General Description
The MAX1795/MAX1796/MAX1797 are high efficiency
step-up DC-DC converters intended for small portable
hand-held devices. These devices feature Maxim’s
True-Shutdown™ circuitry, which fully disconnects the
output from the input in shutdown, improves efficiency,
and eliminates costly external components. All three
devices also feature Maxim’s proprietary LX-damping
circuitry for reduced EMI in noise-sensitive applica-
tions. For additional in-system flexibility, a battery moni-
toring comparator (LBI/LBO) remains active even when
the DC-DC converter is in shutdown.
The input voltage range is +0.7V to VOUT, where VOUT
can be set from +2V to +5.5V. Startup is guaranteed
from +0.85V. The MAX1795/MAX1796/MAX1797 have a
preset, pin-selectable 5V or 3.3V output. The output
can also be adjusted to other voltages, using two exter-
nal resistors. The three devices differ only in their cur-
rent limits, allowing optimization of external components
for different loads: The MAX1795, MAX1796, and
MAX1797 have current limits of 0.25A, 0.5A, and 1A,
respectively. All devices are packaged in a compact 8-
pin µMAX package that is only 1.09mm tall and half the
size of an 8-pin SO.
________________________Applications
Portable Digital Audio Players
PDAs/Palmtops
Wireless Handsets
Portable Terminals
Features
♦>95% Efficiency
♦True-Shutdown Circuitry
Output Disconnects from Input in Shutdown
No External Schottky Diode Needed
♦25µA Quiescent Supply Current
♦Low-Noise Antiringing Feature
♦LBI/LBO Comparator Enabled in Shutdown
♦2µA Shutdown Current
♦8-Pin µMAX Package
MAX1795/MAX1796/MAX1797
Low Supply Current, Step-Up DC-DC Converters
with True-Shutdown
________________________________________________________________ Maxim Integrated Products 1
1
2
3
4
8
7
6
5
BATT
OUT
LX
GND
LBO
FB
LBI
MAX1795
MAX1796
MAX1797
µMAX
TOP VIEW
SHDN
Pin Configuration
GND
LBI
LBO
BATT
FB
LX
OUT
MAX1795
MAX1796
MAX1797
SHDN
OUT
IN
0.7V TO
5.5V
ON
OFF
Typical Operating Circuit
19-1798; Rev 0; 12/00
Ordering Information
PART TEMP. RANGE PIN-PACKAGE
MAX1795 EUA -40°C to +85°C 8 µMAX
MAX1796 EUA -40°C to +85°C 8 µMAX
MAX1797 EUA -40°C to +85°C 8 µMAX
True-Shutdown is a trademark of Maxim Integrated Products.
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.
MAX1795/MAX1796/MAX1797
Low Supply Current, Step-Up DC-DC Converters
with True-Shutdown
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VBATT = +2V, OUT = FB (VOUT = +3.3V), SHDN = LBI = GND, TA= 0°C to +85°C, unless otherwise noted. Typical values are at
TA= +25°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.
