19-4505; Rev 4; 7/05
5V/3.3V/3V/Adjustable, High-Efficiency,
Low IQ, Step-Down DC-DC Converters
____________________________Features
The MAX639/MAX640/MAX653 step-down switching
regulators provide high efficiency over a wide range of
load currents, delivering up to 225mA. A current-limiting
pulse-frequency-modulated (PFM) control scheme gives
the devices the benefits of pulse-width-modulated
(PWM) converters (high efficiency at heavy loads), while
using only 10µA of supply current (vs. 2mA to 10mA for
PWM converters). The result is high efficiency over a
wide range of loads.
♦ High Efficiency for a Wide Range of Load Currents
The MAX639/MAX640/MAX653 input range is 4V to
11.5V, and the devices provide lower preset output voltages of 5V, 3.3V, and 3V, respectively. Or, the output
can be user-adjusted to any voltage from 1.3V to the
input voltage.
♦ Low-Battery Detection Comparator
The MAX639/MAX640/MAX653 have an internal 1A power
MOSFET switch, making them ideal for minimum-component, low- and medium-power applications. For increased
output drive capability, use the MAX649/MAX651/MAX652
step-down controllers, which drive an external P-channel
FET to deliver up to 5W.
________________________Applications
9V Battery to 5V, 3.3V, or 3V Conversion
High-Efficiency Linear Regulator Replacement
Portable Instruments and Handy-Terminals
♦ 10µA Quiescent Current
♦ Output Currents Up to 225mA
♦ Preset or Adjustable Output Voltage:
5.0V (MAX639)
3.3V (MAX640)
3.0V (MAX653)
♦ Current-Limiting PFM Control Scheme
______________Ordering Information
PART
TEMP RANGE
PIN-PACKAGE
MAX639CPA
0°C to +70°C
8 Plastic DIP
MAX639CSA
MAX639C/D
MAX639EPA
MAX639ESA
MAX639MJA
0°C to +70°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
-55°C to +125°C
8 SO
Dice*
8 Plastic DIP
8 SO
8 CERDIP
Ordering Information continued on last page.
*Contact factory for dice specifications.
5V-to-3.3V Converters
__________Typical Operating Circuit
__________________Pin Configuration
TOP VIEW
INPUT
5.5V TO 11.5V
V+
OUTPUT
5V
225mA
LX
VOUT
MAX639
ON/OFF
LOW-BATTERY
DETECTOR
INPUT
SHDN
VOUT
LBI
LBO
LOW-BATTERY
DETECTOR
OUTPUT
8 SHDN
1
LBO
2
LBI
3
GND
4
MAX639
MAX640
MAX653
7
VFB
6
V+
5 LX
DIP/SO
VFB
GND
________________________________________________________________ Maxim Integrated Products
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
1
MAX639/MAX640/MAX653
_______________General Description
MAX639/MAX640/MAX653
5V/3.3V/3V/Adjustable, High-Efficiency,
Low IQ, Step-Down DC-DC Converters
ABSOLUTE MAXIMUM RATINGS
V+...........................................................................................12V
LX .........................................................(V+ - 12V) to (V+ + 0.3V)
LBI, LBO, VFB, SHDN, VOUT........................-0.3V to (V+ + 0.3V)
LX Output Current (Note 1) ......................................................1A
LBO Output Current ............................................................10mA
Continuous Power Dissipation (TA = +70°C)
Plastic DIP (derate 9.09mW/°C above +70°C) .............727mW
SO (derate 5.88mW/°C above +70°C) ..........................471mW
CERDIP (derate 8.00mW/°C above +70°C) ..................640mW
Operating Temperature Ranges:
MAX639C_ _ .......................................................0°C to +70°C
MAX639E_ _ ....................................................-40°C to +85°C
MAX639MJA ..................................................-55°C to +125°C
Storage Temperature Range .............................-65°C to +160°C
Lead Temperature (soldering, 10s) .................................+300°C
Note 1: Peak inductor current must be limited to 600mA by using an inductor of 100µH or greater.
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
(V+ = 9V for the MAX639, V+ = 5V for the MAX640/MAX653, ILOAD = 0mA, TA = TMIN to TMAX, typical values are at TA = +25°C,
unless otherwise noted.)
