_______________General Description
The MAX866 and MAX867 are ultra-small, high-efficiency,
CMOS, step-up, DC-DC switching regulators for 1-cell
battery-powered systems. The MAX866 accepts a posi-
tive input voltage between 0.8V and VOUT and converts it
to a higher, pin-selectable output voltage of 3.3V or 5V.
The MAX867 adjustable version accepts 0.8V to 6.0V
input voltages and generates a higher adjustable output
voltage in the 2.7V to 6.0V range. Typical efficiencies are
greater than 80%. Typical no-load supply current is
100µA (1µA in shutdown).
The MAX866/MAX867 combine ultra-low quiescent sup-
ply current and high efficiency to give maximum battery
life. Its high switching frequency permits the use of
small, low-cost inductors and capacitors. Additionally,
internal peak-current limiting protects the IC.
________________________Applications
Pagers
Remote Controls
Detectors
1-Cell Battery-Operated Equipment
Backup Supplies
____________________________Features
♦0.8V to 6.0V Input Supply Voltage
♦0.9V Guaranteed Start-Up Supply Voltage
♦>80% Efficiency Over Wide Load Range
♦100µA No-Load Battery Current (VOUT = 3.3V)
♦1µA Shutdown Mode
♦Up to 250kHz Switching Frequency
♦±1.5% Reference Tolerance
♦Low-Battery Detector (LBI/LBO)
♦Available in Ultra-Small 8-Pin µMAX Package
(1.11mm high)
♦Circuit Fits in 0.2in2
______________Ordering Information
MAX866/MAX867
3.3V/5V or Adjustable-Output,
Single-Cell DC-DC Converters
________________________________________________________________
Maxim Integrated Products
1
1
2
3
4
8
7
6
5
LX
GND
OUT
LBI
LBO
REF
3/5
SHDN
MAX866
SO/µMAX
TOP VIEW
1
2
3
4
8
7
6
5
LX
GND
OUT
LBI
LBO
REF
FB
SHDN
MAX867
SO/µMAX
_________________Pin Configurations
MAX866
SHDN
3/5
REF
LX
GND
OUT
INPUT
0.8V TO V
OUT
MBRS0520LTI
OR 1N5817
OUTPUT
5V OR 3.3V
LBO
47µF
0.22µF
330µH
LOW-BATTERY
DETECTOR OUTPUT
ON/OFF
3V/5V SELECT
LBI
LOW-BATTERY
DETECTOR
INPUT
__________Typical Operating Circuit
19-0374; Rev 1; 5/96
PART TEMP. RANGE PIN-PACKAGE
MAX866C/D 0°C to +70°C Dice*
MAX866ESA -40°C to +85°C 8 SO
MAX867C/D 0°C to +70°C Dice*
MAX867ESA -40°C to +85°C 8 SO
* Dice are tested at T
A
= +25°C only.
EVALUATION KIT
AVAILABLE
MAX866EUA -40°C to +85°C 8 µMAX
MAX867EUA -40°C to +85°C 8 µMAX
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800
V
MAX866/MAX867
3.3V/5V or Adjustable-Output,
Single-Cell DC-DC Converters
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 2, VIN = 1.2V, ILOAD = 0mA, TA= +25°C, 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.
Supply Voltage (OUT to GND) ...................................-0.3V, +7V
Switch Voltage (LX to GND) .......................................-0.3V, +7V
S
—
H
—
D
—
N
–, LBO to GND....................................................-0.3V, +7V
LBI, REF, 3/–
5
–, FB to GND ............................-0.3V, (VOUT + 0.3V)
Reference Current (IREF) ..................................................2.5mA
Continuous Power Dissipation (TA= +70°C)
SO (derate 5.88mW/°C above +70°C) .........................471mW
µMAX (derate 4.1mW/°C above +70°C) ......................330mW
Reverse Battery Current (TA≤+45°C) (Note 1)................750mA
Operating Temperature Ranges
MAX86_C/D .......................................................0°C to +70°C
MAX86_E_A ....................................................-40°C to +85°C
Junction Temperature .....................................................+150°C
Storage Temperature Range ............................-65°C to +160°C
Lead Temperature (soldering, 10sec) ............................+300°C
Note 1: Reverse battery current is measured from the
Typical Operating Circuit’s
battery input terminal to GND when the battery is
connected backwards. A reverse current of 750mA will not exceed the package dissipation limits but, if left for an extended
time (more than ten minutes), may degrade performance.
