MAX8819A/MAX8819B/MAX8819C
PMIC with Integrated Chargers and Smart
Power Selector in a 4mm x 4mm TQFN
28 ______________________________________________________________________________________
current is first reduced by lowering charge current. If
the junction temperature still reaches +120°C in spite of
charge current reduction, no input current is drawn
from DC; the battery supplies the entire load and SYS is
regulated 70mV below BAT.
Regulator Thermal-Overload Shutdown
The IC disables all regulator outputs and the battery
charger when the junction temperature rises above
+165°C, allowing the device to cool. When the junction
temperature cools by approximately 15°C the regula-
tors and charger resume the state indicated by the
enable input (EN123, EN4, and CEN) by repeating their
soft-start sequence. Please note that this thermal-over-
load shutdown is a fail-safe mechanism; proper thermal
design should ensure that the junction temperature of
the MAX8819_ never exceeds the absolute maximum
rating of +150°C.
Applications Information
Dynamic Output Voltage Adjustment
for Step-Down Converters
Dynamic output voltage adjustment can be implement-
ed for the step-down converter by adding a resistor
and a switch from FB_ to GND. See Figure 9.
To calculate the resistor-divider, start with the lower
voltage desired and calculate the resistor-divider using
R
T
and R
B
only. Setting R
B
= 100kΩ is acceptable. Use
the following equation to calculate R
T
:
where V
OUTL
is the desired lower output voltage and
V
FB
is the feedback regulation voltage, 1V (typ).
R
D
is calculated using the higher set voltage and the
following equations assuming the switch resistance is
negligible:
where R
PAR
is the parallel resistance of R
B
and R
D
,
V
OUTH
is the higher set voltage, and V
FB
is the feed-
back regulation voltage, 1V (typ).
For example, if V
OUTL
= 3V, V
OUTH
= 3.3V, R
B
=
100kΩ, then:
R
T
= 100kΩ x ((3V/1V) - 1) = 200kΩ
R
PAR
= 200kΩ/((3.3V/1V) - 1) = 86.96kΩ
R
D
= 1/((1/86.96kΩ) - (1/100kΩ)) = 666.7kΩ
Choose R
D
= 665kΩ as the closest standard 1% value.
CH1 = gate drive to switch
CH2 = V1, 1V offset; 3V to 3.3V to 3V, 10Ω load
CH3 = RST1
The scope plot (Figure 10) shows V1 switching from 3V
to 3.3V to 3V with the resistor values of the example.
When the switch is turned on, V1 slews from 3V to 3.3V
in about 20μs, which is less than the 50μs RST1 de-
glitch filter, and therefore, RST1 does not trip. When the
switch is turned off, V1 soars to about 3.35V due to the
energy in the inductor. Since V1 is above the regulation
voltage, REG1 skips until V1 decays to the regulation
voltage. The decay rate is determined by the output
capacitance and the load. In this example, the output
capacitance is 10μF and the load is 10Ω, so the time