OUT, LX, SHDN, LBI, LBO, BATT to GND................-0.3V to +6V
FB .............................................................-0.3V to (VOUT + 0.3V)
ILX, IOUT..............................................................................±1.5A
Output Short-Circuit Duration ...................................................5s
Continuous Power Dissipation
8-Pin µMAX (derate 4.1mW/°C above +70°C) .............330mW
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
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Minimum Input Voltage After startup 0.7 V
Operating Voltage VBATT (Note 1) 1.0 5.5 V
Startup Voltage TA = +25°C, RL = 3kΩ0.85 1.0 V
Startup Voltage Tempco -2.2 m V /°C
VOUT FB = OUT 3.17 3.3 3.43
Output Voltage FB = GND 4.80 5.0 5.20 V
Adjustable Output Voltage
Range 2.0 5.5 V
MAX1795 100 180
MAX1796 200 300
BATT = +2V,
FB = OUT
(VOUT = +3.3V) MAX1797 400 550
MAX1795 50 120
MAX1796 100 200
Steady-State Output Current IOUT
BATT = +2V,
FB = GND
(VOUT = +5.0V) MAX1797 250 370
mA
Feedback Set-Point Voltage
(Adjustable Mode) VFB VOUT = +2V to +5.5V 1.20 1.24 1.28 V
Feedback Input Current IFB VFB = +1.24V 4 100 nA
NFET 0.17 0.3
Internal NFET, PFET On-
Resistance RDS
(
ON
)
VOUT = +3.3V,
ILX = 100mA PFET 0.27 0.45 Ω
MAX1795 0.2 0.25 0.35
MAX1796 0.4 0.5 0.625
LX Switch Current Limit (NFET
only) ILIM
MAX1797 0.8 1.0 1.25
A
LX Leakage Current ILEAK VLX = 0 and +5.5V, VOUT = +5.5V 0.2 µA
Synchronous Rectifier Turn-Off
Current Limit 25 mA
Damping Switch On-Resistance RDAMP 100 200 400 Ω
Operating Current into OUT
(Note 2) VFB = +1.4V 25 45 µA
MAX1795/MAX1796/MAX1797
Low Supply Current, Step-Up DC-DC Converters
with True-Shutdown
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(VBATT = +2V, OUT = FB (VOUT = +3.3V), SHDN = LBI = GND, TA= 0°C to +85°C, unless otherwise noted. Typical values are
TA= +25°C.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Operating Current into BATT VFB = +1.4V, VLBI = +1V 2 4 µA
Shutdown Current into BATT SHDN = BATT, VLBI = +1V 2 4 µA
LX Switch MaxImum On-Time tON VFB = +1V, if current limit not reached 3 4 5 µs
LX Switch Minimum Off-Time tOFF VFB = +1V 0.8 1 1.2 µs
VBATT = +2V 0.8 0.85 0.90
LBI Threshold Voltage Falling VLBI VBATT = LBI 0.875 0.925 0.975 V
LBI Hysteresis 25 mV
LBI Input Current ILBI VLBI = +0.8V 9 100 nA
VBATT = VLBI = +0.975V,
sinking 20µA (50Ω typ) 0.1
LBO Low Output Voltage
VBATT = VLBI = +1.1V,
sinking 100µA (25Ω typ) 0.1
V
LBO Off-Leakage Current VLBO = +5.5V 1 100 nA
VIL 0.2 ✕
V
BATT
SHDN Input Voltage
VIH 0.8 ✕
V
BATT
V
Shutdown Input Current VSHDN = 0 and +5.5V 100 nA
ELECTRICAL CHARACTERISTICS
(VBATT = +2V, OUT = FB (VOUT = +3.3V), SHDN = LBI = GND, TA= -40°C to +85°C, unless otherwise noted.) (Note 3)
PARAMETER SYMBOL CONDITIONS MIN MAX UNITS
Operating Voltage VBATT Note 1 1.0 5.5 V
FB = OUT 3.13 3.47
Output Voltage VOUT FB = GND 4.75 5.25 V
Adjustable Output Voltage
Range 2.0 5.5 V
MAX1795 100
MAX1796 200
