19-2248; Rev 1; 12/03
KIT
ATION
EVALU
BLE
AVAILA
Dual-Output Step-Down and LCD Step-Up
Power Supply for PDAs
General Description
The MAX1878 dual power supply contains a step-down
and step-up DC-DC converter in a small 12-pin QFN
package for use in PDAs. The step-down DC-DC convert-
er delivers over 500mA to an output as low as 1.25V for
logic power. The step-up DC-DC converter delivers over
15mA and an output as high as 28V for a liquid crystal dis-
play (LCD). With an input voltage from 2.0V to 5.5V the
MAX1878 is intended for use in systems powered by a
2-cell alkaline or 1-cell lithium-ion (Li+) battery.
Fast switching frequency allows the use of small inductors
and capacitors, and the low 19µA typical quiescent cur-
rent allows high efficiency when the system is in standby
mode. Each output can be independently enabled.
The MAX1878 is available in a small 1mm high 4mm x
4mm 12-pin QFN package and requires no external FETs.
The MAX1878 evaluation kit is available to speed designs.
♦
Two Output Voltages
Main Output: 1.25V to V
IN
LCD Output: Up to 28V
♦
2.0V to 5.5V Input Range
♦
Low 19µA Quiescent Supply Current
♦
1µA Shutdown Supply Current
♦
High Switching Frequency for Small External
Components
♦
Small 1mm High 4mm x 4mm 12-Pin QFN Package
Features
♦
Evaluation Kit Available to Speed Designs
MAX1878
________________________Applications
Personal Digital Assistants (PDA)
Organizers/Translators
MP3 Players
GPS Receivers
PART
MAX1878EGC
Ordering Information
TEMP RANGE
-40°C to +85°C
PIN-
PACKAGE
12-QFN
TOP
MARK
AAAO
__________Typical Operating Circuit
INPUT
2.0V TO 5.5V
10µH
Pin Configuration
PGNDLCD
11
TOP VIEW
IN
LXLCD
FBLCD
AIN1
AIN2
10µH
LCD OUTPUT
UP TO 28V
0.1µF
12
IN
1
2
ONLCD
10
9
8
7
LXLCD
AGND
ON
6
FBLCD
MAX1878
LX
FB
MAIN OUTPUT
1.25V TO V
IN
LX
AIN1
ON
MAIN
LCD
OFF
ON
OFF
ONLCD
ON
3
PGND
4
AIN2
MAX1878EGC
5
FB
PGND
AGND PGNDLCD
4mm x 4mm QFN
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
Dual-Output Step-Down and LCD Step-Up
Power Supply for PDAs
MAX1878
ABSOLUTE MAXIMUM RATINGS
FB, FBLCD, AIN1, AIN2, ON, ONLCD to AGND ......-0.3V to +6V
AIN2 to AIN1..........................................................-0.3V to +0.3V
AIN1, AIN2 to IN ....................................................-0.3V to +0.3V
IN to PGND...............................................................-0.3V to +6V
LX to PGND .................................................-0.3V to (V
IN
+ 0.3V)
LXLCD to PGNDLCD..............................................-0.3V to +30V
PGND, PGNDLCD to AGND..................................-0.3V to +0.3V
LX Current .........................................................................800mA
LXLCD Current..................................................................500mA
Continuous Power Dissipation (T
A
= +70°C)
12-Pin QFN (derate 16.9mW/°C above +70°C) .............1.35W
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
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.
