Datasheet

MAX8819A/MAX8819B/MAX8819C
PMIC with Integrated Chargers and Smart
Power Selector in a 4mm x 4mm TQFN
24 ______________________________________________________________________________________
Step-Down Converter
Active Discharge in Shutdown
Each MAX8819_ step-down converter (REG1, REG2,
REG3) has an internal 1kΩ resistor that discharges the
output capacitor when the converter is off. The dis-
charge resistors ensure that the load circuitry powers
down completely. The internal discharge resistors are
connected when a converter is disabled and when the
device is in UVLO with an input voltage greater than
1.0V. With an input voltage less than 1.0V the internal
discharge resistors are not activated.
Step-Down Converter Enable/
Disable (EN123) and Sequencing
Figure 5a shows the MAX8819A/MAX8819B enable and
disable logic. Figure 5b shows the MAX8819C
enable/disable logic. Figure 6 shows an example of
enable and disable waveforms for the MAX8819A/
MAX8819B.
Figure 6 notes:
1) The device is off with no external power applied to
DC. The system voltage (V
SYS
) is equal to the bat-
tery voltage (V
BAT
).
2) An external supply is applied to DC that causes the
step-down converter to power up after the DC-to-
SYS soft-start time (t
SS-D-S
). When the DC input is
valid and DLIM[1:2] ≠ 11, V
SYS
increases.
3) When V1 reaches the reset trip threshold (V
THRST
),
the reset deassert delay timer starts. When the reset
deassert delay timer expires (t
DRST1
), RST1 goes
high-impedance. If RST1 is connected to the RESET
V
EN123
V
OUT1
V
OUT2
V
OUT3
V
DC
t
SS-D-S
V
SYS
V
SYS
- V
D
V
BAT
HIGH
IMPEDANCE
t
SS1
NOTES
12
t
SS2
t
SS3
V
RST1
t
DRST1
34
V
EN4
5
t
SS4
V
OUT4
V
BAT
78
t
SS_CHG
6
V
SYS
- V
D
V
CEN
V
CHG
V
BAT
< V
SYS
< V
DC
Figure 6. MAX8819A/MAX8819B Enable/Disable Waveforms Example