MIC2875
4.8A ISW, Synchronous Boost Regulator
with Bi-Directional Load Disco nnect
General Descr i ption
The MIC2875 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 operates in bypass
mode automatically when the input voltage is greater than
the target output voltage. At light loads, the boost
converter goes to the PFM mode to improve the efficiency.
To minimize switching artifacts in the audio band, the
MIC2875 is designed to operate with a minimum switching
frequency of 45kHz. The MIC2875 also features an
integrated anti -ringing switch to minimize EMI.
The MIC2875 is avail able in a 8-pin 2mm × 2mm Thin DFN
(TDFN) package, with a junction temperature range of
−40°C to +125°C.
Datasheets and support documentation are available on
Micrel’s web site at: www.micrel.com.
Features
• Input voltage range: 2.5V to 5.5V
• Fully-integrated, high-efficiency, 2MHz synchronous
boost regulator
• Bi-directional true load disconnect
• Integrated ant i -ringing switch
• Minimum switching frequency of 45kHz
• Up to 95% efficiency
• <1µA shutdown cur rent
• Bypass mode for V IN ≥ VOUT
• Overcurrent protectio n and thermal shutd own
• Fixed and adjustable output versions
• 8-pin 2mm × 2mm TDFN package
Applications
• Tablet and smartphones
• USB OTG and HDMI hosts
• Portable power rese rv e supplies
• Low-noise audio applications
• Portable equipment
Simplified Application Schematics
MIC2875 (Adjustable Ou t put )
MIC2875 (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
January 19, 2015 Revision 1.1
Micrel, Inc.
MIC2875
Ordering I nfor m ati on
Part Number Mark Code Output Voltage Temperature R ange Package(1, 2)
MIC2875-4.75YMT 87F 4.75V −40°C to +125°C 8-Pin 2mm × 2mm TDFN
MIC2875-5.0YMT 87G 5.00V −40°C to +125°C 8-Pin 2mm × 2mm TDFN
MIC2875-5.25YMT 87H 5.25V −40°C to +125°C 8-Pin 2mm × 2mm TDFN
MIC2875-5.5YMT 87J 5.50V −40°C to +125°C 8-Pin 2mm × 2mm TDFN
MIC2875-AYMT 87A Adjustable −40°C to +125°C 8-Pin 2mm × 2mm TDFN
Notes:
1. TDFN is a RoHS-compliant package. Lead finish is Pb free and Matte Tin. Mold compound is Hal ogen free.
2. ▲ = TDFN Pin 1 identifier.
Pin Configuration
8-Pin 2mm × 2mm TDFN (MT)
Fixed Output
(Top View)
8-Pin 2mm × 2mm TDFN (MT)
Adjustable Output
(Top View)
Pin Description
Pin Number
Fixed
Output
Pin Number
Adjustable
Output
Pin Name Pin Function
1 1 SW Boost Convert er Switch Node: Connect the inductor between IN and SW pins.
2 2 PGND Power Grou nd: The power ground for the synchronous boos t DC-to-DC
converter power stage.
3 3 IN Supply Input: Connect at least 1µF ceramic capaci tor between IN and AGND
pins.
4 4 AGND Analog Ground: The analog ground for the regulator contr ol loop.
5 − OUTS Output Voltage Sense Pin: For output voltage regulation in fixed voltage
version. Connect to the boost convert er output.
− 5 FB Feedback Pin: For output voltage regulation in adjustable voltage version.
Connect to the feedback resistor divider.
6 6 EN Boost Convert er Enable: When t hi s pin is driven l ow, the IC enters shutdown
mode. The EN pin has an internal 2.5MΩ pull-down resistor. The output is
disabled when this pin is lef t floating.
January 19, 2015 2 Revision 1.1
Micrel, Inc.
MIC2875
Pin Description (Cont inued)
Pin Number
Fixed
Output
Pin Number
Adjustable
Output Pin Name Pin Function
7 7 /PG
Open Drain Powe r Good Output ( Active Low): The /PG pin is high impedance
when the output voltage is below the power good threshold, and becomes low
once the output is above the power good threshold. The /PG pin has a typical
RDS(ON) = 90Ω and requir es a pull up resist or of 1MΩ. Connect /PG pin to
AGND when the / P G signal is not used.
