mic2295a1.08 MB

MIC2295
High Power Density 1.2A Boost Regulator
General Description
Features
The MIC2295 is a 1.2Mhz, PWM dc/dc boost
switching regulator available in low profile Thin
SOT23 and 2mm x 2mm MLF package options.
High power density is achieved with the MIC2295’s
internal 34V / 1.2A switch, allowing it to power large
loads in a tiny footprint.
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The MIC2295 implements constant frequency
1.2MHz PWM current mode control. The MIC2295
offers internal compensation that offers excellent
transient response and output regulation
performance. The high frequency operation saves
board space by allowing small, low-profile external
components. The fixed frequency PWM scheme also
reduces spurious switching noise and ripple to the
input power source.
The MIC2295 is available in a low-profile Thin
SOT23 5-lead package and a 2mm x2mm 8-lead
MLF leadless package. The 2mm x 2mm MLF
package option has an output over-voltage
protection feature.
The MIC2295 has an operating junction temperature
range of –40°C to +125°C.
10µH
VIN
10µH
1-Cell
Li Ion
3V to 4.2V
C1
2.2µF
AGND
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Organic EL power supplies
3.3V to 5V/500mA conversion
TFT-LCD bias supplies
Flash LED drivers
Positive and negative output regulators
SEPIC converters
Positive to negative Cuk converters
12V supply for DSL applications
Multi-output dc/dc converters
R1
100K
MIC2295
OVP
SW
VIN
FB
EN MIC2295
BMLOVP
FB
EN
1µF
Applications
15V /
200mA
SW
VIN
VIN
1-Cell
Li Ion
3V to 4.2V
VOUT
15V
VOUT
100mA
•
2.5V to 10V input voltage range
Output voltage adjustable to 34V
1.2A switch current
1.2MHz PWM operation
Stable with small size ceramic capacitors
High efficiency
Low input and output ripple
<1mA shutdown current
UVLO
Output over-voltage protection (MIC2295BML)
Over temperature shutdown
Thin SOT23-5 package option
2mm x 2mm leadless 8-lead MLF package
option
–40oC to +125oC junction temperature range
R1
100k
PGND
PGND
AGND
R2
9.01K
R2
9.01K
2.2µF
2.2µF
2mm x 2mm Boost Regulator
MLF is a trademark of Amkor Technology.
July 2004
M9999-72104
[email protected] or (408) 955-1690
Micrel
MIC2295
Ordering Information
Output Over
Voltage
Protection
Marking
Code*
Junction
Temperature
Range
Package
Part Number
MIC2295BD5
-
SVAA
-40°C to 125°C
Thin SOT23-5
MIC2295YD5
-
SVAA
-40°C to 125°C
Thin SOT23-5
MIC2295BML
34V
SXA
-40°C to 125°C
2mm x2mm MLF-8L
MIC2295YML
34V
SXA
-40°C to 125°C
* Marking codes to be confirmed by Product Engineering.
2mm x2mm MLF-8L
Lead Finish
Standard
Pb-Free
Standard
Pb-Free
Pin Configuration
Pin Description
MIC2295BD5
Thin SOT-23-5
MIC2295BML
2x2 MLF-8L
Pin Name
Pin Function
1
2
3
7
6
SW
GND
FB
4
3
EN
5
2
1
VIN
OVP
5
4
8
EP
N/C
AGND
PGND
GND
Switch Node (Input): Internal power BIPOLAR collector.
Ground (Return): Ground.
Feedback (Input): 1.24V output voltage sense node.
VOUT = 1.24V ( 1 + R1/R2)
Enable (Input): Logic high enables regulator. Logic low
shuts down regulator.
Supply (Input): 2.5V to 10V input voltage.
Output Over-Voltage Protection (Input): Tie this pin to
VOUT to clamp the output voltage to 34V maximum in
fault conditions. Tie this pin to ground if OVP function
is not required.
No connect. No internal connection to die.
Analog ground
Power ground
Ground (Return). Exposed backside pad.
