MP161 – INTEGRATED POWER SOLUTION FOR HOME/INDUSTRIAL AUTOMATION
Frequency and Peak Current Foldback
8192 consecutive cycles. The validation
time for OLP is able to prevent tripping
during start-up and transient periods.
Due to the constant voltage regulation scheme
adopted by the MP161, its switching frequency
decreases as the load reduces. The MP161
peak current folds back along with the
switching frequency. As a result, the MP161 is
able to achieve excellent overall efficiency. The
switching frequency for continuous conduction
mode (CCM) can be calculated with Equation
(2):
2. Short-Circuit Protection (SCP): If the current
flowing through the internal MOSFET after
LEB2 is higher than the SCP threshold,
SCP is triggered immediately. SCP is
disabled during soft start.
3. Over-Temperature Protection (OTP): To
prevent any thermal-induced damage, the
MP161 is shut down when the junction
temperature exceeds the thermal shutdown
threshold. There is also a hysteresis
implemented for OTP, so the chip does not
recover until the junction temperature drop
exceeds the thermal shutdown recovery
hysteresis.
(V Vo ) Vo
in
fs
(2)
2L(Ipeak Io ) V
in
The switching frequency for discontinuous
conduction mode (DCM) can be calculated with
Equation (3):
2(V VO ) IoVo
in
fs
(3)
4. Brown-Out Protection (BOP): If the turn-on
time hits the maximum limitation for four
consecutive cycles, BOP is triggered.
LI2peak
V
in
When the switching frequency drops into the
audible frequency range under very light-load
condition, the peak current folds back to its
minimal value to minimize the audible noise.
Low-Dropout Linear Regulator (LDO)
The MP161 integrates a low-dropout linear
regulator (LDO). Usually, the LDO input (VIN) is
connected to the output of the switching
regulator. VIN can adapt to any input voltage
below VOVP. The output voltage of the LDO is
internally fixed with two options for fixed voltage
outputs (5V and 3.3V).
Leading-Edge Blanking
An internal leading-edge blanking (LEB) unit
prevents premature switching pulse termination
due to a turn-on spike. The spike is mainly
caused by parasitic capacitance and reverse
recovery of the freewheeling diode (under
CCM).
The LDO itself also implements OTP, which is
independent from the switching regulator.
However, the protection scheme is similar to
the switching regulator’s scheme.
Protections for the Switching Regulator
Whenever a protection condition is triggered,
the IC stops switching, the internal HV current
source is disabled, and the VCC capacitor is
discharged by ICCL. The internal HV current
source is not enabled again until VCC drops
Relay Drivers
The MP161 integrates two channels of relay
drivers, which are compatible to 3.3 - 5V COMS
logic and TTL logic interface.
below VCCpro
.
A low-impedance MOSFET is used to drive the
relay (see Figure 4). There is also an integrated
freewheeling diode to take over the relay coil
current when the MOSFET turns off. An R-C
filter is implemented internally for each channel
to improve noise immunity. The drivers also
feature an internal pull-down resistor to allow
for tri-state input and normal off operation.
The MP161 includes four types of protection.
1. Overload Protection (OLP): The maximum
output power of the switching regulator is
limited by the maximum switching frequency
and peak current limit. If the load exceeds
the power limit, the output voltage is not
able to stay in regulation. OLP is triggered
when the MOSFET off time is at the toffmin
limitation (which indicates that the switching
frequency has reached the maximum) for
MP161 Rev. 1.0
8/4/2017
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