MP161 – INTEGRATED POWER SOLUTION FOR HOME/INDUSTRIAL AUTOMATION
The MP161 implements soft start by decreasing
OPERATION
the minimal off time gradually in eight steps.
There are 640 switching cycles in the soft start.
During soft start, short-circuit protection (SCP)
and overload protection (OLP) are disabled.
The MP161 integrates a 700V switching
regulator, a low-dropout linear regulator, and
relay drivers. The MP161 is an integrated
power stage solution for home automation,
Constant Voltage Operation
industrial
automation,
and
any
other
The MP161 integrates a 700V switching
regulator that regulates the output voltage by
detecting the feedback (FB). The internal
MOSFET is turned on when the FB voltage (VFB)
is lower than the reference voltage (VREF) and is
turned off based on the peak-current limitation
(see Figure 3). In this way, VFB is regulated at
VREF. The output voltage is determined in
Equation (1):
applications that adopt relays and MCUs.
High Voltage (HV) Current Source and VCC
Under-Voltage Lockout (UVLO)
The internal high-voltage (HV) current source
regulates VCC by drawing current from DRAIN.
When VCC reaches VHVoff, the IC starts
switching, and the internal HV current source is
turned off. The internal HV current source turns
on again when VCC falls below VHVon
.
Rup Rlow
VO V
(1)
During start-up under normal operation, the
MP161 VCC voltage is always regulated above
VHVon. A very small VCC capacitor can be used
(in the low μF or hundreds of nF range).
ref
Rlow
VCC under-voltage lockout (UVLO) terminates
the switching when VCC is lower than VCCL to
prevent errors caused by an insufficient supply
voltage. The IC can shut down until VCC is
charged to VHVoff again. This does not occur,
typically, because the HV current source turns
on to supply VCC as soon as VCC drops to
VHVon, which prevents it from dropping to VCCL
(see Figure 2).
Figure 3: Constant Voltage Regulation
An internal resistor divider connected to VCC
and FB provides a fixed output feedback. The
lower resistor of the internal feedback divider is
450kΩ, typically.
To achieve an adjustable output, an external
feedback divider with a much smaller resistance
should be connected to FB so that the internal
feedback is overridden.
Figure 2: HV Current Source and VCC Operation
Soft Start (SS)
A VCC capacitor is used for sampling and
holding the output voltage in addition to
supplying the IC operation.
The MP161 starts switching with a soft-start
period when the device powers on or resumes
operation from a protection mode. Soft start
prevents the inductor current from overshooting.
MP161 Rev. 1.0
8/4/2017
www.MonolithicPower.com
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