19-1794 Rev 0; 10/00
Compact, High-Efficiency, Dual-Output
Step-Up DC-DC Converter
The MAX1817’s main regulator supplies 125mA at
either a preset 3.3V or an adjustable 2.5V to 5.5V output voltage with up to 88% efficiency. A 0.1µA shutdown state also minimizes battery drain. The
MAX1817’s secondary step-up converter provides the
LCD bias voltage and is adjustable up to +28V.
Other features include a fast switching frequency to
reduce the size of external components and a low quiescent current to maximize battery life. Both outputs can
be independently shut down for improved flexibility.
The MAX1817 is supplied in a compact 10-pin µMAX
package. The MAX1817 evaluation kit (MAX1817EVKIT)
is available to speed up design.
Features
♦ Dual Step-Up Converter in a Tiny 10-Pin µMAX
Package
♦ Main Output
Up to 125mA Load Current
Fixed 3.3V or Adjustable 2.5V to 5.5V
Up to 88% Efficiency
Internal Switch
♦ LCD Output
Up to 28V for LCD Bias
Internal Switch
♦ Input Voltage Range +1.5V to +5.5V
♦ Minimal External Components Required
♦ 0.1µA Logic-Controlled Shutdown
♦ Low 15µA Quiescent Supply Current
Ordering Information
________________________Applications
Organizers/Translators
PDAs
PART
TEMP. RANGE
PIN-PACKAGE
MAX1817EUB
-40°C to +85°C
10 µMAX
MP3 Players
GPS Receivers
Typical Operating Circuit
+1.5V
TO +5.5V
Pin Configuration
TOP VIEW
FB 1
LCD
LCD ON/OFF
10 OUT
2
MAX1817
9
LX
ONLCD
3
8
GND
LX
LXLCD
FBLCD
4
7
LXLCD
ONLCD
FBLCD
AGND
5
6
N.C.
µMAX
MAX1817
MAIN ON/OFF
ON
ON
AGND
OUT
FB
GND
MAIN
________________________________________________________________ Maxim Integrated Products
1
For price, delivery, and to place orders, please contact Maxim Distribution at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
MAX1817
General Description
The MAX1817 is a compact, high-efficiency, dual-output step-up converter for portable devices that provides both the main logic supply and the LCD bias. The
device operates from an input voltage of +1.5V to
+5.5V, allowing the use of 2- or 3-cell alkaline batteries,
or 1-cell lithium-ion (Li+) batteries.
MAX1817
Compact, High-Efficiency, Dual-Output
Step-Up DC-DC Converter
ABSOLUTE MAXIMUM RATINGS
OUT to GND .............................................................-0.3V to +6V
ON, ONLCD, FB, FBLCD, LX to GND ......-0.3V to (VOUT + 0.3V)
LXLCD to GND .......................................................-0.3V to +30V
AGND to GND .......................................................-0.3V to +0.3V
Continuous Power Dissipation (TA = +70°C)
10-Pin µMAX (derate 5.6mW/°C above +70°C) ...........444mW
LXLCD, LX Maximum Current ........................................0.5ARMS
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
(VON = VONLCD = VOUT = +3.3V, FB = GND, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
5.5
V
GENERAL
Input Voltage Range
Startup Voltage
1.5
RLOAD = 35Ω
1.5
RLOAD = ∞, VFB = 1.35V
1.2
1.55
5
10
V
Quiescent Current from OUT
(Main Only)
VFB = VFBLCD = 1.35V,
VONLCD = 0
Quiescent Current from OUT
VFB = VFBLCD = 1.35V
15
30
µA
Shutdown Quiescent Current
VON = VONLCD = 0
0.1
1
µA
2.2
2.4
µA
MAIN OUTPUT
OUT Undervoltage Lockout
Fixed-Mode Output Voltage
VOUT rising, VFB = 1.35V
1.95
2.15
VFB ≤ 45mV
3.14
3.3
3.47
V
1.20
1.25
1.30
V
50
nA
105
mV
5.5
V
Adjustable-Mode FB Regulation
Voltage
FB Input Bias Current
TM
FB Dual Mode
VFB = 1.35V
Threshold
45
Output Voltage Adjustment
Range
2.5
Maximum LX On-Time
VFB = 0.5V
Zero Crossing Comparator
Threshold (VLX - VOUT)
75
2.4
5
7.5
µs
0
20
40
mV
22
45
70
µs
Zero Crossing Comparator
Backup Timer
VFB = +0.5V
Line Regulation
IOUT = 100mA,
VIN = +2V to +3V
1.6
%
Load Regulation
VIN = +2.5V,
ILOAD = 10mA to 100mA
1.6
%
LX On-Resistance
VOUT = 3.3V, ILX = 100mA
0.35
0.65
Ω
0.75
1.05
A
LX Current Limit
0.5
Dual Mode is a trademark of Maxim Integrated Products.