With falling edge
3/–
5
–= 3V, -20µA ≤REF load ≤250µA, CREF = 0.22µF
No REF load
0.9V ≤VIN ≤3V
ILOAD = 0mA, 3/–
5
–= 3V, LBI = 1.5V,
VOUT = 3.47V, FB = 1.5V
CONDITIONS
V1.22 1.25 1.28LBI Input Threshold
%0.8 2.0Reference Load Regulation
V1.22 1.25 1.28Reference Voltage
mA500
µA1
Shutdown Quiescent Current
(Note 4)
µA27 60
Quiescent Supply Current in
3.3V mode (Note 4)
4.80 5.0 5.20
3.17 3.3 3.43
4.80 5.0 5.20
4.75 5.0 5.25
3.13 3.3 3.47
4.75 5.0 5.25
Output Voltage
(Note 2)
UNITSMIN TYP MAXPARAMETER
Peak Inductor Current Limit
MAX866, 3/–
5
–= 0V, 0mA ≤ILOAD ≤6mA
MAX866, 3/–
5
–= 3V, 0mA ≤ILOAD ≤8mA
MAX867, VOUT = 5V, 0mA ≤ILOAD ≤ 6mA
MAX866, 3/–
5
–= 0V, 0mA ≤ILOAD ≤6mA
MAX866, 3/–
5
–= 3V, 0mA ≤ILOAD ≤8mA
MAX867, VOUT = 5V, 0mA ≤ILOAD ≤6mA
S
—
H
—
D
—
N
–= 0V, 3/–
5
–= 3V, LBI = 1.5V, VOUT = 3.47V,
FB = 1.5V
0.9V ≤VIN ≤3V
MAX866, 3/–
5
–= 0V, 4.8V ≤VLOAD ≤5.2V
MAX866, 3/–
5
–= 3V, 3.17V ≤VLOAD ≤3.43V
MAX867, VOUT = 5V, 4.8V ≤ VLOAD ≤5.2V
MAX866, 3/–
5
–= 0V, 4.8V ≤VLOAD ≤5.2V
MAX866, 3/–
5
–= 3V, 3.17V ≤VLOAD ≤3.43V
MAX867, VOUT = 5V, 4.8V ≤VLOAD ≤5.2V
69
813
69
10 15
15 23
mA
10 15
Maximum Load Current
(Note 2)
0.9V ≤VIN ≤3V,
TA = TMIN TO TMAX
(Note 3)
1.2V ≤VIN ≤3V
V0.8 0.9
Minimum Start-Up
Supply Voltage
Output set for 3.3V, measured at VIN in Figure 2, VIN = 1.5V µA100No-Load Battery Current
1.2V ≤VIN ≤3V
MAX866, 3/–
5
–= 0V, 0mA ≤ILOAD ≤10mA
MAX866, 3/–
5
–= 3V, 0mA ≤ILOAD ≤15mA
MAX867, VOUT = 5V, 0mA ≤ILOAD ≤ 10mA 4.80 5.0 5.20
3.17 3.3 3.43
4.80 5.0 5.20
MAX866/MAX867
3.3V/5V or Adjustable-Output,
Single-Cell DC-DC Converters
_______________________________________________________________________________________
3
100
0
10
0.01 0.1 110 100 1000
EFFICIENCY vs. LOAD CURRENT (VOUT = 3.3V)
30
20
MAX866/667-01
LOAD CURRENT (mA)
EFFICIENCY (%)
40
50
60
70
80
90
TOP TO BOTTOM:
VIN = 2.0V
VIN = 1.5V
VIN = 1.25V
VIN = 1.0V
VIN = 0.75V
VIN = 0.5V
L = SUMIDA CD73-331 (330µH, 1.5Ω)
100
90
00.01 10.1 10 100
EFFICIENCY vs. LOAD CURRENT (VOUT = 5.0V)
20
MAX866/67-04
LOAD CURRENT (mA)
EFFICIENCY (%)
40
60
80
70
50
30
10
TOP TO BOTTOM:
VIN = 2.0V
VIN = 1.5V
VIN = 1.25V
VIN = 1.0V
VIN = 0.75V
L = COILCRAFT D01608-334 (330 µH, 2.9Ω)
100
90
00.01 10.1 10 100
EFFICIENCY vs. LOAD CURRENT (VOUT = 3.3V)
20
MAX866/67-02
LOAD CURRENT (mA)
EFFICIENCY (%)
40
60
80
70
50
30
10
TOP TO BOTTOM:
VIN = 2.0V
VIN = 1.5V
VIN = 1.25V
VIN = 1.0V
VIN = 0.75V
L = COILCRAFT D01608-334 (330 µH, 2.9Ω)100
0
10
0.01 0.1 110 100 1000
EFFICIENCY vs. LOAD CURRENT (VOUT = 5.0V)
