APW8871 Datasheet, PDF (19/27 Pages) Anpec Electronics Coropration – DDR4 TOTAL POWER SOLUTION (VPP/VDDQ/VTT) SYNCHRONOUS DC/DC CONVERTER for NB/MB

APW8871
Function Description (Cont.)
PMAX Indicator
PMAX is an o pen-drain output and s uppo rts the PMAX
sig nal for VDDQ PWM co nverter p ower indicator. If the
inductor valley current is bigger than 80% of current lim it
thre shold an d counts four cycles con tinually, or the de-
vice tem perature is over 120^oC, th e intern al open-drain
device wil l be turned on. Th e PMAX signal will go low to
in di ca te th at the PMAX co nd itio n h as h app en ed and
pas ses m essag e to the s yste m. Wh en in ducto r val ley
current is less than 80% of current limit threshold, or the
device tem perature is under 120^oC, the PMAX s ignal will
be pulled high immediately. Therefore, this indicatorfunc-
tion is not latch up.
Thermal Shutdown
A the rmal shutdown circuit limits the jun ction tem pera-
ture of APW8871. When the junction temperature exceeds
+150^oC, both PWM converters, VTTLDO and VTTREF are
shut off, allow ing the device to cool down. The regulator
regulates the output again through initiation of a new soft-
start cycl e after the juncti on temperature coo ls by 40^oC ,
resul ting in a pulsed o utput du ring continuous th ermal
overload conditions. The thermal shutdown designed with
a 40^oC hysteresis lowers the average junction tempera-
ture durin g continuous therm al overload conditions, ex-
tending life time of the device.
For normal operation , device powe r dissipation should
be e xterna lly li mited so tha t junction tempera tures will
not exceed +125^oC.
C opyright © ANPEC Electronics C orp.
19
Rev. A.1 - Sep., 2015
www.anpec.com.tw