MIC23158/9
3MHz PWM Dual 2A Buck Regulator
with HyperLight Load® and Power Good
HyperLight Load is a registered trademark of Micrel, Inc.
MLF and MicroLeadFrame are registered trademarks Amkor Technology, Inc.
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
June 2012 M9999-062512-A
General Description
The MIC23158/9 is a high efficiency 3MHz dual 2A
synchronous buck regulator with HyperLight Load mode,
Power Good output indicator, and programmable soft start.
The MIC23159 also provides an auto discharge feature
that switches in a 225 pull down circuit on its output to
discharge the output capacitor when disabled. HyperLight
Load provides very high efficiency at light loads and ultra
fast transient response which makes the MIC23158/9
perfectly suited for supplying processor core voltages. An
additional benefit of this proprietary architecture is very low
output ripple voltage throughout the entire load range with
the use of small output capacitors. The 20-pin 3mm x 4mm
MLF® package saves precious board space and requires
seven external components for each channel.
The MIC23158/9 is designed for use with a very small
inductor, down to 0.47µH, and an output capacitor as small
as 2.2 µF that enables a total solution size, less than 1mm
in height.
The MIC23158/9 has a very low quiescent current of 45µA
and achieves a peak efficiency of 94% in continuous
conduction mode. In discontinuous conduction mode, the
MIC23158/9 can achieve 83% efficiency at 1mA.
The MIC23158/9 is available in a 20-pin 3mm x 4mm MLF
package with an operating junction temperature range
from –40C to +125C.
Datasheets and support documentation can be found on
Micrel’s web site at: www.micrel.com.
Features
Input voltage: 2.7V to 5.5V
Output voltage: Adjustable (down to 1.0V)
2 independent 2A outputs
Up to 94% peak efficiency
83% typical efficiency at 1mA
2 independent Power Good Indicators
Independent programmable Soft Start
45µA typical quiescent current
3MHz PWM operation in continuous conduction mode
Ultra fast transient response
Fully integrated MOSFET switches
Output pre-bias safe
0.01µA shutdown current
Thermal shutdown and current limit protection
20-pin 3mm x 4mm MLF package
Internal 225 pull down circuit on output (MIC23159)
–40C to +125C junction temperature range
Applications
Solid State Drives (SSD)
Smart phones
Tablet PCs
Mobile handsets
Portable devices (PMP, PND, UMPC, GPS)
WiFi/WiMax/WiBro applications
__________________________________________________________________________________________________________
Typical Application
AVIN1
VIN1
SW1
SNS1
EN1
PG1
SS1
PGND1
AGND1
C1
4.7µF/6.3V
R5
10K
R2
158K
R1
301K
C5
470pF
C3
4.7µF/
6.3V
L1
1µH
FB1
VIN
EN1
VOUT1
PG1
MIC23158/9
U1
AVIN2
VIN2
SW2
SNS2
EN2
PG2
SS2
PGND2
AGND2
C2
4.7µF/6.3V
R6
10K
R4
221K
R3
316K
C6
470pF
C4
4.7µF/
6.3V
L2
1µH
FB2
EN2
PG2
VOUT2
Micrel Inc. MIC23158/9
June 2012 2 M9999-062512-A
Ordering Information
Nominal Output Voltage
Part Number VOUT1 V
OUT2
Output Auto
Discharge Junction
Temp. Range Package
MIC23158YML ADJ ADJ NO –40°C to +125°C 20-Pin 3mm x 4mm MLF
MIC23159YML ADJ ADJ YES –40°C to +125°C 20-Pin 3mm x 4mm MLF
Notes:
1. Fixed output voltage options available. Contact Micrel Marketing for details.
2. MLF is a GREEN RoHS compliant package. Lead finish is NiPdAu. Mold compound is Halogen Free.
Pin Configur ation
3mm x 4mm MLF (ML) Adjustable Output Voltage
(Top View)
Pin Description
Pin Number
(Adjustable) Pin Name Pin Function
1 VIN1
Power Input Voltage for regulator 1. Connect a capacitor to ground to decouple noise and
switching transients.
2 PGND1 Power Ground for regulator 1.
3 SW1 Switch (Output): Internal power MOSFET output switches for regulator 1.
4 SW2 Switch (Output): Internal power MOSFET output switches for regulator 2.
5 PGND2 Power Ground for regulator 2.
6 VIN2
Power Input Voltage for regulator 2. Connect a capacitor to ground to decouple noise and
switching transients.