July 2004
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MIC2295
Absolute Maximum Rating (Note 1)
Operating Range (Note 2)
Supply voltage (VIN) ……………………..…
12V
Switch voltage (VSW) ……………………
-0.3V to 34V
Enable pin voltage (VEN) …………..……..…. -0.3 to VIN
FB Voltage (VFB)……...………………………..…………6V
Switch Current (ISW) ………………………..…..….. 2.5A
Ambient Storage Temperature (TS) …. -65°C to +150°C
ESD Rating, Note 3...………………………… ……..2KV
Supply Voltage (VIN) …………………..…… 2.5V to 10V
Junction Temperature Range (TJ) …… -40°C to +125°C
Package Thermal Impedance
JA 2x2 MLF-8L lead ……………………
93°C/W
JA ThinSOT23-5 lead …………………… 256°C/W
Electrical Characteristics T =25 C, V
A
indicate -40°C TJ 125°C.
Parameter
Supply Voltage Range
Under-Voltage Lockout
Quiescent Current
Shutdown Current
Feedback Voltage
Symb
ol
VIN
VUVLO
IVIN
ISD
VFB
o
IN
=VEN = 3.6V, VOUT = 15V, IOUT = 40mA, unless otherwise noted. Bold values
Condition
2.5
1.8
VFB = 2V (not switching)
VEN = 0V. Note 4.
(+/-1%)
(+/-2%) (Over Temp)
Feedback Input Current
Min
1.22
7
1.21
5
Typ
2.1
2.8
0.1
10
2.4
5
1
1.24
1.252
V
-450
Line Regulation
3V VIN 5V
0.04
Load Regulation
5mA IOUT 40mA
Maximum Duty Cycle
DMAX
Switch Current Limit
Switch Saturation Voltage
Switch Leakage Current
ISW
VSW
ISW
Enable Threshold
VEN
Enable Pin Current
Oscillator Frequency
Output over-voltage
protection
Over-Temperature
Threshold Shutdown
IEN
fSW
Note 1:
Note 2:
Note 3:
Note 4:
Note 5:
VOVP
Tj
Note 5
ISW = 1.2A
VEN = 0V, VSW = 10V
TURN ON
TURN OFF
VEN = 10V
MIC2295BML only
nA
1
%
1.5
%
85
90
%
1.2
1.7
600
0.01
5
A
mV
mA
20
1.2
32
0.4
40
1.35
34
1.5
1.05
30
150
10
Hysteresis
Absolute maximum ratings indicate limits beyond which damage to the component may occur. Electrical specifications do not
apply when operating the device outside of its operating ratings. The maximum allowable power dissipation is a function of the
maximum junction temperature, TJ(Max), the junction-to-ambient thermal resistance, JA, and the ambient temperature, TA. The
maximum allowable power dissipation will result in excessive die temperature, and the regulator will go into thermal shutdown.
This device is not guaranteed to operate beyond its specified operating rating.
IC devices are inherently ESD sensitive. Handling precautions required. Human body model rating: 1.5K in series with 100pF.
ISD = IVIN.
Guaranteed by design
July 2004
M9999-052402
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V
V
mA
mA
1.265
VFB = 1.24V
IFB
Max Unit
s
(408) 955-1690
V
mA
MHz
V
°C
°C
Micrel
MIC2295
Typical Characteristics
5V MIC2295 SEPIC with one
coupled inductor
MIC2295 SEPIC 5V Output
Switch Voltage
vs. Supply Voltage
80
78
300
75
250
Switch Voltage (mV)
70
65
74
EFICIENCY (%)
EFFICIENCY (%)
76
72
70
Vin=3V
Vin=3.5V
Vin=4V
Vin=5V
Vin=5.5V
68
66
60
55
50
45
Vin=2.5
V
Vin=3.3
V
Vin=5V
40
35
200
150
100
50
30
64
0
0
50
100
150
200
50
100
250
OUTPUT CURRENT (mA)
1.3
80
250
0
2.5
300
85
1.1
0.9
0.5
2.5
5.5
7
8.5
10
90
5.5
7
8.5
10
12.2
OUTPUT VOLTAGE (V)
EFFICIENCY (%)
75
70
Vin=2.5
V
Vin=3V
65
60
60
0
50
100
150
200
0
OUTPUT CURRENT (mA)
Feedback Voltage
vs. Temperature
1.20
1.18
1.16
1.14
1.12
1.10
-40 -20 0 20 40 60 80 100 120
TEMPERATURE (°C)
40
60
80
1.4
150
200
