Page 1
MIC2570 Micrel
MIC2570
Two-Cell Switching Regulator
Preliminary Information
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 adjustable 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 configured 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°.
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
T ypical Applications
2.0V–3.1V
2 AA Cells
C1
100µF
10V
Two-Cell to 5V DC-to-DC Converter
MIC2570-1
SYNC
7
L1
47µH
8
IN
SW
2.85V
3.3V
5V
GND
2
MBRA140
1
6
5
4
D1
5V/100mA
C2
220µF
10V
2.5V to 4.2V
1 Li Cell
C1
100µF
10V
U1
12
IN
MIC2570
SYNC
GND
7
8
L1
50µH
SW
3.3V
2
C2
100µF
10V
MBRA140
3
D1
1
5
L1
4
3.3V/80mA
C3
330µF
6.3V
V
OUT
Single-Cell Lithium to 3.3V/80mARegulator
4-62 1997
Page 2
MIC2570 Micrel
Ordering Information
Part Number Temperature Range Voltage Frequency Package
MIC2570-1BM –40°C to +85°C Selectable* 20kHz 8-lead SOIC
MIC2570-2BM –40°C to +85°C Adjustable 20kHz 8-lead SOIC
* Externally selectable for 2.85V, 3.3V, or 5V
Pin Configuration
MIC2570-1
SW
GND
NC
5V
1
2
3
4
8
7
6
5
IN
SYNC
2.85V
3.3V
Selectable 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.
MIC2570-2
1
SW
NC
NC
2
3
4
GND
Adjustable Voltage
20kHz Frequency
8
7
6
5
IN
SYNC
FB
NC
4
1997 4-63
Page 3
MIC2570 Micrel
Absolute Maximum Ratings
Supply Voltage (VIN) .....................................................18V
Switch Voltage (VSW)....................................................36V
Switch Current (ISW) .......................................................1A
Sync Voltage (V
) .................................... –0.3V to 15V
SYNC
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
Storage Temperature (TA) ....................... –65°C to +150°C
SOIC Power Dissipation (PD)..................................400mW
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; V
MIC2570-1; V
MIC2570-1; V
2.85V pin
3.3V pin
5V pin
Reference Voltage MIC2570-2, [adj. voltage versions], I
Comparator Hysteresis MIC2570-2, [adj. voltage versions] 6 mV
Output Hysteresis MIC2570-1; V
MIC2570-1; V
MIC2570-1; V
Feedback Current MIC2570-1; V
MIC2570-1; V
MIC2570-1; V
2.85V pin
3.3V pin
5V pin
2.85V pin
3.3V pin
5V pin
MIC2570-2 [adj. voltage versions]; VFB = 0V 25 nA
Reference Line Regulation 1.5V ≤ VIN ≤ 15V 0.35 %/V
Switch Saturation Voltage V
= 1.3V, ISW = 300mA 250 mV
IN
= 1.5V, ISW = 800mA 450 mV
V
IN
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 < V
General Note: Devices are ESD protected; however, handling precautions are recommended.
Note 1: Measured using comparator trip point.
