ZHCSFO3D November 2016 – August 2021 LM5170-Q1
PRODUCTION DATA
The UVLO pin is the LM5170-Q1’s master enable pin. It can be directly controlled by an external control unit like an MCU.
Nevertheless, the UVLO pin can also fulfill the undervoltage lockout function of a particular power rail. The rail can be either the HV-Port, or the LV-Port, or VCC. Use a resistor divider to set the UVLO threshold, as shown in Figure 8-28. The divider should satisfy Equation 21:
The UVLO hysteresis is accomplished with an internal 25-μA current source. When UVLO > 2.5 V, the current source is activated to instantly raise the voltage at the UVLO pin. When the UVLO pin voltage falls below the 2.5-V threshold the current source is turned off, causing the voltage at the UVLO pin to fall. The UVLO hysteresis is determined by Equation 22:
An optional ceramic capacitor CUVLO can be placed in parallel with RUVLO2 to improve the noise immunity. CUVLO is usually between 1 nF to 10 nF. A large CUVLO may cause excessive delay to respond to a real UVLO event.
If Equation 22 does not provide adequate hysteresis voltage, the user can add RUVLO3 as shown in Figure 8-29. The hysteresis voltage is thus given by Equation 23: