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 out-
put 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 applications.
For additional in-system flexibility, a battery monitoring
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 external
resistors. The three devices differ only in their current
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
19-1798; Rev 0; 12/00
True Shutdown is a trademark of Maxim Integrated Products.
Pin Conguration Typical Operating Circuit
Ordering Information
PART TEMP RANGE PIN-PACKAGE
MAX1795EUA -40°C to +85°C 8 μMAX
MAX1796EUA -40°C to +85°C 8 μMAX
MAX1797EUA -40°C to +85°C 8 μMAX
1
2
3
4
8
7
6
5
BATT
OUT
LX
GND
LBO
FB
LBI
MAX1795
MAX1796
MAX1797
µMAX
TOP VIEW
SHDN
GND
LBI
LBO
BATT
FB
LX
OUT
SHDN
OUT
IN
0.7V TO
5.5V
ON
OFF
MAX1795
MAX1796
MAX1797
MAX1795/MAX1796/
MAX1797
Low-Supply Current, Step-Up DC-DC Converters
with True Shutdown
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
(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.)
Absolute Maximum Ratings
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
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 = 3kΩ 0.85 1.0 V
Startup Voltage Tempco -2.2 mV/°C
Output Voltage VOUT
FB = OUT 3.17 3.3 3.43 V
FB = GND 4.80 5.0 5.20
Adjustable Output Voltage Range 2.0 5.5 V
Steady-State Output Current IOUT
BATT = +2V,
FB = OUT
(VOUT = +3.3V)
MAX1795 100 180
mA
MAX1796 200 300
MAX1797 400 550
BATT = +2V,
FB = GND
(VOUT = +5.0V)
MAX1795 50 120
MAX1796 100 200
MAX1797 250 370
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
Internal NFET, PFET
On-Resistance RDS(ON)
VOUT = +3.3V,
ILX = 100mA
NFET 0.17 0.3 Ω
PFET 0.27 0.45
LX Switch Current Limit
(NFET only) ILIM
MAX1795 0.2 0.25 0.35
AMAX1796 0.4 0.5 0.625
MAX1797 0.8 1.0 1.25
LX Leakage Current ILEAK VLX = 0 and +5.5V, VOUT = +5.5V 0.2 µA
Synchronous Rectier 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
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(VBATT = +2V, OUT = FB (VOUT = +3.3V), SHDN = LBI = GND, TA = -40°C to +85°C, unless otherwise noted.) (Note 3)
(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.)
Electrical Characteristics
Electrical Characteristics (continued)
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
LBI Threshold Voltage Falling VLBI
VBATT = +2V 0.8 0.85 0.90 V
VBATT = LBI 0.875 0.925 0.975
LBI Hysteresis 25 mV
LBI Input Current ILBI VLBI = +0.8V 9 100 nA
LBO Low Output Voltage
VBATT = VLBI = +0.975V,
sinking 20µA (50Ω typ) 0.1
V
VBATT = VLBI = +1.1V,
sinking 100µA (25Ω typ) 0.1
LBO Off-Leakage Current VLBO = +5.5V 1 100 nA
SHDN Input Voltage
VIL
0.2 x
VBATT V
VIH
0.8 x
VBATT
Shutdown Input Current VSHDN = 0 and +5.5V 100 nA
PARAMETER SYMBOL CONDITIONS MIN MAX UNITS
Operating Voltage VBATT Note 1 1.0 5.5 V
Output Voltage VOUT
FB = OUT 3.13 3.47 V
FB = GND 4.75 5.25
Adjustable Output Voltage Range 2.0 5.5 V
Steady-State Output Current
(Note 1) IOUT
FB = OUT
(VOUT = +3.3V)
MAX1795 100
mA
MAX1796 200
MAX1797 400
FB = GND
(VOUT = +5.0V)
MAX1795 60
MAX1796 125
MAX1797 250
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
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(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.
