MIC2875/6 Evaluation Board
4.8A I
SW
, Synchronous Boost Regulator
with B i-Directional Load Disconnect
General Description
The MIC2875/6 evaluation board is a compact and highly-
efficient 2MHz synchronous boost regulator with a 4.8A
switch. It features a bi-directional load disconnect function
which pre vents an y leak age curr ent between the i nput and
output when the de vice is disabl ed.
The MIC2875/6 operates in bypass mode automatically
when the input voltage is greater than the target output
voltage. At light loads, the boost converter goes to PFM
mode to improve the efficiency. The part also features an
integrated anti-ringing switch to minimize EMI.
The MIC2875 is designed to operate with a minimum
switching frequency of 45kHz from no load to full load to
minimize switching artifacts in the audio ban d.
Datasheets and support documentation are available on
Micrel’s web site at: www.micrel.com.
Requirements
The MIC2875/6 evaluation board requires a bench input
power source that is adjustable from 2.5V to 5.5V and is
able to deliver greater than 4.5A at 2.5V.
Precautions
The evaluation board does not have reverse polarity
protection. Applying a negative voltage across the VIN
terminal to the ground (GND) terminal can damage the
device. It should not exceed 5.5V on the input.
Input power leads should be kept as short as possible to
minimize the inductance. VIN measurements should be
made at the VIN and GND terminals, to ensure that the
voltage drop on the input power leads are not included.
Getting Started
1. Connect an external supply to the VIN te rminals.
Apply the desired input voltage to the VIN (J1) and
GND (J2) terminals of the evaluation board, paying
careful attention to polarity and supply range (2.5V to
5.5V). An ammeter can be placed between the power
supply and the input terminal of the evaluation board.
Ensure that the supply volt age is monitore d at the VIN
(J1) terminal, as the ammeter and/or power-lead
resistance can reduce the voltage supplied to the
input.
2. Connect a l o ad to VOUT and GND terminals.
The load connected between VOUT (J3) and GND
(J4) terminals of the evaluation board can be either
passive (resistive) or active (electronic load). In case
of electronic load, keep the load disabled until the
MIC2875/6 has been powered up.
An ammeter may be placed between the load and the
output terminal. Ensure the output voltage is monitored
across the VOUT (J3) and GND (J4) terminals.
3. Enable/Disable the MIC2875/6.
The MIC2875/6 evaluation board has an enable (EN)
pin (J8).The MIC2875/6 is in standby mode when the
EN pin is asserted high. Setting the jumper at JP1
connects the EN pin to VIN through a 10kΩ pull-up
resistor. If this pin is driven low, the IC is shut down.
This pin has an internal pull-down resistor and can be
left open.
4. Power Good (/PG).
A power g ood ( /PG) tes t pi n (J 5) is pr o vided to monito r
the power go od function. It is an open drain active low
output power good output. Setting the jumper at JP2
connects the /PG pin to VIN through a 1MΩ pull-up
resistor. This pin is asserted low when the output is
above the power good threshold.
Ordering Information
Part Number Description
MIC2875-AYMT EV MIC2875 Adjustable Output
MIC2875-5.0YMT EV MIC2875-5.0V Fixed Output
MIC2876-AYMT EV MIC2876 Adjustable Output
MIC2876-5.0YMT EV MIC2876-5.0V Fixed Output
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
October 21, 2014 Revision 1.0
Micrel, Inc.
MIC2875/6 Evalu ati on Boar d
Evaluation Board Description
Figure 1. MIC2875-AYMT Evaluation Board
Bi-Directional Output Disconnect
The power stage of the MIC2875/6 consists of a NMOS
transistor as the main s witc h and a PMO S tr ansistor as the
synchronous rectifier. A control circuit turns off the back
gate diode of the PMOS to isolate the output from the input
supply when the chip is disabled (VEN = 0V). An “always
on” maximum supply selector switches the cathode of the
backgate diode to either the IN or the OUT, whichever pin
has a higher voltage. As a result, the output of the
MIC2875/6 is bi-directionally isolated form the input as
long as the device is disabled. The maximum supply
selector and he nce t he ou tput disc onnect functi on r equires
only 0.3V at the IN pin to operate.
Minimum Switching Frequency (MIC2875 Only)
When the MIC2875 enters the pulse-skipping mode for
more than 20µs, an internal control circuitry forces the
PMOS to turn o n brief l y to discharge VOUT to VIN thr ough
the inductor. When the inductor current reaches a
predetermined threshold, the PMOS is turned off and the
NMOS is turned on so that the inductor current can
decrease gradually. Once the inductor current reaches
zero, the NMOS is eventually turned off. The above cycle
repeats if there is no switching activity for another 20µs,
effectively maintaining a minimum switching frequency of
45kHz. The frequency control circuit is disabled when
VOUT is less than or within 200mV of VIN. This minimum
switching frequency feature is advantageous for
applications that are sensitive to low frequency EMI such
as audio systems.