7 AVIN2
Analog Input Voltage for regulator 2. Tie to VIN2 and connect a capacitor to ground to
decouple noise.
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June 2012 3 M9999-062512-A
8 AGND2
Analog Ground for regulator 2. Connect to a central ground point where all high current paths
meet (CIN, COUT, PGND2) for best operation.
9 EN2
Enable input for regulator 2. Logic high enables operation of regulator 2. Logic low will shut
down regulator 2. Do not leave floating.
10 SNS2
Sense input for regulator 2. Connect to the output of regulator 2 as close to the output
capacitor as possible to accurately sense the output voltage.
11 FB2
Feedback input for regulator 2. Connect a resistor divider from the output of regulator 2 to
ground to set the output voltage.
12 PG2
Power Good output for regulator 2. Open drain output for the power good indicator for output
2. Use a pull-up resistor between this pin and VOUT2 to indicate a power good condition.
13 SS2
Soft-Start for regulator 2. Connect a minimum of 200pF capacitor to ground to set the turn-on
time of regulator 2. Do not leave floating.
14 SS1
Soft-Start for regulator 1. Connect a minimum of 200pF capacitor to ground to set the turn-on
time of regulator 1. Do not leave floating.
15 PG1
Power Good output for regulator 1. Open drain output for the power good indicator for output
1. Use a pull-up resistor between this pin and VOUT1 to indicate a power good condition.
16 FB1
Feedback input for regulator 1. Connect a resistor divider from the output of regulator 1 to
ground to set the output voltage.
17 SNS1
Sense input for regulator 1. Connect to the output of regulator 1 as close to the output
capacitor as possible to accurately sense the output voltage.
18 EN1
Enable input for regulator 1. Logic high enables operation of regulator 1. Logic low will shut
down regulator 1. Do not leave floating.
19 AGND1
Analog Ground for regulator 1. Connect to a central ground point where all high current paths
meet (CIN, COUT, PGND1) for best operation.
20 AVIN1
Analog Input Voltage for regulator 1. Tie to VIN1 and connect a capacitor to ground to
decouple noise.
EP ePad Exposed heat sink pad. Connect to PGND.
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June 2012 4 M9999-062512-A
Absolute Maximum Ratings(1)
Supply Voltage (AVIN1, AVIN2, VIN1, VIN2)..... -0.3V to 6V
Switch1 (VSW1), Sense1 (VSNS1)...................... -0.3V to VIN1
Enable1 (VEN1), Power Good1 (VPG1) ............. -0.3V to VIN1
Feedback1 (VFB1) ........................................... -0.3V to VIN1
Switch2 (VSW2), Sense2 (VSNS2)...................... -0.3V to VIN2
Enable2 (VEN2), Power Good2 (VPG2) ............. -0.3V to VIN2
Feedback2 (VFB2) ........................................... -0.3V to VIN2
Power Dissipation TA=70°C......................Internally Limited
Storage Temperature Range .....................-65C to +150C
Lead temperature (soldering, 10s)............................. 260C
ESD Rating(3)..................................................ESD sensitive
Operating Ratings(2)
Supply Voltage (AVIN1, VIN1) ..................... +2.7V to +5.5V
Supply Voltage (AVIN2, VIN2) ..................... +2.7V to +5.5V
Enable Input Voltage (VEN1, VEN2) .....................0V to VIN1,2
Output Voltage Range (VSNS1, VSNS2) .......... +1.0V to +3.3V
Junction Temperature Range (TJ) .......-40C TJ +125C
Thermal Resistance
3mm x 4mm MLF-20 (JA) .................................53C/W
Electrical Characteristics(4)
TA = 25°C; AVIN1,2 = VIN1,2 = VEN1,2 = 3.6V; L1,2 = 1.0µH; COUT1,2 = 4.7µF unless otherwise specified.
Bold values indicate –40°C TJ +125°C, unless noted.