, ISW = 100mA 67 %
REF
= V
= V
= V
= V
= V
= V
= V
, ISW = 100mA 2.85 V
OUT
, ISW = 100mA 3.30 V
OUT
, ISW = 100mA 5.00 V
OUT
= 100mA, Note 1 220 mV
SW
220 mV
= V
= V
, ISW = 100mA 65 mV
OUT
, ISW = 100mA 75 mV
OUT
, ISW = 100mA 120 mV
OUT
OUT
OUT
OUT
6 µA
6 µA
6 µA
4-64 1997
Page 4
MIC2570 Micrel
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)
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)
50
75
100
125
150
175
200
-60 -30 0 30 60 90 120 150
QUIESCENT CURRENT (µA)
TEMPERATURE (°C)
0
25
50
75
100
125
150
175
200
0246810
QUIESCENT CURRENT (µA)
SUPPLY VOLTAGE (V)
0
25
50
75
100
125
150
-60 -30 0 30 60 90 120 150
OUTPUT HYSTERESIS (mV)
TEMPERATURE (°C)
Typical Characteristics
Switch Saturation Voltage
2.0
TA = –40°C
1.5
1.0
0.5
SWITCH CURRENT (A)
0
0 0.2 0.4 0.6 0.8 1.0
VIN= 3.0V
1.5V
SWITCH VOLTAGE (V)
2.5V
2.0V
Oscillator Frequency
vs. Temperature
30
VIN = 2.5V
I
= 100mA
SW
25
20
OSC. FREQUENCY (kHz)
15
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
Switch Saturation Voltage
TA = 25°C
VIN = 3.0V
2.5V
2.0V
1.5V
Oscillator Duty Cycle
vs. Temperature
75
VIN = 2.5V
I
= 100mA
70
SW
65
60
DUTY CYCLE (%)
55
50
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
Switch Saturation Voltage
TA = 85°C
VIN = 3.0V
1.5V
Quiescent Current
vs. Temperature
VIN = 2.5V
4
Feedback Current
10
8
6
4
2
FEEDBACK CURRENT (µA)
0
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
Output Current Limit
1.75
1.50
1.25
1.00
1997 4-65
0.75
0.50
CURRENT LIMIT (A)
0.25
0
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
vs. Temperature
VIN = 2.5V
MIC2570-1
vs. Temperature
Feedback Current
vs. Temperature
50
VIN = 2.5V
40
MIC2570-2
30
20
10
FEEDBACK CURRENT (nA)
0
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
Switch Leakage Current
1000
100
0.1
0.01
SWITCH LEAKAGE CURRENT (nA)
vs. Temperature
10
1
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
Quiescent Current
vs. Supply Voltage
–40°C
+25°C
+85°C
Output Hysteresis
vs. Temperature
5V
3.3V
2.85V
Page 5
MIC2570 Micrel
Block Diagrams
V
V
BATT
BATT
IN
SYNC
MIC2570-1
Oscillator
0.22V
Reference
3.3V5V
2.85V GND
Driver
Selectable Voltage Version with External Components
IN
Oscillator
SYNC
MIC2570-2
SW
V
OUT
V
OUT
0.22V
Reference
Driver
FB
Adjustable Voltage Version with External Components
SW
GND
4-66 1997
Page 6
5V
0V
5V
0mA
I
PEAK
V
IN
Supply
Voltage
Inductor
Current
Output
Voltage
Time
MIC2570 Micrel
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 comparator 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 V
experiences
OUT
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 approximately 3× larger than the input voltage. Other output voltages
are also easily generated but at a small cost in efficiency. 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 V
happens when the voltage at the output (V
OUT
) 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 V
drops low enough to cause the
OUT
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.
1997 4-67
IN
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 resistor.
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 combinations 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
Inductor Current
V + V – V
OUT DIODE
≤
V + V – V
OUT DIODE SAT
Time
IN
Current “ratchet”
without current limit
Current Limit
Threshold
Continuous
Current
Discontinuous
Current
Figure 2. Current Limit Behavior
4
Page 7
MIC2570 Micrel
Figure 2 shows an example of inductor current in the continuous 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 variations
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.
Inductor Current
c.
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 saturates, 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 electrolytic capacitors usually are the worst choice while tantalum
capacitors are typically better. Figure 4 demonstrates the
effect of capacitor ESR on output ripple voltage.
5.25
5.00
OUTPUT VOLTAGE (V)
4.75
0 500 1000 1500
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:
V
I =
t×
L
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:
V = V – V
1IN
SAT
When the output switch turns off, the voltage across the
inductor 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 V
. Therefore, when the
OUT
output switch is off, the voltage across the inductor is:
V = V + V – V
2
OUT DIODE
IN
For normal operation the inductor current is a triangular
waveform which returns to zero current (discontinuous mode)
4-68 1997
Page 8
MIC2570 Micrel
at each cycle. At the threshold between continuous and
discontinuous operation we can use the fact that I1 = I2 to get:
V t = V t
××
11 2 2
1
2
=
t
2
t
1
V
V
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 V
OUT
, V
DIODE
and V
SAT
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.