ELECTRICAL CHARACTERISTICS
(V
IN
= V
AIN
= 2.5V, circuit of Figure 1,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
GENERAL
Input Voltage Range
Undervoltage Lockout Threshold
Undervoltage Lockout Hysteresis
Quiescent Current
Shutdown Quiescent Current
MAIN OUTPUT (Step-Down Converter)
Output Voltage Adjustment Range
FB Regulation Voltage
FB Input Bias Current
Main Output Current
(Note 1)
Line Regulation
Load Regulation
V
MAIN
V
FB
I
FB
I
MAIN
V
IN
= V
AIN
= 2V
V
IN
= V
AIN
= 2V
V
MAIN
= 1.8V
V
IN
= V
AIN
= 2.5V
V
IN
= V
AIN
= 2.0V
250
200
+25°C to +85°C
0°C to +85°C
1.25
1.225
1.220
10
500
350
1
1
150
mV
100
100
0.1
0.55
0.42
5
0.95
0.65
%
µA
Ω
1.250
V
IN
1.275
1.280
50
V
V
nA
mA
%
%
I
AIN1
+
I
AIN2
V
FB
= V
FBLCD
= 1.30V, V
ONLCD
= 0,
step-down converter only
V
FB
= V
FBLCD
= 1.30V
V
ON
= V
ONLCD
= 0
V
IN
, V
AIN
V
UVLO
V
IN
rising
V
IN
falling
1.7
2.0
1.92
1.82
100
19
24
0
30
38
1
µA
5.5
2.0
V
V
mV
µA
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
I
LOAD
= 150mA, V
IN
= V
AIN
= 2V to 3V,
FB = GND
V
IN
= V
AIN
= 2.5V, I
LOAD
= 10mA to 150mA
V
IN
= V
AIN
= 2V, I
LOAD
= 150mA,
V
FB
= 0.8V
V
IN
= V
AIN
= 3V, I
LOAD
= 150mA,
V
FB
= 0.8V
Dropout Voltage
LX Max Duty Cycle
LX Leakage Current
LX P-Channel On-Resistance
V
FB
= 0.8V
V
ON
= 0, V
IN
= 5.5V
V
IN
= V
AIN
= 2V, I
LX
= 300mA
V
IN
= V
AIN
= 3V, I
LX
= 300mA
2
_______________________________________________________________________________________
Dual-Output Step-Down and LCD Step-Up
Power Supply for PDAs
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= V
AIN
= 2.5V, circuit of Figure 1,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
LX N-Channel On-Resistance
LX Current Limit
Idle Mode Threshold
LX Minimum On-Time
LX Minimum Off-Time
ON Input Low Voltage
ON Input High Voltage
ON Input Leakage Current
LCD OUTPUT (Step-Up Converter)
LCD Output Voltage Adjust Range
FBLCD Regulation Voltage
LXLCD On-Resistance
LXLCD Current Limit
LXLCD Leakage Current
LCD Output Current
(Note 2)
FBLCD Input Bias Current
LCD Line Regulation
LCD Load Regulation
LXLCD Maximum On-Time
LXLCD Minimum Off-Time
ONLCD Input Low Voltage
ONLCD Input High Voltage
ONLCD Input Leakage Current
t
LXLCDON
t
LXLCDOFF
V
FBLCD
< 0.9V (soft-start)
2V < V
AIN
= V
IN
< 5.5V
2V < V
AIN
= V
IN
< 5.5V
1.3
-1
1
I
LCD
I
FBLCD
V
LXLCD
= 28V
V
AIN
= V
IN
= 2.5V, V
LCD
= 18V
V
AIN
= V
IN
= 2V, V
LCD
= 18V
V
AIN
= V
IN
= 2V
V
AIN
= V
IN
= 2V to 3V, I
LOAD
= 5mA,
V
LXLCD
= 18V
V
AIN
= V
IN
= 2.5V, I
LOAD
= 1mA to 5mA,
V
LXLCD
= 18V
5.1
0.5
1.3
1.5
1.4
V
LCD
V
FBLCD
V
IN
= V
AIN
= 2V
+25°C to +85°C
0°C to +85°C
V
IN
+ 1V
1.225
1.220
2.8
1.7
140
280
0
7.6
6.6
10
1
1.3
9.8
1.0
2.6
17
1.7
4.4
0.4
50
1.250
28
1.275
1.280
5.0
3.0
440
1
V
V
Ω
mA
µA
mA
nA
%
%
µs
µs
V
V
µA
t
LXON
t
LXOFF
2V < V
IN
< 5.5V
2V < V
IN
< 5.5V
1.3
-1
1
SYMBOL
CONDITIONS
V
IN
= V
AIN
= 2V, I
LX
= 300mA
V
IN
= V
AIN
= 3V, I
LX
= 300mA
330
70
240
200
MIN
TYP
0.62
0.46
550
135
440
390
MAX
0.93
0.65
800
220
740
670
0.4
UNITS
Ω
mA
mA
ns
ns
V
V
µA
MAX1878
V
AIN
= V
IN
= 2V, I
LXLCD
= 150mA
V
AIN
= V
IN
= 3V, I
LXLCD
= 150mA
_______________________________________________________________________________________
3
Dual-Output Step-Down and LCD Step-Up
Power Supply for PDAs
MAX1878
ELECTRICAL CHARACTERISTICS
(V
IN
= V
AIN
= 2.5V, circuit of Figure 1,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 3)
PARAMETER
GENERAL
Quiescent Current from AIN
FB Regulation Voltage
LX Current Limit
LX Minimum On-Time
LX Minimum Off-Time
LCD OUTPUT (Step-Up Converter)
LXLCD Current Limit
LXLCD Maximum On-Time
LXLCD Minimum Off-Time
FBLCD Regulation Voltage
t
LXLCDON
t
LXLCDOFF
V
FBLCD
V
FBLCD
< 0.9V
V
AIN
= V
IN
= 2V
130
5.1
0.5
1.3
1.212
450
17
1.7
4.5
1.288
mA
µs
µs
V
t
LXON
t
LXOFF
I
AIN
V
FB
V
FB
= V
FBLCD
= 1.30V
V
AIN
= V
IN
= 2V
1.212
310
240
200
38
1.288
820
740
670
µA
V
mA
ns
ns
MAIN OUTPUT (Step-Down Converter)
SYMBOL
CONDITIONS
MIN
MAX
UNITS
Note 1:
Main output current is guaranteed by LX current limit, LX on resistance, and LX minimum off-time.