Parameter Condition Min. Typ. Max. Units
Supply Voltage Range 2.7 5.5 V
Under Voltage Lockout Threshold Rising 2.45 2.55 2.65 V
Under Voltage Lockout Hysteresis 75 mV
Quiescent Current IOUT = 0mA , SNS > 1.2 * VOUTNOM (both outputs) 45 90 µA
Shutdown Current VEN = 0V; VIN = 5.5V (per output) 0.1 5 µA
Feedback Regulation Voltage ILOAD = 20mA 0.6045 0.62 0.6355 V
Feedback Bias Current (per output) 0.01 uA
Current Limit SNS = 0.9*VOUTNOM 2.2 4.3 A
VIN = 3.6V to 5.5V if VOUTNOM < 2.5V, ILOAD = 20mA
Output Voltage Line Regulation VIN = 4.5V to 5.5V if VOUTNOM 2.5V, ILOAD = 20mA 0.45 %/V
DCM, VIN = 3.6V if VOUTNOM < 2.5V 0.55
DCM, VIN = 5.0V if VOUTNOM 2.5V 1.0 %
CCM, VIN = 3.6V if VOUTNOM < 2.5V
Output Voltage Load Regulation
CCM, VIN = 5.0V if VOUTNOM 2.5V 0.8
PWM Switch RDSON
ISW1,2 = 100mA PMOS
ISW1,2 = -100mA NMOS 0.20
0.19
Switching Frequency IOUT = 180mA 3 MHz
Soft Start Time VOUT = 90%, CSS = 470pF 300 µs
Soft Start Current VSS = 0V 2.7 µA
Power Good Threshold (Rising) 86 92 96 %
Power Good Threshold Hysteresis 7 %
Power Good Delay Time Rising 68 µs
Power Good Pull Down Resistance 95
Logic Low 0.4 V
Enable Input Voltage Logic High 1.2 V
Enable Input Current 0.1 2 µA
Output Discharge Resistance MIC23159 Only; EN=0V, IOUT = 250µA 225
Over-temperature Shutdown
160 C
Shutdown Hysteresis 20 C
Micrel Inc. MIC23158/9
June 2012 5 M9999-062512-A
Notes:
1. Exceeding the absolute maximum rating may damage the device.
2. The device is not guaranteed to function outside its operating rating.
3. Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5k in series with 100pF.
4. Specification for packaged product only.
Micrel Inc. MIC23158/9
June 2012 6 M9999-062512-A
Typical Characteristics
Efficiency (V
OUT
= 3.3V) vs.
Out put Current
0
10
20
30
40
50
60
70
80
90
100
1 10 100 1000 10000
O UT PUT CURRENT (mA)
EFFICI E NCY (%)
VIN = 4.2V VIN = 5V
C
OUT
=4.7µF
L=1µH
Ef fi ciency ( V
OUT
= 2.5V) vs.
Output Current
0
10
20
30
40
50
60
70
80
90
100
1 10 100 1000 10000
O UTPUT CURRENT ( m A)
EFFI CIENCY (% )
VIN = 4.2V
VIN = 3.6V VIN = 5V
C
OUT
=4.7µF
L=1µH
Eff ici en cy (VOUT = 1.8V ) vs.
Output Current
0
10
20
30
40
50
60
70
80
90
100
1 10 100 1000 10000
O UT PUT CURRE NT ( m A)
EFFICI E NCY ( % )
VIN = 2.7V
VIN = 4.2V
VIN = 3.6V VIN = 5V
C
OUT
=4.7µF
L=1µH
Ef ficiency (V
OUT
= 1.5V) vs.