8 8 OUT Boost Converter Output.
EP EP ePad Exposed Heat Sink Pad. Co nnect to AGND for best thermal performance.
January 19, 2015 3 Revision 1.1
Micrel, Inc.
MIC2875
Absolute Ma xi mu m Ratings(3)
IN, EN, OUT, FB, /PG to PGND ...................... −0.3V to +6V
AGND to PGND. .......................................... −0.3V to +0.3V
Power Dissipat i on .................................. Internally Limit ed(5)
Lead Temperature (soldering, 10s) ............................ 260°C
Storage Temperature (TS) ......................... −65°C to +150°C
ESD Rating(6)
Human Body Model .............................................. 1.5kV
Machine Model ...................................................... 200V
Operating Ratings(4)
Supply Voltage (VIN) ..................................... +2.5V to +5.5V
Output Voltage (V OUT) ......................................... Up to 5.5V
Enable Voltage (VEN) .............................................. 0V to VIN
Junction Tem perat ure (TJ) ........................ –40°C to +125°C
Package Thermal Resistance
8-Pin 2mm × 2mm TDFN (θJA) .......................... 90°C/W
Electric al Characteristics(7)
VIN = 3.6V, VOUT = 5V, CIN = 4.7µF, COUT = 22µF, L = 1µH TA = 25°C, bold values indicate −40°C ≤ TJ ≤ +125°C, unless otherwise
noted.
Symbol
Parameter
Condition
Min.
Typ.
Max.
Unit
Power Supply
VIN Supply Voltage Range 2.5 5.5 V
VUVLOR UVLO Risi ng Threshold 2.32 2.49 V
VUVLOH UVLO Hysteresis 200 mV
IVIN Quiescent Curr ent Operating at minimum switching frequency 1 mA
IVINSD VIN Shutdown Current VEN = 0V, VIN = 5.5V, VOUT = 0V 1
3
µA
IVOUTSD VOUT Shutdown Current VEN = 0V, VIN = 0.3V, VOUT = 5.5V 2
5
µA
VOUT Output Voltage VIN 5.5 V
VFB Feedback Voltage Adjustable version, IOUT = 0A 0.8865 0.9 0.9135 V
Voltage Accuracy Fixed version, IOUT = 0A
−
1.5 +1.5 %
Line Regulat ion 2.5V < VIN < 4.5V, IOUT = 500mA 0.3 %/V
Load Regulati on IOUT = 200mA to 1200mA
0.2 %/A
DMAX Maximum Duty Cycle 92 %
DMIN Minimum Duty Cycle 6.5 %
ILS Low-Side Switch Cur rent Limit (8) VIN = 2.5V 3.8 4.8 5.8 A
PMOS Switch On-Resistance VIN = 3.0V, ISW = 200mA, V OUT = 5.0V 79 mΩ
NMOS VIN = 3.0V, ISW = 200mA, VOUT = 5.0V 82
ISW Switch Leakage Current(8) VEN = 0V, VIN = 5.5V 0.2
5
µA
FSWMIN Minimum Switchin g Frequency IOUT = 0mA 45
kHz
FOSC Oscillator Freq uency 1.6 2 2.4 MHz
TSD Overtemperature Shutdown Thr es hold 155 °C
Overtemperat ure Shutdown H ysteresis 15
Notes:
3. Exceeding the absolute maximum ratings may damage the device.
4. The device is not guaranteed to function outside its operating ratings.
5. The maximum allowable power dissipation of any TA (ambient temperature) is PD(max) = (TJ(max) – TA) / θJA. Exceeding the maximum allowable power
dissipation will result in excessive die temperature, and the regulator will go into thermal shutdown
6. Devices are ESD sensitive. Handling precautions are recommended. Human body model, 1.5kΩ in series with 100pF.
7. Specification for packaged product only.
8. Guaranteed by design and characterization.
January 19, 2015 4 Revision 1.1
Micrel, Inc.
