EVM3810-QB-25-01A Datasheet, PDF (12/17 Pages) MPS Industries, Inc. – 6V Input, 1.2A Module Synchronous Step-Down Converter with Integrated Inductor

MPM3810 –6V, 1.2A PEAK SIMPLE MODULE WITH INTEGRATED INDUCTOR
OPERATION
The DC-DC module has a small surface-mount
QFN-12 (2.5mmx3.0mmx0.9mm) package. The
module’s integrated inductor simplifies the
schematic and layout design. Only FB resistors
and input and output capacitors are needed to
complete the design. MPM3810 uses constant
on-time control (COT) with input voltage feed
forward to stabilize the switching frequency over
a full-input range. At light load, MPM3810
employs a proprietary control of the low-side
switch and inductor current to improve efficiency.
Constant On-Time Control (COT)
Compared to a fixed-frequency PWM control,
constant on-time control (COT) offers the
advantage of a simpler control loop and faster
transient response. Using input voltage feed
forward, the MPM3810 maintains a nearly constant
switching frequency across the input and output
voltage range. The on-time of the switching pulse
is estimated as follows:
T_ON
=
V_OUT
V_IN
⋅ 0.28us
To prevent inductor current run away during load
transition, MPM3810 fixes the minimum off time to
60ns. However, this minimum off-time limit does
not affect operation in a steady state.
Light-Load Operation
In a light-load condition, MPM3810 uses a
proprietary control scheme to save power and
improve efficiency. The MP3810 turns off the
low-side switch when the inductor current begins
to reverse. Then MP3810 works in discontinuous
conduction mode (DCM) operation.
A zero current cross circuit detects if the inductor
current begins to reverse. Considering the
internal circuit propagation time, the typical delay
time is 30ns. This means the inductor current
continues to fall after the ZCD is triggered. If the
inductor current falling slew rate is fast (Vo
voltage is high or close to Vin), the low-side
MOSFET turns off (this means the inductor
current may be negative). This does not allow the
MPM3810 to enter DCM. If DCM is required, the
off-time of the low-side MOSFET in continuous
conduction mode (CCM) should be longer than
60ns. For example, if Vin is 3.6V and Vo is 3.3V,
the off-time in CCM is 24ns. It is difficult to enter
DCM at light load.
Enable (EN)
If the input voltage is greater than the under-
voltage lockout threshold (UVLO), typically 2.3V,
MPM3810 is enabled by pulling EN above 1.2V.
Leaving EN to float or be pulled down to ground
disables MPM3810. There is an internal 1MΩ
resistor from EN to ground.
Soft-Start (SS)
MPM3810 has a built-in soft-start that ramps up
the output voltage in a controlled slew rate. This
avoids overshoot at startup. The soft-start time is
about 1.5ms typically.
Power GOOD Indictor (PGOOD)
MPM3810 has an open drain with a 550kΩ pull-
up resistor pin for the power good indicator
(PGOOD). When FB is within +/-10% of
regulation voltage (i.e. 0.6V), PGOOD is pulled
up to IN by the internal resistor. If FB voltage is
out of the +/-10% window, PGOOD is pulled
down to ground by an internal MOSFET. The
MOSFET has a maximum R_dson of less than
400Ω.
Current Limit
MPM3810 has a typical 2.1A current limit for the
high-side switch. When the high-side switch
reaches the current limit, MPM3810 hits the
hiccup threshold until the current decreases. This
prevents the inductor current from continuing to
build, which results in damage to the components.
Short Circuit and Recovery
MPM3810 enters short-circuit protection (SCP)
mode when the current limit is reached; then it
tries to recover from the short circuit with hiccup
mode. In SCP, MPM3810 disables the output
power stage, discharges the soft-start cap and
then automatically tries to soft-start again. If the
short circuit remains after the soft-start ends,
MPM3810 repeats the cycle until the short circuit
disappears, and the output rises back to the
regulation level.
MPM3810 Rev. 1.1
www.MonolithicPower.com
12
12/8/2014
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