Output Current
0
10
20
30
40
50
60
70
80
90
100
1 10 100 1000 10000
OUTPUT C URRENT (mA)
EFF ICI E NCY (%)
VIN = 2.7V VIN = 4.2V
VIN = 3.6V
VIN = 5V
C
OUT
=4.7µF
L=1µH
V
OUT
Ri se Ti me
vs. C
SS
10
100
1000
10000
100000
1000000
100 1000 10000 100000 1000000
CSS ( pF)
RI S E T IM E (µs )
VOUT = 1.8V
COUT = 4.7
µF
Curre n t Limit
vs. Input Volt age
0.0
1.0
2.0
3.0
4.0
5.0
6.0
2.5 3.0 3.5 4.0 4.5 5.0 5.5
I NPUT VOL TAG E ( V)
CURRENT L IM IIT (A)
V
OUT
= 1.8V
C
OUT
= 4.7
µF
Quiescent Current
vs. Input Voltage
20
25
30
35
40
45
50
55
60
2.5 3.0 3.5 4.0 4.5 5.0 5.5
I NPUT VOLTAG E ( V)
Q UIESCENT CURRENT ( µ A)
No Switching
SNS > V
OUTNOM
* 1.2
C
OUT
= 4.7µF
T = 125°C
T = -40°C
T = 25°C
Shut down Current
vs. Input Vol tage
1
10
100
1000
2.53.03.54.04.55.05.5
I NPUT VOLTAGE ( V)
SHUTDO WN CURRENT ( nA)
Li ne Regul ation
(CCM)
1.60
1.65
1.70
1.75
1.80
1.85
1.90
1.95
2.00
2.5 3.0 3.5 4.0 4.5 5.0 5.5
I NPUT VOLTA GE ( V)
O UTPUT VO LTAG E (V)
I
OUT
= 1A I
OUT
= 300mA
V
OUTNOM
= 1.8V
C
OUT
= 4.7µF
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June 2012 7 M9999-062512-A
Typical Characteristics (Continued)
Li ne Regulation
(HLL)
1.60
1.65
1.70
1.75
1.80
1.85
1.90
1.95
2.00
2.5 3.0 3.5 4.0 4.5 5.0 5.5
I NPUT VOLTA GE ( V)
O UTPUT VO L TAG E ( V)
I
OUT
= 20mA
I
OUT
= 80mA
I
OUT
= 1mA
V
OUTNOM
= 1.8V
C
OUT
= 4.7µF
Load Regulation
(CCM)
1.60
1.65
1.70
1.75
1.80
1.85
1.90
1.95
2.00
200 600 1000 1400 1800
O UTP UT CURRENT ( m A)
O UTPUT VOLTAGE ( V)
V
IN
= 3.6V
V
OUTNOM
= 1.8V
C
OUT
= 4.7µF
Load Regulat ion
(HLL)
1.60
1.65
1.70
1.75
1.80
1.85
1.90
1.95
2.00
0 20 40 60 80 100 120
O UT PUT CURRENT (m A)
O UTPUT VOLTAG E (V)
V
IN
= 3.6V
V
OUTNOM
=1.8V
C
OUT
= 4.7µF
VOUTMAX vs. VIN
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
2.5 3.0 3.5 4.0 4.5 5.0 5.5
I NPUT VOLTAGE ( V)
O UTPUT VOLTAG E ( V)
I
OUT
= 400mA
I
OUT
= 1.2A
I
OUT
= 100mA
T
A
= 25°C
Feedback Voltage
vs. Tem p erature
0.59
0.60
0.61
0.62
0.63
0.64
0.65
-40 -20 0 20 40 60 80 100 120
TEM PERA TURE (°C)
FEEDBACK VOLTAGE ( V)
V
IN
= 3.6V
V
OUT
= 1.8V
Switching Frequency
vs. Temperat ure
0
1
2
3
4
5
-40 -20 0 20 40 60 80 100 120
TEMPERATURE (° C)
SWITCHING FREQUENCY (MHz)
V
IN
= 3.6V
V
OUTNOM
= 1.8V
C
OUT
= 4.7µF
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June 2012 8 M9999-062512-A
Functional Characteristics
Micrel Inc. MIC23158/9
June 2012 9 M9999-062512-A
Functional Characteristics (Continued)
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June 2012 10 M9999-062512-A
Functional Characteristics (Continued)
Micrel Inc. MIC23158/9
June 2012 11 M9999-062512-A
Functional Diagram
Gate
Drive
Control Logic:
Timer & Soft-
Start
Isense
Under-Voltage
Lock Out
Reference
Error
Amplifier
Current
Limit
ZeroX
SW1
PGND1
SS1
SNS1
PG1
FB1 AGND1
VIN1 EN1 AVIN1
Gate
Drive
Control Logic:
Timer & Soft-
Start
Isense
Under-Voltage
Lock Out
Reference
Error
Amplifier
Current
Limit
ZeroX
SW2
PGND2
SS2
SNS2
PG2
FB2
AGND2
VIN2EN2AVIN2
Figure 1. Simplified MIC23158 Functional Block Diagram – Adjustable Output Voltage
Micrel Inc. MIC23158/9
June 2012 12 M9999-062512-A
Gate
Drive
Control Logic:
Timer & Soft-
Start
Isense
Under-Voltage
Lock Out
Reference
Error
Amplifier
Current
Limit
ZeroX
SW1
PGND1
SS1
SNS1
PG1
FB1 AGND1
VIN1 EN1 AVIN1
Gate
Drive
Control Logic:
Timer & Soft-
Start
Isense
Under-Voltage
Lock Out
Reference
Error
Amplifier
Current
Limit
ZeroX
SW2
PGND2
SS2
SNS2
PG2
FB2AGND2
VIN2EN2AVIN2
EN1 EN2
Figure 2. Simplified MIC23159 Functional Block Diagram – Adjustable Output Voltage
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June 2012 13 M9999-062512-A
Functional Description
VIN
The input supply (VIN) provides power to the internal
MOSFETs for the switch mode regulator along with the
internal control circuitry. The VIN operating range is 2.7V
to 5.5V. An input capacitor with a minimum voltage
rating of 6.3V is recommended. Due to the high
switching speed, a minimum 2.2µF bypass capacitor
placed close to VIN and the power ground (PGND) pin is
required. Refer to the layout recommendations for
details.