2
V
VOUT falling, VFB = 1.35V
_______________________________________________________________________________________
Compact, High-Efficiency, Dual-Output
Step-Up DC-DC Converter
(VON = VONLCD = VOUT = +3.3V, FB = GND, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER
CONDITIONS
LX Leakage Current
VON = GND, VLX = 5.5V
ON Input Low Voltage
1.8V < VOUT < 5.5V, VFB = 0.5V
ON Input High Voltage
1.8V < VOUT < 5.5V, VFB = 0.5V
MIN
TYP
0.1
MAX
UNITS
1
µA
400
mV
1.6
V
ON Input Bias Current
1
µA
LCD OUTPUT
LXLCD Voltage
LXLCD On-Resistance
VOUT = 3.3V, ILXLCD = 100mA
LXLCD Current Limit
LXLCD Leakage Current
0.28
VLXLCD = 28V, VONLCD = 0
FBLCD Regulation Voltage
1.20
28
V
1.1
2.0
Ω
0.5
0.7
A
0.1
1
µA
1.25
1.30
V
50
nA
FBLCD Input Bias Current
VFBLCD = 1.35V
LCD Line Regulation
ILOAD = 5mA, VIN = +2V to +3V
0.1
%
LCD Load Regulation
ILOAD = 1mA to 5mA, VIN = +2.5V
0.5
%
Maximum LXLCD On-Time
Minimum LXLCD Off-Time
4
9
14
VFBLCD ≥ 1.2V
0.5
1
1.5
VFBLCD ≤ 0.7V
2.4
5
7.5
ONLCD Input Low Voltage
2.5V < VOUT < 5.5V
ONLCD Input High Voltage
2.5V < VOUT < 5.5V
µs
400
mV
1
µA
1.6
ONLCD Input Bias Current
µs
V
ELECTRICAL CHARACTERISTICS
(VON = VONLCD = VOUT = +3.3V, FB = GND, TA = -40°C to +85°C, unless otherwise noted.) (Note 1)
PARAMETER
CONDITIONS
MIN
MAX
UNITS
1.5
5.5
V
GENERAL
Input Voltage Range
Startup Voltage
RLOAD = ∞, VFB = 1.35V
1.7
V
Quiescent Current from OUT
(Main Only)
VFB = VFBLCD = 1.35V, VONLCD = 0
10
µA
Quiescent Current from OUT
VFB = VFBLCD = 1.35V
30
µA
Shutdown Quiescent Current
VON = VONLCD = 0
1
µA
MAIN OUTPUT
OUT Undervoltage Lockout
Fixed-Mode Output Voltage
VOUT rising, VFB = 1.35V
V
VOUT falling, VFB = 1.35V
1.95
VFB ≤ 45mV
3.14
3.47
V
1.20
1.30
V
50
nA
Adjustable-Mode FB Regulation
Voltage
FB Input Bias Current
2.4
VFB = 1.35V
_______________________________________________________________________________________
3
MAX1817
ELECTRICAL CHARACTERISTICS (continued)
MAX1817
Compact, High-Efficiency, Dual-Output
Step-Up DC-DC Converter
ELECTRICAL CHARACTERISTICS (continued)
(VON = VONLCD = VOUT = +3.3V, FB = GND, TA = -40°C to +85°C, unless otherwise noted.) (Note 1)
MIN
MAX
UNITS
FB Dual Mode Threshold
PARAMETER
45
105
mV
Output Voltage Adjustment Range
2.5
5.5
V
2.4
7.5
µs
0
40
mV
22
70
µs
0.65
Ω
1.05
A
Maximum LX On-Time
CONDITIONS
VFB = 0.5V
Zero Crossing Comparator
Threshold (VLX - VOUT)
Zero Crossing Comparator
Backup Timer
VFB = 0.5V
LX On-Resistance
VOUT = 3.3V, ILX = 100mA
LX Current Limit
0.42
LX Leakage Current
VON = GND, VLX = 5.5V
ON Input Low Voltage