Note 2:
LCD output current is guaranteed by LXLCD current limit, LXLCD on-resistance, and LXLCD minimum off-time, starting into
a resistive load.
Note 3:
Specifications to -40°C are guaranteed by design and not production tested.
4
_______________________________________________________________________________________
Dual-Output Step-Down and LCD Step-Up
Power Supply for PDAs
MAX1878
Typical Operating Characteristics
(V
IN
= V
AIN
= 2.5V, circuit of Figure 1, T
A
= +25°C, unless otherwise noted.)
STEP-DOWN CONVERTER EFFICIENCY
vs. LOAD CURRENT (V
MAIN
= 1.8V)
MAX1878 toc01
STEP-DOWN CONVERTER EFFICIENCY
vs. LOAD CURRENT (V
MAIN
= 1.5V)
MAX1878 toc02
STEP-UP CONVERTER EFFICIENCY
vs. LOAD CURRENT (V
LCD
= 18V)
V
IN
= 5.0V (22µH)
MAX1878 toc03
100
V
IN
= 2.5V
90
EFFICIENCY (%)
80
V
IN
= 5.0V
70
60
50
40
0.1
1
10
100
ONLCD =
PGNDLCD
V
IN
= 3.6V
100
90
EFFICIENCY (%)
80
70
V
IN
= 3.6V
60
50
40
ONLCD =
PGNDLCD
0.1
1
10
100
V
IN
= 5.0V
V
IN
= 2.5V
100
90
80
70
60
50
40
30
ON = PGND
0.01
0.1
1
LOAD CURRENT (mA)
10
V
IN
= 2.5V (10µH)
V
IN
= 3.6V (15µH)
1000
1000
EFFICIENCY (%)
100
LOAD CURRENT (mA)
LOAD CURRENT (mA)
STEP-DOWN CONVERTER OUTPUT VOLTAGE
vs. LOAD CURRENT (V
MAIN
= 1.8V)
MAX1878 toc04
STEP-DOWN CONVERTER OUTPUT VOLTAGE
vs. LOAD CURRENT (V
MAIN
= 1.5V)
MAX1878 toc05
STEP-UP CONVERTER OUTPUT VOLTAGE
vs. LOAD CURRENT (V
LCD
= 18V)
18.8
18.7
18.6
V
MAIN
(V)
18.5
18.4
18.3
18.2
18.1
18.0
17.9
17.8
V
IN
= 2.5V (10µH)
0.01
0.1
1
LOAD CURRENT (mA)
10
100
V
IN
= 3.6V (15µH)
V
IN
= 5.0V (22µH)
ONLCD = PGNDLCD
MAX1878 toc06
1.84
V
IN
= 5.0V
1.83
1.82
V
MAIN
(V)
1.81
1.80
V
IN
= 3.6V
1.79
1.78
1.77
ONLCD = PGNDLCD
0.1
1
10
100
V
IN
= 2.5V
1.535
1.530
1.525
V
MAIN
(V)
1.520
1.515
1.510
1.505
1.500
1.495
V
IN
= 5.0V
18.9
V
IN
= 3.6V
V
IN
= 2.5V
ONLCD = PGNDLCD
0.1
1
10
100
1000
LOAD CURRENT (mA)
1000
LOAD CURRENT (mA)
NO LOAD SUPPLY CURRENT vs.
INPUT VOLTAGE (V
MAIN
= 1.8V, V
LCD
= 18V)
MAX1878 toc07
STEP-DOWN CONVERTER SWITCHING
FREQUENCY vs. SUPPLY VOLTAGE
MAX1878 toc08
STEP-UP CONVERTER CURRENT LIMIT
vs. INPUT VOLTAGE
MAX1878 toc09
140
STEP-UP AND STEP-DOWN
120
SUPPLY CURRENT (µA)
100
STEP-UP
80
60
40
20
0
0
1
2
3
4
5
6
INPUT VOLTAGE (V)
STEP-DOWN
1.2
SWITCHING FREQUENCY (MHz)
1.0
0.8
V
MAIN
= 1.5V
0.6
0.4
0.2
0
2
3
4
SUPPLY VOLTAGE (V)
V
MAIN
= 1.8V
500
450
CURRENT LIMIT (mA)
L2 = 22µH
400
350
300
L2 = 10µH
250
200
L2 = 15µH
I
MAIN
= 150mA
ONLCD = PGNDLCD
5
6
2
3
4
5
SUPPLY VOLTAGE (V)
6
_______________________________________________________________________________________
5
医疗电子
京公网安备 11010802033920号
Copyright © 2005-2026 EEWORLD.com.cn, Inc. All rights reserved
电子工程世界