PARAMETER
CONDITIONS
Supply Voltage
Supply Current
Output Voltage (Note 2)
Dropout Voltage
SHDN = V+, no load
20
µA
5.00
5.20
3.17
3.30
3.43
MAX653, V+ = 4.0V to 11.5V, 0mA < IOUT < 100mA
2.88
3.00
3.12
MAX640
MAX640
MAX653
MAX639
MAX640
MAX653
2
V
10
4.80
IOUT = 100mA, L = 100µH
0.5
IOUT = 100mA, L = 100µH
91
IOUT = 25mA, L = 470µH
94
IOUT = 100mA, L = 100µH
87
IOUT = 25mA, L = 470µH
91
IOUT = 100mA, L = 100µH
85
IOUT = 25mA, L = 470µH
UNITS
11.5
MAX640, V+ = 4.0V to 11.5V, 0mA < IOUT < 100mA
MAX639
Switch Off-Time
MAX
MAX639, V+ = 6.0V to 11.5V, 0mA < IOUT < 100mA
MAX653
Switch On-Time
TYP
4.0
MAX639
Efficiency
MIN
V
V
%
89
V+ = 9V, VOUT = 5V
10.6
12.5
14.4
V+ = 6V, VOUT = 3V
14.2
16.7
19.2
V+ = 9V, VOUT = 3.3V
7.5
8.8
10.1
V+ = 4V, VOUT = 3.3V
60.7
71.4
82.1
V+ = 9V, VOUT = 3V
7.1
8.3
9.5
V+ = 4V, VOUT = 3V
42.5
50.0
57.5
V+ = 9V, VOUT = 5V
9.0
11.7
13.5
V+ = 6V, VOUT = 3V
16.6
19.5
22.4
V+ = 9V, VOUT = 3.3V
13.3
15.6
17.9
V+ = 4V, VOUT = 3.3V
13.3
15.6
17.9
V+ = 9V, VOUT = 3V
14.6
17.2
19.8
V+ = 4V, VOUT = 3V
14.6
17.2
19.8
_______________________________________________________________________________________
µs
µs
5V/3.3V/3V/Adjustable, High-Efficiency,
Low IQ, Step-Down DC-DC Converters
MAX639/MAX640/MAX653
ELECTRICAL CHARACTERISTICS (continued)
(V+ = 9V for the MAX639, V+ = 5V for the MAX640/MAX653, ILOAD = 0mA, TA = TMIN to TMAX, typical values are at TA = +25°C,
unless otherwise noted.)
CONDITIONS
V+ = 9V, TA = +25°C, MAX639/MAX640/MAX653
PARAMETER
LX Switch On-Resistance
MAX
1.5
UNITS
V+ = 6V, TA = TMIN to TMAX, MAX639
2.5
Ω
V+ = 4V, TA = TMIN to TMAX, MAX640/MAX653
2.8
LX Switch Leakage
V+ = 11.5V, VLX = 0V
VFB Bias Current
VFB = 2V
MIN
TYP
0.8
TA = +25°C
0.003
1.0
TA = TMIN to TMAX
30.0
4.0
VFB Dual-Mode Trip Point
15.0
50
VFB Threshold
LBI Bias Current
LBI Threshold
1.26
1.28
1.30
MAX6_ _E/M
1.24
1.28
1.32
2
10
MAX6_ _C
1.26
1.28
1.30
MAX6_ _E/M
1.24
1.28
1.32
MAX639
0.8
2.5
MAX640/MAX653
0.4
1.2
LBO Sink Current
VLBO = 0.4V
LBO Leakage Current
VLBO = 11.5V
LBO Delay
50mV overdrive
SHDN Pull-Up Current
nA
0.1
V
µA
25
SHDN = 0V
V
mA
0.001
SHDN Threshold
nA
mV
MAX6_ _C
VLBI = 2V
µA
µs
0.80
1.15
2.00
V
0.10
0.20
0.40
µA
Note 2: Output guaranteed by correlation to measurements of device parameters (i.e., switch on-resistance, on-times, off-times, and
output voltage trip points).