PARAMETER SYMBOL CONDITIONS MIN MAX UNITS
Internal NFET, PFET
On-Resistance RDS(ON)
VOUT = +3.3V,
ILX = 100mA
NFET 0.3 Ω
PFET 0.45
LX Switch Current Limit
(NFET only) ILIM
MAX1795 0.19 0.37
AMAX1796 0.35 0.7
MAX1797 0.8 1.32
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
LBI Threshold Voltage VLBI
VBATT = +2V 0.8 0.90 V
VBATT = LBI 0.875 0.975
LBI Input Current ILBI VLBI = +0.8V 100 nA
LBO Low Output Voltage
VBATT = VLBI = +0.975V,
sinking 20µA (50Ω typ) 0.1
V
VBATT = VLBI = +1.1V,
sinking 100µA (25Ω typ) 0.1
LBO Off-Leakage Current VLBO = +5.5V 100 nA
SHDN Input Voltage
VIL
0.2 x
VBATT V
VIH
0.8 x
VBATT
Shutdown Input Current VSHDN = 0 and +5.5V 100 nA
Electrical Characteristics (continued)
MAX1795/MAX1796/
MAX1797
Low-Supply Current, Step-Up DC-DC Converters
with True Shutdown
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(L = 22μH, CIN = 47μF, COUT = 47μF, TA = +25°C, unless otherwise noted.)
Typical Operating Characteristics
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
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
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
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
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
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
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
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
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
MAX1795/MAX1796/
MAX1797
Low-Supply Current, Step-Up DC-DC Converters
with True Shutdown
Maxim Integrated
│
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(L = 22μH, CIN = 47μF, COUT = 47μF, TA = +25°C, unless otherwise noted.)
Typical Operating Characteristics (continued)
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
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 (A)
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
0.800
0.875
0.900
0.925
0.950
-40 10-15 35 60 85
MAX1795/96/97 toc11
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
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
MAX1795/MAX1796/
MAX1797
Low-Supply Current, Step-Up DC-DC Converters
with True Shutdown
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│
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(L = 22μH, CIN = 47μF, COUT = 47μF, TA = +25°C, unless otherwise noted.)
Typical Operating Characteristics (continued)
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
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
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
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
Low-Supply Current, Step-Up DC-DC Converters
with True Shutdown
Maxim Integrated
│
7
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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 section 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, respectively.
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-sensi-
tive 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-modulation (PWM)
device with the ultra-low quiescent current 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).
Figure 1. Typical Application Circuit
Dual Mode is a trademark of Maxim Integrated Products.
Pin Description
PIN NAME FUNCTION
1 LBI Low-Battery Comparator Input. Internally set to trip at +0.85V. This function remains operational in
shutdown.
2 FB 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
GND
LBO
LBI
*SEE TABLE 1 FOR COMPONENT VALUES.
BATT
FB
LX
OUT
SHDN
VOUT = 3.3V
COUT*
VIN
VIN
22µH 47µF
1M
MAX1795
MAX1796
MAX1797
MAX1795/MAX1796/
MAX1797
Low-Supply Current, Step-Up DC-DC Converters
with True Shutdown
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Synchronous Rectication
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 Characteristics section.
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
shutdown mode. In shutdown, OUT becomes a high-
impedance node. The LBI/LBO comparator remains
active in shutdown.
As shown in Figure 1, the MAX1795/MAX1796/MAX1797
can be automatically shut down when the input voltage
drops below a preset threshold by connecting LBO to
SHDN (see the Low-Battery Detection section).
BATT/Damping Switch
The MAX1795/MAX1796/MAX1797 each contain an inter-
nal damping switch to minimize ringing at LX. The damp-
ing 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 dissipated through the series
resistance of the inductor. The damping switch supplies a
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
47F
47µF
GND
LX
BATT
OUT
SHDN
0.85V
ZERO-
CROSSING
AMPLIFIER
MAX1795/MAX1796/
MAX1797
Low-Supply Current, Step-Up DC-DC Converters
with True Shutdown
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path to quickly dissipate this energy, minimizing the ringing
at LX. Damping LX ringing does not reduce VOUT ripple,
but does reduce EMI (Figure 3, Figure 4, and Figure 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 can 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 function 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 current
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]
Figure 3. Simplified Diagram of Inductor Damping Switch
Figure 6. Setting an Adjustable Output
Figure 5. LX Waveform with Damping Switch
Figure 4. LX Ringing for Conventional Step-Up Converter
(without Damping Switch)
MAX1795
MAX1796
MAX1797 DAMPING
SWITCH
BATT R1
200Ω
LX
OUT
22µH
VIN
47µF
VOUT
2µs/div
VLX
1V/div
2µs/div
VLX
1V/div
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
MAX1795/MAX1796/
MAX1797
Low-Supply Current, Step-Up DC-DC Converters
with True Shutdown
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VTRIP is the input voltage where the low-battery detector
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 the Typical Operating Characteristics section).