V I
×
Average I =
IN(max)
OUT OUT(max)
V Efficiency
IN(min)
×
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:
V
L =
L =
where t =
t1×
I
V
IN(min)
×
2 Average I
duty cycle
1
f
OSC
IN(max)
×
t
1
To illustrate the use of these equations a design example will
be given:
Assume:
MIC2570-1 (fixed oscillator)
V
= 5V
OUT
I
OUT(max)
V
IN(min)
=50mA
= 1.8V
efficiency = 75%.
×
Average I =
L =
IN(max)
1.8V 0.7
2 185.2mA 20kHz
××
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).
4
1997 4-69
Page 9
MIC2570 Micrel
GND
3.3V
SW
MIC2570
SYNC
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
V
OUT
3.3V/150mA
2.0V to 3.1V
2 Cells
C1
100µF
10V
D1
MBRA140
L1
47µH
U1
Application Examples
MBRA140
2.0V to 3.1V
2 Cells
L1
47µH
C1
100µF
10V
U1
8
IN
SW
MIC2570
5V
GND
SYNC
7
2
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
D1
1
4
5V/100mA
C2
220µF
10V
V
OUT
2.0V to 3.1V
2 Cells
Example 1. 5V/100mA Regulator
MBRA140
L1
47µH
C1
100µF
10V
U1
8
IN
SW
MIC2570
FB
SYNC
GND
7
2
V
= 0.22V (1+R2/R1)
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
OUT
D1
R2
1
6
1M
1%
R1
18.7k
1%
Example 3. 12V/40mA Regulator
L1
47µH
MIC2570
SYNC
7
8
IN
GND
SW
FB
2
2.0V to 3.1V
2 Cells
C1
100µF
10V
U1
12V/40mA
C2
33µF
25V
MBRA140
1
6
V
D1
OUT
2.5V to 4.2V
1 Li Cell
6V
R2
523k
1%
R1
20k
1%
Example 2. 3.3V/150mA Regulator
C2
SW
100µF
10V
MBRA140
3
D1
1
5
L1
4
L1
50µH
12
C1
100µF
10V
U1
8
IN
MIC2570
3.3V
SYNC
GND
7
2
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
Example 4. Single Cell Lithium
to 3.3V/80mA Regulator
U2
C2
220µF
10V
3
IN
MIC5203
2
EN
GND
V
= 0.22V (1+R2/R1)
OUT
4
OUT
1
5V/80mA
C3
1µF
16V
V
OUT
3.3V/80mA
C3
330µF
6.3V
V
OUT
U1 Micrel MIC2570-2BM
U2 Micrel MIC5203-5.0BM4
C1 AVX TPSD107M010R0100 Tantalum ESR = 0.1Ω
C2 AVX TPSE227M010R0300 Tantalum ESR = 0.1Ω
C3 Sprague 293D105X0016A2W Tantalum
D1 Motorola MBRA140T3
L1 Coilcraft DO3316P-473 DCR = 0.12Ω
Example 5. Low-Noise 5V/80mA Regulator
4-70 1997
Page 10
MIC2570 Micrel
U2
3
IN
2
EN
OUT
MIC5203
GND
1
= 0.22V (1+R2/R1)
4
1µF
16V
C3
V
OUT
3.3V/80mA
2.0V to 3.1V
2 Cells
D1L1
47µH
MIC2570
SYNC
7
8
IN
GND
2
U1
C1
100µF
10V
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
SW
FB
MBRA140
1
6
R2
374k
1%
R1
20k
1%
4.3V
C2
220µF
10V
V
OUT
Example 6. Low-Noise 3.3V/80mA Regulator
D2
MBRA140
D1
C3
220µF
10V
MBRA140
D3
+V
OUT
5V/50mA
–I
≤ +I
OUT
C2
220µF
10V
C4
220µF
10V
–4.5V to –5V/50mA
–V
OUT
OUT
L1
47µH
MIC2570
SYNC
7
8
IN
SW
5V
1
4
GND
2
2.0V to 3.1V
2 Cells
C1
100µF
16V
U1
MBRA140
