August 2007 1 MIC2570
MIC2570 Micrel, Inc.
MIC2570
Two-Cell Switching Regulator
General Description
Micrel’s MIC2570 is a micropower boost switching regulator
that operates from two alkaline, two nickel-metal-hydride
cells, or one lithium cell.
The MIC2570 accepts a positive input voltage between 1.3V
and 15V. Its typical no-load supply current is 130µA.
The MIC2570 is available in selectable fixed output or ad-
justable output versions. The MIC2570-1 can be configured
for 2.85V, 3.3V, or 5V by connecting one of three separate
feedback pins to the output. The MIC2570-2 can be config-
ured for an output voltage ranging between its input voltage
and 36V, using an external resistor network.
The MIC2570 has a fixed switching frequency of 20kHz. An
external SYNC connection allows the switching frequency to
be synchronized to an external signal.
The MIC2570 requires only four components (diode, inductor,
input capacitor and output capacitor) to implement a boost
regulator. A complete regulator can be constructed in a 0.6
in2 area.
All versions are available in an 8-lead SOIC with an operating
range from –40°C to +85°.
Typical Applications
Features
• Operates from a two-cell supply
1.3V to 15V operation
• 130µA typical quiescent current
• Complete regulator fits 0.6 in2 area
• 2.85V/3.3V/5V selectable output voltage (MIC2570-1)
• Adjustable output up to 36V (MIC2570-2)
• 1A current limited pass element
• Frequency synchronization input
• 8-lead SOIC package
Applications
• LCD bias generator
• Glucose meters
• Single-cell lithium to 3.3V or 5V converters
• Two-cell alkaline to ±5V converters
• Two-cell alkaline to –5V converters
• Battery-powered, hand-held instruments
• Palmtop computers
• Remote controls
• Detectors
• Battery Backup Supplies
Two-Cell to 5V DC-to-DC Converter
IN
S W
GND
MIC2570-1
C2
220µF
10V
5V/100mA
C1
100µF
10V
2.0V–3.1V
2 AA Cells 2.85V
3.3V
5V
2
4
5
6
1
7
8
L1
47µH
S Y N C
D1
MBRA140
Single-Cell Lithium to 3.3V/80mARegulator
GND
3.3V
S W
MIC2570
S Y N C
7
5
1
2
8
IN
C3
330µF
6.3V
V
OU T
3.3V/80mA
2.5V to 4.2V
1 Li Cell
C1
100µF
10V
D1
MBRA140
L1
50µH
L1
C2
100µF
10V
U1
1 2
3
4
Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
MIC2570 Micrel, Inc.
MIC2570 2 August 2007
Ordering Information
Part Number Temperature
Range
Voltage
Frequency
Package
Standard Pb-Free
MIC2570-1BM MIC2570-1YM –40ºC to +85ºC Selectable* 20kHz 8-pin SOIC
MIC2570-2BM MIC2570-2YM –40ºC to +85ºC Adjustable 20kHz 8-pin SOIC
* Externally selectable for 2.85V, 3.3V, or 5V
Pin Configuration
1
2
3
4
8
7
6
5
S W
GND
NC
5V
IN
S Y N C
2.85V
3.3V
MIC2570-1
Selectable Voltage
20kHz Frequency
1
2
3
4
8
7
6
5
IN
S Y N C
FB
NC
S W
GND
NC
NC
MIC2570-2
Adjustable Voltage
20kHz Frequency
8-Lead SOIC (M)
Pin Description
Pin No. (Version†) Pin Name Pin Function
1 SW Switch: NPN output switch transistor collector.
2 GND Power Ground: NPN output switch transistor emitter.
3 NC Not internally connected.
4 (-1) 5V 5V Feedback (Input): Fixed 5V feedback to internal resistive divider.
4 (-2) NC Not internally connected.
5 (-1) 3.3V 3.3V Feedback (Input): Fixed 3.3V feedback to internal resistive divider.
5 (-2) NC Not internally connected.
6 (-1) 2.85V 2.85V Feedback (Input): Fixed 2.85V feedback to internal resistive divider.
6 (-2) FB Feedback (Input): 0.22V feedback from external voltage divider network.
7 SYNC Synchronization (Input): Oscillator start timing. Oscillator synchronizes to
falling edge of sync signal.
8 IN Supply (Input): Positive supply voltage input.
† Example: (-1) indicates the pin description is applicable to the MIC2570-1 only.
August 2007 3 MIC2570
MIC2570 Micrel, Inc.