FB = OUT
(VOUT = +3.3V)
MAX1797 400
MAX1795 60
MAX1796 125
Steady-State Output Current
(Note 1) IOUT
FB = GND
(VOUT = +5.0V) MAX1797 250
mA
Feedback Set-Point Voltage
(Adjustable Mode) VFB VOUT = +2V to +5.5V 1.19 1.29 V
Feedback Input Current IFB VFB = +1.25V 100 nA
MAX1795/MAX1796/MAX1797
Low Supply Current, Step-Up DC-DC Converters
with True-Shutdown
4 _______________________________________________________________________________________
PARAMETER SYMBOL CONDITIONS MIN MAX UNITS
NFET 0.3
Internal NFET, PFET On-
Resistance RDS
(
ON
)
VOUT = +3.3V,
ILX = 100mA PFET 0.45 Ω
ILIM MAX1795 0.19 0.37
MAX1796 0.35 0.7
LX Switch Current Limit (NFET
only)
MAX1797 0.8 1.32
A
LX Leakage Current ILEAK VLX = 0 and +5.5V, VOUT = +5.5V µA
Damping Switch On-Resistance RDAMP 100 400 Ω
Operating Current into OUT
(Note 2) VFB = +1.4V 45 µA
Operating Current into BATT VFB = +1.4V, VLBI = +1V 4 µA
Shutdown Current into BATT SHDN = BATT, VLBI = +1V 4 µA
LX Switch Maximum On-Time tON VFB = +1V, if current limit not reached 2.75 5.25 µs
LX Switch Minimum Off-Time tOFF VFB = +1V 0.7 1.3 µs
VBATT = +2V 0.8 0.90
LBI Threshold Voltage VLBI VBATT = LBI 0.875 0.975 V
LBI Input Current ILBI VLBI = +0.8V 100 nA
VBATT = VLBI = +0.975V,
sinking 20µA (50Ω typ) 0.1
LBO Low Output Voltage
VBATT = VLBI = +1.1V,
sinking 100µA (25Ω typ) 0.1
V
LBO Off-Leakage Current VLBO = +5.5V 100 nA
VIL 0.2 ✕
V
BATT
SHDN Input Voltage
VIH 0.8 ✕
V
BATT
V
Shutdown Input Current VSHDN = 0 and +5.5V 100 nA
ELECTRICAL CHARACTERISTICS (continued)
(VBATT = +2V, OUT = FB (VOUT = +3.3V), SHDN = LBI = GND, TA= -40°C to +85°C, unless otherwise noted.) (Note 3)
Note 1: Operating Voltage: Since the regulator is bootstrapped to the output, once started it will operate down to a 0.7V input.
Note 2: Device is bootstrapped (power to IC comes from OUT). This correlates directly with the actual battery supply current.
Note 3: Specifications to -40°C are guaranteed by design, not production tested.
MAX1795/MAX1796/MAX1797
Low Supply Current, Step-Up DC-DC Converters
with True-Shutdown
_______________________________________________________________________________________ 5
100
0
0.1 1 10 100 1000
MAX1795
EFFICIENCY vs. LOAD CURRENT (+5V)
20
MAX1795/96/97 toc01
LOAD CURRENT (mA)
EFFICIENCY (%)
40
60
80
70
50
30
10
90
VBATT = +2.4V VBATT = +1.2V
VBATT = +3.6V 100
0
0.1 1 10 100 1000
MAX1795
EFFICIENCY vs. LOAD CURRENT (+3.3V)
20
MAX1795/96/97 toc02
LOAD CURRENT (mA)
EFFICIENCY (%)
40
60
80
70
50
30
10
90
VBATT = +1.2V
L = 10µH
VBATT = +2.4V 100
0
0.1 1 10 100 1000
MAX1796
EFFICIENCY vs. LOAD CURRENT (+5V)
20
MAX1795/96/97 toc03
LOAD CURRENT (mA)
EFFICIENCY (%)
40
60
80
70
50
30
10
90
VBATT = +1.2V
VBATT = +2.4V
VBATT = +3.6V
100
0
0.1 1 10 100 1000
MAX1796
EFFICIENCY vs. LOAD CURRENT (+3.3V)
20
MAX1795/96/97 toc04
LOAD CURRENT (mA)
EFFICIENCY (%)
40
60
80
70
50
30
10
90
VBATT = +1.2V
VBATT = +2.4V 100
0
0.1 1 10 100 1000
MAX1797
EFFICIENCY vs. LOAD CURRENT (+5V)