EN
A logic high signal on the enable pin activates the output
voltage of the device. A logic low signal on the enable
pin deactivates the output and reduces supply current to
0.1µA. Do not leave the EN pin floating. When disabled,
the MIC23159 switches in a 225 load from the SNS pin
to AGND, to discharge the output capacitor.
SW
The switch (SW) 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
load, SNS pin, and output capacitor. Due to the high
speed switching on this pin, the switch node should be
routed away from sensitive nodes whenever possible.
SNS
The sense (SNS) pin is connected to the output of the
device to provide feedback to the control circuitry. The
SNS connection should be placed close to the output
capacitor. Refer to the layout recommendations for more
details. The SNS pin also provides the output active
discharge circuit path to pull down the output voltage
when the device is disabled.
AGND
The analog ground (AGND) is the ground path for the
biasing and control circuitry. The current loop for the
signal ground should be separate from the power ground
(PGND) loop. Refer to the layout recommendations for
more details.
PGND
The power ground pin is the ground path for the high
current in PWM mode. The current loop for the power
ground should be as small as possible and separate
from the analog ground (AGND) loop as applicable.
Refer to the layout recommendations for more details.
PG
The power good (PG) pin is an open drain output which
indicates when the output voltage is within regulation.
This is indicated by a logic high signal when the output
voltage is above the PG threshold. Connect a pull up
resistor greater than 5k from PG to VOUT.
SS
An external soft start circuitry set by a capacitor on the
SS pin reduces inrush current and prevents the output
voltage from overshooting at start up. The SS pin is used
to control the output voltage ramp up time and the
approximate equation for the ramp time in milliseconds
is 296 x 103 x ln(10) x CSS. For example, for a CSS =
470pF, TRISE 300µs. Refer to the “VOUT Rise Time vs.
CSS” graph in the Typical Characteristics section. The
minimum recommended value for CSS is 200pF.
FB
The feedback (FB) pin is provided for the adjustable
voltage option. This is the control input for setting 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 calculated using the following
equation:
R2
R1
1VV REFOUT
Recommended feedback resistor values:
VOUT R1 R2
1.2V 274k 294k
1.5V 316k 221k
1.8V 301k 158k
2.5V 324k 107k
3.3V 309k 71.5k
Micrel Inc. MIC23158/9
June 2012 14 M9999-062512-A
Application Information
The MIC23158/9 is a high performance DC-DC step
down regulator offering a small solution size. Supporting
two outputs of up to 2A each in a 3mm x 4mm MLF
package. Using the HyperLight Load switching scheme,
the MIC23158/9 is able to maintain high efficiency
throughout the entire load range while providing ultra
fast load transient response. The following sections
provide additional device application information.
Input Capacitor
A 2.2µF ceramic capacitor or greater should be placed
close to the VIN pin and PGND pin for bypassing. A
Murata GRM188R60J475KE19D, size 0603, 4.7µF
ceramic capacitor is recommended based upon
performance, size and cost. A X5R or X7R temperature
rating is recommended for the input capacitor.
Output Capacitor
The MIC23158/9 is designed for use with a 2.2µF or
greater ceramic output capacitor. Increasing the output
capacitance will lower output ripple and improve load
transient response but could also increase solution size
or cost. A low equivalent series resistance (ESR)
ceramic output capacitor such as the Murata
GRM188R60J475KE19D, size 0603, 4.7µF ceramic
capacitor is recommended based upon performance,
size and cost. Both the X7R or X5R temperature rating
capacitors are recommended.
