AME5250 Datasheet, PDF (9/21 Pages) Analog Microelectronics – 1A, 1.5MHz Synchronous Step-Down Converter

AME
AME5250
1A, 1.5MHz Synchronous
Step-Down Converter
The selection of C_OUT is determined by the effective se-
ries resistance(ESR) that is required to minimize voltage
ripple and load step transients. The output ripple, V_OUT, is
determined by:
∆V_OUT ≅ ∆I _L
ESR + ¹
8 fC_OUT
Using Ceramic Input and Output Capacitors
Higher values, lower cost ceramic capacitors are now
becoming available in smaller case sizes. Their high ripple
current, high voltage rating and low ESR make them ideal
for switching regulator applications. However, care must
be taken when these capacitors are used at the input and
output. When a ceramic capacitor is used at the input and
the power is supplied by a wall adapter through long wires,
a load step at the output can induce ringing at the input,
V_IN. At best, this ringing can couple to the output and be
mistaken as loop instability. At worst, a sudden inrush of
current through the long wires can potentially cause a volt-
age spike at V_IN large enough to damage the part.
Output Voltage Programming
The output voltage is set by an external resistive divider
according to the following equation:
V_OUT
= V_REF ×
1 + ^R1
R2
Thermal Considerations
In most applications the AME5250 does not dissipate
much heat due to its high efficiency. But, in applications
where the AME5250 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 maximum
junction temperature of the part. If the junction tempera-
ture reaches approximately 160^OC, both power switches
will be turned off and the SW node will become high im-
pedance. To avoid the AME5250 from exceeding the maxi-
mum junction temperature, the user will need to do some
thermal analysis. The goal of the thermal analysis is to
determine whether the power dissipated exceeds the
maximum junction temperature of the part. The tempera-
ture rise is given by:
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.
Where V_REF equals to 0.6V typical. The resistive divider
allows the FB pin to sense a fraction of the output voltage
as shown in Figure 4.
0.6V ≤ VOUT ≤ 5.5V
R1
FB
AME5250
R2
GND
Figure 4. Setting the AME5250 Output Voltage
Rev.B.04
9