19-0204; Rev 1; 5/94
UAL
IT MAN
TION K
A
EET
EVALU
ATA SH
OWS D
FOLL
5V/3.3V/3V/Adjustable-Output,
Step-Up/Step-Down DC-DC Converters
____________________________Features
o
Regulates from Inputs Above & Below the Output
o
1V to 6.2V Supply-Voltage Range
o
Internal 1A Active Rectifier with Input-to-Output
Disconnect in Shutdown
o
Up to 210mA Load Currents, Guaranteed
o
85% Efficiency
o
Only 3 External Components
o
Adjustable Current Limit
o
195µA Quiescent Supply Current
o
20µA Shutdown Supply Current
o
3V/3.3V/5V and Adjustable Output Voltage Versions
o
Available in 8-Pin DIP and SO Packages
_______________General Description
The MAX877/MAX878/MAX879 are pulse-skipping, step-
up/step-down DC-DC converters that provide a regulated
output from inputs both above and below the output. They
require only three external components—an inductor
(typically 22µH) and two filter capacitors.
The MAX877 delivers a regulated 5V output from 2.5V to
6.2V inputs. The MAX878 generates pin-selectable volt-
ages of 3.0V or 3.3V from 1.5V to 6.2V inputs. The MAX879
output can be adjusted from 2.5V to 6V via an external
resistor divider from 2.5V to 6.2V inputs.
A unique high-power, internal, synchronous rectifier design
(Active Rectifier™) enables the devices to regulate in a
switched linear mode if the input voltage is higher than the
desired output voltage. When the input voltage falls below
the output voltage, the MAX877/MAX878/MAX879 will
smoothly switch into a pulse-skipping boost mode and
step up from input voltages as low as 1V. In shutdown, the
active rectifier disconnects the output from the source. This
stops the current drain from input to output associated with
conventional step-up converters.
High-frequency operation (up to 300kHz) allows the use of
small surface-mount inductors. Supply current is 195µA
under no load, and only 20µA in shutdown mode. For 1-cell
(1V) step-up converters with similar performance and the
same pinout, refer to the MAX777/MAX778/MAX779 data
sheet.
MAX877/MAX878/MAX879
______________Ordering Information
PART
MAX877CPA
MAX877CSA
MAX877C/D
MAX877EPA
MAX877ESA
MAX877MJA
TEMP. RANGE
0°C to +70°C
0°C to +70°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
-55°C to +125°C
PIN-PACKAGE
8 Plastic DIP
8 SO
Dice*
8 Plastic DIP
8 SO
8 CERDIP
________________________Applications
Two or Three NiCd Cells to 3V/3.3V Conversion
Three or Four Alkaline Cells to 5V Conversion
One Lithium Cell to 3V/3.3V Conversion
Pagers
Palmtop and Notebook Computers
Battery-Powered and Hand-Held Instruments
Ordering Information continued on last page.
* Contact factory for dice specifications.
__________Typical Operating Circuit
__________________Pin Configuration
TOP VIEW
INPUT
1.8V TO 6.2V
2
22µF
IN
ILIM
MAX878
SHDN
SEL
8
PGND
4
LX
OUT
AGND
3
5
6
22µH
ILIM 1
IN 2
AGND 3
PGND 4
8
N.C. (MAX877)
*
SHDN
ON/OFF
OUT
LX
1
7
MAX877
MAX878
MAX879
7
6
5
OUTPUT
3.3V
210mA
100µF
DIP/SO
*
SEL (MAX878), FB (MAX879)
™ Active Rectifier is a trademark of Maxim Integrated Products.
________________________________________________________________
Maxim Integrated Products
1
Call toll free 1-800-998-8800 for free samples or literature.
