AME
1.5MHz, 600mA
Synchronous Buck Converter
AME5258
Output Voltage Programming
VIN
The output voltage is set by an external resistive divider
according to the following equation :
VOUT
1.2V
2.2mH
2.5V to5.5V
IN
SW
FB
22pF
COUT
10mF
CER
R2
AME5258
GND
=
(1+
)
VOUT
VREF
R1
EN
604K
Where VREF equals to 0.6V typical. The resistive di-
vider allows the FB pin to sense a fraction of the output
voltage as shown in Figure 4.
COUT
4.7mF
CER
604K
0.6V £ VOUT £ 5.5V
Figure 5: 1.2V Step-Down Regulator
R2
FB
VIN
VOUT
1.5V
2.2mH
3.3V to 5.5V
IN
SW
FB
AME5258
R1
22pF
COUT
GND
AME5258
GND
10mF
CER
EN
475K
COUT
4.7mF
CER
Figure 4: Setting the AME5258 Output Voltage
316K
Thermal Considerations
In most applications the AME5258 does not dissipate
much heat due to its high efficiency. But, in applications
where the AME5258 is running at high ambient tempera-
ture with low supply voltage and high duty cycles, such
as in dropout, the heat dissipated may exceed the maxi-
mum junction temperature of the part. If the junction tem-
perature reaches approximately 160OC, both power
switches will be turned off and the SW node will become
high impedance. To avoid the AME5258 from exceeding
the maximum junction temperature, the user will need to
do some thermal analysis. The goal of the thermal analy-
sis is to determine whether the power dissipated exceeds
the maximum junction temperature of the part. The tem-
perature rise is given by:
Figure 6: 1.5V Step-Down Regulator
VIN
VOUT
2.5V
2.2mH
2.7V to5.5V
IN
SW
FB
22pF
1M
COUT
10mF
CER
AME5258
GND
EN
COUT
4.7mF
CER
316K
TR
q
=( )( )
PD
JA
Figure 7: 2.5V Step-Down Regulator
Where PD is the power dissipated by the regulator and
qJA is the thermal resistance from the junction of the die
to the ambient temperature.
10
Rev.A.05
AMETHERM [ AMETHERM CIRCUIT PROTECTION THERMISTORS ]