1.8V < VOUT < 5.5V, VFB = 0.5V
ON Input High Voltage
1.8V < VOUT < 5.5V, VFB = 0.5V
1
µA
400
mV
1.6
ON Input Bias Current
V
1
µA
28
V
2
Ω
LCD OUTPUT
LXLCD Voltage
LXLCD On-Resistance
VOUT = 3.3V, ILXLCD = 100mA
LXLCD Current Limit
LXLCD Leakage Current
0.25
VLXLCD = 28V, VONLCD = 0
FBLCD Regulation Voltage
FBLCD Input Bias Current
1.20
µA
V
70
nA
4
14
µs
VFBLCD ≥ 1.2V
0.5
1.5
VFBLCD ≤ 0.7V
2.2
7.5
ONLCD Input Low Voltage
2.5V < VOUT < 5.5V
ONLCD Input High Voltage
2.5V < VOUT < 5.5V
Note 1: Specifications to -40°C are guaranteed by design and not production tested.
_______________________________________________________________________________________
µs
400
mV
1
µA
1.6
ONLCD Input Bias Current
4
A
1
1.30
VFBLCD = 1.35V
Maximum LXLCD On-Time
Minimum LXLCD Off-Time
0.7
V
Compact, High-Efficiency, Dual-Output
Step-Up DC-DC Converter
LCD OUTPUT EFFICIENCY
vs. LOAD CURRENT
65
50
45
40
1
10
100
25
0.01
1000
0.1
1
10
80
60
0
1.0
100
1.1
1.2
1.3
1.4
1.5
1.6
1.7
STARTUP VOLTAGE (V)
LOAD CURRENT (mA)
LOAD CURRENT (mA)
NO-LOAD SUPPLY CURRENT
vs. INPUT VOLTAGE
NO-LOAD SUPPLY CURRENT
vs. INPUT VOLTAGE (LCD OFF)
18
450
MAX1817 toc04
16
14
VOUT = 3.3V
VLCD = 18V, NO LOAD
R1 = 1MΩ, R2 = 75kΩ
400
SUPPLY CURRENT (µA)
0.1
100
20
VOUT = 3.3V,
NO LOAD
30
CIRCUIT OF FIGURE 2
120
40
35
E: VIN = 1.8V,
VOUT = 3.3V
70
A: VIN = +2.4V, VLCD = 12V
B: VIN = +2.4V, VLCD = 18V
C: VIN = +2.4V, VLCD = 24V
D: VIN = +1.8V, VLCD = 12V
E: VIN = +1.8V, VLCD = 18V
F: VIN = +1.8V, VLCD = 24V
55
RESISTIVE LOAD
LCD OFF
140
12
10
8
6
MAX1817-05
75
A
LOAD CURRENT (mA)
D: VIN = 1.8V,
VOUT = 5V
C: VIN = 2.4V,
VOUT = 3.3V
B
D
F E
60
EFFICIENCY (%)
80
C
160
MAX1817-02
70
85
SUPPLY CURRENT (µA)
EFFICIENCY (%)
90
B: VIN = 2.4V,
VOUT = 5V
A: VIN = 3.3V,
VOUT = 5V
STARTUP VOLTAGE vs. LOAD CURRENT
75
MAX1817-01
95
MAX1817 toc03
MAIN OUTPUT EFFICIENCY
vs. LOAD CURRENT
350
300
250
200
150
4
100
2
50
0
0
1.0
1.5
2.0
2.5
3.0
3.5
0
4.0
1
2
3
4
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
MAIN CONVERTER
SWITCHING WAVEFORM
LCD CONVERTER
SWITCHING WAVEFORM
A
A
0
0
B
B
C
C
10µs/div
A: ILX, 500mA/div
B: VOUT, 50mV/div, AC-COUPLED
C: VLX, 5V/div
VIN = 2.4V, VOUT = 3.3V, ILOAD,OUT = 50mA, VONLCD = 0
6
MAX1817-07
MAX1817-06
0
5
0
4µs/div
A: ILXLCD, 500mA/div
B: VLCD, 100mV/div, AC-COUPLED
C: VLXLCD, 10V/div
VIN = 2.4V, VOUT = 3.3V, ILOAD,OUT = 0,
VLCD = 18V, ILOAD,LCD = 5mA
_______________________________________________________________________________________
5
MAX1817
Typical Operating Characteristics
(Circuit of Figure 3, TA = +25°C, unless otherwise noted.)