__________________________________________Typical Operating Characteristics
(Circuit of Figure 3, internal feedback, L = 100µH, TA = +25°C, unless otherwise noted.)
100
MAX639
MAX640
MAX653
70
EFFICIENCY (%)
EFFICIENCY (%)
80
MAX639, V+ = 6V
MAX640, V+ = 4.3V
MAX653, V+ = 4V
80
70
10µ
100µ
1m
10m
OUTPUT CURRENT (A)
100m
1
MAX639
MAX640
MAX653
70
50
50
50
80
60
60
60
L = 470µH
V+ = 9V
90
90
90
EFFICIENCY (%)
L = 470µH
MAX639-3
L = 100µH
V+ = 9V
MAX639-2
100
MAX639-1
100
EFFICIENCY vs.
OUTPUT CURRENT
EFFICIENCY vs.
OUTPUT CURRENT
EFFICIENCY vs.
OUTPUT CURRENT
10µ
100µ
1m
10m
OUTPUT CURRENT (A)
100m
10µ
100µ
1m
10m
100m
OUTPUT CURRENT (A)
_______________________________________________________________________________________
3
_____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 3, internal feedback, L = 100µH, TA = +25°C, unless otherwise noted.)
EFFICIENCY vs.
INPUT VOLTAGE
IOUT = 100mA
80
MAX639, V+ = 6V
MAX640, V+ = 4.3V
MAX653, V+ = 4V
70
L = 470µH
IOUT = 25mA
MAX639
95
EFFICIENCY (%)
EFFICIENCY (%)
90
100
MAX639
95
EFFICIENCY (%)
L = 100µH
MAX639-05
100
MAX639-4
100
EFFICIENCY vs.
INPUT VOLTAGE
90
MAX640
MAX639-06
EFFICIENCY vs.
OUTPUT CURRENT
90
MAX640
85
85
MAX653
60
MAX653
80
10µ
1m
100µ
10m
100m
4
5
6
7
8
10
9
11
12
3
4
5
6
7
8
10
9
11
OUTPUT CURRENT (A)
V+ (V)
V+ (V)
MAXIMUM OUTPUT CURRENT vs.
INPUT VOLTAGE
MAXIMUM OUTPUT CURRENT vs.
INPUT VOLTAGE
MAX639
OUTPUT VOLTAGE RIPPLE vs.
INPUT VOLTAGE
MAX640
MAX653
150
MAX639
150
IOUT = 25mA
OUTPUT VOLTAGE RIPPLE (mV)
L = 470µH
MAXIMUM OUTPUT CURRENT (mA)
L = 100µH
MAX639-08
75
MAX639-07
250
200
80
3
1
65
MAX639
55
MAX640
45
MAX653
35
125
12
MAX639-09
50
MAXIMUM OUTPUT CURRENT (mA)
L = 100µH
100
75
50
L = 220µH
25
L = 470µH
25
3
4
5
6
7
8
10
9
11
0
3
12
4
5
6
7
8
9
10
11
5
6
7
125
L = 100µH
100
75
L = 220µH
50
150
ILOAD = 25mA
OUTPUT VOLTAGE RIPPLE (mV)
IOUT = 25mA
9
MAX653
OUTPUT VOLTAGE RIPPLE vs.
INPUT VOLTAGE
MAX639-10
150
8
L = 470µH
125
100
L = 100µH
75
L = 220µH
50
25
25
0
0
L = 470µH
3
4
5
6
7
8
V+ (V)
9
10
11
12
10
INPUT VOLTAGE (V)
MAX640
OUTPUT VOLTAGE RIPPLE vs.
INPUT VOLTAGE
4
12
V+ (V)
V+ (V)
MAX639-11
100
OUTPUT VOLTAGE RIPPLE (mV)
MAX639/MAX640/MAX653
5V/3.3V/3V/Adjustable, High-Efficiency,
Low IQ, Step-Down DC-DC Converters
3
4
5
6
7
8
9
10
11
V+ (V)
_______________________________________________________________________________________
12
11
12
5V/3.3V/3V/Adjustable, High-Efficiency,
Low IQ, Step-Down DC-DC Converters
START-UP TIME (ms)
8
V+ = 9.0V
6
4
6
MEASURED FROM THE RISING EDGE
OF V+ OR SHDN TO (VOUT = 5.0V)
L = 470µH.