30
20
MAX866/667-03
LOAD CURRENT (mA)
EFFICIENCY (%)
40
50
60
70
80
90
TOP TO BOTTOM:
VIN = 2.0V
VIN = 1.5V
VIN = 1.25V
VIN = 1.0V
VIN = 0.75V
VIN = 0.5V
L = SUMIDA CD73-331 (330 µH, 1.5Ω)
1200
00 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
NO-LOAD BATTERY CURRENT
vs. BATTERY VOLTAGE (VOUT = 3.3V)
400
200
1000
MAX866/67-05
BATTERY VOLTAGE (V)
BATTERY CURRENT (µA)
800
600
DECREASING
BATTERY
VOLTAGE
INCREASING
BATTERY
VOLTAGE
4000
00 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
NO-LOAD BATTERY CURRENT
vs. BATTERY VOLTAGE (VOUT = 5V)
1000
500
3500
MAX866/67-06
BATTERY VOLTAGE (V)
BATTERY CURRENT (µA)
2000
2500
3000
1500
DECREASING
BATTERY
VOLTAGE
INCREASING
BATTERY
VOLTAGE
__________________________________________Typical Operating Characteristics
(Circuits of Figure 2, TA= +25°C, unless otherwise noted.)
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 2, VIN = 1.2V, ILOAD = 0mA, TA= +25°C, unless otherwise noted.)
Note 2: Output current specified with circuit of Figure 2 and CoilCraft D01608-334 inductor for test purposes only. More (or less)
output current can be supplied with other coil types depending on inductance value and coil resistance. See
Typical Operating
Characteristics
for other coil types. Output voltage and output current are guaranteed over this VIN operating range once the
device has started up. Actual V IN start-up voltage depends on load current.
Note 3: Output voltage specifications over temperature are guaranteed by design to limits that are 6 sigma from either side of the mean.
Note 4: Current measured into OUT. VOUT is forced to 3.47V to maintain LX off when measuring device current.
PARAMETER CONDITIONS MIN TYP MAX UNITS
S
—
H
—
D
—
N
–, 3/–
5
–Input Voltage High 0.32 x VOUT V
S
—
H
—
D
—
N
–, 3/–
5
–, FB, LBI Input Current LBI = 1.5V, FB = 1.5V, –
S
—
H
—
D
—
N
–= 0V or 3V, 3/–
5
–= 0V or 3V ±40 ±100 nA
FB Voltage MAX867, output in regulation 1.22 1.25 1.28 V
Output Voltage Range MAX867 2.7 6.0 V
–
S
—
H
—
D
—
N
–, 3/–
5
–Input Voltage Low 0.08 x VOUT V
LBO Output Leakage Current LBO = 5V 1 µA
LBI Input Hysteresis 25 mV
LBO Output Voltage Low ISINK = 2mA, open-drain output 0.4 V
MAX866/MAX867
3.3V/5V or Adjustable-Output,
Single-Cell DC-DC Converters
4 _______________________________________________________________________________________
____________________________Typical Operating Characteristics (continued)
(Circuits of Figure 2, TA= +25°C, unless otherwise noted.)