MAX1817
Compact, High-Efficiency, Dual-Output
Step-Up DC-DC Converter
Typical Operating Characteristics (continued)
(Circuit of Figure 3, TA = +25°C, unless otherwise specified)
MAIN LOAD TRANSIENT RESPONSE
LCD LOAD TRANSIENT RESPONSE
MAX1817-08
MAX1817-09
A
A
B
B
0
0
400µs/div
A: VOUT, 100mV/div, AC-COUPLED
B: ILOAD, OUT, 50mA/div
VIN = 2.4V, VOUT = 3.3V
200µs/div
A: VLCD, 50mV/div, AC-COUPLED
B: ILOAD, OUT, 10mA/div
VIN = 2.4V, VOUT = 3.3V (NO LOAD), VLCD = 18V
MAIN LINE TRANSIENT RESPONSE
LCD LINE TRANSIENT RESPONSE
MAX1817-10
MAX1817-11
A
2.4V
B
1.8V
400µs/div
A: VOUT, 100mV/div, AC-COUPLED
B: VIN, 1V/div
A
2.4V
B
1.8V
200µs/div
A: VLCD, 100mV/div, AC-COUPLED
B: VIN, 1V/div
VOUT = 3.3V (NO LOAD), VLCD = 18V, ILOAD,LCD = 2mA
VOUT = 3.3V, ILOAD,MAIN = 20mA, VONLCD = 0
MAIN OUTPUT TURN-ON/TURN-OFF
RESPONSE
LCD OUTPUT TURN-ON/TURN-OFF
RESPONSE
MAX1817-12
MAX1817-13
A
0
A
0
B
0
B
0
C
C
0
100µs/div
A: VOUT, 2V/div
B: IIN, 500mA/div
C: VON, 5V/div
VIN = 2.4V, RLOAD,MAIN = 165Ω, VONLCD = 0
6
0
400µs/div
A: VLCD, 10V/div
B: IIN, 200mA/div
C: VONLCD, 5V/div
VIN = 2.4V, VOUT = 3.3V (NO LOAD), RLOAD,LCD = 9kΩ
_______________________________________________________________________________________
Compact, High-Efficiency, Dual-Output
Step-Up DC-DC Converter
PIN
NAME
FUNCTION
1
FB
Main Output Feedback Input. Connect FB to GND for fixed 3.3V main output. For other output
voltages, use a resistive voltage-divider to set the output voltage. The feedback regulation voltage
is 1.25V at FB.
2
ON
Main Step-Up Converter On/Off Control. Connect ON to OUT for automatic startup. Connect ON to
GND to put the IC into shutdown mode.
3
ONLCD
LCD Output On/Off Control. Connect ONLCD to OUT to enable the LCD output. Connect ONLCD
to GND to disable the LCD output. The main output must be ≥2.4V to enable the LCD output.
4
FBLCD
LCD Output Feedback Input. Use a resistive voltage-divider from the LCD output to FBLCD to set
the voltage. The feedback regulation voltage is 1.25V at FBLCD.
5
AGND
Analog Ground. Connect AGND to GND as close to the IC as possible.
6
N.C.
7
LXLCD
8
GND
9
LX
Main Output Switching Node. Drain of the internal N-channel MOSFET that drives the main output.
Connect an external inductor and rectifier to LX.
