MAX8633–MAX8636
Dual 300mA Pin-Programmable LDO
Linear Regulators
10 ______________________________________________________________________________________
Input-Output Voltage (Dropout Voltage)
A regulator’s minimum input-output voltage differential
(or dropout voltage) determines the lowest usable sup-
ply voltage. In battery-powered systems, this deter-
mines the useful end-of-life battery voltage. Because
the MAX8633–MAX8636 use a p-channel MOSFET
pass transistor, dropout voltage is a function of drain-
to-source on-resistance (R
DS(ON)
) multiplied by the
load current (see
Typical Operating Characteristics
).
Calculating Maximum Output Power
The maximum output power of the MAX8633–MAX8636
is limited by the maximum power dissipation of the
package. By calculating the power dissipation of the
device as a function of the input voltage, output volt-
ages, and output currents, the worst-case power dissi-
pation can be obtained. The worst-case power
dissipation should not exceed the package’s maximum
power rating:
where:
V
IN(MAX)
= Maximum input voltage
V
OUT1
= Output voltage of OUT1
V
OUT2
= Output voltage of OUT2
I
OUT1
= Maximum output current of OUT1
I
OUT2
= Maximum output current of OUT2
P
D
must be less than P
DMAX
, the maximum power dis-
sipation of the package. If P
D
is greater than P
DMAX
,
consider using the 8-pin TDFN package.
P
DMAX
= 380mW for the 8-pin µDFN. Derate by
4.8mW/°C above +70°C.
P
DMAX
= 1904mW for the 8-pin TDFN. Derate by
23.8mW/°C above +70°C.
PC Board Layout Guidelines
Follow these guidelines for good PC board layout:
• Keep the input and output traces short and wide if
possible, especially at the ground terminals.
• Use thick copper PC boards to enhance thermal
performance. Connect the exposed paddle of the
TDFN package to the ground plane or a large cop-
per pad.
• Place output, input, and bypass capacitors as close
as possible to the IC.
• Ensure the noise bypass capacitor and associated
PC board traces are routed away from noise
sources to ensure low-output voltage noise.
An evaluation kit (MAX8633EVKIT) is available for a lay-
out example to speed designs.