1.5
1.4
1.3
1.2
1.1
1.0
0.8
0.5 0.1 1 100
START-UP INPUT VOLTAGE vs. LOAD CURRENT
(VOUT = 3.3V)
0.7
0.6
0.9
MAX186-14AMAX866/67-07
LOAD CURRENT (mA)
START-UP INPUT VOLTAGE (V)
10
100µH 47µH
220µH
330µH
1mH
1.5
1.4
1.3
1.2
1.1
1.0
0.8
0.5 0.1 1 100
START-UP INPUT VOLTAGE vs. LOAD CURRENT
(VOUT = 5V)
0.7
0.6
0.9
MAX186-14A
LOAD CURRENT (mA)
START-UP INPUT VOLTAGE (V)
10
100µH
47µH
220µH
330µH
MAX866/67-08
1 10 1000
INPUT VOLTAGE vs. LOAD CURRENT
(VOUT = 3.3V)
MAX186-14AMAX866/67-09
LOAD CURRENT (mA)
INPUT VOLTAGE (V)
100
100µH 47µH
22µH
330µH
1mH
3.0
2.5
1.5
0
1.0
0.5
2.0
1 10 1000
INPUT VOLTAGE vs. LOAD CURRENT
(VOUT = 5V)
MAX186-14AMAX866/67-10
LOAD CURRENT (mA)
INPUT VOLTAGE (V)
3.0
2.5
1.5
0
1.0
0.5
2.0
100
22µH
330µH
47µH
100µH
A: 3.3V OUTPUT VOLTAGE, AC COUPLED 20mV/div
B: INPUT VOLTAGE (0.9V AND 1.4V) 500mV/div
ILOAD = 10mA, COUT = 47µF
MAX866 LINE-TRANSIENT RESPONSE
(3.3V MODE)
1ms/div
A
B
5
0
REFERENCE VOLTAGE
vs. REFERENCE CURRENT
6
10
MAX866/67-11
REFERENCE LOAD CURRENT (µA)
VREF LOAD REGULATION (mV)
8
7
100 200
9
50 150 250
4
3
2
1
0
A: 5.0V OUTPUT VOLTAGE, AC COUPLED 20mV/div
B: INPUT VOLTAGE (0.9V AND 1.4V) 500mV/div
ILOAD = 10mA, COUT = 47µF
MAX866 LINE-TRANSIENT RESPONSE
(5V MODE)
1ms/div
A
B
MAX866/MAX867
3.3V/5V or Adjustable-Output,
Single-Cell DC-DC Converters
_______________________________________________________________________________________
5
A: 5.0V OUTPUT VOLTAGE, AC COUPLED 20mV/div
B: OUTPUT CURRENT (0mA AND 10mA) 5mV/div
(TEKTRONIX P6042 CURRENT PROBE)
ILOAD = 5mA, COUT = 47µF, VIN = 1.25V
MAX866 LOAD-TRANSIENT RESPONSE
(5V MODE)
1ms/div
A
B
A: 3.3V OUTPUT VOLTAGE, 2V/div
B: SHDN INPUT VOLTAGE (0V AND 5V) 2V/div
ILOAD = 10mA
MAX866 SHUTDOWN RESPONSE
(3.3V MODE)
10ms/div
A
B
A: 5.0V OUTPUT VOLTAGE, 2V/div
B: SHDN INPUT VOLTAGE (0V AND 5V) 5V/div
ILOAD = 10mA
MAX866 SHUTDOWN RESPONSE
(5V MODE)
10ms/div
A
B
____________________________Typical Operating Characteristics (continued)
(Circuits of Figure 2, TA= +25°C, unless otherwise noted.)
1.250
-60
MAX867 LBI AND FB THRESHOLD
vs. TEMPERATURE
1.260
MAX866/67-24
TEMPERATURE (°C)
LBI, FB VOLTAGE (V)
060
-20-40 20 8040 100
1.240
LBI
VFB (MAX867)
0
-60
MAX866 OUTPUT VOLTAGE ERROR
vs. TEMPERATURE
0.5
MAX866/67-25
TEMPERATURE (°C)
OUTPUT VOLTAGE ERROR (%)
060
-20-40 20 8040 100
-0.5
5V MODE
ILOAD= OA
3.3V MODE
-60
START-UP VOLTAGE
vs. TEMPERATURE
1.0
0.9
0.8
0.7
0.6
MAX866/67-26
TEMPERATURE (°C)
START-UP VOLTAGE (V)
060
-20-40 20 8040 100
0.5
ILOAD = 0A
A: 3.3V OUTPUT VOLTAGE, AC COUPLED 20mV/div
B: OUTPUT CURRENT (0mA AND 10mA) 5mV/div
(TEKTRONIX P6042 CURRENT PROBE)
ILOAD = 5mA, COUT = 47µF, VIN = 1.25V
MAX866 LOAD-TRANSIENT RESPONSE
(3.3V MODE)
1ms/div
A
B
MAX866/MAX867
3.3V/5V or Adjustable-Output,
Single-Cell DC-DC Converters
6 _______________________________________________________________________________________
______________________________________________________________Pin Description
N-Channel Power-MOSFET Drain88
Low-Battery Output. An open-drain N-channel MOSFET sinks current when the voltage at
LBI drops below 1.25V.