Electrical Characteristics
VIN = 2.5V; TA = 25°C, bold indicates –40°C ≤ TA ≤ 85°C; unless noted
Parameter Condition Min Typ Max Units
Input Voltage Startup guaranteed, ISW = 100mA 1.3 15 V
Quiescent Current Output switch off 130 µA
Fixed Feedback Voltage MIC2570-1; V2.85V pin = VOUT, ISW = 100mA 2.7 2.85 3.0 V
MIC2570-1; V3.3V pin = VOUT, ISW = 100mA 3.14 3.30 3.47 V
MIC2570-1; V5V pin = VOUT, ISW = 100mA 4.75 5.00 5.25 V
Reference Voltage MIC2570-2, [adj. voltage versions], ISW = 100mA, Note 1 208 220 232 mV
Comparator Hysteresis MIC2570-2, [adj. voltage versions] 6 mV
Output Hysteresis MIC2570-1; V2.85V pin = VOUT, ISW = 100mA 65 mV
MIC2570-1; V3.3V pin = VOUT, ISW = 100mA 75 mV
MIC2570-1; V5V pin = VOUT, ISW = 100mA 120 mV
Feedback Current MIC2570-1; V2.85V pin = VOUT 6 µA
MIC2570-1; V3.3V pin = VOUT 6 µA
MIC2570-1; V5V pin = VOUT 6 µA
MIC2570-2 [adj. voltage versions]; VFB = 0V 25 nA
Reference Line Regulation 1.5V ≤ VIN ≤ 15V 0.35 %/V
Switch Saturation Voltage VIN = 1.3V, ISW = 300mA 250 mV
VIN = 1.5V, ISW = 800mA 450 mV
VIN = 3.0V, ISW = 800mA 450 mV
Switch Leakage Current Output switch off, VSW = 36V 1 µA
Oscillator Frequency MIC2570-1, -2; ISW = 100mA 20 kHz
Maximum Output Voltage 36 V
Sync Threshold Voltage 0.7 V
Switch On-Time 35 µs
Currrent Limit 1.1 A
Duty Cycle VFB < VREF, ISW = 100mA 67 %
General Note: Devices are ESD protected; however, handling precautions are recommended.
Note 1: Measured using comparator trip point.
Absolute Maximum Ratings
Supply Voltage (VIN) ...................................................... 18V
Switch Voltage (VSW) .................................................... 36V
Switch Current (ISW) ........................................................ 1A
Sync Voltage (VSYNC) ......................................–0.3V to 15V
Storage Temperature (TA) ......................... –65°C to +150°C
SOIC Power Dissipation (PD) .................................. 400mW
Operating Ratings
Supply Voltage (VIN) ..................................... +1.3V to +15V
Ambient Operating Temperature (TA) ......... –40°C to +85°C
Junction Temperature (TJ) ........................ –40°C to +125°C
SOIC Thermal Resistance (θJA) ............................ 140°C/W
MIC2570 Micrel, Inc.
MIC2570 4 August 2007
Typical Characteristics
0
0.5
1.0
1.5
2.0
0 0.2 0.4 0.6 0.8 1.0
SWITCH CURRENT (A)
SWITCH VOLTAGE (V)
Switch Saturation Voltage
TA= –40°C
VIN= 3.0V 2.5V
2.0V
1.5V
0
0.5
1.0
1.5
2.0
0 0.2 0.4 0.6 0.8 1.0
SWITCH CURRENT (A)
SWITCH VOLTAGE (V)
Switch Saturation Voltage
TA= 25°C
VIN = 3.0V
2.0V
2.5V
1.5V
0
0.5
1.0
1.5
2.0
0 0.2 0.4 0.6 0.8 1.0
SWITCH CURRENT (A)
SWITCH VOLTAGE (V)
Switch Saturation Voltage
TA= 85°C
1.5V
VIN = 3.0V
15
20
25
30
-60 -30 0 30 60 90 120 150
OSC. FREQUENCY (kHz)
TEMPERATURE (°C)
Oscillator Frequency
vs. Temperature
VIN = 2.5V
IS W = 100mA
50
55
60
65
70
75
-60 -30 0 30 60 90 120 150
DUTY CYCLE (%)
TEMPERATURE (°C)
Oscillator Duty Cycle
vs. Temperature
VIN = 2.5V
IS W = 100mA
50
75
100
125
150
175
200
-60 -30 0 30 60 90 120 150
QUIESCENT CURRENT (µA)
TEMPERATURE (°C)
Quiescent Current
vs. Temperature
VIN = 2.5V
0
2
4
6
8
10
-60 -30 0 30 60 90 120 150
FEEDBACK CURRENT (µA)
TEMPERATURE (°C)
Feedback Current
vs. Temperature
VIN = 2.5V
MIC2570-
1
0
10
20
30
40
50
-60 -30 0 30 60 90 120 150
FEEDBACK CURRENT (nA)
TEMPERATURE (°C)
Feedback Current
vs. Temperature
VIN = 2.5V
MIC2570-2
0
25
50
75
100
125
150
175
200
0246810
QUIESCENT CURRENT (µA)
SUPPLY VOLTAGE (V)
Quiescent Current
vs. Supply Voltage
–40°C
+85°C
+25°C
0
0.25
0.50
0.75
1.00
1.25
1.50
1.75
-60 -30 0 30 60 90 120 150
CURRENT LIMIT (A)
TEMPERATURE (°C)
Output Current Limit
vs. Temperature
0.01
0.1
1
10
100
1000
-60 -30 0 30 60 90 120 150
SWITCH LEAKAGE CURRENT (nA)
TEMPERATURE (°C)
Switch Leakage Current
vs. Temperature
0
25
50
75
100
125
150
-60 -30 0 30 60 90 120 150
OUTPUT HYSTERESIS (mV)