Integrated Anti-Ringing Switch
The MIC2875/6 includes an anti-ringing switch that
eliminates the ringing on the SW node of a conventional
boost converter operating in the discontinuous conduction
mode (DCM). At the end of a switching cycle during DCM
operation, both the NMOS and PMOS are turned off. The
anti-ringing switch in the MIC2875/6 clamps the SW pin
voltage to IN to dissipate the remaining energy stored in
the inductor and the parasitic elements of the power
switches.
Automatic Bypass Mode (when VIN > VOUT)
The MIC2875/6 automatically operates in bypass mode
when the input voltage is higher than the target output
voltage. In b ypass m ode, the NMOS is turned off while the
PMOS is fully turned on to provide a very low impedance
path from IN to OUT.
Soft-Start
The MIC2875/6 integrates an internal soft-start circuit to
limit the inrush current during start-up. W hen the device is
enabled, the PMOS is turned on slowly to charge the
output capacitor to a voltage close to the input voltage.
Then, the device begins boost switching cycles to
gradually charge up the output voltage to the target VOUT.
Output Voltage Programming
The MIC2875/6 has an adjustable version that allows the
output voltage to be set by an external resistor divider R2
and R3. The typical feedback voltage is 900mV and the
recommended maximum and minimum output voltage is
5.5V and 3.2V respectively. The current through the
resistor divider should be significantly larger than the
current i nto the FB pin (0. 01µA t ypica l). It is rec omm ended
that the total resistance of R2 + R3 should be
approximately 1MΩ. The appropriate R2 and R3 values for
the desired output voltage are calculated by:
−×= 1
V9.0
V
3R2R
OUT
Eq. 1
October 21, 2014 2 Revision 1.0
Micrel, Inc.
MIC2875/6 Evalu ati on Boar d
Safe Operating Area (SOA)
The safe operating area (SOA) curves represent the
boundary of the maximum safe operating current and
maximum safe operating junction temperature.
Figure 2. MIC2875/6 Safe Operating Area (SOA) Curves
Figure 2 illustrates the SOA for various VIN mounted on the
MIC2875/6 EVB from 0°C to +155°C.
0.0
0.5
1.0
1.5
2.0
2.5
3.0
025 50 75 100 125 150 175
MAXIMUM LOAD CURRENT (A)
AMBIENT TEMPERATURE (℃)
Maximum Load Current
vs. A mbient Temperature
V
OUT
=5.0V
C
OUT
= 22µF
L = 1µH
V
IN
= 3.0V
V
IN
= 3.2V
V
IN
= 3.6V
ADJUSTABLE
R2 = 910kΩ
R3 = 200kΩ
October 21, 2014 3 Revision 1.0
Micrel, Inc.
MIC2875/6 Evalu ati on Boar d
Evaluation Board Schematics (MIC2875/6-AYMT)
MIC2875/6-AYMT (VIN
≤
5.0V)
Bill of Materials
Item Part Number Manufacturer Description Qty.
C1 C1608X5R1A475K080AC TDK(1) Capacitor 4.7μF, 10V, 10%, X5R, 0603 1
C2 LMK212BJ226MG-T Taiyo Yuden(2) Capacitor 22μF, 10V, 20%, X5R, 0805 (VIN ≤ 5.00V) 1
Capacitor 22μF, 10V, 20%, X5R, 0805 (VIN > 5.00V, in par al l el) 3
C3 GRM188R61A105KA61J Murata(3) Capacitor 1μF, 10V, 10%, X5R, 0603 1
C4 − − Not Fitted, Size 0603 0
L1 PIMB042T-1R0MS-39 Cyntec(4) Inductor 1μH, 4.5A, SMD, 4.2mm × 4.0mm × 1.8mm 1
R1 ERJ-3GEYJ105V
Panasonic(5)
Resistor 1MΩ, 5%, 0603 1
R2 1-1879417-8
TE(6)
Resistor 910kΩ, 0.1%, 0603 1
R3 ERA-3AEB204V Panasonic Resistor 200kΩ, 0.1%, 0603 1
R4 ERJ-3GEYJ103V Panasonic Resistor 10kΩ, 5%, 0603 1
R5, R7 CRCW0603000Z0EA Vishay(7) Resistor 0Ω, 0603 2
U1 MIC2875-xYMT Micrel, Inc.(8) 4.8A ISW, Synchronous Boost Regulator with Bi-Directional
Load Disconnect 1
MIC2876-xYMT
Notes:
1. TDK: www.tdk.com.
2. Taiyo Yuden: www.t-yuden.com.
3. Murata: www.murata.com.
4. Cyntec: www.cyntec.com
5. Panasonic: www.panasonic.com.
6. TE: www.te.com.
7. Vishay: www.vishay.com.
8. Micrel, Inc.: www.micrel.com.
October 21, 2014 4 Revision 1.0
Micrel, Inc.
