MAX8805Y MAXIM [Maxim Integrated Products], MAX8805Y Datasheet - Page 16

• Manufacturer Part Number: MAX8805Y
• Description: 600mA PWM Step-Down Converters in 2mm x 2mm WLP for WCDMA PA Power
• Manufacturer: MAXIM [Maxim Integrated Products]

In most applications, the MAX8805Y/MAX8805Z do not
dissipate much heat due to their high efficiency.
However, in applications where the MAX8805Y/
MAX8805Z run at high ambient temperature with heavy
loads, the heat dissipated may exceed the maximum
junction temperature of the IC. If the junction tempera-
ture reaches approximately +160°C, all power switches
are turned off and LX and PA_ become high imped-
ance, and LDO1 and LDO2 are pulled down to ground
through an internal 1kΩ pulldown resistor.
The MAX8805Y/MAX8805Z maximum power dissipation
depends on the thermal resistance of the IC package
and circuit board, the temperature difference between
the die junction and ambient air, and the rate of airflow.
The power dissipated in the device is:
where η
verter and P
converter.
The maximum allowed power dissipation is:
600mA PWM Step-Down Converters in
2mm x 2mm WLP for WCDMA PA Power
16
P
DISS
______________________________________________________________________________________
= P
PA
PA
is the efficiency of the PA step-down con-
PA
x (1/η
P
is the output power of the PA step-down
MAX
I
LDO2
PA
= (T
x (V
- 1) + I
Thermal Considerations
JMAX
IN2
LDO1
-V
- T
LDO2
A
) / θ
x (V
)
JA
IN2
- V
LDO1
) +
where (T
between the MAX8805Y/MAX8805Z die junction and
the surrounding air; θ
junction through the PCB, copper traces, and other
materials to the surrounding air.
High switching frequencies and relatively large peak
currents make the PCB layout a very important part of
design. Good design minimizes excessive EMI on the
feedback paths and voltage gradients in the ground
plane, resulting in a stable and well-regulated output.
Connect C
the inductor and output capacitor as close as possible
to the IC and keep their traces short, direct, and wide.
Keep noisy traces, such as the LX node, as short as
possible. Figure 3 illustrates an example PCB layout
and routing scheme.
JMAX
IN1
close to IN1A/IN1B and PGND. Connect
- T
A
) is the temperature difference
JA
is the thermal resistance of the
PCB Layout