_______________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 22H) 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 RectifierTM) 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 195A
under no load, and only 20A 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.
________________________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
____________________________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
195A Quiescent Supply Current
o
20A Shutdown Supply Current
o
3V/3.3V/5V and Adjustable Output Voltage Versions
o
Available in 8-Pin DIP and SO Packages
______________Ordering Information
Ordering Information continued on last page.
* Contact factory for dice specifications.
MAX877/MAX878/MAX879
5V/3.3V/3V/Adjustable-Output,
Step-Up/Step-Down DC-DC Converters
________________________________________________________________
Maxim Integrated Products
1
INPUT
1.8V TO 6.2V
IN
ILIM
SHDN
100F
OUTPUT
3.3V
210mA
AGND
MAX878
LX
OUT
PGND
22H
ON/OFF
22
F
1
2
7
8
3
6
5
SEL
4
__________________Pin Configuration
1
2
3
4
DIP/SO
TOP VIEW
MAX877
MAX878
MAX879
8
7
6
5
N.C. (MAX877)
*
SHDN
OUT
LX
ILIM
IN
AGND
PGND
*
SEL (MAX878), FB (MAX879)
__________Typical Operating Circuit
Call toll free 1-800-998-8800 for free samples or literature.
19-0204; Rev 1; 5/94
PART
TEMP. RANGE
PIN-PACKAGE
MAX877
CPA
0C to +70C
8 Plastic DIP
MAX877CSA
0C to +70C
8 SO
MAX877C/D
0C to +70C
Dice*
MAX877ESA
-40C to +85C
8 SO
MAX877EPA
-40C to +85C
8 Plastic DIP
MAX877MJA
-55C to +125C
8 CERDIP
TM Active Rectifier is a trademark of Maxim Integrated Products.
EVALUATION KIT MANUAL
FOLLOWS DATA SHEET
MAX877/MAX878/MAX879
5V/3.3V/3V/Adjustable-Output,
Step-Up/Step-Down DC-DC Converters
2
_______________________________________________________________________________________
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,
S
--
H
--
D
--
N...........................................................-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
= +70C)
Plastic DIP (derate 9.09mW/C above +70C) ............727mW
SO (derate 5.88mW/C above +70C) .........................471mW
CERDIP (derate 8.00mW/C above +70C) .................640mW
Operating Temperature Ranges:
MAX87_C_A ........................................................0C to +70C
MAX87_E_A .....................................................-40C to +85C
MAX87_MJA ..................................................-55C to +125C
Storage Temperature Range .............................-65C to +150C
Lead Temperature (soldering, 10sec) .............................+300C
ELECTRICAL CHARACTERISTICS
(V
IN
= 2.7V, I
LOAD
= 0mA, LX = 22H, C
OUT
= 100F,
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
= +25C, unless otherwise noted.)
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.