5V/3.3V/3V/Adjustable-Output,
Step-Up/Step-Down DC-DC Converters
MAX877/MAX878/MAX879
ABSOLUTE MAXIMUM RATINGS
Supply Voltage (IN to PGND) .......................................0V to +7V
Output Short-Circuit Duration to PGND, AGND (Note 1)....30sec
Voltage Applied to:
LX (switch off).......................................................-0.3V to +7V
(switch on) ...................................30sec short to IN or OUT
–—
——
OUT, SHDN...........................................................-0.3V to +7V
FB ..........................................................-0.3V to (OUT + 0.3V)
AGND to PGND ........................................................-0.3V, +0.3V
Reverse Battery Current....................................................900mA
Continuous Power Dissipation (T
A
= +70°C)
Plastic DIP (derate 9.09mW/°C above +70°C) ............727mW
SO (derate 5.88mW/°C above +70°C) .........................471mW
CERDIP (derate 8.00mW/°C above +70°C) .................640mW
Operating Temperature Ranges:
MAX87_C_A ........................................................0°C to +70°C
MAX87_E_A .....................................................-40°C to +85°C
MAX87_MJA ..................................................-55°C to +125°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10sec) .............................+300°C
Note 1:
The output may be shorted to ground continuously if the package power dissipation is not exceeded.
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
– —
— —
(V
IN
= 2.7V, I
LOAD
= 0mA, LX = 22µH, C
OUT
= 100µF, S H D N and ILIM connected to IN, AGND connected to PGND,
T
A
= T
MIN
to T
MAX
, typical values are at T
A
= +25°C, unless otherwise noted.)
PARAMETER
CONDITIONS
I
LOAD
= 0mA, T
A
= +25°C
Minimum Start-Up Voltage
(Notes 2, 6)
MAX877/MAX879 (V
OUT
= 5V), 0mA < I
LOAD
< 180mA,
T
A
= +25°C
MAX878/MAX879 (V
OUT
= 3.3V), 0mA < I
LOAD
< 120mA,
T
A
= +25°C
(Notes 2, 3)
MAX877C/MAX879C: 0mA
≤
I
LOAD
≤
240mA,
2.7V
≤
V
IN
≤
6.2V;
Output Voltage
(MAX879 set to 5V)
(Note 3)
MAX877E/MAX879E: 0mA
≤
I
LOAD
≤
220mA,
2.7V
≤
V
IN
≤
6.2V;
MAX877M/MAX879M: 0mA
≤
I
LOAD
≤
180mA,
2.7V
≤
V
IN
≤
6.2V
MAX878C/MAX879C: 0mA
≤
I
LOAD
≤
210mA,
1.8V
≤
V
IN
≤
6.2V;
Output Voltage
(MAX879 set to
3.3V)
(Note 3)
SEL = 0V
MAX878E/MAX879E: 0mA
≤
I
LOAD
≤
200mA,
1.8V
≤
V
IN
≤
6.2V;
MAX878M/MAX879M: 0mA
≤
I
LOAD
≤
180mA,
1.8V
≤
V
IN
≤
6.2V
MAX878C: 0mA
≤
I
LOAD
≤
210mA, 1.8V
≤
V
IN
≤
6.2V;
SEL = Open MAX878E: 0mA
≤
I
LOAD
≤
200mA, 1.8V
≤
V
IN
≤
6.2V;
MAX878M: 0mA
≤
I
LOAD
≤
180mA, 1.8V
≤
V
IN
≤
6.2V
Output Voltage Range
Efficiency
No-Load Supply Current
Shutdown Supply Current
–— –
— —
SHDN Bias Current
MAX879, I
LOAD
= 0mA (Note 4)
MAX877/MAX879 (V
OUT
= 5V), I
LOAD
= 100mA, V
IN
= 4V
MAX878/MAX879 (V
OUT
= 3.3V), I
LOAD
= 100mA, V
IN
= 2.5V
I
LOAD
= 0mA (switch off)
–— –
— —
SHDN = 0V
–— –
— —
0V < SHDN < V
IN
–— –
— —
V
IN
< SHDN < 5V
MAX87_C, MAX87_E
MAX87_M
2.88
2.5
85
82
195
20
20
15
12
310
30
35
100
40
3.00
3.12
6.0
V
%
µA
µA
nA
µA
3.17
3.30
3.43
V
4.80
5.00
5.20
V
6.2
MIN
TYP
1
2.5
1.5
V
V
MAX
UNITS
ELECTRICAL CHARACTERISTICS
Maximum Operating Voltage
2
_______________________________________________________________________________________
5V/3.3V/3V/Adjustable-Output,
Step-Up/Step-Down DC-DC Converters
ELECTRICAL CHARACTERISTICS (continued)
MAX877/MAX878/MAX879
– ——–
—
(V
IN
= 2.7V, I
LOAD
= 0mA, LX = 22µH, C
OUT
= 100µF, S H D N and ILIM connected to IN, AGND connected to PGND,
T
A
= T
MIN
to T
MAX
, typical values are at T
A
= +25°C, unless otherwise noted.)