MIC2875
Electric al Characteristics(7) (Continued)
VIN = 3.6V, VOUT = 5V, CIN = 4.7µF, COUT = 22µF, L = 1µH TA = 25°C, bold values indicate −40°C ≤ TJ ≤ +125°C, unless otherwise
noted.
Symbol Parameter Condition Min. Typ. Max. Unit
Soft-Start
TSS Soft-Start Time VOUT = 5.0V 1.1 ms
EN, /PG Control Pins
VEN EN Threshold V ol tage Boost c onverter and chip logic ON 1.5 V
Boost converter and chip lo gic OFF 0.4
EN Pin Current VIN = VEN = 3.6V 1.5 3 µA
V/PG-THR Power-Good Thers hold (Rising) 0.90 × VOUT V
V/PG-THF Power-Good Thers hold (Falli ng) 0.83 × VOUT V
January 19, 2015 5 Revision 1.1
Micrel, Inc.
MIC2875
Typical Characteristics
50
60
70
80
90
100
0.001 0.010 0.100 1.000
EFFICIENCY (%)
LOAD CURRENT (A)
Efficiency
vs. Load Curre nt
V
IN
= 3.6V
V
IN
= 3.0V
V
IN
= 2.5V
V
OUT
=5.0V
L = 1µH
C
OUT
= 22µF
4.90
4.95
5.00
5.05
5.10
0.0 0.5 1.0 1.5 2.0
OUTPUT VOLTAGE (V)
LOAD CURRENT (A)
Output Voltage
vs. Load Curre nt
V
IN
=3.5V
V
OUT
=5.0V
L = 1µH
C
OUT
= 22µF
T
A
= 125℃
T
A
= -40℃
ADJUSTABLE
R2 = 910kΩ
R3 = 200kΩ
T
A
= 25℃
4.80
4.90
5.00
5.10
5.20
2.5 3.0 3.5 4.0 4.5 5.0
OUTPUT VOLTAGE (V)
INPUT VOLTAGE(V)
Output Voltage
vs. Input Voltage
V
OUT
=5.0V
L = 1µH
C
OUT
= 22µF
I
OUT
= 500mA
ADJUSTABLE
R2 = 910kΩ
R3 = 200kΩ
T
A
= 125℃
T
A
= 25℃
T
A
= -40℃
1.96
1.98
2.00
2.02
2.04
-50 -25 025 50 75 100 125 150
OSCILLATOR FREQUENCY (MHz)
TEMPERATURE (℃)
Oscillator Frequency
vs. Temper atur e
VIN =3.6V
VOUT =5.0V
L = 1µH
COUT = 22µF
IOUT = 0A
1.00
1.50
2.00
2.50
3.00
3.50
4.00
-50 -25 025 50 75 100 125 150
SHUTDOWN CURRENT (µA)
TEMPERATURE (℃)
Output Shutdown Current
vs. Temper atur e
V
EN
=0V
V
IN
= 0.3V
V
OUT
= 5.5V
ADJUSTABLE
R2 = 910kΩ
R3 = 200kΩ
0.896
0.898
0.900
0.902
0.904
-50 -25 025 50 75 100 125 150
FEEDBACK VOLTAGE (V)
TEMPERATURE (℃)
Feedback Voltage
vs. Temper atur e
ADJUSTABLE
V
OUT
= 5.0V
R2 = 910kΩ
R3 = 200kΩ
2.00
2.10
2.20
2.30
2.40
-50 -25 025 50 75 100 125 150
INPUT VOLTAGE (V)
TEMPERATURE (℃)
UVLO Threshold
vs. Temper atur e
RISING
FALLING
0.60
0.80
1.00
1.20
-50 -25 025 50 75 100 125 150
ENABLE THRESHOLDVOLTAGE (V)
TEMPERATURE (℃)
Enable Threshold
vs. Temper atur e
RISING
FALLING
3.80
4.00
4.20
4.40
4.60
4.80
-50 -25 025 50 75 100 125 150
/PG THRESHOLD VOLT AGE (V)
TEMPERATURE (℃)
Power Good Threshold
vs. Temper atur e
RISING
FALLING
ADJUSTABLE
R2 = 910kΩ
R3 = 200kΩ
V
OUT
=5.0V
January 19, 2015 6 Revision 1.1
Micrel, Inc.