PARAMETER
SEL = 0V
CONDITIONS
MIN
TYP
MAX
Output Voltage
(MAX879 set to
3.3V)
(Note 3)
V
UNITS
MAX878/MAX879 (V
OUT
= 3.3V), I
LOAD
= 100mA, V
IN
= 2.5V
MAX877/MAX879 (V
OUT
= 5V), I
LOAD
= 100mA, V
IN
= 4V
MAX879, I
LOAD
= 0mA (Note 4)
SEL = Open
0V <
S
--
H
--
D
--
N
< V
IN
V
IN
<
S
--
H
--
D
--
N
< 5V
S
--
H
--
D
--
N
= 0V
20
35
A
Efficiency
MAX87_C, MAX87_E
Output Voltage Range
S
--
H
--
D
--
N
Bias Current
MAX87_M
Maximum Operating Voltage
(Notes 2, 3)
6.2
V
Shutdown Supply Current
15
100
nA
Output Voltage
(MAX879 set to 5V)
(Note 3)
MAX877C/MAX879C: 0mA
I
LOAD
240mA,
2.7V
V
IN
6.2V;
MAX877E/MAX879E: 0mA
I
LOAD
220mA,
2.7V
V
IN
6.2V;
MAX877M/MAX879M: 0mA
I
LOAD
180mA,
2.7V
V
IN
6.2V
4.80
5.00
5.20
V
MAX878C/MAX879C: 0mA
I
LOAD
210mA,
1.8V
V
IN
6.2V;
MAX878E/MAX879E: 0mA
I
LOAD
200mA,
1.8V
V
IN
6.2V;
MAX878M/MAX879M: 0mA
I
LOAD
180mA,
1.8V
V
IN
6.2V
3.17
3.30
3.43
12
40
A
I
LOAD
= 0mA, T
A
= +25C
1
2.88
3.00
3.12
MAX877/MAX879 (V
OUT
= 5V), 0mA < I
LOAD
< 180mA,
T
A
= +25C
2.5
2.5
6.0
V
Minimum Start-Up Voltage
(Notes 2, 6)
85
MAX878/MAX879 (V
OUT
= 3.3V), 0mA < I
LOAD
< 120mA,
T
A
= +25C
1.5
V
MAX878C: 0mA
I
LOAD
210mA, 1.8V
V
IN
6.2V;
MAX878E: 0mA
I
LOAD
200mA, 1.8V
V
IN
6.2V;
MAX878M: 0mA
I
LOAD
180mA, 1.8V
V
IN
6.2V
82
%
No-Load Supply Current
I
LOAD
= 0mA (switch off)
195
310
A
20
30
Note 1:
The output may be shorted to ground continuously if the package power dissipation is not exceeded.
MAX877/MAX878/MAX879
5V/3.3V/3V/Adjustable-Output,
Step-Up/Step-Down DC-DC Converters
_______________________________________________________________________________________
3
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= 2.7V, I
LOAD
= 0mA, LX = 22H, C
OUT
= 100F,
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
= +25C, unless otherwise noted.)
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.
PARAMETER
Maximum Switch On Time
CONDITIONS
MIN
TYP
MAX
V
IN
= 1V
12.6
UNITS
I
SW
= 400mA
s
0.275
MAX877/MAX879
Current-Limit Temperature
Coefficient
1.3
-0.3
%/C
Current Limit
1.0
s
Minimum Switch Off Time
I
SW
= 600mA
0.33
Switch Saturation Voltage
I
SW
= 1000mA
0.50
V
MAX878
2.3
s
I
SW
= 400mA
V
IN
= 2.5V
4.0
0.21
V
IN
= 1.8V
5.9
I
SW
= 600mA
0.31
Rectifier Forward Voltage Drop
S
--
H
--
D
--
N
Threshold
I
SW
= 1000mA
0.50
V
V
IN
= 1V to 6.2V
VIN/2 +0.25
Error-Comparator Trip Point
(V
REF
)
MAX879, V
IN
= 1.8V to 5V (Note 5)
197.5
202.5
207.5
mV
FB Pin Bias Current
V
IN
= 2.7V
1.3
1.7
MAX879
10
40
nA
Switch Off Leakage Current
S
--
H
--
D
--
N
Enable Delay
0.1
150
Rectifier Off Leakage Current
0.1
A
V
A
A
MAX877/MAX878/MAX879
5V/3.3V/3V/Adjustable-Output,
Step-Up/Step-Down DC-DC Converters
4
_______________________________________________________________________________________
__________________________________________Typical Operating Characteristics
(Circuit of Figure 4, T
A
= +25C, unless otherwise noted.)