TEMPERATURE (°C)
Output Hysteresis
vs. Temperature
2.85V
3.3V
5V
August 2007 5 MIC2570
MIC2570 Micrel, Inc.
Block Diagrams
Oscillator
0.22V
Reference
Driver
IN
VBATT
2.85V GND
S W
S Y N C
3.3V5V
VOUT
MIC2570-1
Selectable Voltage Version with External Components
Oscillator
0.22V
Reference
Driver
IN
VBATT
GND
S W
S Y N C
MIC2570-2
VOUT
FB
Adjustable Voltage Version with External Components
MIC2570 Micrel, Inc.
MIC2570 6 August 2007
Functional Description
The MIC2570 switch-mode power supply (SMPS) is a gated
oscillator architecture designed to operate from an input
voltage as low as 1.3V and provide a high-efficiency fixed or
adjustable regulated output voltage. One advantage of this
architecture is that the output switch is disabled whenever the
output voltage is above the feedback comparator threshold
thereby greatly reducing quiescent current and improving
efficiency, especially at low output currents.
Refer to the Block Diagrams for the following discription of
typical gated oscillator boost regulator function.
The bandgap reference provides a constant 0.22V over a
wide range of input voltage and junction temperature. The
comparator senses the output voltage through an internal
or external resistor divider and compares it to the bandgap
reference voltage.
When the voltage at the inverting input of the comparator is
below 0.22V, the comparator output is high and the output of
the oscillator is allowed to pass through the AND gate to the
output driver and output switch. The output switch then turns
on and off storing energy in the inductor. When the output
switch is on (low) energy is stored in the inductor; when the
switch is off (high) the stored energy is dumped into the output
capacitor which causes the output voltage to rise.
When the output voltage is high enough to cause the compara-
tor output to be low (inverting input voltage is above 0.22V)
the AND gate is disabled and the output switch remains off
(high). The output switch remains disabled until the output
voltage falls low enough to cause the comparator output to
go high.
There is about 6mV of hysteresis built into the comparator to
prevent jitter about the switch point. Due to the gain of the
feedback resistor divider the voltage at VOUT experiences
about 120mV of hysteresis for a 5V output.
Appications Information
Oscillator Duty Cycle and Frequency
The oscillator duty cycle is set to 67% which is optimized
to provide maximum load current for output voltages ap-
proximately 3× larger than the input voltage. Other output
voltages are also easily generated but at a small cost in ef-
ficiency. The fixed oscillator frequency (options -1 and -2)
is set to 20kHz.
Output Waveforms
The voltage waveform seen at the collector of the output
switch (SW pin) is either a continuous value equal to VIN
or a switching waveform running at a frequency and duty
cycle set by the oscillator. The continuous voltage equal to
VIN happens when the voltage at the output (VOUT) is high
enough to cause the comparator to disable the AND gate.
In this state the output switch is off and no switching of the
inductor occurs. When VOUT drops low enough to cause
the comparator output to change to the high state the output
switch is driven by the oscillator. See Figure 1 for typical
voltage waveforms in a boost application.
Figure 1. Typical Boost Regulator Waveforms
Synchronization
The SYNC pin is used to synchronize the MIC2570 to an
external oscillator or clock signal. This can reduce system
noise by correlating switching noise with a known system
frequency. When not in use, the SYNC pin should be
grounded to prevent spurious circuit operation. A falling
edge at the SYNC input triggers a one-shot pulse which
resets the oscillator. It is possible to use the SYNC pin to
generate oscillator duty cycles from approximately 20% up
to the nominal duty cycle.