MIC2875
Functional Characteristics
January 19, 2015 7 Revision 1.1
Micrel, Inc.
MIC2875
Functional Characteristics ( C ontinued)
January 19, 2015 8 Revision 1.1
Micrel, Inc.
MIC2875
Functional Characteristics (Continued)
January 19, 2015 9 Revision 1.1
Micrel, Inc.
MIC2875
Functional Diagram
Simplified Adjustable Output
Simplified Fixed Output
January 19, 2015 10 Revision 1.1
Micrel, Inc.
MIC2875
Functional Descript ion
Input (IN)
The input supply provides power to the internal
MOSFETs gate drivers and control circuitry for the boost
regulator. The operating input voltage range is from 2.5V
to 5.5V. A 1µF low-ESR ceramic input capacitor should
be connected from IN to AGND as close to MIC2875 as
possible to ensure a clean supply voltage for the device.
A minimum voltage rating of 10V is recommended for the
input capacitor.
Switch Node (SW)
The MIC2875 has internal low-side and synchronous
MOSFET switches. The switch node (SW) between the
internal MOSFET switches connects directly to one end
of the inductor and provides the current path during
switching cycles. The other end of the inductor is
connected to the input supply voltage. Due to the high-
speed switching on this pin, the switch node should be
routed away from sen sitive nodes wherever possible.
Ground Path (AGND)
The ground path (AGND) is for the internal biasing and
control circuitry. AGND should be connected to the PCB
pad for the package exposed pad. The current loop of the
analog ground should be separated from that of the
power ground (PGND). AGND should be connected to
PGND and EP at a single point.
Power Ground (PGND)
The power ground (PGND) is the ground path for the high
current in the boost switches. The current loop for the
power ground should be as short as possible and
separate from t he A G ND l oop as applicable.
Boost Converter Output (OUT)
A low-ESR ceramic capacitor of 22µF (for operation with
VIN ≤ 5.0V), or 66µF (for operation with VIN > 5.0V) should
be connected from VOUT to PGND as close as possible
to the MIC2875. A minimum voltage rating of 10V is
recommended for t he output capacitor.
Enable (EN)
Enable pin of the MIC2875. A logic high on this pin
enables the MIC2875. When this pin is driven low, the
MIC2875 enters the shutdown mode. When the EN pin is
left floating, it is pulled-down internally by a built-in 2.5MΩ
resistor.
Feedback/Output Voltage Sense (FB/OUTS)
Feedback or output voltage sense pin for the boost
converter. For the fixed voltage version, this pin should
be connected to the OUT pin. For the adjustable version,
connect a resistor divider to set the output voltage (see
“Output Voltage P rogramming” for more informatio n).
Power-Good Output (/PG)
The open-drain active-low power-good output (/PG) is
low when the output voltage is above the power-good
threshold. A pull-up resistor of 1MΩ is recommended.
Exposed Heat Sin k Pad (EP)
The exposed heat sink pad, or ePad (EP), should be
connected to AGND for best thermal performance.
January 19, 2015 11 Revision 1.1
Micrel, Inc.
MIC2875
Application Inform ation
General Descripti on
The MIC2875 is a 2MHz, current-mode, PWM,
synchronous boost converter with an operating input
voltage range of 2.5V to 5.5V. At light lo ad, the converter
enters pulse-skipping mode to maintain high efficiency
over a wide range of load current. The maximum peak
current in the boost switch is limited to 4.8A (t ypical).