20
MAX1795/96/97 toc05
LOAD CURRENT (mA)
EFFICIENCY (%)
40
60
80
70
50
30
10
90 VBATT = +3.6V
VBATT = +2.4V
VBATT = +1.2V
100
0
0.1 1 10 100 1000
MAX1797
EFFICIENCY vs. LOAD CURRENT (+3.3V)
20
MAX1795/96/97 toc06
LOAD CURRENT (mA)
EFFICIENCY (%)
40
60
80
70
50
30
10
90 VBATT = +2.4V
VBATT = +1.2V
0
100
50
200
150
250
300
0 1.0 1.5 2.00.5 2.5 3.0 3.5 4.0 4.5 5.0 5.5
NO-LOAD BATTERY CURRENT
vs. INPUT BATT VOLTAGE
BATT VOLTAGE (V)
BATTERY CURRENT (µA)
MAX1795/96/97 toc07
VOUT = +3.3V
VOUT = +5V
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
0.1 10 1001 1000
STARTUP VOLTAGE
vs. LOAD CURRENT
MAX1795/96/97 toc08
LOAD CURRENT (mA)
EFFICIENCY (%)
VOUT = +3.3V
0
1.0
0.5
2.0
1.5
2.5
3.0
0 1.0 1.5 2.00.5 2.5 3.0 3.5 4.0 4.5 5.0 5.5
SHUTDOWN THRESHOLD
vs. INPUT BATT VOLTAGE
BATT VOLTAGE (V)
SHUTDOWN THRESHOLD (V)
MAX1795/96/97 toc09
Typical Operating Characteristics
(L = 22µH, CIN = 47µF, COUT = 47µF, TA = +25°C, unless otherwise noted.)
MAX1795/MAX1796/MAX1797
Low Supply Current, Step-Up DC-DC Converters
with True-Shutdown
6 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(L = 22µH, CIN = 47µF, COUT = 47µF, TA = +25°C, unless otherwise noted.)
0.800
0.850
0.825
0.900
0.875
0.925
0.950
0 1.0 1.5 2.00.5 2.5 3.0 3.5 4.0 4.5 5.0 5.5
LOW-BATTERY INPUT THRESHOLD
vs. INPUT BATT VOLTAGE
BATT VOLTAGE (V)
LOW-BATTERY INPUT THRESHOLD (V)
MAX1795/96/97 toc10
INCREASING VLBI
DECREASING VLBI
0
50
100
150
200
250
0 1.5 2.00.5 1.0 2.5 3.0 3.5 4.0 4.5
MAX1795
MAXIMUM OUTPUT CURRENT
vs. BATT INPUT VOLTAGE
MAX1795/96/97 toc12
BATT VOLTAGE (V)
LOAD CURRENT (mA)
VOUT = +5.0V
VOUT = +3.3V
0.800
0.875
0.900
0.925
0.950
-40 10-15 35 60 85
MAX1795/96/97 toc12
TEMPERATURE (°C)
LOW-BATTERY INPUT THRESHOLD (V)
LOW-BATTERY INPUT THRESHOLD
vs. TEMPERATURE
VBATT = +3.6V
INCREASING VLBI
DECREASING VLBI
0.850
0.825
0
100
200
300
400
500
0 1.5 2.00.5 1.0 2.5 3.0 3.5 4.0 4.5
MAX1796
MAXIMUM OUTPUT CURRENT
vs. BATT INPUT VOLTAGE
MAX1795/96/97 toc13
BATT VOLTAGE (V)
LOAD CURRENT (mA)
VOUT = +5.0V
VOUT = +3.3V
0
200
400
600
800
1000
0 1.5 2.00.5 1.0 2.5 3.0 3.5 4.0 4.5
MAX1795/96/97 toc14
BATT VOLTAGE (V)
LOAD CURRENT (mA)
MAX1797
MAXIMUM OUTPUT CURRENT
vs. BATT INPUT VOLTAGE
VOUT = +3.3V
VOUT = +5.0V
0
0.4
0.8
1.2
1.6
2.0
0 1.0 1.50.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
OUT LEAKAGE CURRENT
vs. OUTPUT VOLTAGE
MAX1795/96/97 toc15
OUTPUT VOLTAGE (V)
OUT LEAKAGE CURRENT (µA)
SHDN = BATT
VOUT = +5V
VBATT = +2.4V
OUT BIASED WITH
EXTERNAL VOLTAGE
SOURCE
4.00µs/div
HEAVY-LOAD SWITCHING WAVEFORMS
MAX1795/96/97 toc16
VLX
5V/div
IINDUCTOR
500mA/div
VOUT
(AC-COUPLED)
100mV/div
VIN = +3.6V
VOUT = +5.0V
ILOAD = 400mA
MAX1795/MAX1796/MAX1797
Low Supply Current, Step-Up DC-DC Converters
with True-Shutdown
_______________________________________________________________________________________ 7
Typical Operating Characteristics (continued)
(L = 22µH, CIN = 47µF, COUT = 47µF, TA = +25°C, unless otherwise noted.)
