Maxim MAX866ESA 3.3v/5v or adjustable-output, single-cell dc-dc converter Datasheet

19-0374; Rev 1; 5/96
KIT
ATION
EVALU
BLE
A
IL
A
V
A
3.3V/5V or Adjustable-Output,
Single-Cell DC-DC Converters
____________________________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
________________________Applications
Pagers
Remote Controls
Detectors
1-Cell Battery-Operated Equipment
Backup Supplies
PART
TEMP. RANGE
PIN-PACKAGE
MAX866C/D
0°C to +70°C
Dice*
MAX866ESA
-40°C to +85°C
8 SO
MAX866EUA
MAX867C/D
MAX867ESA
MAX867EUA
-40°C to +85°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
8 µMAX
Dice*
8 SO
8 µMAX
* Dice are tested at TA = +25°C only.
__________Typical Operating Circuit
INPUT
0.8V TO VOUT
TOP VIEW
330µH
OUTPUT
5V OR 3.3V
ON/OFF
_________________Pin Configurations
SHDN
LX
MBRS0520LTI
OR 1N5817
SHDN
1
8
LX
3/5
2
7
GND
6
OUT
5
LBI
REF 3
MAX866
LBO 4
SO/µMAX
47µF
MAX866
3V/5V SELECT
LOW-BATTERY
DETECTOR
INPUT
3/5
OUT
LBI
REF
GND
LBO
LOW-BATTERY
DETECTOR OUTPUT
SHDN
1
8
LX
FB
2
7
GND
6
OUT
5
LBI
REF 3
MAX867
LBO 4
0.22µF
SO/µMAX
________________________________________________________________ Maxim Integrated Products
1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800
MAX866/MAX867
_______________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 positive 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 supply 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.
MAX866/MAX867
3.3V/5V or Adjustable-Output,
Single-Cell DC-DC Converters
ABSOLUTE MAXIMUM RATINGS
Supply Voltage (OUT to GND) ...................................-0.3V, +7V
Switch Voltage (LX to GND) .......................................-0.3V, +7V
———–
SHDN , 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.
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
(Circuit of Figure 2, VIN = 1.2V, ILOAD = 0mA, TA = +25°C, unless otherwise noted.)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
0.8
0.9
V
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
4.80
5.0
5.20
Minimum Start-Up
Supply Voltage
0.9V ≤ VIN ≤ 3V
Output Voltage
(Note 2)
––
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
0.9V ≤ VIN ≤ 3V,
––
TA =TMIN TO TMAX MAX866, 3/ 5 = 3V, 0mA ≤ ILOAD ≤ 8mA
(Note 3)
MAX867, V
= 5V, 0mA ≤ I
≤ 6mA
OUT
1.2V ≤ VIN ≤ 3V
––
MAX866, 3/ 5 = 0V, 0mA ≤ ILOAD ≤ 10mA
––
MAX866, 3/ 5 = 3V, 0mA ≤ ILOAD ≤ 15mA
3.17
3.3
3.43
4.80
5.0
5.20
6
9
0.9V ≤ VIN ≤ 3V
MAX867, VOUT = 5V, 0mA ≤ ILOAD ≤ 10mA
––
MAX866, 3/ 5 = 0V, 4.8V ≤ VLOAD ≤ 5.2V
––
MAX866, 3/ 5 = 3V, 3.17V ≤ VLOAD ≤ 3.43V
8
13
6
9
10
15
1.2V ≤ VIN ≤ 3V
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
15
23
MAX867, VOUT = 5V, 4.8V ≤ VLOAD ≤ 5.2V
10
15
Maximum Load Current
(Note 2)
Quiescent Supply Current in
3.3V mode (Note 4)
No-Load Battery Current
Shutdown Quiescent Current
(Note 4)
LOAD
––
ILOAD = 0mA, 3/ 5 = 3V, LBI = 1.5V,
VOUT = 3.47V, FB = 1.5V
27
Output set for 3.3V, measured at VIN in Figure 2, VIN = 1.5V
———–
––
SHDN = 0V, 3/ 5 = 3V, LBI = 1.5V, VOUT = 3.47V,
FB = 1.5V
Reference Voltage
60
500
1.22
Reference Load Regulation
LBI Input Threshold
With falling edge
1.22
µA
µA
1
No REF load
––
3/ 5 = 3V, -20µA ≤ REF load ≤ 250µA, CREF = 0.22µF
2
mA
100
Peak Inductor Current Limit
V
µA
mA
1.25
1.28
V
0.8
2.0
%
1.25
1.28
V
_______________________________________________________________________________________
3.3V/5V or Adjustable-Output,
Single-Cell DC-DC Converters
MAX866/MAX867
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 2, VIN = 1.2V, ILOAD = 0mA, TA = +25°C, unless otherwise noted.)