Inductor Selection
When selecting an inductor, it is important to consider
the following factors:
Inductance
Rated current value
Size requirements
DC resistance (DCR)
The MIC23158/9 is designed for use with a 0.47µH to
2.2µH inductor. For faster transient response, a 0.47µH
inductor will yield the best result. For lower output ripple,
a 2.2µH inductor is recommended.
Maximum current ratings of the inductor are generally
given in two methods; permissible DC current, and
saturation current. Permissible DC current can be rated
either for a 40°C temperature rise or a 10% to 20% loss
in inductance. Ensure the inductor selected can handle
the maximum operating current. When saturation current
is specified, make sure that there is enough margin so
that the peak current does not cause the inductor to
saturate. Peak current can be calculated as follows:
Lf2
/VV1
VII INOUT
OUTOUTPEAK
As shown by the calculation above, the peak inductor
current is inversely proportional to the switching
frequency and the inductance. The lower the switching
frequency or the inductance, the higher the peak current.
As input voltage increases, the peak current also
increases.
The size of the inductor depends on the requirements of
the application. Refer to the Typical Application Circuit
and Bill of Materials for details.
DC resistance (DCR) is also important. While DCR is
inversely proportional to size, DCR can represent a
significant efficiency loss. Refer to the Efficiency
Considerations.
The transition between Continuous Conduction Mode
(CCM) to HyperLight Load mode is determined by the
inductor ripple current and the load current.
The diagram shows the signals for High Side switch
Drive (HSD) for Ton control, the Inductor current, and
the Low Side switch Drive (LSD) for TOFF control.
In HLL mode, the inductor is charged with a fixed Ton
pulse on the high side switch. After this, the low side
switch is turned on and current falls at a rate VOUT/L. The
controller remains in HLL mode while the inductor falling
current is detected to cross approximately -50mA. When
the LSD (or TOFF) time reaches its minimum and the
inductor falling current is no longer able to reach the
threshold, the part is in CCM mode.
Once in CCM mode, the TOFF time will not vary.
Therefore, it is important to note that if L is large enough,
the HLL transition level will not be triggered.
That inductor is:
mA502
ns135V
LOUT
MAX
Micrel Inc. MIC23158/9
June 2012 15 M9999-062512-A
Efficiency Considerations
Efficiency is defined as the amount of useful output
power, divided by the amount of power supplied.
100
IV
IV
%Efficiency
ININ
OUTOUT
There are two types of losses in switching converters;
DC losses and switching losses. DC losses are simply
the power dissipation of I2R. Power is dissipated in the
high side switch during the on cycle. Power loss is equal
to the high side MOSFET RDSON multiplied by the switch
current squared. During the off cycle, the low side N-
channel MOSFET conducts, also dissipating power.
Device operating current also reduces efficiency. The
product of the quiescent (operating) current and the
supply voltage represents another DC loss. The current
required driving the gates on and off at a constant 3MHz
frequency and the switching transitions make up the
switching losses.
Efficiency (V
OUT
= 1.8V) vs.
Output Current
0
10
20
30
40
50
60
70
80
90
100
1 10 100 1000 10000
OUTPUT CURRENT (m A)
EFFICI ENCY (% )
VIN = 2.7V
VIN = 4.2V
VIN = 3.6V VIN = 5V
C
OUT
=4.7µF
L=1µH
Figure 3. Efficiency Under Load
The figure above shows an efficiency curve. From 1mA
load to 2A, efficiency losses are dominated by quiescent
current losses, gate drive and transition losses. By using
the HyperLight Load mode, the MIC23158/9 is able to
maintain high efficiency at low output currents.
Over 180mA, efficiency loss is dominated by MOSFET
RDSON and inductor losses. Higher input supply voltages
will increase the gate-to-source threshold on the internal
MOSFETs, thereby reducing the internal RDSON. This
improves efficiency by reducing DC losses in the device.
All but the inductor losses are inherent to the device. In
which case, inductor selection becomes increasingly
critical in efficiency calculations. As the inductors are
reduced in size, the DC resistance (DCR) can become
quite significant. The DCR losses can be calculated as
follows:
P
DCR = IOUT
2 x DCR
From that, the loss in efficiency due to inductor
resistance can be calculated as follows:
100
PIV
IV
1LossEfficiency
DCROUTOUT
OUTOUT
Efficiency loss due to DCR is minimal at light loads and
gains significance as the load is increased. Inductor
selection becomes a trade off between efficiency and
size in this case.