20µs/div
LIGHT-LOAD SWITCHING WAVEFORMS
MAX1795/96/97 toc17
VLX
5V/div
IINDUCTOR
500mA/div
VOUT
(AC-COUPLED)
100mV/div
VBATT = +3.6V
VOUT = +5.0V
ILOAD = 40mA
10µs/div
LINE-TRANSIENT RESPONSE
MAX1795/96/97 toc18
VBATT
+2.7V TO +3V
VOUT
(AC-COUPLED)
20mV/div
VBATT = +2.7V TO +3V
VOUT = +5.0V
NO LOAD
LOAD-TRANSIENT RESPONSE
MAX1795/96/97 toc19
IOUT
100mA/div
VOUT
100mV/div
40µs/div
VBATT = +2.4V
VOUT = +3.3V
ILOAD = 0 TO 325mA
STARTUP-SHUTDOWN WAVEFORMS
MAX1795/96/97 toc20
VSHDN
5V/div
IINDUCTOR
500mA/div
VOUT
2V/div
2ms/div
VBATT = +2.4V
VOUT = +5.0V
ILOAD = 200mA
MAX1795/MAX1796/MAX1797
Detailed Description
The MAX1795/MAX1796/MAX1797 compact step-up
DC-DC converters start up with voltages as low as
0.85V and operate with an input voltage down to +0.7V.
Consuming only 25µA of quiescent current, these
devices have an internal synchronous rectifier that
reduces cost by eliminating the need for an external
diode and improves overall efficiency by minimizing
losses in the circuit (see Synchronous Rectification sec-
tion for details). The internal N-channel MOSFET power
switch resistance is typically 0.17Ω, which minimizes
losses. The LX switch current limits of the MAX1795/
MAX1796/MAX1797 are 0.25A, 0.5A, and 1A, respec-
tively.
All three devices offer Maxim’s proprietary True-
Shutdown circuitry, which disconnects the output from
the input in shutdown and puts the output in a high
impedance state. These devices also feature Maxim’s
proprietary LX-damping circuitry, which reduces EMI in
noise-sensitive applications. For additional in-system
flexibility, the LBI/LBO comparator remains active in
shutdown. (Figure 1 is a typical application circuit).
Control Scheme
A unique minimum-off-time, current-limited control
scheme is the key to the MAX1795/MAX1796/
MAX1797s’ low operating current and high efficiency
over a wide load range. The architecture combines the
high output power and efficiency of a pulse-width-mod-
ulation (PWM) device with the ultra-low quiescent cur-
rent of a traditional pulse-skipping controller (Figure 2).
Switching frequency depends upon the load current
and input voltage, and can range up to 500kHz. Unlike
conventional pulse-skipping DC-DC converters (where
ripple amplitude varies with input voltage), ripple in
these devices does not exceed the product of the
switch current limit and the filter-capacitor equivalent
series resistance (ESR).
Low Supply Current, Step-Up DC-DC Converters
with True-Shutdown
8 _______________________________________________________________________________________
Figure 1. Typical Application Circuit
GND
LBO
LBI
*SEE TABLE 1 FOR COMPONENT VALUES.
BATT
FB
LX
OUT
MAX1795
MAX1796
MAX1797
SHDN
VOUT = 3.3V
COUT*
VIN
VIN
22µH47µF
1M
PIN NAME FUNCTION
1 LBI Low-Battery Comparator Input. Internally set to trip at +0.85V. This function remains operational in
shutdown.