CONDITIONS
PARAMETER
MIN
TYP
LBI Input Hysteresis
MAX
UNITS
25
LBO Output Voltage Low
ISINK = 2mA, open-drain output
LBO Output Leakage Current
–———– ––
SHDN , 3/ 5 Input Voltage Low
———– ––
SHDN , 3/ 5 Input Voltage High
———– ––
SHDN , 3/ 5, FB, LBI Input Current
LBO = 5V
FB Voltage
MAX867, output in regulation
1.22
Output Voltage Range
MAX867
2.7
mV
0.4
V
1
µA
0.08 x VOUT
V
0.32 x VOUT
–———–
––
LBI = 1.5V, FB = 1.5V, SHDN = 0V or 3V, 3/ 5 = 0V or 3V
V
±40
±100
nA
1.25
1.28
V
6.0
V
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 VIN 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.
__________________________________________Typical Operating Characteristics
(Circuits of Figure 2, TA = +25°C, unless otherwise noted.)
EFFICIENCY vs. LOAD CURRENT (VOUT = 3.3V)
L = COILCRAFT D01608-334 (330µH, 2.9Ω)
70
70
70
TOP TO BOTTOM:
VIN = 2.0V
VIN = 1.5V
VIN = 1.25V
VIN = 1.0V
VIN = 0.75V
VIN = 0.5V
40
30
20
10
60
TOP TO BOTTOM:
VIN = 2.0V
VIN = 1.5V
VIN = 1.25V
VIN = 1.0V
VIN = 0.75V
50
40
30
20
10
100
0
0.01
1000
0.1
L = COILCRAFT D01608-334 (330µH, 2.9Ω)
60
50
TOP TO BOTTOM:
VIN = 2.0V
VIN = 1.5V
VIN = 1.25V
VIN = 1.0V
VIN = 0.75V
10
1200
BATTERY CURRENT (µA)
EFFICIENCY (%)
80
70
20
100
DECREASING
BATTERY
VOLTAGE
1000
INCREASING
BATTERY
VOLTAGE
1
10
LOAD CURRENT (mA)
100
100
1000
4000
3500
DECREASING
BATTERY
VOLTAGE
3000
2500
2000
1500
INCREASING
BATTERY
VOLTAGE
1000
500
0
0.1
10
NO-LOAD BATTERY CURRENT
vs. BATTERY VOLTAGE (VOUT = 5V)
600
400
1
0.1
LOAD CURRENT (mA)
800
200
0
0.01
0.01
NO-LOAD BATTERY CURRENT
vs. BATTERY VOLTAGE (VOUT = 3.3V)
MAX866/67-04
100
30
10
LOAD CURRENT (mA)
EFFICIENCY vs. LOAD CURRENT (VOUT = 5.0V)
40
1
BATTERY CURRENT (µA)
10
MAX866/67-05
1
0.1
LOAD CURRENT (mA)
90
20
0
0.01
TOP TO BOTTOM:
VIN = 2.0V
VIN = 1.5V
VIN = 1.25V
VIN = 1.0V
VIN = 0.75V
VIN = 0.5V
40
30
10
0
60
50
MAX866/67-06
50
EFFICIENCY (%)
80
60
L = SUMIDA CD73-331 (330µH, 1.5Ω)
90
80
MAX866/667-03
90
EFFICIENCY vs. LOAD CURRENT (VOUT = 5.0V)
100
80
EFFICIENCY (%)
EFFICIENCY (%)
MAX866/667-01
L = SUMIDA CD73-331 (330µH, 1.5Ω)
90
100
MAX866/67-02
EFFICIENCY vs. LOAD CURRENT (VOUT = 3.3V)
100
0
0
0.2
0.4
0.6
0.8 1.0 1.2
BATTERY VOLTAGE (V)
1.4 1.6
0
0.2
0.4
0.6
0.8 1.0 1.2
1.4 1.6
BATTERY VOLTAGE (V)
_______________________________________________________________________________________
3
____________________________Typical Operating Characteristics (continued)
(Circuits of Figure 2, TA = +25°C, unless otherwise noted.)