HyperLight Load Mode
The MIC23158/9 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-on-time. This increases the output voltage. If
the output voltage is over the regulation threshold, then
the error comparator turns the PMOS off for a minimum-
off-time until the output drops below the threshold. The
NMOS acts as an 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 synchronous 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 MIC23158/9
works in HyperLight Load to regulate the output. As the
output current increases, the off time decreases, thus
provides more energy to the output. This switching
scheme improves the efficiency of MIC23158/9 during
light load currents by only switching when it is needed.
As the load current increases, the MIC23158/9 goes into
continuous conduction mode (CCM) and switches at a
frequency centered at 3MHz. The equation to calculate
the load when the MIC23158/9 goes into continuous
conduction mode may be approximated by the following
formula:
f2L
D)V(V
IOUTIN
LOAD
As shown in the previous equation, the load at which the
MIC23158/9 transitions from HyperLight Load mode to
PWM mode is a function of the input voltage (VIN), output
voltage (VOUT), duty cycle (D), inductance (L) and
frequency (f). As shown in Figure 4, as the Output
Current increases, the switching frequency also
increases until the MIC23158/9 goes from HyperLight
Load mode to PWM mode at approximately 180mA. The
MIC23158/9 will switch at a relatively constant frequency
around 3MHz once the output current is over 180mA.
Micrel Inc. MIC23158/9
June 2012 16 M9999-062512-A
Swit ching Frequency
vs. O utput Current
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
0.1 1 10 100 1000 10000
OUTPUT CURRENT (m A)
SWITCHING FREQUENCY (MHz)
L=1.0µH
L=0.47µH
Figure 4. SW Frequency vs. Output Current
Micrel Inc. MIC23158/9
June 2012 17 M9999-062512-A
Typical Application Circuit (Adjustable Output)
Bill of Materials
Item Part Name Manufacturer Description Qty.
06036D105KAT2A AVX
(1)
GRM188R60J105KA01D Murata
(2)
C1, C2
C1608X5R0J105K TDK
(3)
1µF, 0603, 6.3V 2
06036D475KAT2A AVX
GRM188R60J475KE19D Murata
C3, C4, C5, C6
C1608X5R0J475K TDK
4.7µF, 6.3V, X5R, 0603 4
06035A471JAT2A AVX
GRM1885C1H471JA01D Murata
C7, C8
C1608C0G1H471J TDK
470pF, 50V, 0603 2
CDRH4D28CLDNP-1R0P SUMIDA
(4) 1µH, 3.0A, 14m, L5.1mm x W5.1mm x H3.0mm
L1, L2 LQH44PN1R0NJ0 MURATA 1µH, 2.8A, 14m, L5.1mm x W5.1mm x H3.0mm 2
R1 CRCW06033013FKEA Vishay/Dale
(5) 301K, 1%, 1/10W, 0603 1
R2 CRCW06031583FKEA Vishay/Dale 158K, 1%, 1/10W, 0603 1
R3 CRCW06033163FKEA Vishay/Dale 316K, 1%, 1/10W, 0603 1
R4 CRCW06032213FKEA Vishay/Dale 221K, 1%, 1/10W, 0603 1
R5, R6 CRCW06031003FKEA Vishay/Dale 100K, 1%, 1/10W, 0603 2
R7, R8 CRCW06031002FKEA Vishay/Dale 10K, 1%, 1/10W, 0603 2
U1 MIC23158/9YML Micrel, Inc
(6) 3MHz PWM Dual 2A Buck Regulator with Hyperlight
Load and Power Good 1
Notes:
1. AVX: www.avx.com
2. Murata: www.murata.com
Micrel Inc. MIC23158/9
June 2012 18 M9999-062512-A
3. TDK: www.tdk.com
4. Sumida: www.sumida.com
5. Vishay/Dale: www.vishay.com
6. Micrel, Inc.: www.micrel.com
Micrel Inc. MIC23158/9
June 2012 19 M9999-062512-A
PCB Layout Recommendations
Top Layer
Bottom Layer
Micrel Inc. MIC23158/9
June 2012 20 M9999-062512-A
Package Information
20-Pin 3mm x 4mm MLF
Micrel Inc. MIC23158/9
June 2012 21 M9999-062512-A
Recommended Land Pattern
Micrel Inc. MIC23158/9
June 2012 22 M9999-062512-A
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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,
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