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 adjust-
able 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, induc-
tor, input capacitor and output capacitor) to implement a
boost regulator. A complete regulator can be constructed in
a 0.6 in
2
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 in
2
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
Typical Applications
L1
47µH
8
D1
MBRA140
5V/100mA
1
L1
50µH
C2
100µF
10V MBRA140
2
3
2.0V–3.1V
2 AA Cells
C1
100µF
10V
IN
MIC2570-1
SW
2.85V
3.3V
5V
1
6
5
4
U1
2.5V to 4.2V
1 Li Cell
C2
220µF
10V
C1
100µF
10V
IN
8
D1
L1
SW
1
4
V
OUT
3.3V/80mA
MIC2570
3.3V
SYNC GND
7
2
5
SYNC
7
GND
2
C3
330µF
6.3V
Two-Cell to 5V DC-to-DC Converter
Single-Cell Lithium to 3.3V/80mARegulator
4-62
1997
MIC2570
Micrel
Ordering Information
Part Number
MIC2570-1BM
MIC2570-2BM
Temperature Range
–40°C to +85°C
–40°C to +85°C
Voltage
Selectable*
Adjustable
Frequency
20kHz
20kHz
Package
8-lead SOIC
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
SW
GND
NC
NC
1
2
3
4
MIC2570-2
8
7
6
5
IN
SYNC
FB
NC
Selectable Voltage
20kHz Frequency
Adjustable Voltage
20kHz Frequency
8-Lead SOIC (M)
Pin Description
Pin No. (Version
†
)
1
2
3
4 (-1)
4 (-2)
5 (-1)
5 (-2)
6 (-1)
6 (-2)
7
8
†
Pin Name
SW
GND
NC
5V
NC
3.3V
NC
2.85V
FB
SYNC
IN
Pin Function
Switch: NPN output switch transistor collector.
Power Ground: NPN output switch transistor emitter.
Not internally connected.
5V Feedback (Input): Fixed 5V feedback to internal resistive divider.
Not internally connected.
3.3V Feedback (Input): Fixed 3.3V feedback to internal resistive divider.
Not internally connected.
2.85V Feedback (Input): Fixed 2.85V feedback to internal resistive divider.
Feedback (Input): 0.22V feedback from external voltage divider network.
Synchronization (Input): Oscillator start timing. Oscillator synchronizes to
falling edge of sync signal.
Supply (Input): Positive supply voltage input.
4
Example: (-1) indicates the pin description is applicable to the MIC2570-1 only.
1997
4-63
MIC2570
Micrel
Absolute Maximum Ratings
Supply Voltage (V
IN
) ..................................................... 18V
Switch Voltage (V
SW
) .................................................... 36V
Switch Current (I
SW
) ....................................................... 1A
Sync Voltage (V
SYNC
) .................................... –0.3V to 15V
Storage Temperature (T
A
) ....................... –65°C to +150°C
SOIC Power Dissipation (P
D
) .................................. 400mW
Operating Ratings
Supply Voltage (V
IN
) .................................... +1.3V to +15V
Ambient Operating Temperature (T
A
) ........ –40°C to +85°C
Junction Temperature (T
J
) ....................... –40°C to +125°C
SOIC Thermal Resistance
(θ
JA
) ............................ 140°C/W
Electrical Characteristics
V
IN
= 2.5V; T
A
= 25°C,
bold
indicates –40°C
≤
T
A
≤
85°C; unless noted
Parameter
Input Voltage
Quiescent Current
Fixed Feedback Voltage
Condition
Startup guaranteed, I
SW
= 100mA
Output switch off
MIC2570-1; V
2.85V pin
= V
OUT
, I
SW
= 100mA
MIC2570-1; V
3.3V pin
= V
OUT
, I
SW
= 100mA
MIC2570-1; V
5V pin
= V
OUT
, I
SW
= 100mA
MIC2570-2, [adj. voltage versions], I
SW
= 100mA,
Note 1
