Datasheet

MAX8819A/MAX8819B/MAX8819C
PMIC with Integrated Chargers and Smart
Power Selector in a 4mm x 4mm TQFN
______________________________________________________________________________________ 23
As the load current is increased beyond this point, the
output voltage sags and the converter goes out of regu-
lation because the inductor current cannot increase
above the p-channel peak current limit.
Step-Down Converter Short-Circuit Protection
The step-down converter implements short-circuit protec-
tion by monitoring the feedback voltage, V
FB_
. After soft-
start, if V
FB_
drops below 0.23V, the converter reduces its
switching frequency to f
S
/3. The inductor current still
reaches the p-channel peak current limit, however, at
one-third the frequency. Therefore, the output and input
currents are reduced to approximately one-third of the
maximum value in response to an output short circuit to
ground. When the short is removed, the inductor current
raises the voltage on the output capacitor and the step-
down converter resumes normal operation.
REG1 Reset (RST1)
RST1 is an active-low, open-drain output that pulls low
to indicate that FB1 is below its regulation threshold.
RST1 goes high 200ms after FB1 reaches its regulation
threshold. RST1 is high-impedance when EN123 is
high. See Figures 6 and 7.
A 50μs blanking delay is provided when FB1 is falling,
so that RST1 does not glitch if the REG1 output voltage
is dynamically adjusted by altering the resistors in its
feedback network.
+
-
+
-
+
-
+
-
6.0V RISING
400mV HYST.
4.0V RISING
500mV HYST.
SOFT-START
REG2
EN
OK
REG1OK
SOFT-START
REG1
EN
OK
REG2OK
SOFT-START
REG3
EN
OK
REG3OK
2.5V RISING
100mV HYST.
2MHz
OSC
BIAS
AND
REF
64 CYCLE
DELAY
(32μs)
+165°C
DIE TEMP
SYS
DC
EN4
DCPOK
READY
READY
REGON
DCOVLO
DCUVLO
SYSOK
DT165
SOFT-START
REG4
EN OK
REG4OK
EN123
REGON
MAX8819C
Figure 5b. MAX8819C Enable Logic