MP2160 – 1.2A PEAK, 6V, 3.5MHz SYNCHRONOUS STEP-DOWN SWITCHER
MP2160 Rev. 1.03 www.MonolihicPower.com 9
7/5/2016 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2016 MPS. All Rights Reserved.
OPERATION
MP2160 uses constant on-time control with
input voltage feed forward to stabilize the
switching frequency over full input range. At
light load, MP2160 employs a proprietary
control of low side switch and inductor current
to eliminate ringing on switching node and
improve efficiency.
Constant On-time Control
Compare to fixed frequency PWM control,
constant on-time control offers the advantage of
simpler control loop and faster transient response.
By using input voltage feed forward, MP2160
maintains a nearly constant switching frequency
across input and output voltage range. The on-
time of the switching pulse can be estimated as:
OUT
ON
IN
V
T0.285s
V
To prevent inductor current run away during load
transient, MP2160 fixes the minimum off time to
be 30ns. However, this minimum off time limit will
not affect operation of MP2160 in steady state in
any way.
Light Load Operation
In light load condition, MP2160 uses a
proprietary control scheme to save power and
improve efficiency. The MP2160 will turn off the
low side switch when inductor current starts to
reverse. Then MP2160 works in discontinuous
conduction mode (DCM) operation.
For COT part, the efficiency can be improved if
using smaller inductor. That because smaller
inductor can transfer more energy in single on
pulse, and can save more driver loss.
Considering the internal circuit propagation time,
the typical delay is 50ns. It means the inductor
current still fall after the ZCD is trigger in this
delay. If the inductor current falling slew rate is
fast (VOUT voltage is high or close to Vin), the
low side MOSFET is turned off and inductor
current may be negative. This phenomena will
cause MP2160 can not enter DCM operation. If
the DCM mode is required, the off time of low
side MOSFET in CCM should be longer than
100ns. For example, Vin is 3.6V and Vo is 3.3V,
the off time in CCM is 60ns. It is difficult to enter
DCM at light load. And using smaller inductor
can improve it and make it enter DCM easily.
Enable
When input voltage is greater than the under-
voltage lockout threshold (UVLO), typically 2.3V,
MP2160 can be enabled by pulling EN pin to
higher than 1.2V. Leaving EN pin float or pull
down to ground will disable MP2160. There is
an internal 1Meg Ohm resistor from EN pin to
ground.
Soft Start
MP2160 has built-in soft start that ramps up the
output voltage in a controlled slew rate,
avoiding overshoot at startup. The soft start
time is about 1.5ms typical.
Power GOOD Indicator
MP2160 has an open drain with 550k pull-up
resistor pin for power good indicator PG. When
FB pin is within +/-10% of regulation voltage, i.e.
0.6V, PG pin is pulled up to VIN by the internal
resistor. If FB pin voltage is out of the +/-10%
window, PG pin is pulled down to ground by an
internal MOSFET. The MOSFET has a
maximum R
dson
of less than 100 Ohm.
Current limit
MP2160 has a typical 1.6A current limit for the
high side switch. When the high side switch hits
current limit, MP2160 will touch the hiccup
threshold until the current lower down. This will
prevent inductor current from continuing to build
up which will result in damage of the
components.
Short Circuit and Recovery
MP2160 enters short circuit protection mode
also when the current limit is hit, and tries to
recover from short circuit with hiccup mode. In
short circuit protection, MP2160 will disable
output power stage, discharge soft-start cap
and then automatically try to soft-start again. If
the short circuit condition still holds after soft-
start ends, MP2160 repeats this operation cycle
till short circuit disappears and output rises
back to regulation level.