Current Limit
Current limit for the MIC2570 is internally set with a resis-
tor. It functions by modifying the oscillator duty cycle and
frequency. When current exceeds 1.2A, the duty cycle is
reduced (switch on-time is reduced, off-time is unaffected)
and the corresponding frequency is increased. In this way
less time is available for the inductor current to build up while
maintaining the same discharge time. The onset of current
limit is soft rather than abrupt but sufficient to protect the
inductor and output switch from damage. Certain combina-
tions of input voltage, output voltage and load current can
cause the inductor to go into a continuous mode of operation.
This is what happens when the inductor current can not fall
to zero and occurs when:
duty cycle ≤
VOUT + VDIODE – VIN
VOUT + VDIODE – VSAT
Time
Inductor Current
Current “ratchet”
without current limit
Current Limit
Threshold
Continuous
Current
Discontinuous
Current
Figure 2. Current Limit Behavior
August 2007 7 MIC2570
MIC2570 Micrel, Inc.
Figure 2 shows an example of inductor current in the continu-
ous mode with its associated change in oscillator frequency
and duty cycle. This situation is most likely to occur with
relatively small inductor values, large input voltage varia-
tions and output voltages which are less than ~3× the input
voltage. Selection of an inductor with a saturation threshold
above 1.2A will insure that the system can withstand these
conditions.
Inductors, Capacitors and Diodes
The importance of choosing correct inductors, capacitors and
diodes can not be ignored. Poor choices for these components
can cause problems as severe as circuit failure or as subtle
as poorer than expected efficiency.
a.
b.
c.
Inductor Current
Time
Figure 3. Inductor Current: a. Normal,
b. Saturating, and c. Excessive ESR
Inductors
Inductors must be selected such that they do not saturate
under maximum current conditions. When an inductor satu-
rates, its effective inductance drops rapidly and the current
can suddenly jump to very high and destructive values.
Figure 3 compares inductors with currents that are correct
and unacceptable due to core saturation. The inductors
have the same nominal inductance but Figure 3b has a lower
saturation threshold. Another consideration in the selection of
inductors is the radiated energy. In general, toroids have the
best radiation characteristics while bobbins have the worst.
Some bobbins have caps or enclosures which significantly
reduce stray radiation.
The last electrical characteristic of the inductor that must be
considered is ESR (equivalent series resistance). Figure
3c shows the current waveform when ESR is excessive.
The normal symptom of excessive ESR is reduced power
transfer efficiency.
Capacitors
It is important to select high-quality, low ESR, filter capacitors
for the output of the regulator circuit. High ESR in the output
capacitor causes excessive ripple due to the voltage drop
across the ESR. A triangular current pulse with a peak of
500mA into a 200mΩ ESR can cause 100mV of ripple at the
output due the capacitor only. Acceptable values of ESR are
typically in the 50mΩ range. Inexpensive aluminum electro-
lytic capacitors usually are the worst choice while tantalum
capacitors are typically better. Figure 4 demonstrates the
effect of capacitor ESR on output ripple voltage.
4.75
5.00
5.25
0 500 1000 1500
OUTPUT VOLTAGE (V)
TIME (µs)
Figure 4. Output Ripple
Output Diode
Finally, the output diode must be selected to have adequate
reverse breakdown voltage and low forward voltage at the
application current. Schottky diodes typically meet these
requirements.
Standard silicon diodes have forward voltages which are too
large except in extremely low power applications. They can
also be very slow, especially those suited to power rectification
such as the 1N400x series, which affects efficiency.
Inductor Behavior
The inductor is an energy storage and transfer device. Its
behavior (neglecting series resistance) is described by the
following equation:
I =
V
L× t
where:
V = inductor voltage (V)
L = inductor value (H)
t = time (s)
I = inductor current (A)
If a voltage is applied across an inductor (initial current is zero)
for a known time, the current flowing through the inductor is
a linear ramp starting at zero, reaching a maximum value
at the end of the period. When the output switch is on, the
voltage across the inductor is:
V1 = VIN – VSAT
When the output switch turns off, the voltage across the in-
ductor changes sign and flies high in an attempt to maintain
a constant current. The inductor voltage will eventually be
clamped to a diode drop above VOUT. Therefore, when the
output switch is off, the voltage across the inductor is:
V2 = VOUT + VDIODE – VIN
For normal operation the inductor current is a triangular
waveform which returns to zero current (discontinuous mode)
MIC2570 Micrel, Inc.