Connect a pullup resistor of 100kΩ or 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 voltage 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 current capabil-
ity. Circuits using larger inductance values exhibit higher
output current capability, but are physically 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 efficiency. Table 1 lists some sug-
gested components for typical applications.
The inductor’s DC resistance significantly affects efficien-
cy. Calculate the maximum output current (IOUT(MAX))
as follows, using inductor ripple current (IRIP) and duty
cycle (D):
OUT LIM PFET ESR BATT
RIP
PFET ESR
OFF
RIP
OUT LIM PFET ESR BATT
RIP
OUT LIM PFET NFET ESR
V I (R L ) V
I(R L )
L
t2
I
V I (R L ) V
2
DI
V I (R R L )
2
and
+× + −
= +
+
+− × + −
=
+− × − +
RIP
OUT(MAX ) LIM
I
II
2
= +
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 suggested 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 capacitors 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.
MAX1795/MAX1796/
MAX1797
Low-Supply Current, Step-Up DC-DC Converters
with True Shutdown
www.maximintegrated.com Maxim Integrated
│
11
Table 1. Suggested Components for Typical Applications
Table 2. Component Suppliers
COMPONENT
COMPONENT VALUE
(MAX1797,
1A CURRENT LIMIT)
COMPONENT VALUE
(MAX1796,
0.5A CURRENT LIMIT)
COMPONENT VALUE
(MAX1795, 0.25A CURRENT LIMIT)
Inductor
Sumida CDRH6D28-220, 22µH Sumida CDRH4D28-220, 22µH
Sumida CR32-220, 22µH
Sumida CR32-100, 10µH
Murata CQH3C100K34, 10µH
Coilcraft DS3316P-223, 22µH Coilcraft DS1608C-223, 22µH
Murata CQH4N100K(J)04, 10µH
Coilcraft DS1608C-223, 22µH
Coilcraft DS1608C-103, 10µH
Input Capacitor Sanyo POSCAP 6TPA47M,
47µF
Sanyo POSCAP 6TPA47M,
47µF Sanyo POSCAP 6TPA47M, 47µF
Output Capacitor
AVX TPSD476M016R0150,
47µF
AVX TPSD226M016R0150,
22µF AVX TPSD106M016R0150, 10µF
Taiyo Yuden UMK316BI150KH,
0.1µF
Taiyo Yuden UMK316BI150KH,
0.1µF Taiyo Yuden UMK316BI150KH, 0.1µF
COMPANY PHONE FAX
AVX USA 803-946-0690 USA 803-626-3123
Coilcraft USA 847-639-6400 USA 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
USA 619-661-6835
Japan 81-7-2070-
6306
USA 619-661-1055
Japan 81-7-2070-
1174
Sprague USA 603-224-1961 USA 603-224-1430
Sumida
USA 647-956-0666
Japan 81-3-3607-
5111
USA 647-956-0702
Japan 81-3-3607-
5144
Taiyo
Yuden USA 408-573-4150 USA 408-573-4159
Chip Information
TRANSISTOR COUNT: 1100
PROCESS: BiCMOS
MAX1795/MAX1796/
MAX1797
Low-Supply Current, Step-Up DC-DC Converters
with True Shutdown
www.maximintegrated.com Maxim Integrated
│
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Package Information
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses
are implied. Maxim Integrated reserves the right to change the circuitry and specications without notice at any time. The parametric values (min and max limits)
shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.
MAX1795/MAX1796/
MAX1797
Low-Supply Current, Step-Up DC-DC Converters
with True Shutdown
© 2000 Maxim Integrated Products, Inc.
│
13
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.