2FB
Dual-Mode™ Feedback Input. Connect to GND for preset 5.0V output. Connect to OUT for preset
3.3V output. Connect a resistive voltage-divider from OUT to GND to adjust the output voltage from
2V to 5.5V.
3 LBO Low-Battery Comparator Output, Open-Drain Output. LBO is high impedance when VLBI < 0.85V.
This function remains operational in shutdown.
4 SHDN Shutdown Input. If SHDN is high, the device is in shutdown mode, OUT is high impedance, and
LBI/LBO are still operational. Connect shutdown to GND for normal operation.
5 GND Ground
6 LX Inductor Connection
7 OUT Power Output. OUT provides bootstrap power to the IC.
8 BATT Battery Input and Damping Switch Connection
Pin Description
Dual Mode is a trademark of Maxim Integrated Products.
Synchronous Rectification
The internal synchronous rectifier eliminates the need
for an external Schottky diode, reducing cost and
board space. During the cycle off-time, the P-channel
MOSFET turns on and shunts the MOSFET body diode.
As a result, the synchronous rectifier significantly
improves efficiency without the addition of an external
component. Conversion efficiency can be as high
as 95%, as shown in the Typical Operating Char-
acteristics.
Shutdown
The device enters shutdown when VSHDN is high,
reducing supply current to less than 2µA. During shut-
down, the synchronous rectifier disconnects the output
from the input, eliminating the DC conduction path that
normally exists with traditional boost converters in shut-
down mode. In shutdown, OUT becomes a high-imped-
ance node. The LBI/LBO comparator remains active in
shutdown.
As shown in Figure 1, the MAX1795/MAX1796/MAX1797
may be automatically shut down when the input voltage
drops below a preset threshold by connecting LBO to
SHDN (see Low-Battery Detection section).
BATT/Damping Switch
The MAX1795/MAX1796/MAX1797 each contain an
internal damping switch to minimize ringing at LX. The
damping switch connects a resistor across the inductor
when the inductor’s energy is depleted (Figure 3).
Normally, when the energy in the inductor is insufficient
to supply current to the output, the capacitance and
inductance at LX form a resonant circuit that causes
ringing. The ringing continues until the energy is dissi-
pated through the series resistance of the inductor.
The damping switch supplies a path to quickly dissi-
MAX1795/MAX1796/MAX1797
Low Supply Current, Step-Up DC-DC Converters
with True-Shutdown
_______________________________________________________________________________________ 9
Figure 2. Functional Diagram
MAX1795
MAX1796
MAX1797
Q
S
R
+
_
+
_
+
_
Q
S
R
Q
S
R
+
_
+
_
FB SELECT
OUT
START
TIMER BLOCK
LBO
LBI
R1
1M
TON MAX TOFF
MAX
R2
FB
ERROR
AMPLIFIER
CURRENT-LIMIT
AMPLIFIER
BATT
BATT
BODY
DIODE
CONTROL
OUT
R3 REFERENCE
22µH
47µF
47µF
GND
LX
BATT
OUT
SHDN
0.85V
-
+
ZERO-
CROSSING
AMPLIFIER
MAX1795/MAX1796/MAX1797
pate this energy, minimizing the ringing at LX.
Damping LX ringing does not reduce VOUT ripple, but
does reduce EMI (Figures 3, 4, and 5).
Setting the Output Voltage
VOUT can be set to 3.3V or 5.0V by connecting the FB
pin to GND (5V) or OUT (3.3V). To adjust the output
voltage, connect a resistive voltage-divider from OUT to
FB to GND (Figure 6). Choose a value less than 250kΩ
for R2.
Use the following equation to calculate R1:
R1 = R2 [(VOUT / VFB) - 1]
where VFB = +1.245V, and VOUT may range from +2V
to +5.5V.