30
START-UP TIME (ms)
MEASURED FROM THE RISING EDGE OF V+
OR SHDN TO (VOUT = 3.3V)(MAX640) OR
(VOUT = 3.0V)(MAX653). THE START-UP
TIME DIFFERENCE BETWEEN THE
MAX640 AND THE MAX653
IS NEGLIGIBLE.
8
V+ = 5.5V
40
MAX639-13
MEASURED FROM THE RISING EDGE
OF V+ OR SHDN TO (VOUT = 5V).
V+ = 5.0V
4
V+ = 5.5V
20
V+ = 9.0V
2
V+ = 11.5V
L = 100µH
0
10 20 30 40 50 60 70 80 90 100
0
0
5
15
20
25
30
NO-LOAD SUPPLY CURRENT vs.
INPUT VOLTAGE
20
V+ = 5.0V
V+ = 9.0V
MAX639-16
70
NO-LOAD SUPPLY CURRENT (µA)
MEASURED FROM THE RISING EDGE OF
V+ OR SHDN TO (VOUT = 3.3V)(MAX640)
OR (VOUT = 3.0V)(MAX653). THE
START-UP TIME DIFFERENCE BETWEEN
THE MAX640 AND THE MAX653 IS
NEGLIGIBLE.
L = 470µH
10
10
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
MAX640/MAX653
START-UP TIME vs.
OUTPUT CURRENT
30
0
10 20 30 40 50 60 70 80 90 100
OUTPUT CURRENT (mA)
40
10
V+ = 11.5V
0
0
V+ = 9.0V
V+ = 11.5V
MAX639-15
2
START-UP TIME (ms)
START-UP TIME (ms)
10
MAX639-12
12
10
MAX639
START-UP TIME vs.
OUTPUT CURRENT
MAX640/MAX653
START-UP TIME vs.
OUTPUT CURRENT
MAX639-14
MAX639
START-UP TIME vs.
OUTPUT CURRENT
60
MAX639, VOUT = 5V
50
40
MAX653, VOUT = 3V
30
20
10
V+ = 11.5V
0
0
0
5
10
15
20
OUTPUT CURRENT (mA)
25
30
0 1
2
3 4
5
6
7 8
9 10 11 12
INPUT VOLTAGE (V)
_______________________________________________________________________________________
5
MAX639/MAX640/MAX653
_____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 3, internal feedback, L = 100µH, TA = +25°C, unless otherwise noted.)
MAX639/MAX640/MAX653
5V/3.3V/3V/Adjustable, High-Efficiency,
Low IQ, Step-Down DC-DC Converters
_____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 3, internal feedback, L = 100µH, TA = +25°C, unless otherwise noted.)
MAX639
LOAD-TRANSIENT RESPONSE
MAX653
LOAD-TRANSIENT RESPONSE
A
A
B
B
1ms/div
1ms/div
A: ILOAD, 0mA TO 200mA, 100mA/div
B: VOUT, 100mV/div, AC COUPLED
VIN = 9V, VOUT = 5V
A: ILOAD, 0mA TO 100mA, 50mA/div
B: VOUT, 100mV/div, AC COUPLED
VIN = 5V, VOUT = 3V
MAX639
LINE-TRANSIENT RESPONSE
MAX653
LINE-TRANSIENT RESPONSE
A
A
B
10ms/div
A: VIN, 4V TO 8V, 2V/div
B: VOUT, 100mV/div
VOUT = 3V, ILOAD = 100mA
6
B
10ms/div
A: VIN, 6V TO 11.5V, 2V/div
B: VOUT, 100mV/div
VOUT = 5V, ILOAD = 100mA
_______________________________________________________________________________________
5V/3.3V/3V/Adjustable, High-Efficiency,
Low IQ, Step-Down DC-DC Converters
PIN
NAME
FUNCTION
1
VOUT
2
LBO
3
LBI
4
GND
5
LX
Drain of a PMOS power switch that has its source connected to V+. LX drives the external inductor,
which provides current to the load.