44
Low-Battery Input. When the voltage on LBI drops below 1.25V, LBO sinks current.
If not used, connect to VIN.
55
Connect OUT to the regulator output. OUT provides bootstrap power to the IC.66 Power Ground. Must be low impedance; solder directly to ground plane.77
1.25V Reference Voltage Output. Bypass with 0.22µF to GND (0.1µF if there is no external
reference load). Maximum load capability is 250µA source, 20µA sink.
33
Feedback Input for adjustable-output operation. Connect to an external resistor voltage
divider between OUT and GND.
2—
Selects the output voltage; connect to GND for 5V output, and to OUT for 3.3V output.—2
Shutdown Input. When low, the entire circuit is off and VOUT = VIN - VD, where VDis the
forward voltage drop of the external Schottky rectifier.
11
FUNCTION
PIN
LX
LBO
LBI
OUT
GND
REF
FB
3/–
5
–
–
S
—
H
—
D
—
N
–
NAME
MAX866 MAX867
____________________________Typical Operating Characteristics (continued)
(Circuits of Figure 2, TA= +25°C, unless otherwise noted.)
24
-60
QUIESCENT SUPPLY CURRENT
vs. TEMPERATURE
30
28
26
22
MAX866/67-28
TEMPERATURE (°C)
QUIESCENT SUPPLY CURRENT (µA)
060
-20-40 20 8040 100
20
IOUT
VOUT = 3.47V
1.250
-60
REFERENCE VOLTAGE
vs. TEMPERATURE
1.255
MAX866/67-29
TEMPERATURE (°C)
REFERENCE VOLTAGE (V)
060
-20-40 20 8040 100
1.245
IREF = 0A
-60
OUTPUT CURRENT CAPABILITY
vs. TEMPERATURE
30
25
20
15
MAX866/67-27
TEMPERATURE (°C)
OUTPUT CURRENT (mA)
060
-20-40 20 8040 100
10
VIN = 0.9V
3.3V MODE
VIN = 1.2V
_______________Detailed Description
Operating Principle
The MAX866/MAX867 combine a switch-mode regula-
tor, N-channel power MOSFET, precision voltage refer-
ence, and power-fail detector in a single monolithic
device. The MOSFET is a “sense-FET” type for best effi-
ciency, and has a very low gate threshold voltage to
ensure start-up with low battery voltages (0.8V typ).
PFM Control Scheme
The MAX866/MAX867 control scheme (Figure 1) com-
bines low-voltage efficiency (80% typ) with low battery
drain (100µA typ). There is no oscillator; switching is
accomplished by a pair of one shots that set a maxi-
mum LX on-time (4.5µs typ) and a minimum LX off-time
(1µs). LX on-time will be terminated early if the inductor
current reaches 0.5A before 4.5µs elapses. With the
standard application circuit (Figure 2a), LX current is
typically less than 50mA, so LX on-time is normally not
terminated by the 0.5A limit and lasts the complete
4.5µs. The LX on-resistance is typically 1Ωto minimize
switch losses. The MAX866/MAX867 switching frequen-
cy depends on load, input voltage, and inductor value,
and it can range up to 250kHz with typical component
values.
MAX866/MAX867
3.3V/5V or Adjustable-Output,
Single-Cell DC-DC Converters
_______________________________________________________________________________________ 7
MAX866/MAX867
SHDN
3/5*
LBO
LBI
N
LBI COMPARATOR
ERROR COMPARATOR
CURRENT-LIMIT
COMPARATOR
ONE-SHOT
TRIG Q
QONE-SHOTTRIG
SQ
R
F/F
MINIMUM
OFF-TIME
ONE-SHOT
VBATT
LX
N
GND
OUT
VOUT
**
FB**
**
*
*
REF
REFERENCE
MAXIMUM
ON-TIME
ONE-SHOT
*MAX866 ONLY
**MAX867 ONLY
Figure 1. Block Diagram
MAX866/MAX867
3.3V/5V or Adjustable-Output,
Single-Cell DC-DC Converters
8 _______________________________________________________________________________________
Voltage Reference
The precision voltage reference is suitable for driving
external loads, such as an analog-to-digital converter.