PARAMETER
–— –
— —
SHDN Threshold
–— –
— —
SHDN Enable Delay
Current Limit
Current-Limit Temperature
Coefficient
I
SW
= 400mA
Switch Saturation Voltage
I
SW
= 600mA
I
SW
= 1000mA
V
IN
= 2.5V
Maximum Switch On Time
V
IN
= 1.8V
V
IN
= 1V
Minimum Switch Off Time
MAX877/MAX879
MAX878
I
SW
= 400mA
Rectifier Forward Voltage Drop
Error-Comparator Trip Point
(V
REF
)
FB Pin Bias Current
Switch Off Leakage Current
Rectifier Off Leakage Current
I
SW
= 600mA
I
SW
= 1000mA
MAX879, V
IN
= 1.8V to 5V (Note 5)
MAX879
197.5
V
IN
= 1V to 6.2V
V
IN
= 2.7V
1.3
150
1.0
-0.3
0.275
0.33
0.50
4.0
5.9
12.6
1.3
2.3
0.21
0.31
0.50
202.5
10
0.1
0.1
207.5
40
mV
nA
µA
µA
V
µs
µs
V
CONDITIONS
MIN
TYP
VIN/2 +0.25
1.7
MAX
UNITS
V
µs
A
%/°C
Note 2:
Output in regulation, V
OUT
= V
OUT
(nominal) ±4%.
Note 3:
At high V
IN
to V
OUT
differentials, the maximum load current is limited by the maximum allowable power dissipation in the
package (see
Absolute Maximum Ratings
and Maximum Output Current graphs in the
Typical Operating Characteristics).
Note 4:
Minimum value is production tested. Maximum value is guaranteed by design and is not production tested.
Note 5:
V
OUT
is set to a target value of 5V by 0.1% external feedback resistors. V
OUT
is measured to be within 5V ±2.5%
to guarantee error-comparator trip point.
Note 6:
Startup guaranteed under these load conditions.
_______________________________________________________________________________________
3
5V/3.3V/3V/Adjustable-Output,
Step-Up/Step-Down DC-DC Converters
MAX877/MAX878/MAX879
__________________________________________Typical Operating Characteristics
(Circuit of Figure 4, T
A
= +25°C, unless otherwise noted.)
