Dual PWM Step-Down Converter in a 2mm x
2mm Package for WCDMA PA and RF Power
14 ______________________________________________________________________________________
Input Capacitor Selection
The input capacitor (C
IN
) reduces the current peaks
drawn from the battery or input power source and
reduces switching noise in the MAX8896. The imped-
ance of C
IN
at the switching frequency should be kept
very low. Ceramic capacitors with X5R or X7R tempera-
ture characteristics are highly recommended due to
their small size, low ESR, and small temperature coeffi-
cients. A 4.7礔 capacitor is recommended for C
IN1
and
2.2礔 for C
IN2
. For optimum noise immunity and low
input ripple, the input capacitor value can be
increased.
Note that some ceramic dielectrics exhibit large capac-
itance and ESR variation with temperature and DC bias.
Ceramic capacitors with Z5U or Y5V temperature char-
acteristics should be avoided.
Thermal Considerations
In most applications, the MAX8896 does not dissipate
much heat due to its high efficiency. But in applications
where the MAX8896 runs at high ambient temperature
with heavy loads, the heat dissipated may exceed the
maximum junction temperature of the part. If the junction
temperature reaches approximately +160癈, the thermal-
overload protection is activated.
2MHz
OUT1
LX1
PGND1
PAOUT
IN1
RFEN1
REFIN
REF
REFBP
*DE2818C
AGND
LDO
IN2
PAEN
CONTROL
PA ENABLE
RF ENABLE 1
ANALOG
CONTROL
2MHz
OUT2
LX2
PGND2
RFEN2
OUT2
1000pF
RF ENABLE 2
2.7V TO 5.5V
0.1礔
V
CC
4.7礔
0.033礔
2.2礖
BRL2012T 2R2M
2.2礔
V
RF
(2.8V)
2.2礔
4.7礖*
V
PA
4.7礔
MAX8896
V
OUT2
(3.1V)
LDO
OUT2
1礔
Figure 3. Typical Applications Circuit