The voltage-reference output changes less than ±2%
when sourcing up to 250µA and sinking up to 20µA. If
the reference drives an external load, bypass it with
0.22µF to GND. If the reference is unloaded, bypass it
with at least 0.1µF.
Logic Inputs and Outputs
The 3/5 input is internally diode clamped to GND and
OUT, and should not be connected to signals outside
this range. The SHDN input and LBO output (open-
drain) are not clamped to V+ and can be pulled as high
as 7V regardless of the voltage at OUT. Do not leave
control inputs (3/5, LBI, or SHDN) floating.
__________________Design Procedure
Output Voltage Selection
For the MAX866, you can select a 3.3V or 5V output volt-
age under logic control, or by tying 3/5 to GND or OUT.
The MAX867’s output voltage is set by two resistors, R1
and R2 (Figure 2b), which form a voltage divider
between the output and FB. Use the following equation
to determine the output voltage:
R1 + R2
VOUT = VREF (________ )
R2
where VREF = 1.25V.
To simplify resistor selection:
VOUT
R1 = R2 (_____ - 1)
VREF
C1
47µFL1
330µF
VIN
D1
C2
47µF
R1
R2
LX
OUT
FB
LBO
LBI
REF
SHDN
GND
C3
0.1µF
VOUT
5
1
3
8
6
2
4
7
MAX867
L1 = COILCRAFT DO1608-334
D1 = MOTOROLA MBR0520LTI
C1
47µFL1
330µH
VIN
D1
C2
47µF
R1
LX
OUT
3/5
LBO
LBI
REF
SHDN
GND
C3
0.1µF
VOUT
5
1
3
8
6
2
4
7
MAX866
L1 = COILCRAFT DO1608-334
OUTPUT
SELECT
D1 = MOTOROLA MBR0520LTI
Figure 2b. Standard Application Circuit—Adjustable Output
Voltage
Figure 2a. Standard Application Circuit—Preset Output
Voltage
MAX866/MAX867
3.3V/5V or Adjustable-Output,
Single-Cell DC-DC Converters
_______________________________________________________________________________________ 9
Since the input bias current at FB has a maximum value
of 100nA, large values (10kΩto 300kΩ) can be used
for R1 and R2 with no significant accuracy loss. For 1%
error, the current through R1 should be at least 100
times FB’s bias current.
Low-Battery Detection, V
TH
>
1.25V
The MAX866 series contains an on-chip comparator for
low-battery detection. If the voltage at LBI falls below
the regulator’s internal reference voltage (1.25V), LBO
(an open-drain output) sinks current to GND. The low-
battery monitor’s threshold is set by two resistors, R3
and R4 (Figure 3). Set the threshold voltage using the
following equation:
VTH
R3 = R4 (____ - 1)
VREF
where VTH is the desired threshold of the low-battery
detector and VREF is the internal 1.25V reference.
Since the LBI current is less than 100nA, large resistor
values (typically 10kΩto 300kΩ) can be used for R3
and R4 to minimize loading of the input supply.
When the voltage at LBI is below the internal threshold,
LBO sinks current to GND. Connect a pull-up resistor of
100kΩor more from LBO to OUT when driving CMOS
circuits. When LBI is above the threshold, the LBO out-
put is off. If the low-battery comparator is not used,
connect LBI to VIN and leave LBO open.
Low-Battery Detection, V
TH
< 1.25V
When the low-battery detection threshold voltage is
below 1.25V, use the circuit shown on the right in
Figure 3. This circuit uses VOUT (3.3V or 5.0V in the
MAX866, adjustable in MAX867) as a reference. The
voltage divider formed by R5 and R6 allows the effec-
tive trip point of VIN to be set below 1.25V. R6 is usually
set to approximately 100kΩ, and R5 is given by the
formula: R5 = [R6 x (VREF - VTH)] / (VOUT - VREF)
Note that LBI drops below the 1.25V LBI threshold trip
point when either VIN or VOUT is low.
Since VOUT regulation and the LBI threshold are derived
from the same internal voltage reference, they track
together over temperature.
Low-Battery Start-Up
The MAX866/MAX867 are bootstrapped circuits; they
can start under no-load conditions at much lower bat-
tery voltages than under full load. Once started, the out-
put can maintain a moderate load as the battery volt-
age decreases below the start-up voltage (see
Typical
Operating Characteristics
). The circuit shown in Figure
4 allows the circuit to start with no load, then uses the
LBI circuit and an external low-threshold P-channel
MOSFET switch to apply the load after the output has
started.
