MIC2875/6 Evaluation Board
4.8A I
SW
, Synchronous Boost Regulator
with Bi-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 prevents any leakage current between the input and
output when the device is disabled.
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 band.
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 terminals.
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 voltage is monitored at the VIN
(J1) terminal, as the ammeter and/or power-lead
resistance can reduce the voltage supplied to the
input.
2. Connect a load 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 good (/PG) test pin (J5) is provided to monitor
the power good 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
MIC2875-AYMT EV
MIC2875-5.0YMT EV
MIC2876-AYMT EV
MIC2876-5.0YMT EV
Description
MIC2875 Adjustable Output
MIC2875-5.0V Fixed Output
MIC2876 Adjustable Output
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 Evaluation Board
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 V
IN
> V
OUT
)
The MIC2875/6 automatically operates in bypass mode
when the input voltage is higher than the target output
voltage. In bypass mode, 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. When 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 into the FB pin (0.01µA typical). It is recommended
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:
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 switch and a PMOS transistor 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 (V
EN
= 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 hence the output disconnect function requires
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 on briefly to discharge VOUT to VIN through
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.
V
R 2
=
R3
×
OUT
−
1
0.9 V
Eq. 1
October 21, 2014
2
Revision 1.0
Micrel, Inc.
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.
MIC2875/6 Evaluation Board
Maximum Load Current
vs. Ambient Temperature
3.0
ADJUSTABLE
R2 = 910kΩ
R3 = 200kΩ
MAXIMUM LOAD CURRENT (A)
2.5
2.0
1.5
1.0
V
IN
= 3.0V
V
IN
= 3.2V
V
IN
= 3.6V
0.5
V
OUT
= 5.0V
C
OUT
= 22µF
L = 1µH
0
25
50
75
100
125
150
175
0.0
AMBIENT TEMPERATURE (℃)
Figure 2. MIC2875/6 Safe Operating Area (SOA) Curves
Figure 2
illustrates the SOA for various V
IN
mounted on the
MIC2875/6 EVB from 0°C to +155°C.
October 21, 2014
3
Revision 1.0
Micrel, Inc.
MIC2875/6 Evaluation Board
Evaluation Board Schematics (MIC2875/6-AYMT)
MIC2875/6-AYMT (V
IN
≤
5.0V)
Bill of Materials
Item
C1
C2
C3
C4
L1
R1
R2
R3
R4
R5, R7
U1
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.
Part Number
C1608X5R1A475K080AC
LMK212BJ226MG-T
GRM188R61A105KA61J
−
PIMB042T-1R0MS-39
ERJ-3GEYJ105V
1-1879417-8
ERA-3AEB204V
ERJ-3GEYJ103V
CRCW0603000Z0EA
MIC2875-xYMT
MIC2876-xYMT
Manufacturer
TDK
(1)
Description
Capacitor 4.7μF, 10V, 10%, X5R, 0603
Capacitor 22μF, 10V, 20%, X5R, 0805 (V
IN
≤ 5.00V)
Capacitor 22μF, 10V, 20%, X5R, 0805 (V
IN
> 5.00V, in parallel)
Capacitor 1μF, 10V, 10%, X5R, 0603
Not Fitted, Size 0603
Inductor 1μH, 4.5A, SMD, 4.2mm × 4.0mm × 1.8mm
Resistor 1MΩ, 5%, 0603
Resistor 910kΩ, 0.1%, 0603
Resistor 200kΩ, 0.1%, 0603
Resistor 10kΩ, 5%, 0603
Resistor 0Ω, 0603
Qty.
1
1
3
1
0
1
1
1
1
1
2
1
Taiyo Yuden
Murata
−
Cyntec
(6)
(4)
(3)
(2)
Panasonic
TE
(5)
Panasonic
Panasonic
Vishay
(7)
Micrel, Inc.
(8)
4.8A I
SW
, Synchronous Boost Regulator with Bi-Directional
Load Disconnect
October 21, 2014
4
Revision 1.0
Micrel, Inc.
MIC2875/6 Evaluation Board
Evaluation Board Schematics (MIC2875/6-5.0YMT)
MIC2875/6-5.0YMT (V
IN
≤
5.0V)
Bill of Materials
Item
C1
C2
C3
C4
L1
R1
R2, R5,
R7
R3
R4
U1
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.
Part Number
C1608X5R1A475K080AC
LMK212BJ226MG-T
GRM188R61A105KA61J
−
PIMB042T-1R0MS-39
ERJ-3GEYJ105V
CRCW0603000Z0EA
−
ERJ-3GEYJ103V
MIC2875-xYMT
MIC2876-xYMT
Manufacturer
TDK
(9)
Description
Capacitor 4.7μF, 10V, 10%, X5R, 0603
Capacitor 22μF, 10V, 20%, X5R, 0805 (V
IN
≤ 5.00V)
Capacitor 22μF, 10V, 20%, X5R, 0805 (V
IN
> 5.00V, in parallel)
Capacitor 1μF, 10V, 10%, X5R, 0603
Not Fitted, Size 0603
Inductor 1μH, 4.5A, SMD, 4.2mm × 4.0mm × 1.8mm
Resistor 1MΩ, 5%, 0603
Resistor 0Ω, 0603
Not Fitted, Size 0603
Resistor 10kΩ, 5%, 0603
4.8A I
SW
, Synchronous Boost Regulator with
Bi-Directional Load Disconnect
Qty.
1
1
3
1
0
1
1
3
0
1
1
Taiyo Yuden
Murata
−
Cyntec
(12)
(11)
(10)
Panasonic
Vishay
−
(13)
(14)
Panasonic
Micrel, Inc.
(15)
October 21, 2014
5
Revision 1.0
NXP MCU
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