START-UP INPUT VOLTAGE vs. LOAD CURRENT
(VOUT = 5V)
47µH
1.2
100µH
1.1
1.0
0.9
0.8
220µH
0.7
330µH
0.6
1.4
100µH
2.5
1.3
1.2
47µH
1.1
1.0
0.9
100µH
0.8
0.7
330µH
220µH
1mH
330µH
2.0
1.5
22µH
1.0
0.5
0.5
0.5
10
1
0
0.1
100
1
10
100
INPUT VOLTAGE (V)
330µH
1.5
47µH
1.0
22µH
0.5
MAX866/67-11
10
9
VREF LOAD REGULATION (mV)
100µH
2.5
100
REFERENCE VOLTAGE
vs. REFERENCE CURRENT
MAX186-14AMAX866/67-10
3.0
10
LOAD CURRENT (mA)
INPUT VOLTAGE vs. LOAD CURRENT
(VOUT = 5V)
2.0
1
LOAD CURRENT (mA)
LOAD CURRENT (mA)
8
7
6
5
4
3
2
1
0
0
1
10
100
1000
LOAD CURRENT (mA)
MAX866 LINE-TRANSIENT RESPONSE
(3.3V MODE)
0
100
200
50
150
REFERENCE LOAD CURRENT (µA)
250
MAX866 LINE-TRANSIENT RESPONSE
(5V MODE)
A
A
B
B
1ms/div
A: 3.3V OUTPUT VOLTAGE, AC COUPLED 20mV/div
B: INPUT VOLTAGE (0.9V AND 1.4V) 500mV/div
ILOAD = 10mA, COUT = 47µF
4
47µH
0.6
1mH
0.1
3.0
INPUT VOLTAGE (V)
1.3
1.5
MAX866/67-08
MAX186-14A
1.4
START-UP INPUT VOLTAGE (V)
MAX186-14AMAX866/67-07
1.5
INPUT VOLTAGE vs. LOAD CURRENT
(VOUT = 3.3V)
MAX186-14AMAX866/67-09
START-UP INPUT VOLTAGE vs. LOAD CURRENT
(VOUT = 3.3V)
START-UP INPUT VOLTAGE (V)
MAX866/MAX867
3.3V/5V or Adjustable-Output,
Single-Cell DC-DC Converters
1ms/div
A: 5.0V OUTPUT VOLTAGE, AC COUPLED 20mV/div
B: INPUT VOLTAGE (0.9V AND 1.4V) 500mV/div
ILOAD = 10mA, COUT = 47µF
_______________________________________________________________________________________
1000
3.3V/5V or Adjustable-Output,
Single-Cell DC-DC Converters
MAX866 LOAD-TRANSIENT RESPONSE
(3.3V MODE)
MAX866 LOAD-TRANSIENT RESPONSE
(5V MODE)
A
A
B
B
1ms/div
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
1ms/div
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 SHUTDOWN RESPONSE
(5V MODE)
MAX866 SHUTDOWN RESPONSE
(3.3V MODE)
A
A
B
B
10ms/div
10ms/div
A: 5.0V OUTPUT VOLTAGE, 2V/div
B: SHDN INPUT VOLTAGE (0V AND 5V) 5V/div
ILOAD = 10mA
MAX867 LBI AND FB THRESHOLD
vs. TEMPERATURE
VFB (MAX867)
1.240
-60 -40 -20 0 20 40 60
TEMPERATURE (°C)
80 100
1.0
3.3V MODE
ILOAD = 0A
START-UP VOLTAGE (V)
1.250
START-UP VOLTAGE
vs. TEMPERATURE
MAX866/67-25
MAX866/67-24
LBI
0.5
OUTPUT VOLTAGE ERROR (%)
LBI, FB VOLTAGE (V)
1.260
MAX866 OUTPUT VOLTAGE ERROR
