AME5250A Datasheet, PDF (9/22 Pages) Analog Microelectronics – 1A, 1.5MHz Synchronous Step-Down Converter

AME
AME5250A
The selection of C_OUT is determined by the effective
series resistance(ESR) that is required to minimize volt-
age 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 voltage spike at V_IN large enough to damage the
part.
Output Voltage Programming
The output voltage is set by an external resistive di-
vider according to the following equation:
V_OUT
= V_REF ×
1 + ^R1
R2
Where V_REF 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 ≤ VOUT ≤ 5.5V
R1
FB
AME5250A
R2
GND
1A, 1.5MHz Synchronous
Step-Down Converter
Thermal Considerations
In most applications the AME5250A does not dissi-
pate much heat due to its high efficiency. But, in appli-
cations where the AME5250A is running at high ambient
temperature 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
temperature reaches approximately 160^OC, both power
switches will be turned off and the SW node will become
high impedance. To avoid the AME5250A from exceed-
ing the maximum 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 temperature 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.
Figure 4. Setting the AME5250A Output Voltage
Rev.A.03
9