MIC24046-H Datasheet, PDF (9/24 Pages) Micrel Semiconductor – Pin-Programmable, 4.5V − 19V, 5A Step-Down Converter

Micrel, Inc.
Functional Description
The MIC24046-H is a pin-programmable, 5A valley
current-mode controlled regulator, with an input voltage
range from 4.5V to 19V.
The MIC24046-H requires a minimal amount of external
components. Only inductor, supply decoupling capacitors
and compensation network are external. The flexibility in
designing the external compensation allows the user to
optimize the design across the entire input voltage and
selectable output voltages range.
Theory of Operation
Valley current-mode control is a fixed-frequency, leading-
edge-modulated PWM current mode control. As opposed
to peak-current-mode, in valley current mode the clock
marks the turn-off of the high-side switch, and the turn on
of the low-side switch. After this instant, in the MIC24046-
H the low-side switch current level is compared against
the reference current signal from the error amplifier. As
soon as the falling low-side switch current signal drops
below the current reference signal, the high side switch is
turned on. As a result, the inductor valley current is
regulated to a level dictated by the output of the error
amplifier.
As shown in the “Compensation Design” sub-section
within the Application Information section, the feedback
loop includes an internal programmable reference
(REF_DAC) and output voltage sensing attenuator (R2/R1),
removing the need for external feedback components
and improving regulation accuracy. Output voltage
feedback is achieved by connecting OUTSNS directly to
the output. The high-performance transconductance error
amplifier drives an external compensation network at the
COMP pin. The voltage at COMP represents the
reference current signal. The latter is fed to the valley
current mode modulator, which also adds slope
compensation to guarantee current-loop stability. Valley
current-mode control requires slope compensation at
duty cycles less than 50% for current-loop stability. The
slope compensation circuit is internal, and it is
automatically adapted in amplitude depending upon the
frequency, output voltage range, and voltage differential
(V_VIN − V_OUTSNS). Internal low-R_DS(ON) power MOSFETs,
the associated adaptive gate driver and internal bootstrap
diode complete the power train.
Overcurrent protection and thermal shutdown protect the
MIC24046-H from faults or abnormal operating
conditions.
MIC24046-H
Internal LDO, Supply Rails
(VIN, VINLDO, VDDA, VDDP)
VIN represents the power train input. These pins are the
drain connection of the internal high-side MOSFET and
should be bypassed to GND with a X5R or X7R 10µF
(minimum) ceramic capacitor, placed as close as
possible to the IC. A combination of ceramic capacitors of
different sizes is recommended.
An internal LDO (input = VINLDO) provides a clean
supply (5.1V typ.) for the analog circuits at pin VDDA.
The internal LDO is typically powered from the same
power rail fed at VIN; however VINLDO can also be
higher or lower than VIN and can be connected to any
other voltage within its recommended limits. VINLDO and
VDDA should be locally bypassed (see Pin Description).
A small series resistor (typically 2Ω-10Ω) can be used in
combination with the VINLDO bypass capacitor to
implement a RC filter for suppression of large high-
frequency switching noise.
The internal LDO is enabled when the voltage at the
EN/DLY pin exceeds about 0.51V and regulation takes
place as soon as enough voltage has established
between the VINLDO and VDDA pins. If an external
5V±10% is available it is possible to bypass the internal
LDO by connecting VINLDO, VDDA and VDDP together
at the external 5V rail, thus improving overall efficiency.
An internal undervoltage lock-out circuit (UVLO) monitors
the level of VDDA.
VDDP is the power supply rail for the gate drivers and
bootstrap circuit. This pin is subject to high-current spike
with high-frequency content. To prevent these from
polluting the analog VDDA supply, a separate capacitor is
needed for VDDP pin bypassing.
An internal 10Ω resistor is provided between VDDA and
VDDP allowing a switching noise attenuation RC filter
with the minimum amount of external components to be
implemented. It is possible − although typically not
necessary − to lower the RC time constant by connecting
an external resistor between VDDA and VDDP.
Enable/Delay (EN/DLY)
EN/DLY is a dual-threshold pin that turns the internal
LDO ON/OFF and starts/stops the power delivery to the
output. This is shown in Figure 1:
July 7, 2015
9
Revision 1.1