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
4
2.0V to 3.1V
2 Cells
100µF
–V
Example 7. ±5V/50mA Regulator
1N4148
C1
22µF
35V
D2
MBRA140
D3
L1
47µH
MIC2570
SYNC
7
8
IN
SW
FB
1
6
GND
2
D1
MBRA140
U1
C1
10V
= –0.22V (1+R2/R1) + 0.6V
OUT
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
Example 8. –24V/20mA Regulator
R2
549k
1%
R1
4.99k
1%
R3
220k
C3
0.1µF
C2
22µF
35V
–V
–24V/20mA
OUT
1997 4-71
Page 11
MIC2570 Micrel
C2
68µF, 35V
2.0V to 3.1V
2 Cell
D1L1
47µH
MIC2570
SYNC
7
8
IN
SW
GND
2
U1
C1
330µF
16V
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
1N5819D21N5819D31N5819
1
6
FB
Example 9. Voltage Doubler
L1
47µH
MIC2570
SYNC
7
8
IN
SW
FB
GND
2
I = 0.22V/R1
2.0V to 3.1V
2 Cell
C1
100µF
10V
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
U1
C3
68µF
35V
V
= 0.22 1+R2/R1)
OUT
D1
MBRA140
D2
LED
1
X5
R1
11k
1%
I
6
LED
R2
2.2M
1%
R1
10k
1%
C2
220µF
10V
50V/10mA
C4
82µF
63V
V
OUT
2.0V to 3.1V
2 Cell
Example 10. Constant-Current LED Supply
D1L1
47µH
C1
100µF
10V
U1
8
IN
SW
MIC2570
FB
SYNC
GND
7
2
= 0.22V (1+R2/R1)
V
OUT
Enable
Shutdown
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
1
6
1N4148
74C04
MBRA140
D2
R3
100k
R2
434k
1%
R1
20k
1%
C2
220µF
10V
Example 11. 5V/100mA Regulator with Shutdown
V
OUT
5V/100mA
4-72 1997
Page 12
MIC2570 Micrel
R1
510
Ω
2.0V to 3.1V
2 Cell
D1L1
47µH
8
IN
SW
MIC2570
C1
100µF
10V
U1
FB
SYNC
GND
7
2
1N4148
V
= 0.22V (1+R2/R1)
OUT
Enable
Shutdown
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
1
6
74C04
D2
MBRA140
R3
100k
R2
434k
1%
R1
20k
1%
Q1
ZTX7888
C2
220µF
10V
5V/100mA
C3
220µF
10V
V
OUT
Example 12. 5V/100mA Regulator with Shutdown and Output Disconnect
2.0V to 3.1V
2 Cell
D2
MBRS130L
C1
100µF
10V
U1
SYNC
8
IN
MIC2570
7
GND
L1
47µH
SW
5V
2
1
4
D1
MBRA140
5V/70mA
C2
220µF
10V
V
OUT
4
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
Example 13. Reversed-Battery Protected Regulator
2.0V to 3.1V
2 Cell
body diode
Q1
Si9434
1N4148
R1
C4
100k
0.1µF
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 = 0.12Ω
Q1 Siliconix Si9434 PMOS
D3
C3
0.1µF
D2
1N4148
C1
100µF
10V
U1
SYNC
MIC2570
7
L1
47µH
8
IN
SW
5V
MBRA140
1
4
GND
2
Example 14. Improved Reversed-Battery Protected Regulator
D1
5V/100mA
C2
220µF
10V
V
OUT
1997 4-73
Page 13
MIC2570 Micrel
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
4-74 1997
Page 14
MIC2570 Micrel
Evaluation Board Layout
Component Side and Silk Screen (Not Actual Size)
Solder Side and Silk Screen (Not Actual Size)
4
1997 4-75
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