MAX877/MAX879
EFFICIENCY vs. LOAD CURRENT
MAX877-1
MAX878
EFFICIENCY vs. LOAD CURRENT
MAX877-2
MAX877/MAX879 MAXIMUM OUTPUT
CURRENT AT LOW INPUT VOLTAGE
300
OUTPUT CURRENT (mA)
250
200
150
100
50
V
OUT
= 5V
0
MAX877-3
90
V
OUT
= 5V
80
EFFICIENCY (%)
70
60
50
40
30
0.1
V
IN
= 4V
90
V
OUT
= 3.3V OR 3.0V
80
EFFICIENCY (%)
70
60
50
40
30
0.1
V
IN
= 2.5V
V
IN
= 3.3V
V
IN
= 1.8V
350
V
IN
= 5V
V
IN
= 2.5V
V
IN
= 6.2V
V
IN
= 1.8V
1
10
100
1000
V
IN
= 5V
VIN = 6.2V
1
10
100
1000
0
1
2
3
LOAD CURRENT (mA)
LOAD CURRENT (mA)
INPUT VOLTAGE (V)
MAX878 MAXIMUM OUTPUT
CURRENT vs. INPUT VOLTAGE
MAX877-4
NO-LOAD SUPPLY CURRENT
vs. SUPPLY VOLTAGE AND TEMPERATURE
MAX877-5
SHUTDOWN SUPPLY CURRENT
vs. INPUT VOLTAGE AND TEMPERATURE
70
60
50
40
30
20
10
0
1
2
3
T
A
= 0°C
T
A
= -40°C
4
5
6
7
T
A
= +85°C
MAX877-6
350
300
OUTPUT CURRENT (mA)
250
200
150
100
50
0
0
1
2
3
4
5
6
7
INPUT VOLTAGE (V)
V
OUT
= 3.0V
T
A
= +70°C
DIP PACKAGE
DISSIPATION LIMIT
SO PACKAGE
DISSIPATION LIMIT
300
280
NO-LOAD SUPPLY CURRENT (µA)
260
240
220
200
180
160
140
120
100
1
(SWITCH = OFF)
T
A
= +85°C
T
A
= +25°C
80
SHUTDOWN SUPPLY CURRENT (µA)
T
A
= 0°C
T
A
= -40°C
2
3
4
5
6
7
SUPPLY VOLTAGE (V)
INPUT VOLTAGE (V)
SHDN THRESHOLD VOLTAGE
vs. INPUT VOLTAGE AND TEMPERATURE
MAX877-7
LOAD-TRANSIENT RESPONSE
LINE-TRANSIENT RESPONSE
3.5
SHDN THRESHOLD VOLTAGE (V)
3.0
2.5
2.0
1.5
1.0
0.5
1
2
3
4
5
6
7
INPUT VOLTAGE (V)
T
A
= +25°C
T
A
= -55°C
T
A
= +125°C
A
A
GND
B
B
2ms/div
A: I
OUT
, 200mA/div, 0mA to 200mA
B: V
OUT
, 50mV/div, AC COUPLED
MAX878, V
OUT
= 3.3V, V
IN
= 2.5V
2ms/div
A: V
IN
, 2V/div, 2V to 4V
B: V
OUT
, 50mV/div, AC COUPLED
I
OUT
= 240mA
MAX878, V
OUT
= 3.3V, C
INBYPASS
= 47µF
4
_______________________________________________________________________________________
5V/3.3V/3V/Adjustable-Output,
Step-Up/Step-Down DC-DC Converters
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 4, T
A
= +25°C, unless otherwise noted.)
SWITCHING WAVEFORMS—
CONTINUOUS CONDUCTION
SWITCHING WAVEFORMS—
DISCONTINUOUS CONDUCTION
MAX877/MAX878/MAX879
STEP-DOWN CONVERSION
A
A
A
B
0mA
C
5µs/div
A: SWITCH VOLTAGE (LX PIN), 2V/div
B: INDUCTOR CURRENT, 0.5A/div
C: OUTPUT VOLTAGE RIPPLE, 50mV/div
MAX877, V
IN
= 1.5V, I
OUT
= 100mA
B
0mA
C
B
0mA
C
5µs/div
A: SWITCH VOLTAGE (LX PIN), 2V/div
B: INDUCTOR CURRENT, 0.5A/div
C: OUTPUT VOLTAGE RIPPLE, 50mV/div
MAX878, V
IN
= 6.0V, V
OUT
= 5.0V, I
OUT
= 210mA
2µs/div
A: SWITCH VOLTAGE (LX PIN), 2V/div
B: INDUCTOR CURRENT, 0.5A/div
C: OUTPUT VOLTAGE RIPPLE, 50mV/div
MAX877, V
IN
= 3V, I
OUT
= 70mA
STEP-UP/STEP-DOWN
OPERATION
MAX878
START-UP TIME
A
A
GND
GND
B
B
GND
20ms/div
A: INPUT VOLTAGE, 2V/div, 2V to 6V
B: OUTPUT VOLTAGE, 50mV/div
MAX878, I
OUT
= 100mA, V
OUT
= 3.3V
A: SHDN, 2V/div
B: V
OUT
, 1V/div
V
OUT
= 3V
10ms/div
_______________________________________________________________________________________
5
Embedded System
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