MP2162 – 2A, 6V, 1.5MHz SYNCHRONOUS STEP-DOWN SWITCHER
MP2162 Rev. 1.03 www.MonolihicPower.com 9
6/8/2017 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2017 MPS. All Rights Reserved.
OPERATION
MP2162 uses constant on-time control with
input voltage feed forward to stabilize the
switching frequency over full input range. At
light load, MP2162 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, MP2162
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
T0.667s
V
To prevent inductor current run away during load
transient, MP2162 fixes the minimum off time to
be 60ns. However, this minimum off time limit will
not affect operation of MP2162 in steady state in
any way.
Light Load Operation
In light load condition, MP2162 uses a
proprietary control scheme to save power and
improve efficiency. The MP2162 will turn off the
low side switch when inductor current starts to
reverse. Then MP2162 works in discontinuous
conduction mode (DCM) operation.
The DCM mode happens only after low side
switch turned off by ZCD circuit. Considering
the ZCD circuit propagation time, the typical
delay is 30ns. It means the inductor current still
fall after the ZCD is trigger during this delay. If
the inductor current falling slew rate is fast (Vo
voltage is high or close to Vin), the low side
MOSFET is turned off at the moment inductor
current may be negative. This phenomena will
cause MP2162 can not enter DCM operation. If
the DCM mode is required, the off time of low
side MOSFET in CCM should be longer than
60ns. It means the maximum duty is 90% to
guarantee DCM mode at light load.
For example, V
IN
is 3.4V and V
OUT
is 3.3V, the
off time in CCM is 20ns. 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,
MP2162 can be enabled by pulling EN pin to
higher than 1.2V. Leaving EN pin float or pull
down to ground will disable MP2162. There is
an internal 1Meg Ohm resistor from EN pin to
ground.
Soft Start
MP2162 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 Indictor
MP2162 has an open drain with 550k pull-up
resistor pin for power good indicator PGOOD.
When FB pin is within +/-10% of regulation
voltage, i.e. 0.6V, PGOOD pin is pulled up to
VIN by the internal resistor. If FB pin voltage is
out of the +/-10% window, PGOOD pin is pulled
down to ground by an internal MOS FET. The
MOS FET has a maximum R
dson
of less than
100 Ohm.
Current limit
MP2162 has a typical 3.2A current limit for the
high side switch. When the high side switch hits
current limit, MP2162 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
MP2162 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, MP2162 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, MP2162 repeats this operation cycle
till short circuit disappears and output rises
back to regulation level.