Low-Battery Detection
The MAX1795/MAX1796/MAX1797 each contain an on-
chip comparator for low-battery detection. If the voltage
at LBI is above 0.85V, LBO (an open-drain output)
sinks current to GND. If the voltage at LBI is below
0.85V, LBO goes high impedance. The LBI/LBO func-
tion remains active even when the part is in shutdown.
Connect a resistive voltage-divider to LBI from BATT to
GND. The low-battery monitor threshold is set by two
resistors, R3 and R4 (Figure 6). Since the LBI bias cur-
rent is typically 2nA, large resistor values (R4 up to
250kΩ) can be used to minimize loading of the input
supply.
Calculate R3 using the following equation:
R3 = R4[(VTRIP / 0.85V) - 1]
Low Supply Current, Step-Up DC-DC Converters
with True-Shutdown
10 ______________________________________________________________________________________
Figure 3. Simplified Diagram of Inductor Damping Switch
MAX1795
MAX1796
MAX1797 DAMPING
SWITCH
BATT R1
200Ω
LX
OUT
22µH
VIN
47µF
VOUT
2µs/div
VLX
1V/div
Figure 4. LX Ringing for Conventional Step-Up Converter
(without Damping Switch)
2µs/div
VLX
1V/div
Figure 5. LX Waveform with Damping Switch
Figure 6. Setting an Adjustable Output
GND
LBI
LBO
BATT
R3
R4
FB
LX
OUT
MAX1795
MAX1796
MAX1797
SHDN
47µF
1M
OUTPUT
2V TO 5.5V
LOW-BATTERY
OUTPUT
R1
R2
47µF
VIN
VTRIP is the input voltage where the low-battery detec-
tor output goes high impedance.
For single-cell applications, LBI may be connected to
the battery. When VBATT <1.0V>, the LBI threshold
increases to 0.925V (see Typical Operating Char-
acteristics).
Connect a pullup resistor of 100kΩor greater from LBO
to OUT for a logic output. LBO is an open-drain output
and can be pulled as high as 6V regardless of the volt-
age at OUT. When LBI is below the threshold, the LBO
output is high impedance. If the low-battery comparator
is not used, ground LBI and LBO.
Applications Information
Inductor Selection
An inductor value of 22µH performs well in most appli-
cations. The MAX1795/MAX1796/MAX1797 will also
work with inductors in the 10µH to 47µH range. Smaller
inductance values typically offer a smaller physical size
for a given series resistance, allowing the smallest
overall circuit dimensions, but have lower output cur-
rent capability. Circuits using larger inductance values
exhibit higher output current capability, but are physi-
cally larger for the same series resistance and current
rating.
The inductor’s incremental saturation current rating
should be greater than the peak switch-current limit,
which is 0.25A for the MAX1795, 0.5A for the MAX1796,
and 1A for the MAX1797. However, it is generally
acceptable to bias the inductor into saturation by as
much as 20% although this will slightly reduce efficien-
cy. Table 1 lists some suggested components for typi-
cal applications.
The inductor’s DC resistance significantly affects effi-
ciency. Calculate the maximum output current
(IOUT(MAX)) as follows, using inductor ripple current
(IRIP) and duty cycle (D):
and
where: IRIP = Inductor ripple current (A)
VOUT = Output voltage (V)
ILIM = Device current limit (0.25A, 0.5A, or 1A)
RPFET = On-resistance of P-channel MOSFET
(Ω) (typ 0.27Ω)
LESR = ESR of Inductor (Ω) (typ 0.095Ω)
VBATT = Input voltage (V)
L = Inductor value in µH
tOFF = LX switch’s off-time (µs) (typ 1µs)
D = Duty cycle
RNFET = On-resistance of N-channel MOSFET
(Ω) (typ 0.17Ω)
IOUT(MAX) = Maximum output current (A)
Capacitor Selection
Table 1 lists suggested tantalum or polymer capacitor
values for typical applications. The ESR of both input
bypass and output filter capacitors affects efficiency
and output ripple. Output voltage ripple is the product
of the peak inductor current and the output capacitor
ESR. High-frequency output noise can be reduced by
connecting a 0.1µF ceramic capacitor in parallel with
the output filter capacitor. (See Table 2 for a list of sug-
gested component suppliers.)