10
OUT
Main Step-Up Converter Output. OUT is used to measure the output voltage in fixed mode (FB =
GND) and is the internal bias supply input to the IC. When shut down (ON = ONLCD = GND), OUT
is high impedance, drawing 1µA (max).
No Connection. Not internally connected.
LCD Output Switching Node. Drain of the internal N-channel MOSFET that drives the LCD output.
Connect an external inductor and rectifier to LXLCD.
Power Ground. Connect GND to AGND as close to the IC as possible.
________________Detailed Description
The MAX1817 dual step-up converter is designed to
supply the main power and LCD bias for low-power,
hand-held devices. The MAX1817’s main step-up converter includes a 0.35Ω N-channel power MOSFET
switch and provides a fixed 3.3V or adjustable 2.5V to
5.5V output at up to 125mA from an input as low as
1.5V. The MAX1817’s LCD bias step-up converter
includes a high-voltage 1.1Ω power MOSFET switch to
support as much as 5mA at 28V (Figure 1). During
startup, the MAX1817 extends the LCD MOSFET switch
minimum off-time, limiting surge current. Both converters require an inductor and external rectifier.
The MAX1817 runs in bootstrap mode, powering the IC
from the main step-up converter’s output. Independent
logic-controlled shutdown for the main and LCD stepup converters reduces quiescent current to 0.1µA.
Main Step-Up Converter
The MAX1817 main step-up converter runs from a
+1.5V to +5.5V input voltage and produces a fixed 3.3V
or adjustable 2.5V to 5.5V output voltage as well as
biasing the internal control circuitry. The MAX1817
switches only as often as is required to supply sufficient
power to the load. This allows the converter to operate
at lower frequencies at light loads, improving efficiency.
The control scheme maintains regulation when the error
amplifier senses the output voltage is below the feedback threshold, turning on the internal N-channel MOSFET and initiating an on-time. The on-time is terminated
when the 0.75A current limit is reached or when the
maximum on-time is reached. The N-channel MOSFET
remains off until the inductor current drops to 0, forcing
discontinuous inductor current. At the end of a cycle,
the error comparator waits for the voltage at FB to drop
below the regulation threshold, at which time another
cycle is initiated.
The main step-up converter uses a startup oscillator to
allow it to start from an input voltage as low as +1.2V.
This is necessary since the control circuitry is powered
from the step-up converter output (OUT). When the
voltage at OUT is below the OUT undervoltage lockout,
a fixed 50% duty cycle drives the internal N-channel
MOSFET, forcing the main output voltage to rise. Once
_______________________________________________________________________________________
7
MAX1817
Pin Description
MAX1817
Compact, High-Efficiency, Dual-Output
Step-Up DC-DC Converter
VIN
DUAL-MODE FEEDBACK
OUT
ZEROCROSSING
DETECTOR
ERROR
COMPARATOR
MAIN
FB
LX
MAIN
LXLCD
LCD
CONTROL
LOGIC
MAIN
1.25V
AGND
75mV
ON
ON
OFF
STARTUP
CURRENT
LIMIT
MAIN
SHUTDOWN
LOGIC
MAIN
GND
UNDERVOLTAGE
LOCKOUT
ON
ONLCD
OFF
SHUTDOWN
LOGIC
LCD
CONTROL
LOGIC
LCD
BIAS
LCD
1.25V
AGND
ERROR
COMPARATOR
LCD
CURRENT
LIMIT
LCD
MAX1817
GND
AGND
FBLCD
GND
Figure 1. MAX1817 Simplified Functional Diagram
the output voltage rises above the undervoltage threshold, the control circuitry is enabled, allowing proper
regulation of the output voltage.
LCD Step-Up Converter
The MAX1817’s LCD step-up converter generates an
LCD bias voltage up to 28V by use of a 500mA, 1.1Ω
internal N-channel switching MOSFET (Figure 1). The
LCD step-up converter control circuitry is powered from
the main step-up converter output (OUT), so the voltage
at OUT must be above the OUT undervoltage lockout
voltage for the LCD step-up converter to operate.
8
During startup, the MAX1817 extends the minimum offtime to 5µs for VFBLCD voltages