MIC2570 8 August 2007
at each cycle. At the threshold between continuous and dis-
continuous operation we can use the fact that I1 = I2 to get:
V1 × t1 = V2 × t2
V1
V2
t2
t1
=
This relationship is useful for finding the desired oscillator
duty cycle based on input and output voltages. Since input
voltages typically vary widely over the life of the battery, care
must be taken to consider the worst case voltage for each
parameter. For example, the worst case for t1 is when VIN
is at its minimum value and the worst case for t2 is when VIN
is at its maximum value (assuming that VOUT, VDIODE and
VSAT do not change much).
To select an inductor for a particular application, the worst
case input and output conditions must be determined. Based
on the worst case output current we can estimate efficiency
and therefore the required input current. Remember that
this is power conversion, so the worst case average input
current will occur at maximum output current and minimum
input voltage.
Average IIN(max) =
VOUT × IOUT(max)
VIN(min) × Efficiency
Referring to Figure 1, it can be seen the peak input current
will be twice the average input current. Rearranging the
inductor equation to solve for L:
L = V
I× t1
L =
VIN(min)
2 × Average IIN(max)
× t1
where t1 = duty cycle
fOSC
To illustrate the use of these equations a design example
will be given:
Assume:
MIC2570-1 (fixed oscillator)
VOUT = 5V
IOUT(max) =50mA
VIN(min) = 1.8V
efficiency = 75%.
L = 1.8V × 0.7
2 × 185.2mA × 20kHz
Average IIN(max) = 5V × 50mA
1.8V × 0.75 × 185.2mA
L = 170µH
Use the next lowest standard value of inductor and verify
that it does not saturate at a current below about 400mA
(< 2 × 185.2mA).
August 2007 9 MIC2570
MIC2570 Micrel, Inc.
Application Examples
GND
5V
S W
MIC2570
S Y N C
U1 Micrel MIC2570-1BM
C1 AVX TPSD107M010R0100 Tantalum, ESR = 0.1Ω
C2 AVX TPSE227M010R0100 Tantalum, ESR = 0.1Ω
D1 Motorola MBRA140T3
L1 Coilcraft DO3316P-473, DCR = 0.12Ω
7
4
1
2
8
IN
C2
220µF
10V
VOUT
5V/100mA
2.0V to 3.1V
2 Cells
C1
100µF
10V
D1
MBRA140
L1
47µH
U1
Example 1. 5V/100mA Regulator
GND
3.3V
S W
MIC2570
S Y N C
U1 Micrel MIC2570-1BM
C1 AVX TPSD107M010R0100 Tantalum, ESR = 0.1Ω
C2 AVX TPSE337M006R0100 Tantalum, ESR = 0.1Ω
D1 Motorola MBRA140T3
L1 Coilcraft DO3316P-473, DCR = 0.12Ω
7
5
1
2
8
IN
C2
330µF
6.3V
VOUT
3.3V/150mA
2.0V to 3.1V
2 Cells
C1
100µF
10V
D1
MBRA140
L1
47µH
U1
Example 2. 3.3V/150mA Regulator
GND
FB
S W
MIC2570
S Y N C
U1 Micrel MIC2570-2BM
C1 AVX TPSD107M010R0100 Tantalum, ESR = 0.11Ω
C2 AVX TPSE336M025R0300 Tantalum, ESR = 0.3Ω
D1 Motorola MBRA140T3
L1 Coilcraft DO3316P-473, DCR = 0.12Ω
7
6
1
2
8
IN
C2
33µF
25V
VOUT
12V/40mA
2.0V to 3.1V
2 Cells
C1
100µF
10V
D1
MBRA140
L1
47µH
R2
1M
1%
R1
18.7k
1%
VOUT
= 0.22V × (1+R2/R1)
U1
Example 3. 12V/40mA Regulator
GND
3.3V
S W
MIC2570
S Y N C
U1 Micrel MIC2570-1BM
C1 AVX TPSD107M010R0100 Tantalum, ESR = 0.1Ω
C2 AVX TPSD107M010R0100 Tantalum, ESR = 0.1Ω
C3 AVX TPSE337M006R0100 Tantalum, ESR = 0.1Ω
D1 Motorola MBRA140T3
L1 Coiltronics CTX50-4P DCR = 0.097Ω
7
5
1
2
8
IN
C3
330µF
6.3V
VOUT
3.3V/80mA
2.5V to 4.2V
1 Li Cell
C1
100µF
10V
D1
MBRA140
L1
50µH
L1
C2
100µF
10V
U1
1 2
3
4
Example 4. Single Cell Lithium
to 3.3V/80mA Regulator
GND
FB
S W
MIC2570
S Y N C
U1 Micrel MIC2570-2BM
U2 Micrel MIC5203-5.0BM4
C1 AVX TPSD107M010R0100 Tantalum ESR = 0.1Ω
C2 AVX TPSE227M010R0300 Tantalum ESR = 0.1
Ω
C3 Sprague 293D105X0016A2W Tantalum
D1 Motorola MBRA140T3
L1 Coilcraft DO3316P-473 DCR = 0.12Ω
7
6
1
2
8
IN
C1
100µF
10V
D1
L1
47µH
2.0V to 3.1V
2 Cells
VOUT
= 0.22V × (1+R2/R1)
U1
MBRA140
C2
220µF
10V
MIC5203
IN
EN
GND
OUT VOUT
5V/80mA
C3
1µF
16V
1
2
34
R1
20k
1%
R2
523k
1%
6V
U2
Example 5. Low-Noise 5V/80mA Regulator
MIC2570 Micrel, Inc.