MIC2570-2, [adj. voltage versions]
MIC2570-1; V
2.85V pin
= V
OUT
, I
SW
= 100mA
MIC2570-1; V
3.3V pin
= V
OUT
, I
SW
= 100mA
MIC2570-1; V
5V pin
= V
OUT
, I
SW
= 100mA
MIC2570-1; V
2.85V pin
= V
OUT
MIC2570-1; V
3.3V pin
= V
OUT
MIC2570-1; V
5V pin
= V
OUT
MIC2570-2 [adj. voltage versions]; V
FB
= 0V
1.5V
≤
V
IN
≤
15V
V
IN
= 1.3V, I
SW
= 300mA
V
IN
= 1.5V, I
SW
= 800mA
V
IN
= 3.0V, I
SW
= 800mA
Output switch off, V
SW
= 36V
MIC2570-1, -2; I
SW
= 100mA
Min
1.3
130
2.85
3.30
5.00
220
220
6
65
75
120
6
6
6
25
0.35
250
450
450
1
20
36
0.7
35
1.1
V
FB
< V
REF
, I
SW
= 100mA
67
Typ
Max
15
Units
V
µA
V
V
V
mV
mV
mV
mV
mV
mV
µA
µA
µA
nA
%/V
mV
mV
mV
µA
kHz
V
V
µs
A
%
Reference Voltage
Comparator Hysteresis
Output Hysteresis
Feedback Current
Reference Line Regulation
Switch Saturation Voltage
Switch Leakage Current
Oscillator Frequency
Maximum Output Voltage
Sync Threshold Voltage
Switch On-Time
Currrent Limit
Duty Cycle
General Note:
Devices are ESD protected; however, handling precautions are recommended.
Note 1:
Measured using comparator trip point.
4-64
1997
MIC2570
Micrel
Typical Characteristics
Switch Saturation Voltage
2.0
SWITCH CURRENT (A)
SWITCH CURRENT (A)
T
A
= –40°C
1.5
2.0
Switch Saturation Voltage
2.0
2.5V
V
IN
= 3.0V
2.0V
1.5V
SWITCH CURRENT (A)
T
A
= 25°C
1.5
Switch Saturation Voltage
T
A
= 85°C
1.5
V
IN
= 3.0V
1.5V
1.0
V
IN
= 3.0V
2.5V
1.0
1.0
0.5
1.5V
0
2.0V
0.5
0.5
0
0.2
0.4
0.6
0.8
SWITCH VOLTAGE (V)
1.0
0
0
0.2
0.4
0.6
0.8
SWITCH VOLTAGE (V)
1.0
0
0
0.2
0.4
0.6
0.8
SWITCH VOLTAGE (V)
1.0
Oscillator Frequency
vs. Temperature
30
OSC. FREQUENCY (kHz)
V
IN
= 2.5V
I
SW
= 100mA
25
75
70
65
60
55
Oscillator Duty Cycle
vs. Temperature
200
V
IN
= 2.5V
I
SW
= 100mA
QUIESCENT CURRENT (µA)
175
150
125
100
75
Quiescent Current
vs. Temperature
V
IN
= 2.5V
DUTY CYCLE (%)
20
4
15
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
50
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
50
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
Feedback Current
vs. Temperature
10
FEEDBACK CURRENT (µA)
FEEDBACK CURRENT (nA)
8
6
4
2
0
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
V
IN
= 2.5V
MIC2570-1
50
40
30
20
10
Feedback Current
vs. Temperature
200
V
IN
= 2.5V
MIC2570-2
QUIESCENT CURRENT (µA)
175
150
125
100
75
50
25
0
0
Quiescent Current
vs. Supply Voltage
–40°C
+25°C
+85°C
0
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
2
4
6
8
SUPPLY VOLTAGE (V)
10
SWITCH LEAKAGE CURRENT (nA)
Output Current Limit
vs. Temperature
1.75
1.50
CURRENT LIMIT (A)
1.25
1.00
0.75
0.50
0.25
0
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
Switch Leakage Current
vs. Temperature
1000
OUTPUT HYSTERESIS (mV)
100
10
1
0.1
0.01
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
150
125
100
Output Hysteresis
vs. Temperature
5V
3.3V
75
50
25
0
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
2.85V
1997
4-65
MIC2570
Micrel
Block Diagrams
V
BATT
IN
SYNC
MIC2570-1
Oscillator
0.22V
Reference
V
OUT
Driver
SW
5V
3.3V
2.85V
GND
Selectable Voltage Version with External Components
V
BATT
IN
SYNC
MIC2570-2
Oscillator
0.22V
Reference
V
OUT
Driver
SW
FB
GND
Adjustable Voltage Version with External Components
4-66
1997
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