vs. TEMPERATURE
0
5V MODE
MAX866/67-26
A: 3.3V OUTPUT VOLTAGE, 2V/div
B: SHDN INPUT VOLTAGE (0V AND 5V) 2V/div
ILOAD = 10mA
0.9
0.8
0.7
0.6
ILOAD= OA
-0.5
-60 -40 -20 0 20 40 60
TEMPERATURE (°C)
80 100
0.5
-60 -40 -20 0 20 40 60
TEMPERATURE (°C)
80 100
_______________________________________________________________________________________
5
MAX866/MAX867
____________________________Typical Operating Characteristics (continued)
(Circuits of Figure 2, TA = +25°C, unless otherwise noted.)
____________________________Typical Operating Characteristics (continued)
(Circuits of Figure 2, TA = +25°C, unless otherwise noted.)
20
VIN = 0.9V
15
3.3V MODE
10
-60 -40 -20 0 20 40 60
TEMPERATURE (°C)
80 100
26
IOUT
24
MAX866/67-29
VOUT = 3.47V
28
REFERENCE VOLTAGE (V)
25
30
1.255
MAX866/67-28
VIN = 1.2V
QUIESCENT SUPPLY CURRENT (µA)
MAX866/67-27
30
REFERENCE VOLTAGE
vs. TEMPERATURE
QUIESCENT SUPPLY CURRENT
vs. TEMPERATURE
OUTPUT CURRENT CAPABILITY
vs. TEMPERATURE
OUTPUT CURRENT (mA)
MAX866/MAX867
3.3V/5V or Adjustable-Output,
Single-Cell DC-DC Converters
1.250
IREF = 0A
22
20
-60 -40 -20 0 20 40 60
TEMPERATURE (°C)
80 100
1.245
-60 -40 -20 0 20 40 60
TEMPERATURE (°C)
80 100
______________________________________________________________Pin Description
PIN
6
NAME
FUNCTION
MAX866
MAX867
1
1
–———–
SHDN
2
—
––
3/ 5
Selects the output voltage; connect to GND for 5V output, and to OUT for 3.3V output.
—
2
FB
Feedback Input for adjustable-output operation. Connect to an external resistor voltage
divider between OUT and GND.
3
3
REF
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.
4
4
LBO
Low-Battery Output. An open-drain N-channel MOSFET sinks current when the voltage at
LBI drops below 1.25V.
5
5
LBI
Low-Battery Input. When the voltage on LBI drops below 1.25V, LBO sinks current.
If not used, connect to VIN.
6
6
OUT
Connect OUT to the regulator output. OUT provides bootstrap power to the IC.
7
7
GND
Power Ground. Must be low impedance; solder directly to ground plane.
8
8
LX
Shutdown Input. When low, the entire circuit is off and VOUT = VIN - VD, where VD is the
forward voltage drop of the external Schottky rectifier.
