MIC2570
Micrel
4-62
1997
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 130
A.
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
.
Typical Applications
Features
Operates from a two-cell supply
1.3V to 15V operation
130
A 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
Two-Cell to 5V DC-to-DC Converter
IN
SW
GND
MIC2570-1
C2
220F
10V
5V/100mA
C1
100F
10V
2.0V3.1V
2 AA Cells
2.85V
3.3V
5V
2
4
5
6
1
7
8
L1
47H
SYNC
D1
MBRA140
Single-Cell Lithium to 3.3V/80mARegulator
GND
3.3V
SW
MIC2570
SYNC
7
5
1
2
8
IN
C3
330F
6.3V
V
OUT
3.3V/80mA
2.5V to 4.2V
1 Li Cell
C1
100F
10V
D1
MBRA140
L1
50H
L1
C2
100F
10V
U1
1
2
3
4
1997
4-63
MIC2570
Micrel
4
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
1
2
3
4
8
7
6
5
SW
GND
NC
5V
IN
SYNC
2.85V
3.3V
MIC2570-1
Selectable Voltage
20kHz Frequency
1
2
3
4
8
7
6
5
IN
SYNC
FB
NC
SW
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.
MIC2570
Micrel
4-64
1997
Electrical Characteristics
V
IN
= 2.5V; T
A
= 25
C, bold indicates 40
C
T
A
85
C; unless noted
Parameter
Condition
Min
Typ
Max
Units
Input Voltage
Startup guaranteed, I
SW
= 100mA
1.3
15
V
Quiescent Current
Output switch off
130
A
Fixed Feedback Voltage
MIC2570-1; V
2.85V pin
= V
OUT
, I
SW
= 100mA
2.85
V
MIC2570-1; V
3.3V pin
= V
OUT
, I
SW
= 100mA
3.30
V
MIC2570-1; V
5V pin
= V
OUT
, I
SW
= 100mA
5.00
V
Reference Voltage
MIC2570-2, [adj. voltage versions], I
SW
= 100mA, Note 1
220
mV
220
mV
Comparator Hysteresis
MIC2570-2, [adj. voltage versions]
6
mV
Output Hysteresis
MIC2570-1; V
2.85V pin
= V
OUT
, I
SW
= 100mA
65
mV
MIC2570-1; V
3.3V pin
= V
OUT
, I
SW
= 100mA
75
mV
MIC2570-1; V
5V pin
= V
OUT
, I
SW
= 100mA
120
mV
Feedback Current
MIC2570-1; V
2.85V pin
= V
OUT
6
A
MIC2570-1; V
3.3V pin
= V
OUT
6
A
MIC2570-1; V
5V pin
= V
OUT
6
A
MIC2570-2 [adj. voltage versions]; V
FB
= 0V
25
nA
Reference Line Regulation
1.5V
V
IN
15V
0.35
%/V
Switch Saturation Voltage
V
IN
= 1.3V, I
SW
= 300mA
250
mV
V
IN
= 1.5V, I
SW
= 800mA
450
mV
V
IN
= 3.0V, I
SW
= 800mA
450
mV
Switch Leakage Current
Output switch off, V
SW
= 36V
1
A
Oscillator Frequency
MIC2570-1, -2; I
SW
= 100mA
20
kHz
Maximum Output Voltage
36
V
Sync Threshold Voltage
0.7
V
Switch On-Time
35
s
Currrent Limit
1.1
A
Duty Cycle
V
FB
< V
REF
, I
SW
= 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 (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
(
JA
) ............................ 140
C/W
1997
4-65
MIC2570
Micrel
4
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
T
A
= 40
C
V
IN
= 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
T
A
= 25
C
V
IN
= 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
T
A
= 85
C
1.5V
V
IN
= 3.0V
15
20
25
30
-60 -30
0
30
60
90 120 150
OSC. FREQUENCY (kHz)
TEMPERATURE (
C)
Oscillator Frequency
vs. Temperature
V
IN
= 2.5V
I
SW
= 100mA
50
55
60
65
70
75
-60 -30
0
30
60
90 120 150
DUTY CYCLE (%)
TEMPERATURE (
C)
Oscillator Duty Cycle
vs. Temperature
V
IN
= 2.5V
I
SW
= 100mA
50
75
100
125
150
175
200
-60 -30
0
30
60
90 120 150
QUIESCENT CURRENT (
A)
TEMPERATURE (
C)
Quiescent Current
vs. Temperature
V
IN
= 2.5V
0
2
4
6
8
10
-60 -30
0
30
60
90 120 150
FEEDBACK CURRENT (
A)
TEMPERATURE (
C)
Feedback Current
vs. Temperature
V
IN
= 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
V
IN
= 2.5V
MIC2570-2
0
25
50
75
100
125
150
175
200
0
2
4
6
8
10
QUIESCENT CURRENT (
A)
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
MIC2570
Micrel
4-66
1997
Block Diagrams
Oscillator
0.22V
Reference
Driver
IN
V
BATT
2.85V
GND
SW
SYNC
3.3V
5V
V
OUT
MIC2570-1
Selectable Voltage Version with External Components
Oscillator
0.22V
Reference
Driver
IN
V
BATT
GND
SW
SYNC
MIC2570-2
V
OUT
FB
Adjustable Voltage Version with External Components
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