Resistors R7 and R8 are selected to trip the LBI detec-
tor at about 90% of the output voltage. On start-up, LBI
and LBO are low, Q2 is off, and transistor Q1’s gate is
held high by R11. This disconnects the load, allowing
the MAX866 to bootstrap itself at the lowest possible
voltage. When the output reaches its final output volt-
age, LBI and LBO go high, turning on Q2, Q1, and the
load.
Figure 3. Low-Battery Detector Circuits Figure 4. Low-Voltage Start-Up Circuit
MAX866
LBI
OUT
5
6
R6
R5
VIN
MAX866
LBI 5
R4
R3
VIN
FOR VTH > 1.25V
R3 = R4 -1
WHERE VTH = THE VIN TRIP THRESHOLD WHERE VTH = THE VIN TRIP THRESHOLD
FOR VTH < 1.25V
VTH
VREF
()
R5 = R6 VREF - VTH
VOUT - VREF
()
MAX866
OUT
LBO
LBI
6
4
5
R11
1M
R9
1M
R10
1M
R8
1M
R7
VOUT (3.3V/5V)
Q1
MMDFZP02E
Q2
2N3904
(1.25V)
LOAD
MAX866/MAX867
3.3V/5V or Adjustable-Output,
Single-Cell DC-DC Converters
10 ______________________________________________________________________________________
Inductor Selection
An inductor value of 330µH works well in most applica-
tions, supplying loads over 10mA and allowing typical
start-up voltages of 0.8V. The inductor value is not
critical, and the MAX866/MAX867 can operate with val-
ues from 22µH to 1mH. In general, smaller inductor val-
ues supply more output current while larger values start
with lower input voltage. Several inductor suppliers and
part numbers are listed in Tables 1 and 2.
The peak inductor current should not exceed the induc-
tor’s current rating. Since the MAX866/MAX867 current
limit of 0.5A will not be reached in most applications,
the peak coil current (IPK) is:
IPK = (VIN(max) x 4.5µs) / L
For a typical 1-cell alkaline design, VIN(max) is 1.55V,
so: IPK = (1.55V x 4.5µs) / 330µH = 21.14mA
which is well within the ratings of most surface-mount
coils. Higher efficiency and output current are achieved
with lower inductor resistance, but unfortunately this is
inversely related to physical size. Table 2 indicates
resistance and height for each coil. Some of the small-
est coils have resistances over 10Ω, and will not pro-
vide the same output power or efficiency of a 1Ωcoil.
At light loads however (below 5mA), the efficiency dif-
ferences between low- and high-resistance coils may
be only a percent or two. The
Typical Operating
Characteristics
graphs show efficiency and output cur-
rent plots for 1.5Ωand 2.9Ω, 330µH coils.
Capacitor Selection
A 47µF, 6V, 0.85Ω, surface-mount tantalum (SMT)
output filter capacitor typically provides 15mV output
ripple when stepping up from 0.9V to 1.4V at 10mA.
Smaller capacitors (down to 10µF with higher ESRs) are
acceptable for light loads or in applications that can
Table 1. Component Suppliers
(847) 390-4405USA: (847) 390-4461TDK
(805) 867-2698
81-3-3494-7414
USA: (805) 867-2555
Japan: 81-3-3494-7411
Nihon
(847) 639-1469USA: (847) 639-6400Coilcraft
(310) 515-1962USA: (310) 515-1720J.W. Miller
(847) 956-0702
81-3-3607-5144
USA: (847) 956-0666
Japan:81-3-3607-5111
Sumida
(619) 661-1055
81-7-2070-1174
USA: (619) 661-6835
Japan:81-7-2070-6306
Sanyo
(814) 238-0490USA: (800) 831-9172Murata-Erie
(602) 244-4015USA: (602) 244-5303Motorola
(714) 960-6492USA: (714) 969-2491Matsuo
(803) 626-3123USA: (803) 946-0690AVX
FAXPHONECOMPANY
PRODUCTION
METHOD INDUCTORS CAPACITORS
Surface Mount See Table 2
Matsuo 267 series
Sprague 595D series
AVX TPS series
Motorola MBR 0530
Nihon EC15QS02L
Miniature
Through Hole Sumida
RCH654-220
Sanyo
OS-CON series
low-ESR organic
semiconductor
Motorola 1N5017
RECTIFIERS
tolerate higher output ripple. Values in the 10µF to 47µF
range are recommended.