N-Channel Power-MOSFET Drain
_______________________________________________________________________________________
3.3V/5V or Adjustable-Output,
Single-Cell DC-DC Converters
MAX866/MAX867
MINIMUM
OFF-TIME
ONE-SHOT
VBATT
TRIG
Q
ONE-SHOT
SHDN
LX
VOUT
F/F
S
N
Q
R
3/5*
MAXIMUM
ON-TIME
ONE-SHOT
GND
Q
TRIG
ONE-SHOT
CURRENT-LIMIT
COMPARATOR
OUT
MAX866/MAX867
**
*
FB**
**
*
ERROR COMPARATOR
LBO
REF
N
LBI COMPARATOR
LBI
REFERENCE
*MAX866 ONLY
**MAX867 ONLY
Figure 1. Block Diagram
_______________Detailed Description
Operating Principle
The MAX866/MAX867 combine a switch-mode regulator, N-channel power MOSFET, precision voltage reference, and power-fail detector in a single monolithic
device. The MOSFET is a “sense-FET” type for best efficiency, 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) combines 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 maximum 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 1Ω to minimize
switch losses. The MAX866/MAX867 switching frequency depends on load, input voltage, and inductor value,
and it can range up to 250kHz with typical component
values.
_______________________________________________________________________________________
7
MAX866/MAX867
3.3V/5V or Adjustable-Output,
Single-Cell DC-DC Converters
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 (opendrain) 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 voltage 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 - 1
R1 = R2 ( _____
)
VREF
VIN
VIN
C1
47µF
5
LX
LBI
MAX866
OUT
1
3
C3
0.1µF
3/5
SHDN
LBO
REF
8
6
2
D1
R1
VOUT
5
MAX867
OUT
1
4
GND
L1 = COILCRAFT DO1608-334
D1 = MOTOROLA MBR0520LTI
Figure 2a. Standard Application Circuit—Preset Output
Voltage
LX
LBI
C2
47µF
OUTPUT
SELECT
7
8
C1
47µF
L1
330µH
3
C3
0.1µF
FB
SHDN
LBO
REF
L1
330µF
8
D1
6
R1
VOUT
C2
47µF
2
4
R2
GND
7
L1 = COILCRAFT DO1608-334
D1 = MOTOROLA MBR0520LTI
Figure 2b. Standard Application Circuit—Adjustable Output
Voltage
_______________________________________________________________________________________
3.3V/5V or Adjustable-Output,
Single-Cell DC-DC Converters
FOR VTH < 1.25V
VIN
OUT
Q1
MMDFZP02E VOUT (3.3V/5V)
6
R9
1M
R5
MAX866
MAX866
LBI
R3
LBI
VIN
MAX866
5
LBO
R10
1M
R7
R6
Q2
2N3904
5
OUT
6
LBI
R11
1M
4
5
R4
MAX866/MAX867
FOR VTH > 1.25V
(1.25V)
R8
1M
(
)
VTH
-1
VREF
WHERE VTH = THE VIN TRIP THRESHOLD
R3 = R4
(
LOAD
)
VREF - VTH
VOUT - VREF
WHERE VTH = THE VIN TRIP THRESHOLD
R5 = R6
Figure 3. Low-Battery Detector Circuits
Figure 4. Low-Voltage Start-Up Circuit
Since the input bias current at FB has a maximum value
of 100nA, large values (10kΩ to 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.
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 effective 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 Detection, VTH > 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 lowbattery monitor’s threshold is set by two resistors, R3
and R4 (Figure 3). Set the threshold voltage using the
following equation:
Low-Battery Start-Up
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 10kΩ to 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
100kΩ or more from LBO to OUT when driving CMOS
circuits. When LBI is above the threshold, the LBO output is off. If the low-battery comparator is not used,
connect LBI to VIN and leave LBO open.
Low-Battery Detection, VTH < 1.25V
When the low-battery detection threshold voltage is
below 1.25V, use the circuit shown on the right in
The MAX866/MAX867 are bootstrapped circuits; they
can start under no-load conditions at much lower battery voltages than under full load. Once started, the output can maintain a moderate load as the battery voltage 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 detector 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 voltage, LBI and LBO go high, turning on Q2, Q1, and the
load.