MIC2570 10 August 2007
GND
FB
S W
MIC2570
S Y N C
U1 Micrel MIC2570-2BM
U2 Micrel MIC5203-3.3BM4
C1 AVX TPSD107M010R0100 Tantalum ESR = 0.1Ω
C2 AVX TPSE227M010R0100 Tantalum ESR = 0.1Ω
C3 Sprague 293D105X0016A2W Tantalum
D1 Motorola MBRA140T3
L1 Coilcraft DO3316P-473 DCR = 0.12Ω
7
6
1
2
8
IN
C1
100µF
10V
D1
L1
47µH
2.0V to 3.1V
2 Cells
VOUT
= 0.22V ×(1+R2/R1)
U1
MBRA140
C2
220µF
10V
MIC5203
IN
EN
GND
OUT
VOUT
3.3V/80mA
C3
1µF
16V
1
2
34
R1
20k
1%
R2
374k
1%
U2
4.3V
Example 6. Low-Noise 3.3V/80mA Regulator
GND
5V
S W
MIC2570
S Y N C
U1 Micrel MIC2570-1BM
C1 AVX TPSD107M010R0100 Tantalum, ESR = 0.1Ω
C2 AVX TPSE227M010R0100 Tantalum, ESR = 0.1Ω
C3 AVX TPSE227M010R0100 Tantalum, ESR = 0.1Ω
C4 AVX TPSE227M010R0100 Tantalum, ESR = 0.1Ω
D1 Motorola MBRA140T3
D2 Motorola MBRA140T3
D3 Motorola MBRA140T3
L1 Coilcraft DO3316P-473, DCR = 1.2Ω
7
4
1
2
8
IN
C2
220µF
10V
+VOU T
5V/50mA
2.0V to 3.1V
2 Cells
C1
100µF
16V
D1
MBRA140
L1
47µH
C3
220µF
10V
D2
MBRA140
D3
MBRA140
C4
220µF
10V –V
OUT
–4.5V to –5V/50mA
– IOUT≤ +IOUT
U1
Example 7. ±5V/50mA Regulator
GND
FB
S W
MIC2570
S Y N C
U1 Micrel MIC2570-2BM
C1 AVX TPSD107M010R0100, Tantalum ESR = 0.1Ω
C2 AVX TPSE226M035R0300, Tantalum ESR = 0.3Ω
C3 AVX TPSE226M035R0300, Tantalum ESR = 0.3Ω
D1 Motorola MBRA140T3
D2 Motorola MBRA140T3
L1 Coilcraft DO3316P-473, DCR = 0.12Ω
7
6
1
2
8
IN
C3
0.1µF
C1
100µF
10V
D3
1N4148
L1
47µH
R2
549k
1%
R1
4.99k
1%
2.0V to 3.1V
2 Cells
R3
220k
C2
22µF
35V
–V
OUT
–24V/20mA
D2
MBRA140
D1
MBRA140
C1
22µF
35V
–V
OUT
= –0.22V × (1+R2/R1) + 0.6V
U1
Example 8. –24V/20mA Regulator
August 2007 11 MIC2570
MIC2570 Micrel, Inc.
