Microchip MIC23451-AAAYFL Manual

Microchip Ikke kategoriseret MIC23451-AAAYFL

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Side 1/7
MIC23451 Evaluation Board
3MHz PWM Triple 2A Buck Regulator with
HyperLight Load
®
and Power Good
HyperLight Load is a trademark of Micrel, Inc.registered
Micrel Inc. • 2180 Fortune Drive • Jose, CA 95131 • USA • tel +1 (408) 944 0800 • fax + 1 (408) 474 1000 • San - - http://www.micrel.com
October 14, 2013
Revision 1.0
General Description
This board allows the customer to evaluate the MIC23451,
a fully- -integrated, triple output, 2A, 3MHz switching
regulator that features HyperLight Load® mode and Power
Good output indicators. The MIC23451 is highly efficient
throughout the output range, drawing just 24current µA of
quiescent current for each channel in operation. The tiny
4mm × 4mm DFN package saves precious board space
and requires few external components. The MIC23451
provides accurate output voltage regulation under the most
demanding conditions, each channel respondwith ing
extremely quickly to a load transient with exceptionally
small output voltage ripple.
Requirements
This board needs a single bench power source 20W
adjustable from 2.7V to 5.5V. The loads can be either
active (electronic load) or passive (resistor), and must be
able to dissipate 10 . It is ideal, but not essential, to have W
an oscilloscope available to view the circuit waveforms.
The simplest tests require two voltage meters to measure
input and output voltage. Efficiency measurements for a
single channel require two voltage meters and two
ammeters to prevent errors caused by measurement
inaccuracies.
Precautions
There is no reverse input protection on this board. Be
careful when connecting the input source to make sure
correct polarity is observed.
Datasheets and support documentation are available on
Micrel’s web site at: www.micrel.com.
Getting Started
1. Connect an external supply to the VIN (J1) terminal
and GND (J ).2
With the output of the power supply disabled, set its
voltage to the desired input test voltage (2.7V ≤ VIN ≤
5.5V). An ammeter may be placed between the input
supply and the VIN (J1) terminal. Be sure to monitor
the supply voltage at the VIN (J1) terminal, as the
ammeter and/or power lead resistance can reduce the
voltage supplied to the device.
2. Connect a load to the VOUT terminals (J6, J7, J8)
and ground (J3, J4, J5) terminals.
The load can be either passive (resistive) or active
(electronic load). An ammeter may be placed between
the loads and the output terminal sure the s. Make
output voltage is monitored at the VOUT (J6, J7, J8)
terminals.
3. Enable the MIC23451.
The MIC23451 evaluation board has a pull-up resistor
to VIN for each channel. By default, output voltage each
is enabled when an input supply of > V is applied. 2.7
To disable the device, apply a voltage below 0.4V to
the EN (J10, J12, J14) terminals.
4. Power Good.
The board provides a ood test point 9, J11, GPower (J
J13) to monitor the Power Good function for each
individual channel. The Power Good output goes high
(VOUT) approximately after the output voltage 60µs
reaches 90% of its nominal voltage.
Ordering Information
Part Number Description
MIC23451-AAAYFL EV Adjustable Output Evaluation Board
Micrel, Inc.
MIC23451 Evaluation Board
October 14, 2013
2 Revision 1.0
Evaluation Board
Other Features
Soft- Start Capacitor
The MIC23451 has an internal soft start for each individual -
channel and no external soft start capacitor. The requires -
typical soft- µ start time for each channel is 150 s.
Feedback Resistors (R7−
−
−
−−R12)
The feedback (FB) pin is the control input for programming
the output voltage. A resistor divider network is connected
to this pin from the output and is compared to the internal
0.62V reference within the regulation loop. The output
voltage can be programmed between 1V and 3.3V using
Equation 1:
Eq. 1
Where: R7 is the top, VOUT connected resistor, and R8 is
the bottom, AGND connected resistor.
Table 1. Example Feedback Resistor Values
VOUT R7 R8
1.2V 274k 294k Ω Ω
1.5V 316k 221k Ω Ω
1.8V 301k 158k Ω Ω
2.5V 324k 107k Ω Ω
3.3V 309k 71.5k Ω Ω
Power Good (PG)
The evaluation board has a test point for each individual
channel to monitor the PG signal. This is an open-drain
connection to voltage with an on board pullthe output - -up
resistor of . This is asserted high approximately 10kΩ60µs
after the output voltage passes of the nominal set 90%
voltage.
HyperLight Load Mode
MIC23451 uses a minimum on and off time proprietary
control loop (patented by Micrel). When the output voltage
falls below the regulation threshold, the error comparator
begins a switching cycle that turns the PMOS on and
keeps it on for the duration of the minimum time. This -on-
increases the output voltage. If the output voltage is over
the regulation threshold, the error comparator turns the
PMOS off for a minimum-off-time until the output drops
below the threshold. The acts as an NMOS ideal rectifier
that conducts when the PMOS is off. Using an NMOS
switch instead of a diode allows for lower voltage drop
across the switching device when it is on. The
asynchronous switching combination between the PMOS
and the NMOS allows the control loop to work in
discontinuous mode for light load operations. In
discontinuous mode, the MIC23 works in pulse 451
frequency modulation (PFM) to regulate the output. As the
output current increases, the off time decrea- ses, which
provides more energy to the output. This switching
scheme improves the efficiency of MIC23 during light 451
load currents by switching only when it is needed. As the
load current increases, the MIC23 goes into 451
continuous conduction mode (CCM) and switches at a
frequency centered at 3MHz. The equation to calculate the
load when the MIC23 goes into continuous conduction 451
mode is approximated by Equation 2:
×
×−
>fL2
D)VV(
I
OUTIN
LOAD
Eq. 2
E quation 2 shows that the load at which MIC23451
transitions from Hyper Light Load mode to PWM mode is a
function of the input voltage (VIN), output voltage (VOUT),
duty cycle (D), inductance (L) and frequency (, f T). he
“ . ” Switching Frequency vs Load graph in the “Evaluation
Board Performance” section shows that, as the output
current increases, the switching frequency also increases
until the MIC23 goes from Hyper Light Load mode to 451
PWM mode at approximately mA. The MIC23120 451 will
switch at a relatively constant frequency around 3MHz
after the output current is over 120mA.

Produkt Specifikationer

Mærke: Microchip
Kategori: Ikke kategoriseret
Model: MIC23451-AAAYFL

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