Bi-Direction al Output Disconnect
The power stage of the MIC2875 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 (VEN = 0V). An
“always on” maximum supply selector switches the
cathode of the back gate diode to either the IN or the
OUT (whichever of the two has the higher voltage). As a
result, the output of the MIC2875 is bi-directionally
isolated from 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 S witching Frequency
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
45 kHz. 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 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 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 By pass Mode (when VIN > VOUT)
The MIC2875 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 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 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, 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 (typically 0.01µA). It is
recommended that the total resistance of R2 + R3 should
be around 1MΩ. The appropriate R2 and R3 values for
the desired output voltage are calculated as in Equation
1:
−×= 1
V9.0
V
3R2R OUT
Eq. 1
January 19, 2015 12 Revision 1.1
Micrel, Inc.
MIC2875
Component Selecti on
Inductor
Inductor selection is a trade-off between efficiency,
stability, cost, size, and rated current. Since the boost
converter is compensated internally, the recommended
inductance is limited from 1µH to 2.2µH to ensure system
stability and presents a good balance between these
considerations.
A large inductance value reduces the peak-to-peak
inductor ripple current hence the output ripple voltage. This
also reduces both the DC loss and the transition loss at
the same inductor’s DC resistance (DCR). However, the
DCR of an inductor usually increases with the inductance
in the same package size. This is due to the longer
windings required for an increase in inductance. Since the
majority of the input current passes through the inductor,
the higher the DCR the lower the efficiency is, and more
significantly at higher load currents. On the other hand,
inductor with smaller DCR but the same inductance
usually has a larger size. The saturation current rating of
the selected inductor must be higher than the maximum
peak inductor current to be encountered and should be at
least 20% to 30% higher than the average inductor current
at maximum output current.
Input Capacitor to the Devi ce S upply
A ceramic capacitor of 1µF or larger with low ESR is
recommended to reduce the input voltage ripple to ensure
a clean supply voltage for the device. The input capacitor
should be placed as close as possible to the MIC2875 IN
pin and AGND pin with short traces to ensure good noise
performance. X5R or X7R type ceramic capacitors are
recommended for better tolerance over temperature. The
Y5V and Z5U type temperature rating ceramic capacitors
are not recommended due to their large reduction in
capacitance over temperature and increased resistance at
high frequencies. The use of these reduces the ability to
filter out high-frequency noise. The rated voltage of the
input capacitor should be at least 20% higher than the
maximum operating input voltage over the operating
temperature range.
Input Capacitor to the Power Path
A ceramic capacitor of a 4.7µF of larger with low ESR is
recommended to reduce the input voltage fluctuation at the
voltage supply of the high current power path. An input
capacitor should be placed close to the VIN supply to the
power inductor and PGND for good device performance at
heavy load condition. X5R or X7R type ceramic capacitors
are recommended for better tolerance ov ertemperature.
The Y5V and Z5U type temperature rating ceramic
capacitors are not recommended due to their large
reduction in capacitance over temperature and increased
resistance at high frequencies. These reduce their ability
to filter out high-frequency noise. The rated voltage of the
input capacitor should be at least 20% higher than the
maximum operating input voltage over the operating
temperature range.
Output Capacitor
Output capacitor selection is also a trade-off between
performance, size, and cost. Increasing output capacitor
will lead to an improved transient response, however, the
size and cost also increase. For operation with VIN ≤ 5.0V,
a minimum of 22µF output capacitor with ESR less than
10mΩ is required. For operation with VIN > 5.0V, a
minimum of 66µF output capacitor with ESR less than
10mΩ is required. X5R or X7R type cer am i c cap acitors are
recommended for better tolerance over temperature.
Additional capacitors can be added to improve the
transient response, and to reduce the ripple of the output
when the MIC2875 op erates in and out of bypass mode.
The Y5V and Z5U type ceramic capacitors are not
recommended due to their wide variation in capacitance
over temperature and increased resistance at high
frequencies. The rated voltage of the output capacitor
should be at least 20% higher than the maximum
operating output voltage over the operating temperature
range. 0805 size ceramic capacitor is recommended for
smaller ESL at output capacitor which contributes smaller
voltage spike at the output voltage of high-frequency
switching boost converter.