GND
FB
S W
MIC2570
S Y N C
U1 Micrel MIC2570-2BM
C1 Sanyo 16MV330GX Electrolytic ESR = 0.1Ω
C2 Sanyo 35MV68GX Electrolytic ESR = 0.22Ω
C3 Sanyo 35MV68GX Electrolytic ESR = 0.22Ω
C4 Sanyo 63MV826X Electrolytic ESR = 0.34Ω
D1 Motorola 1N5819
D2 Motorola 1N5819
D3 Motorola 1N5819
L1 Sumida RCH106-470k DCR = 0.16Ω
7
6
1
2
8
IN
C1
330µF
16V
D1L1
47µH
2.0V to 3.1V
2 Cell
1N5819
D2
1N5819
D3
1N5819
C3
68µF
35V
R2
2.2M
1%
R1
10k
1%
C4
82µF
63V
VOUT
50V/10mA
C2
68µF, 35V
U1
V
OUT
= 0.22 ×(1+R2/R1)
Example 9. Voltage Doubler
GND
FB
S W
MIC2570
S Y N C
U1 Micrel MIC2570-2BM
C1 AVX TPSD107M010R0100 Tantalum ESR = 0.1Ω
C2 AVX TPSE227M010R0100 Tantalum ESR = 0.1Ω
D1 Motorola MBRA140T3
L1 Coilcraft DO3316P-473 DCR = 0.12Ω
7
6
1
2
8
IN
C2
220µF
10V
2.0V to 3.1V
2 Cell
C1
100µF
10V
D1
MBRA140
L1
47µH
R1
11k
1%
I = 0.22V/R1
D2
LED
X5 IL E D
U1
Example 10. Constant-Current LED Supply
Enable
Shutdown
GND
FB
S W
MIC2570
S Y N C
U1 Micrel MIC2570-2BM
C1 AVX TPSD107M010R0100 Tantalum ESR = 0.1Ω
C2 AVX TPSE227M010R0100 Tantalum ESR = 0.1Ω
D1 Motorola MBRA140T3
L1 Coilcraft DO3316P-473 DCR = 0.12Ω
7
6
1
2
8
IN
C1
100µF
10V
D1L1
47µH
2.0V to 3.1V
2 Cell
VOUT
= 0.22V × (1+R2/R1)
MBRA140
C2
220µF
10V
R1
20k
1%
R2
434k
1%
D2
1N4148
74C04
VOUT
5V/100mA
U1
R3
100k
Example 11. 5V/100mA Regulator with Shutdown
MIC2570 Micrel, Inc.
MIC2570 12 August 2007
GND
FB
S W
MIC2570
S Y N C
U1 Micrel MIC2570-2BM
C1 AVX TPSD107M010R0100 Tantalum ESR = 0.1Ω
C2 AVX TPSE227M010R0100 Tantalum ESR = 0.1Ω
C3 AVX TPSE227M010R0100 Tantalum ESR = 0.1Ω
D1 Motorola MBRA140T3
L1 Coilcraft DO3316P-473 DCR = 0.12Ω
Q1 Zetex ZTX7888
7
6
1
2
8
IN
C1
100µF
10V
D1L1
47µH
2.0V to 3.1V
2 Cell
V
OUT
= 0.22V × (1+R2/R1)
MBRA140
C3
220µF
10V
R1
20k
1%
R2
434k
1%
D2
1N4148
74C04
VOUT
5V/100mA
C2
220µF
10V
R1
510Ω
Enable
Shutdown
Q1
ZTX7888
U1
R3
100k
Example 12. 5V/100mA Regulator with Shutdown and Output Disconnect
GND
5V
S W
MIC2570
S Y N C
U1 Micrel MIC2570-1BM
C1 AVX TPSD107M010R0100 Tantalum ESR = 0.1Ω
C2 AVX TPSE227M010R0100 Tantalum ESR = 0.1Ω
D1 Motorola MBRA140T3
D2 Motorola MBRS130L
L1 Coilcraft DO3316P-473 DCR = 0.12Ω
7
4
1
2
8
IN
C2
220µF
10V
VOUT
5V/70mA
2.0V to 3.1V
2 Cell
C1
100µF
10V
D1
MBRA140
L1
47µH
D2
MBRS130L
U1
Example 13. Reversed-Battery Protected Regulator
GND
5V
S W
MIC2570
S Y N C
U1 Micrel MIC2570-1BM
C1 AVX TPSD107M010R0100 Tantalum ESR = 0.1Ω
C2 AVX TPSE227M010R0100 Tantalum ESR = 0.1Ω
D1 Motorola MBRA140T3
D2 Motorola MBRS130LT3
D3 Motorola MBRS130LT3
L1 Coilcraft DO3316P-473 DCR = 0.12
Q1 Siliconix Si9434 PMOS
7
4
1
2
8
IN
C2
220µF
10V
VOUT
5V/100mA
C1
100µF
10V
D1
MBRA140
L1
47µH
D3
1N4148
D2
1N4148
C3
0.1µF
2.0V to 3.1V
2 Cell
R1
100k
C4
0.1µF
Q1
Si9434
U1
body diode
Example 14. Improved Reversed-Battery Protected Regulator
August 2007 13 MIC2570
MIC2570 Micrel, Inc.
