AME
AME5258
Output Voltage Programming
The output voltage is set by an external resistive divider
according to the following equation :
1.5MHz, 600mA
Synchronous Buck Converter
V
IN
2.5V to 5.5V
IN
AME5258
EN
C
OUT
4.7µF
CER
GND
604K
FB
604K
SW
22pF
2.2µH
V
OUT
1.2V
C
OUT
10µF
CER
V
OUT
=
V
REF
⋅
(
1
+
R
2
)
R
1
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.
0.6V
≤
V
OUT
≤
5.5V
Figure 5: 1.2V Step-Down Regulator
R2
FB
V
IN
3.3V to 5.5V
2.2µH
IN
AME5258
EN
FB
475K
GND
316K
SW
22pF
V
OUT
1.5V
C
OUT
10µF
CER
AME5258
GND
R1
Figure 4: Setting the AME5258 Output Voltage
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 160
O
C, 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:
C
OUT
4.7µF
CER
Figure 6: 1.5V Step-Down Regulator
V
IN
2.7V to 5.5V
2.2µH
IN
AME5258
EN
FB
1M
GND
316K
SW
22pF
V
OUT
2.5V
C
OUT
10µF
CER
C
OUT
4.7µF
CER
T
R
=
(
PD
)(
θ
JA
)
Where PD is the power dissipated by the regulator and
θ
JA
is the thermal resistance from the junction of the die
to the ambient temperature.
Figure 7: 2.5V Step-Down Regulator
10
Rev.A.05
AMETHERM [ AMETHERM CIRCUIT PROTECTION THERMISTORS ]