PC Board Layout and Grounding
Careful printed circuit layout is important for minimizing
ground bounce and noise. Keep the IC’s GND pin and
the ground leads of the input and output filter capaci-
tors less than 0.2in (5mm) apart. In addition, keep all
connections to the FB and LX pins as short as possible.
In particular, when using external feedback resistors,
locate them as close to FB as possible. To maximize
output power and efficiency and minimize output ripple
voltage, use a ground plane and solder the IC’s GND
pin directly to the ground plane.
II
ID
OUT MAX LIM RIP
()
()=−
−
2
1
I =
D =
RIP
VIR LV
L
t
RL
VI
IRLV
VI
IRR
OUT LIM PFET ESR BATT
OFF
PFET ESR
OUT LIM RIP PFET ESR BATT
OUT LIM RIP PFET NFET
( )
( )
( )
(
+× + −
++
+−
+−
+−
−+
2
2
2
LLESR )
MAX1795/MAX1796/MAX1797
Low Supply Current, Step-Up DC-DC Converters
with True-Shutdown
______________________________________________________________________________________ 11
MAX1795/MAX1796/MAX1797
Low Supply Current, Step-Up DC-DC Converters
with True-Shutdown
12 ______________________________________________________________________________________
Table 1. Suggested Components for Typical Applications
COMPONENT
COMPONENT VALUE
(MAX1797, 1A CURRENT
LIMIT)
COMPONENT VALUE
(MAX1796, 0.5A CURRENT
LIMIT)
COMPONENT VALUE
(MAX1795, 0.25A CURRENT LIMIT)
Sumida CR32-220, 22µH
Sumida CR32-100, 10µH
Sumida CDRH6D28-220, 22µH Sumida CDRH4D28-220, 22µH
Murata CQH3C100K34, 10µH
Murata CQH4N100K(J)04, 10µH
Coilcraft DS1608C-223, 22µH
Inductor
Coilcraft DS3316P-223, 22µH Coilcraft DS1608C-223, 22µH
Coilcraft DS1608C-103, 10µH
Input Capacitor Sanyo POSCAP 6TPA47M,
47µF
Sanyo POSCAP 6TPA47M,
47µFSanyo POSCAP 6TPA47M, 47µF
AVX TPSD476M016R0150,
47µF
AVX TPSD226M016R0150,
22µFAVX TPSD106M016R0150, 10µF
Output Capacitor
Taiyo Yuden UMK316BI150KH,
0.1µF
Taiyo Yuden UMK316BI150KH,
0.1µFTaiyo Yuden UMK316BI150KH, 0.1µF
Table 2. Component Suppliers
COMPANY PHONE FAX
AVX USA 803-946-0690 USA 803-626-3123
Coilcraft USA 847-639-6400 U S A 847- 639-1238-
469
Coiltronics USA 561-241-7876 USA 561-241-9339
Murata USA 814-237-1431
1-800-831-9172 USA 814-238-0490
Nihon
USA 805-867-2555
Japan 81-3-3494-
7411
USA 805-867-2556
Japan 81-3-3494-
7414
Sanyo
U S A 61 9- 6 61 - 68 35
Ja p a n 81- 7- 207 0-
63 06
U S A 61 9- 6 61 - 10 55
Ja p a n 81- 7- 207 0-
11 74
Sprague USA 603-224-1961 USA 603-224-1430
Sumida
USA 647-956-0666
Japan 81-3-3607-
5111
U S A 64 7- 9 56 - 07 02
Ja p a n 81- 3- 360 7-
51 44
Taiyo
Yuden USA 408-573-4150 USA 408-573-4159
Chip Information
TRANSISTOR COUNT: 1100
PROCESS: BiCMOS
Package Information
8LUMAXD.EPS
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 _____________________13
© 2000 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
Low Supply Current, Step-Up DC-DC Converters
with True-Shutdown
MAX1795/MAX1796/MAX1797