100
12
11.95
11.9
0.8
0.6
0.4
0.2
0
-40 -20 0 20 40 60 80 100 120
TEMPERATURE (°C)
VIN = 3.6V
11.85
11.8
0
1.4
1.2
1.0
Load Regulation
12.1
Current Limit
vs. Temperature
July 2004
100
12.05
OUTPUT CURRENT (mA)
CURRENT LIMIT (A)
1.30
1.28
1.26
1.24
1.22
20
50
12.15
FREQUENCY (MHz)
EFFICIENCY (%)
65
FEEDBACK VOLTAGE (V)
0
OUTPUT CURRENT (mA)
80
Vin=3.3V
Vin=4.2V
Vin=3.6V
Vin=3.3V
Vin=4V
Vin=4.2V
60
4
85
70
70
65
85
75
75
15V Short circuit
protected Boost
MIC2295 12V output Efficiency
80
80
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
8.5
MIC2295 15V output Efficiency
75
4
6.5
90
0.7
70
2.5
4.5
Input Voltage (V)
EFFICIENCY (%)
95
FREQUENCY (MHz)
DUTY CYCLE
100
1.5
85
200
Input Voltage
vs. Supply Voltage
Max Duty Cycle vs Input Voltage
90
150
LOAD CURRENT (mA)
25
50 75 100 125 150
LOAD (mA)
Frequency
vs. Temperature
1.3
1.2
1.1
1.0
0.9
0.8
-40 -20 0 20 40 60 80 100 120
TEMPERATURE (°C)
M9999-052402
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(408) 955-1690
90
88
86
84
82
80
2.5
Maximum Duty Cycle
vs. Supply Voltage
700
4
5.5
7
8.5
SUPPLY VOLTAGE (V)
FB Pin Current
vs. Temperature
99
MAXIMUM DUTY CYCLE (%)
100
98
96
94
92
MIC2295
FEEDBACK CURRENT (nA)
MAXIMUM DUTY CYCLE (%)
Micrel
600
500
400
300
200
100
0
-40 -20 0 20 40 60 80 100 120
TEMPERATURE (°C)
10
97
95
93
91
89
87
VIN = 3.6V
85
-40 -20 0 20 40 60 80 100 120
TEMPERATURE (°C)
Switching Waveforms
4.2V
3.2V
12VOUT
150mA Load
Time (400µs/div)
OUTPUT VOLTAGE
(50mV/div)
Output Voltage
Inductor Current
(10µH)
SWITCH SATURATION
(5V/div)
INDUCTOR CURRENT
(500mA/div)
OUTPUT VOLTAGE
(1mV/div) AC-Coupled
Line Transient Response
INPUT VOLTAGE
(2V/div)
Maximum Duty Cycle
vs. Temperature
VSW
3.6VIN
12VOUT
150mA
Time (400ns/div)
Enable Characteristics
LOAD CURRENT
OUTPUT VOLTAGE
(2V/div.)
(5V/div.)
VIN = 3.6V
VIN=3.6V
3.6VIN
12VOUT
150mA Load
TIME (400µs/div.)
July 2004
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MIC2295
the output of the slope compensation ramp
generator. This summed current-loop signal is fed to
one of the inputs of the PWM generator.
The gm error amplifier measures the feedback
voltage through the external feedback resistors and
amplifies the error between the detected signal and
the 1.24V reference voltage. The output of the gm
error amplifier provides the voltage-loop signal that
is fed to the other input of the PWM generator.
When the current-loop signal exceeds the voltageloop signal, the PWM generator turns off the bipolar
output transistor. The next clock period initiates the
next switching cycle, maintaining constant frequency
current-mode PWM control.
Functional Description
The MIC2295 is a high power density, PWM dc/dc
boost regulator. The block diagram is shown in
Figure 1. The MIC2295 is composed of an oscillator,
slope compensation ramp generator, current
amplifier, gm error amplifier, PWM generator, and a
1.2A bipolar output transistor. The oscillator
generates a 1.2MHz clock. The clock’s two functions
are to trigger the PWM generator that turns on the
output transistor, and to reset the slope
compensation ramp generator. The current amplifier
is used to measure the switch current by amplifying
the voltage signal from the internal sense resistor.