January 19, 2015 13 Revision 1.1
Micrel, Inc.
MIC2875
Power Di ssipation
As with all power devices, the ultimate current rating of the
output is limited by the thermal properties of the device
package and the PCB on which the device is mounted.
There is a simple, Ohm’s law-type relationship between
thermal resistance, power dissipation, and temperature
which are analogous t o an electrical circuit (Figure 1):
Figure 1. Series Electrical Resistance Circu it
From this simple circuit we can calculate VX if we know
ISOURCE, VZ and the resistor values, RXY and RYZ using
Equation 2:
VX = ISOURCE × (RXY + RYZ) + VZ Eq. 2
Thermal circuits can be considered using this same rule
and can be drawn similarly by replacing current sources
with power dissipation (in watts), resistance with thermal
resistance (in °C/W) and voltage sources with temperature
(in °C).
Figure 2. Series Thermal Resistance Circui t
Now replacing the variables in the equation for VX, we can
find the junction temperature (TJ) from the power
dissipation, ambient temperature and the known thermal
resistance of the PCB (θCA) and the package (θJC).
TJ = PDISS × (θJC + θCA) + TA Eq. 3
As can be seen in the diagram, total thermal resistance
θJA = θJC + θCA. This can also be writt en as in Equation 4:
TJ + PDISS × (θJA) + TA Eq. 4
Given that all of the power losses (minus the inductor
losses) are effectively in the converter are dissipated
within the MIC2875 package, PDISS can be calculated
thusly:
Linear Mode:
DCRI
1
1
PP 2
OUT
OUTDISS ×−
−
η
×
=
Eq. 5
Boost Mode:
DCR
D
1
I
1
1
PP 2
OUT
OUT
DISS ×
−
−
−
η
×=
Eq. 6
Duty Cycle (Boost Mode):
OUT
INOUT
VVV
D−
+
Eq. 7
where:
η = Efficiency taken from efficiency curves and DCR =
inductor DCR. θJC and θJA are found in the operating
ratings section of the datasheet.
January 19, 2015 14 Revision 1.1
Micrel, Inc.
MIC2875
Where the real board area differs from 1” square, θCA (the
PCB thermal resistance), values for various PCB copper
areas can be taken from Figure 3. (Note: Figure 3 taken
from Designing with Low Dropout Voltage Regulators
available from Micrel’s web site at: www.micrel.com.)
Figure 3. Determining PC Board Area for a G iven PCB
Thermal Resistance
Figure 3 shows the total area of a round or square pad,
centered on the device. The solid trace represents the
area of a square, single-sided, horizontal, solder-masked,
copper PC board trace heat sink, measured in square
millimeters. No airflow is assumed. The dashed line shows
PC boards trace heat sink covered in black oil-based paint
and with 1.3m/sec (250 feet per minute) airflow. This
approaches a “best case” pad heat sink. Conservative
design dictates using the solid trace data, which indicates
that a maximum pad size of 5000 mm2 is needed. This is a
pad 71mm × 71mm (2.8 i nches per side).
January 19, 2015 15 Revision 1.1
Micrel, Inc.
MIC2875
PCB Layout Guideli nes
PCB layout is critical to achieve reliable, stable and
efficient performance. A ground plane is required to control
EMI and minimize the inductance in power, signal and
return paths. The following guidelines should be followed
to ensure proper operation of the device:
IC (Integrated Circuit)
• Place the IC close to the point-of-load.
• Use fat traces to route the input and output power
lines.
• Analog grounds and power ground should be kept
separate and connected at a single location at the
PCB pad for exposed pad of the IC.
• Place as much as thermal vias on the PCB pad for
exposed pad and connected it to the ground plane to
ensure a good PCB thermal resistance can be
achieved.
IN Decoupling Capacitor
• The IN decoupling capacitor must be placed close to
the IN pin of the IC and preferably connected directly
to the pin and not through any via. The capacitor must
be located right at the IC.
• The IN decoupling capacitor should be connected as
close as possible to AGND.