Component Cross Reference
Capacitors
AVX Sprague Sanyo Sanyo
Surface Mount Surface Mount Through Hole Through Hole
(Tantalum) (Tantalum) (OS-CON) (AL Electrolytic)
330µF/6.3V TPSE337M006R0100 593D337X06R3E2W 10SA220M 16MV330GX (330µF/16V)
220µF/10V TPSE227M010R0100 593D227X0010E2W 10SA220M 16MV330GX (330µF/16V)
100µF/10V TPSD107M010R0100 593D107X0010D2W 10SA100M 16MV330GX (330µF/16V)
33µF/25V TPSE336M025R0300 593D336X0025E2W 35MV68GX (68µF/35V)
22µF/35V TPSE226M035R0300 593D226X0035E2W 35MV68GX (68µF/35V)
Diodes
Motorola GI IR Motorola
Surface Mount Surface Mount Surface Mount Through Hole
(Schottky) (Schottky) (Schottky) (Schottky)
1A/40V MBRA140T3 SS14 10MQ40 1N5819
1A/20V 1N5817
Inductors
Coilcraft Coiltronics Sumida Sumida
Surface Mount Surface Mount Surface Mount Through Hole
(Button Cores) (Torriod) (Button Cores) (Button Cores)
22µH DO3308P-223
47µH DO3316P-473 CD75-470LC RCH-106-470k
50µH CTX50-4P
Suggested Manufacturers List
Inductors Capacitors Diodes Transistors
Coilcraft AVX Corp. General Instruments (GI) Siliconix
1102 Silver Lake Rd. 801 17th Ave. South 10 Melville Park Rd. 2201 Laurelwood Rd.
Cary, IL 60013 Myrtle Beach, SC 29577 Melville, NY 11747 Santa Clara, CA 96056
tel: (708) 639-2361 tel: (803) 448-9411 tel: (516) 847-3222 tel: (800) 554-5565
fax: (708) 639-1469 fax: (803) 448-1943 fax: (516) 847-3150
Coiltronics Sanyo Video Components Corp. International Rectifier Corp. Zetex
6000 Park of Commerce Blvd. 2001 Sanyo Ave. 233 Kansas St. 87 Modular Ave.
Boca Raton, FL 33487 San Diego, CA 92173 El Segundo, CA 90245 Commack, NY 11725
tel: (407) 241-7876 tel: (619) 661-6835 tel: (310) 322-3331 tel: (516) 543-7100
fax: (407) 241-9339 fax: (619) 661-1055 fax: (310) 322-3332
Sumida Sprague Electric Motorola Inc.
Suite 209 Lower Main St. MS 56-126
637 E. Golf Road 60005 Sanford, ME 04073 3102 North 56th St.
Arlington Heights, IL tel: (207) 324-4140 Phoenix, AZ 85018
tel: (708) 956-0666 tel: (602) 244-3576
fax: (708) 956-0702 fax: (602) 244-4015
MIC2570 Micrel, Inc.
MIC2570 14 August 2007
Component Side and Silk Screen (Not Actual Size)
Solder Side and Silk Screen (Not Actual Size)
Evaluation Board Layout
August 2007 15 MIC2570
MIC2570 Micrel, Inc.
Package Information
45°
0°–8°
0.244 (6.20)
0.228 (5.79)
0.197 (5.0)
0.189 (4.8) SEATING
PLANE
0.026 (0.65)
MAX)
0.010 (0.25)
0.007 (0.18)
0.064 (1.63)
0.045 (1.14)
0.0098 (0.249)
0.0040 (0.102)
0.020 (0.51)
0.013 (0.33)
0.157 (3.99)
0.150 (3.81)
0.050 (1.27)
TYP
PIN 1
DIMENSIONS:
INCHES (MM)
0.050 (1.27)
0.016 (0.40)
8-Pin SOIC (M)
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
This information furnished by�
Micrel reserves the right to change circuitry and specifications at any time without notification to the customer.
Micrel Products are not�
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 Pr�
Micrel for any damages resulting from such use or sale.
© 2005 Micrel, Inc.