90
40
0.1
1
1000
MAX877/MAX879
EFFICIENCY vs. LOAD CURRENT
50
MAX877-1
LOAD CURRENT (mA)
EFFICIENCY (%)
60
70
80
10
100
30
V
IN
= 2.5V
V
IN
= 6.2V
V
IN
= 1.8V
V
OUT
= 5V
V
IN
= 5V
V
IN
= 4V
90
40
0.1
1
1000
MAX878
EFFICIENCY vs. LOAD CURRENT
50
MAX877-2
LOAD CURRENT (mA)
EFFICIENCY (%)
60
70
80
10
100
30
V
IN
= 2.5V
V
IN
= 3.3V
V
IN
= 1.8V
V
OUT
= 3.3V OR 3.0V
V
IN
= 5V
VIN = 6.2V
350
100
0
1
MAX877/MAX879 MAXIMUM OUTPUT
CURRENT AT LOW INPUT VOLTAGE
150
MAX877-3
INPUT VOLTAGE (V)
OUTPUT CURRENT (mA)
200
250
300
2
3
0
V
OUT
= 5V
50
350
50
0
3
MAX878 MAXIMUM OUTPUT
CURRENT vs. INPUT VOLTAGE
100
MAX877-4
INPUT VOLTAGE (V)
OUTPUT CURRENT (mA)
150
200
250
6
7
0
T
A
= +70C
300
1
2
4
5
V
OUT
= 3.0V
DIP PACKAGE
DISSIPATION LIMIT
SO PACKAGE
DISSIPATION LIMIT
2.0
1
2
5
SHDN THRESHOLD VOLTAGE
vs. INPUT VOLTAGE AND TEMPERATURE
2.5
MAX877-7
INPUT VOLTAGE (V)
SHDN THRESHOLD VOLTAGE (V)
3.0
3.5
3
4
1.5
0.5
1.0
7
6
T
A
= +25C
T
A
= -55C
T
A
= +125C
300
200
1
2
5
NO-LOAD SUPPLY CURRENT
vs. SUPPLY VOLTAGE AND TEMPERATURE
220
MAX877-5
SUPPLY VOLTAGE (V)
NO-LOAD SUPPLY CURRENT (A)
240
260
280
3
4
180
(SWITCH = OFF)
120
140
160
100
7
6
T
A
= 0C
T
A
= -40C
T
A
= +25C
T
A
= +85C
50
1
2
5
SHUTDOWN SUPPLY CURRENT
vs. INPUT VOLTAGE AND TEMPERATURE
60
MAX877-6
INPUT VOLTAGE (V)
SHUTDOWN SUPPLY CURRENT (
A)
70
80
3
4
40
10
20
30
0
7
6
T
A
= 0C
T
A
= -40C
T
A
= +85C
A: I
OUT
, 200mA/div, 0mA to 200mA
B: V
OUT
, 50mV/div, AC COUPLED
MAX878, V
OUT
= 3.3V, V
IN
= 2.5V
LOAD-TRANSIENT RESPONSE
A
B
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
= 47
F
LINE-TRANSIENT RESPONSE
GND
2ms/div
A
B
MAX877/MAX878/MAX879
5V/3.3V/3V/Adjustable-Output,
Step-Up/Step-Down DC-DC Converters
_______________________________________________________________________________________
5
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
SWITCHING WAVEFORMS--
CONTINUOUS CONDUCTION
A
B
C
0mA
5
s/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
SWITCHING WAVEFORMS--
DISCONTINUOUS CONDUCTION
A
B
C
2
s/div
0mA
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
STEP-DOWN CONVERSION
A
B
C
5
s/div
0mA
A: SHDN, 2V/div
B: V
OUT
, 1V/div
V
OUT
= 3V
MAX878
START-UP TIME
GND
GND
10ms/div
A
B
A: INPUT VOLTAGE, 2V/div, 2V to 6V
B: OUTPUT VOLTAGE, 50mV/div
MAX878, I
OUT
= 100mA, V
OUT
= 3.3V
STEP-UP/STEP-DOWN
OPERATION
A
B
20ms/div
GND
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 4, T
A
= +25C, unless otherwise noted.)
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