• The IN terminal is noise sensitive and the placement of
capacitor is very crit ical.
VIN Power Path Bulk Capacitor
• The VIN power path bulk capacitor should be placed
and connected close to the VIN supply to the power
inductor and the PGND of the IC.
• Use either X5R or X7R temperature rating ceramic
capacitors. Do not use Y5V or Z5U type ceramic
capacitors.
Inductor
• Keep both the inductor connections to the switch node
(SW) and input power line short and wide enough to
handle the switching current. Keep the areas of the
switching current loops small to minimize the EMI
problem.
• Do not route any digital lines underneath or close to
the inductor.
• Keep the switch node (SW) away from the noise
sensitive pins.
• To minimize noise, place a ground plane underneath
the inductor.
Output Capacitor
• Use wide and short traces to connect the output
capacitor as close as possible to the OUT and PGND
pins without going through via holes to minimize the
switching current loop during the main switch off cycle
and the switching noi se.
• Use either X5R or X7R temperature rating ceramic
capacitors. Do not use Y5V or Z5U type ceramic
capacitors.
Figure 4. Suggested PCB Routing
January 19, 2015 16 Revision 1.1
Micrel, Inc.
MIC2875
Typical Applicatio n Schematics
MIC2875-AYMT Typical Application Schematic − VIN ≤ 5.0V
MIC2875-5.0YMT Typical Applicatio n S chematic − VIN ≤ 5.0V
MIC2875-AYMT Typical Application Schematic − VIN > 5.0V
MIC2875-5.0YMT Typical Applicatio n S chematic − VIN > 5.0V
January 19, 2015 17 Revision 1.1
Micrel, Inc.
MIC2875
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 (V IN ≤ 5.00V) 1
Capacitor 22μF, 10V, 20%, X5R, 0805 (VIN > 5.00V, in parallel ) 3
C3 GRM188R61A105KA61J Murata(11) Capacitor 1μF, 10V, 10%, X5R, 0603 1
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 1-1879417-8 TE(14)
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
UI MIC2875-xxxYMT Micrel, Inc.(15) 4. 8A ISW, Synchronous Boost Regulator with Bi-Directional
Load Disconnect 1
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. TE: www.te.com.
15. Micrel, Inc.: www.micrel.com.
January 19, 2015 18 Revision 1.1
Micrel, Inc.
MIC2875
PCB Layout Recommendations
Top Layer
Bottom Layer
January 19, 2015 19 Revision 1.1
Micrel, Inc.
MIC2875
MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http://www.micrel.com
Micrel, Inc. is a leading global manufacturer of IC solutions for the worldwide high
-
performance linear and power, LAN, and timing & communications
markets. The Company’s products include advanced
mixed-signal, analog & power semiconductors; high-
performance communication, clock
management,
MEMs-based clock oscillators & crystal-less clock generators, Ethernet switches, and physical layer transceiver ICs.
Company
customers include leading manufact
urers of enterprise, consumer, industrial, mobile, telecommunications, 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 technology design centers situated throughout the Americas, Europe, and Asia.
Additionally, the Company maintains an extensive network
of distributors and reps worldwide.
Micrel makes no representations or warranties with respect to the accuracy
or completeness of the information furnished in this data
sheet. 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 ti
me without notice.
No license, whether express, implied, arising by estoppel or otherwise, to any intellectual
property rights
is granted by this document. Except as provided in Micrel’s terms and conditions of sale for such products, Micrel assumes no li
ability
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 particular purpose, merchantability, or infringement of any patent, copy
right, or other intellectual property right.
Micrel Products 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
implant into the body or (b) support or sus tain l ife, and whose failure to perform can b e reasonably expected to result in a si gnificant i njury to the user. A
Purchaser’s u
se or sale of Micrel Products for use i n life s upport appli ances, dev ices or s ystems is a P urchaser’s own risk and Purchas er
agrees to fully
indemnify Micrel for any damages resulting from such use or sale.
© 2014 Micrel, Incorporated.
January 19, 2015 21 Revision 1.1
