AME, Inc.
AME5150
n
Detailed Description
The AME5150 features a constant off-time control
scheme. Operation can be best understood by referring
to Figure 3. When the voltage at the NFB pin is larger
than -1.23V, the Enable Comp in Figure 3 enables the
device and the NMOS switch is turned on, pulling the
SW pin to ground. When the NMOS switch is on, load
current is supplied by the output capacitor C3. Once the
current in the inductor reaches the peak current limit, the
400ns One Shot turns off the NMOS switch. During this
time the energy stored in the inductor is transferred to C3
and the load. After the 400ns off-time the NMOS switch
is turned on and energy is stored in the inductor again.
This energy transfer from the inductor to the output causes
a stepping effect in the output ripple.
This cycle is continued until the voltage at NFB pin
reaches -1.23V. When NFB pin reaches this voltage, the
enable comparator then disables the device turning off
the NMOS switch and reducing the quiescent current of
the device to 65µA. The load current is then supplied
solely by C3 indicated by the gradually decreasing volt-
age at the output. When the NFB pin drops slightly be-
low -1.23V, the enable comparator enables the device
and begins the cycle as described previously. The EN
pin can be used to turn off the AME5150 and reduce the
quiescent current to 0.1µA.
Micropower Inverting
DC/DC Converter
Rev.A.01
7
AME [ ANALOG MICROELECTRONICS ]
