AME5125 Datasheet, PDF (6/11 Pages) Analog Microelectronics – High Efficiency 500KHz

AME
AME5125
n Application Information
Over Voltage Protection
The AME5125 has output over-voltage protections. The
thresholds output OVP circuit minimum 116% x V_OUT,
respectively. Once the output voltage is higher than the
threshold, the NMOS driver is turned off. When the out-
put voltage drops lower than the threshold, the NMOS
driver will be enabled again.
Inductor Selection
The inductor is required to supply current to the load
while being driven by the switched input voltage. It will
result in less ripple current that will in turn result in lower
output ripple voltage. In addition minimum inductance value
is proportional to the operating frequency. Make sure
that the peak inductor current is below the maximum
switch current limit. Determine inductance is to allow
the peak-to-peak ripple current to be approximately 30%
of the maximum load current. The inductance value can
be calculated by:
L=(V_IN/V_OUT)² (V_OUT-V_IN) / F_SW x I_OUT x 40%
cuFrr^Se^Wnits. ^{the switching frequency IOUT is the max output}
Over Current Protection
The AME5125 cycle-by-cycle limits the peak inductor
current to protect NMOS driver. The NMOS driver will
turn off when switching current reaches OCP level that
can be set by external RISET.
Thermal Shutdown
The AME5125 protects itself from overheating with an
internal thermal shutdown circuit. If the junction tem-
perature exceeds the thermal shutdown trigger point, the
NMOS driver is turned off. The part is restarted when the
junction temperature drops 20^oC below the thermal shut-
down trigger point.
Setting the Output Voltage
The output voltage is using a resistive voltage divider
connected from the output voltage to FB. It divides the
output voltage down to the feedback voltage by the ratio:
6
High Efficiency 500KHz
Step-Up Converter
V_OUT=0.6x(1+R1/R2)
VOUT
0.6V
R1
EA
FB
R2
Input Capacitor C_IN
The input current to the boost converter is discontinu-
ous, therefore a capacitor is required to supply the AC
current while maintaining the DC input voltage. Use low
ESR capacitors for the best performance. Ceramic ca-
pacitors are preferred.
The ripple current through input capacitor is calculated
was list below:
I_{CIN_RMS}=V_INx(V_OUT-V_IN)/3.46xLxF_SWxV_OUT
The input capacitor is selected to handle the input ripple
noise requirements. Suggesting to use X5R or X7R grade
ceramic capacitor.
Output capacitor C_OUT
The outpour capacitor is required to maintain the DC
output voltage. Ceramic, tantalum, or low ESR electro-
lytic capacitors are recommended. The Low ESR ca-
pacitors are preferred to keep the lower output voltage
ripple. It's recommended X5R or X7R ceramic capacitor
with enough voltage rating.
The Enable Operation
Pulling the EN pin low (<0.6V) will shutdown the de-
vice. At the shutdown mode, the AME5125 output drop
to zero in addition only below 1uA standby current. When
EN Pin >1.4, the AME5125 will turn on device. If EN Pin
floating the AME5125 into shutdown mode.
Rev.P01