The equivalent series resistance (ESR) of both bypass
and filter capacitors affects efficiency and output ripple.
Use low-ESR capacitors for best performance, or con-
nect two or more filter capacitors in parallel. Low-ESR,
SMT tantalum capacitors are currently available from
Sprague (595D series) and AVX (TPS series). See
Table 1 for a list of suggested capacitor suppliers.
Rectifier Diode
For optimum performance, a switching Schottky diode
(such as the 1N5817 or MBR0520LTI) is recommended.
Refer to Table 1 for a list of component suppliers. For
low output power applications, a PN-junction switching
diode (such as the 1N4148) will also work well,
although its greater forward voltage drop will reduce
efficiency and raise the start-up voltage.
PC Layout and Grounding
The circuit’s high-frequency operation makes PC layout
important for minimizing ground bounce and noise.
Keep the IC’s GND pin and the ground leads of C1 and
C2 (Figure 2) less than 0.2in (5mm) apart. Also keep all
connections to the FB and LX pins as short as possible.
To maximize output power and efficiency and minimize
output ripple voltage, use a ground plane and solder
the IC’s GND (pin 7) directly to the ground plane.
MAX866/MAX867
3.3V/5V or Adjustable-Output,
Single-Cell DC-DC Converters
______________________________________________________________________________________ 11
Table 2. Surface-Mount Inductor Information
MANUFACTURER/PART INDUCTANCE
(
m
H) RESISTANCE
(
W
)RATED CURRENT
(A) HEIGHT
(mm)
Sumida CD73-331 330 1.5 0.28 3.5
Sumida CD104-331 330 1.1 0.42 4
Murata-Erie LQH4N331K04M00** 330 8.2 0.095 2.6
TDK NLC565050T-331K** 330 4.9 0.14 5
Coilcraft D01608-334 330 2.9 0.16 3.2
Coilcraft DT1608-334 330* 2.9 0.16 3.2
Coilcraft D03316-334 330 0.7 0.6 5.4
Coilcraft DT3316-334 330* 0.7 0.6 5.4
J.W. Miller PM105-331K 330 1.1 0.52 5.4
* Shielded
** Low cost
___________________Chip Topography
TRANSISTOR COUNT: 357;
SUBSTRATE IS CONNECTED TO OUT.
GND
LBI
OUT
3/5
OR FB*
REF
LX
0.084"
(2.1336mm)
0.058"
(1.4732mm)
SHDN
LBO
*3/5 FOR MAX866; FB FOR MAX867.
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.
12
__________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600
© 1996 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
MAX866/MAX867
3.3V/5V or Adjustable-Output,
Single-Cell DC-DC Converters
________________________________________________________Package Information
L
α
C
A1B
DIM
A
A1
B
C
D
E
e
H
L
α
MIN
0.036
0.004
0.010
0.005
0.116
0.116
0.188
0.016
0°
MAX
0.044
0.008
0.014
0.007
0.120
0.120
0.198
0.026
6°
MIN
0.91
0.10
0.25
0.13
2.95
2.95
4.78
0.41
0°
MAX
1.11
0.20
0.36
0.18
3.05
3.05
5.03
0.66
6°
INCHES MILLIMETERS
8-PIN µMAX
MICROMAX SMALL OUTLINE
PACKAGE
0.650.0256
A
e
E H
D
0.101mm
0.004 in
DIM
A
A1
B
C
E
e
H
L
MIN
0.053
0.004
0.014
0.007
0.150
0.228
0.016
MAX
0.069
0.010
0.019
0.010
0.157
0.244
0.050
MIN
1.35
0.10
0.35
0.19
3.80
5.80
0.40
MAX
1.75
0.25
0.49
0.25
4.00
6.20
1.27
INCHES MILLIMETERS
21-0041A
Narrow SO
SMALL-OUTLINE
PACKAGE
(0.150 in.)
DIM
D
D
D
MIN
0.189
0.337
0.386
MAX
0.197
0.344
0.394
MIN
4.80
8.55
9.80
MAX
5.00
8.75
10.00
INCHES MILLIMETERS
PINS
8
14
16
1.270.050
L
0°-8°
HE
D
e
A
A1 C
0.101mm
0.004in.
B