The output of the current amplifier is summed with
VIN
FB
OVP*
EN
MIC2295
OVP*
SW
PWM
Generator
gm
VREF
1.24V
Σ
1.2MHz
Oscillator
Ramp
Generator
CA
GND
*OVP available on MLFTM package option only.
MIC2295 Block Diagram
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MIC2295
feedback voltage. As a result the output voltage will
climb out of control. This may cause the switch
node voltage to exceed its maximum voltage rating,
possibly damaging the IC and the external
components. To ensure the highest level of
protection, the MIC2295 OVP pin will shut the switch
off when an over-voltage condition is detected
saving itself and other sensitive circuitry
downstream.
Applications Information
DC to DC PWM Boost Conversion
The MIC2295 is a constant frequency boost
converter. It operates by taking a DC input voltage
and regulating a higher DC output voltage. Figure 2
shows a typical circuit.
L1
10uH
Vin
D1
1A/40V
Schottky
VIN
EN
Vout
Component Selection
SW
OVP
MIC2288BML
R1
C2
10uF
FB
Inductor
R2
Inductor selection is a balance between efficiency,
stability, cost, size and rated current. For most
applications a 10uH is the recommended inductor
value. It is usually a good balance between these
considerations. Efficiency is affected by inductance
value in that larger inductance values reduce the
peak to peak ripple current. This has an effect of
reducing both the DC losses and the transition
losses.
GND
Gnd
Gnd
Figure 2. Typical Application
regulati
Boost regulation is achieved by turning on an
internal switch, which draws current through the
inductor (L1). When the switch turns off, the
inductor’s magnetic field collapses, causing the
current to be discharged into the output capacitor
through an external Schottkey diode (D1). Voltage
regulation is achieved my modulating the pulse
width or pulse width modulation (PWM).
There is also a secondary effect of an inductors DC
resistance (DCR). The DCR of an inductor will be
higher for more inductance in the same package
size. This is due to the longer windings required for
an increase in inductance. Since the majority of
input current (minus the MIC2295 operating current)
is passed through the inductor, higher DCR
inductors will reduce efficiency.
Also, to maintain stability, increasing inductor size
will have to be met with an increase in output
capacitance. This is due to the unavoidable “right
half plane zero” effect for the continuous current
boost converter topology. The frequency at which
the right half plane zero occurs can be calculated as
follows;
Duty Cycle Considerations
Duty cycle refers to the switch on-to-off time ratio
and can be calculated as follows for a boost
regulator;
D =1
Vin
Vout
The duty cycle required for voltage conversion
should be less than the maximum duty cycle of 85%.
Also, in light load conditions where the input voltage
is close to the output voltage, the minimum duty
cycle can cause pulse skipping. This is due to the
energy stored in the inductor causing the output to
overshoot slightly over the regulated output voltage.
During the next cycle, the error amplifier detects the
output as being high and skips the following pulse.
This effect can be reduced by increasing the
minimum load or by increasing the inductor value.
Increasing the inductor value reduces peak current,
which in turn reduces energy transfer in each cycle.
Frhpz =
Vin 2
Vout L Iout 2
The right half plane zero has the undesirable effect
of increasing gain, while decreasing phase. This
requires that the loop gain is rolled off before this
has significant effect on the total loop response. This
can be accomplished by either reducing inductance
(increasing RHPZ frequency) or increasing the
output capacitor value (decreasing loop gain).
Over Voltage Protection
For MLF package of MIC2295, there is an over
voltage protection function. If the feedback resistors
are disconnected from the circuit or the feedback pin
is shorted to ground, the feedback pin will fall to
ground potential. This will cause the MIC2295 to
switch at full duty-cycle in an attempt to maintain the
Output Capacitor
Output capacitor selection is also a trade-off
between performance, size and cost. Increasing
output capacitance will lead to an improved transient
July 2004
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MIC2295
response, but also an increase in size and cost. X5R
or X7R dielectric ceramic capacitors are
recommended for designs with the MIC2295. Y5V
values may be used, but to offset their tolerance
over temperature, more capacitance is required. The
following table shows the recommended ceramic
(X5R) output capacitor value vs. output voltage.