_______________________________________________________________________________________
9
MAX866/MAX867
3.3V/5V or Adjustable-Output,
Single-Cell DC-DC Converters
Table 1. Component Suppliers
PRODUCTION
METHOD
INDUCTORS
Surface Mount
See Table 2
Miniature
Through Hole
Sumida
RCH654-220
COMPANY
CAPACITORS
RECTIFIERS
Matsuo 267 series
Sprague 595D series
AVX TPS series
Motorola MBR 0530
Nihon EC15QS02L
Sanyo
OS-CON series
low-ESR organic
semiconductor
Motorola 1N5017
PHONE
FAX
AVX
USA: (803) 946-0690
(803) 626-3123
Coilcraft
USA: (847) 639-6400
(847) 639-1469
Matsuo
USA: (714) 969-2491
(714) 960-6492
Motorola
USA: (602) 244-5303
(602) 244-4015
Murata-Erie
USA: (800) 831-9172
(814) 238-0490
Nihon
USA: (805) 867-2555
Japan: 81-3-3494-7411
(805) 867-2698
81-3-3494-7414
Sanyo
USA: (619) 661-6835
Japan: 81-7-2070-6306
(619) 661-1055
81-7-2070-1174
Sumida
USA: (847) 956-0666
Japan: 81-3-3607-5111
(847) 956-0702
81-3-3607-5144
TDK
USA: (847) 390-4461
(847) 390-4405
J.W. Miller
USA: (310) 515-1720
(310) 515-1962
Inductor Selection
An inductor value of 330µH works well in most applications, 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 values from 22µH to 1mH. In general, smaller inductor values 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 inductor’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
10
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 smallest coils have resistances over 10Ω, and will not provide the same output power or efficiency of a 1Ω coil.
At light loads however (below 5mA), the efficiency differences between low- and high-resistance coils may
be only a percent or two. The Typical Operating
Characteristics graphs show efficiency and output current plots for 1.5Ω and 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
______________________________________________________________________________________
3.3V/5V or Adjustable-Output,
Single-Cell DC-DC Converters
MAX866/MAX867
Table 2. Surface-Mount Inductor Information
INDUCTANCE
(mH)
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
MANUFACTURER /PART
* Shielded
** Low cost
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 connect 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.
___________________Chip Topography
LX
SHDN
3/5
OR FB*
GND 0.084"
(2.1336mm)
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.
REF
OUT
LBI
LBO
0.058"
(1.4732mm)
*3/5 FOR MAX866; FB FOR MAX867.
TRANSISTOR COUNT: 357;
SUBSTRATE IS CONNECTED TO OUT.
______________________________________________________________________________________
11
MAX866/MAX867
3.3V/5V or Adjustable-Output,
Single-Cell DC-DC Converters
________________________________________________________Package Information
DIM
C
α
A
0.101mm
0.004 in
e
B
A1
E
L
A
A1
B
C
D
E
e
H
L
α
INCHES
MAX
MIN
0.044
0.036
0.008
0.004
0.014
0.010
0.007
0.005
0.120
0.116
0.120
0.116
0.0256
0.198
0.188
0.026
0.016
6°
0°
MILLIMETERS
MIN
MAX
0.91
1.11
0.10
0.20
0.25
0.36
0.13
0.18
2.95
3.05
2.95
3.05
0.65
4.78
5.03
0.41
0.66
0°
6°
H
8-PIN µMAX
MICROMAX SMALL OUTLINE
PACKAGE
D
DIM
D
0°-8°
A
0.101mm
0.004in.
e
B
A1
E
C
L
Narrow SO
SMALL-OUTLINE
PACKAGE
(0.150 in.)
H
A
A1
B
C
E
e
H
L
INCHES
MAX
MIN
0.069
0.053
0.010
0.004
0.019
0.014
0.010
0.007
0.157
0.150
0.050
0.244
0.228
0.050
0.016
DIM PINS
D
D
D
8
14
16
MILLIMETERS
MIN
MAX
1.35
1.75
0.10
0.25
0.35
0.49
0.19
0.25
3.80
4.00
1.27
5.80
6.20
0.40
1.27
INCHES
MILLIMETERS
MIN MAX
MIN
MAX
0.189 0.197 4.80
5.00
0.337 0.344 8.55
8.75
0.386 0.394 9.80 10.00
21-0041A
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.