MIC2875/6 Evalu ati on Boar d
Evaluation Board Schematics (MIC2875/6-5.0YMT)
MIC2875/6-5.0YMT (VIN
≤
5.0V)
Bill of Materials
Item Part Number Manufacturer Description Qty.
C1 C1608X5R1A475K080AC TDK(9) Capacitor 4.7μF, 10V, 10%, X5R, 0603 1
C2 LMK212BJ226MG-T Taiyo Yuden(10) Capacitor 22μF, 10V, 20%, X5R, 0805 (VIN ≤ 5.00V) 1
Capacitor 22μF, 10V, 20%, X5R, 0805 (VIN > 5.00V, in par al l el) 3
C3 GRM188R61A105KA61J Murata(11) Capacitor 1μF, 10V, 10%, X5R, 0603 1
C4 − − Not Fitted, Size 0603 0
L1 PIMB042T-1R0MS-39 Cyntec(12) Inductor 1μH, 4.5A, SMD, 4.2mm × 4.0mm × 1.8mm 1
R1 ERJ-3GEYJ105V
Panasonic(13)
Resistor 1MΩ, 5%, 0603 1
R2, R5,
R7 CRCW0603000Z0EA Vishay(14) Resistor 0Ω, 0603 3
R3 − − Not Fitted, Size 0603 0
R4 ERJ-3GEYJ103V Panasonic Resistor 10kΩ, 5%, 0603 1
U1 MIC2875-xYMT Micrel, Inc.(15) 4.8A ISW, Synchronous Boost Regulator with
Bi-Directional Load Disconnect 1
MIC2876-xYMT
Notes:
9. TDK: www.tdk.com.
10. Taiyo Yuden: www.t-yuden.com.
11. Murata: www.murata.com.
12. Cyntec: www.cyntec.com.
13. Panasonic: www.panasonic.com.
14. Vishay: www.vishay.com.
15. Micrel, Inc.: www.micrel.com.
October 21, 2014 5 Revision 1.0
Micrel, Inc.
MIC2875/6 Evalu ati on Boar d
PCB Layout Recommendations
Top Layer
Bottom Layer
October 21, 2014 6 Revision 1.0
Micrel, Inc.
MIC2875/6 Evalu ati on Boar d
MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL +1 (408) 944-0800 FAX +1 (408) 474-100 0 WEB http://www.micrel.com
Micrel, Inc. is a leading global manufacturer of IC s olutions for the worldwide high
-
perform ance linear and po wer, LAN, and tim ing & communications
markets. The Company’s products include advanced mixed
-signal, analog & power semiconductors; high-performan
ce communication, clock
management,
MEMs-based clock oscillators & crystal-less clock generators, Ethernet switches, and physical layer transceiver ICs.
Company
customers include leading manufacturers of enterprise, consumer, industrial, mobile, telecommu
nications, automotive, and computer products.
Corporation headquarters and state
-of-the-
art wafer fabrication facilities are located in San Jose, CA, with regional sales and support offices and
advanced technol ogy design centers s ituated throughout the A
mericas, E urope, and Asia.
Additionally, the Company maintains an extensive network
of distribut ors and reps worldwide.
Micrel makes no representations or warranties with respect to the accuracy or completeness of the information furnished in th
is datash
eet. This
information is not intended as a warranty and Micrel does not assume responsibility for its use.
Micrel reserves the right to change circuitry,
specifications and descriptions at any time without notice.
No license, whether express, implied, ar
ising by estoppel or otherwise, to any intellectual
property rights is granted by this document. E xcept as provided in Micrel’s terms and conditions of sale for such produc ts, Micrel assumes no liability
whatsoever, and Micrel disclaims any express or implied warranty relating to the sale and/or use of Micrel products including liability or warranties
relating to fitness for a partic ular purpose, merchant abi lit y, or inf ri ngem ent of any patent, copyright, or other int el l ectua
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Micrel Product
s are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a
product
can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical
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© 2014 Micrel, Incorporated.
October 21, 2014 7 Revision 1.0