Output Voltage
<6V
<16V
<34V
D =1
Vin
Vout
The actual duty-cycle, D, cannot surpass the
maximum rated duty-cycle, Dmax.
Output Voltage Setting:
The following equation can be used to select the
feedback resistors R1 and R2 (see figure 1).
Recommended Output Capacitance
22uF
10uF
4.7uF
Vout
R1 = R2 1
1.24V
Diode Selection
A high value of R2 can increase the whole system
efficiency, but the feedback pin input current (IFB) of
the gm operation amplifier will affect the output
voltage. An R2 value of xx KW is suitable for most
applications
Inductor Selection:
In MIC2295, the switch current limit is 1A. The
selected inductor should handle at least 1A current
without saturating. The inductor should have a low
DC resistor to minimize power losses. The inductor’s
value can be 4.7uH to 10uH for most applications.
Capacitor Selection:
Multi-layer ceramic capacitors are the best choice for
input and output capacitors. They offer extremely
low ESR, allowing very low ripple, and are available
in very small, cost effective packages. X5R
dielectrics are preferred. A 4.7uF to 10uF output
capacitor is suitable for most applications.
Diode Selection:
For maximum efficiency, Schottky diode is
recommended for use with MIC2295. An optimal
component selection can be made by choosing the
appropriate reverse blocking voltage rating and the
average forward current rating for a given
application. For the case of maximum output voltage
(34V) and maximum output current capability, a 40V
/ 1A Schottky diode should be used.
Open-Circuit Protection
For MLF package option of MIC2295, there is an
output over-voltage protection function that clamps
the output to below 34V in fault conditions. Possible
fault conditions may include: if the device is
configured in a constant current mode of operation
and the load opens, or if in the standard application
the feedback resistors are disconnected from the
circuit. In these cases the FB pin will pull to ground,
causing the MIC2295 to switch with a high dutycycle. As a result, the output voltage will climb out of
regulation, causing the SW pin to exceed its
The MIC2295 requires an external diode for
operation. A Schottkey diode is recommended for
most applications due to their lower forward voltage
drop and reverse recovery time. Ensure the diode
selected can deliver the peak inductor current and
the maximum reverse voltage is rated greater than
the output voltage.
Input Capacitor
A minimum 1uF ceramic capacitor is recommended
for designing with the MIC2295. Increasing input
capacitance will improve performance and greater
noise immunity on the source. The input capacitor
should be as close as possible to the inductor and
the MIC2295, with short traces for good noise
performance.
Feedback Resistors
The MIC2295 utilizes a feedback pin to compare the
output to an internal reference. The output voltage is
adjusted by selecting the appropriate feedback
resistor values. The desired output voltage can be
calculated as follows;
R1 Vout = Vref + 1
R2 Where Vref is equal to 1.24V.
Application Information
Duty-Cycle:
The MIC2295 is a general-purpose step up DC-DC
converter. The maximum difference between the
input voltage and the output voltage is limited by the
maximum duty-cycle (Dmax) of the converter. In the
case of MIC2295, DMAX = 85%. The actual duty
cycle for a given application can be calculated as
follows:
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MIC2295
maximum voltage rating and possibly damaging the
IC and the external components. To ensure the
highest level of safety, the MIC2295 has a dedicated
pin, OVP, to monitor and clamp the output voltage in
over-voltage conditions. The OVP function is
offered in the 2mm x 2mm MLF-8L package option
only. To disable OVP function, tie the OVP pin to
ground.
MICREL, INC. 1849 FORTUNE DRIVE SAN JOSE, CA 95131 USA
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The information furnished by Micrel in this data sheet is believed to be accurate and reliable. However, no responsibility is assumed by Micrel
for its use. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer.
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 sustain life, and whose failure to perform can be reasonably expected to result in a
significant injury to the user. A Purchaser’s use or sale of Micrel Products for use in life support appliances, devices or systems is a
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© 2004 Micrel, Incorporated.
July 2004
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