for supplies operating from utility power as well as battery power. It can be used for sequencing, ensuring reliable operation, or supply protection, such as a battery. An external logic signal can also be used to drive EN input for system sequencing and protection.

Figure 12. V_IN UVLO

With a selected R_ENT, the R_ENB can be calculated by:

Equation 4.

where

• V_{IN_ON_H} is the desired supply voltage threshold to turn on this device
• V_{EN_VOUT_H} could be taken from device data sheet

Note that the divider adds to supply quiescent current by V_IN / (R_ENT + R_ENB). Small R_ENT and R_ENB values add more quiescent current loss. However, large divider values make the node more sensitive to noise. R_ENT in the hundreds of kΩ range is a good starting point.