6
V+
Positive Supply-Voltage Input. Should not exceed 11.5V
7
VFB
8
SHDN
Sense Input for regulated-output operation. Internally connected to an on-chip voltage divider and to
the variable duty-cycle, on-demand oscillator. It must be connected to the external regulated output.
Low-Battery Output. An open-drain N-channel MOSFET sinks current when the voltage at LBI drops
below 1.28V.
Low-Battery Input. When the voltage at LBI drops below 1.28V, LBO sinks current.
Ground
Dual-Mode Feedback Pin. When VFB is grounded, the internal voltage divider sets the output to 5V
(MAX639), 3.3V (MAX640) or 3V (MAX653). For adjustable operation, connect VFB to an external voltage divider.
Shutdown Input — active low. When pulled below 0.8V, the LX power switch stays off, shutting down
the regulator. When the shutdown input is above 2V, the regulator stays on. Tie SHDN to V+ if shutdown mode is not used.
____________________Getting Started
Designing power supplies with the MAX639/MAX640/
MAX653 is easy. The few required external components
are readily available. The most general applications use
the following components:
(3) Inductor: For the highest output current, choose a
100µH inductor with an incremental saturation current rating of at least 600mA. To obtain the highest
efficiencies and smallest size, refer to the Inductor
Selection section.
VL
VOUT
COUT
V+
Figure 1. Simplified Step-Down Converter
MAX639 FG02
(1) Capacitors: For the input and output filter capacitors, try using electrolytics in the 100µF range, or
use low-ESR capacitors to minimize output ripple.
Capacitor values are not critical.
(2) Diode: Use the popular 1N5817 or equivalent
Schottky diode.
IL
L
IL AT 200mA/div
_______________Detailed Description
Figure 1 shows a simplified, step-down DC-DC converter. When the switch is closed, a voltage equal to
(V+ - V OUT) is applied to the inductor. The current
through the inductor ramps up, storing energy in the
inductor’s magnetic field. This same current also flows
into the output filter capacitor and load. When the switch
opens, the current continues to flow through the inductor
in the same direction, but must also flow through the
diode. The inductor alone supplies current to the load
when the switch is open. This current decays to zero as
the energy stored in the inductor’s magnetic field is
transferred to the output filter capacitor and the load.
0A
0V
VL AT 5V/div
SWITCH ON
SWITCH OFF
SWITCH ON
SWITCH OFF
Figure 2. Simplified Step-Down Converter Operation
_______________________________________________________________________________________
7
MAX639/MAX640/MAX653
______________________________________________________________Pin Description
MAX639/MAX640/MAX653
5V/3.3V/3V/Adjustable, High-Efficiency,
Low IQ, Step-Down DC-DC Converters
Figure 2 shows what happens to the ideal circuit of
Figure 1 if the switch turns on with a 66% duty cycle and
V+ = 3/2 VOUT. The inductor current rises more slowly
than it falls because the magnitude of the voltage
applied during tON is less than that applied during tOFF.
Varying the duty cycle and switching frequency keeps
the peak current constant as input voltage varies. The
MAX639/MAX640/MAX653 control the switch (tON and
tOFF) according to the following equations:
Equation (1) tON = 50µsV / (V+ - VOUT)
Equation (2) tOFF ≥ 50µsV / VOUT
When the output dips:
(1) The error comparator switches high.
Equation (3) IPEAK = 50µsV / L
These three equations ensure constant peak currents for
a given inductor value, across all input voltages (ignoring
the voltage drop across the diode (D1) and the resistive
losses in the switch and inductor). The variable duty
cycle also ensures that the current through the inductor
discharges to zero at the end of each pulse.
(3) The oscillator shuts down to save power.
Figure 3 shows the MAX639/MAX640/MAX653 block diagram and a typical connection in which 9V is converted
to 5V (MAX639), 3.3V (MAX640), or 3.0V (MAX653). The
sequence of events in this application is as follows:
(2) The internal oscillator starts (15µs start-up time)
and connects to the gate of the LX output driver.
(3) LX turns on and off according to tON and tOFF,
charging and discharging the inductor, and supplying current to the output (as described above).
When the output voltage recovers:
(1) The comparator switches low.
(2) LX turns off.
Fixed or Adjustable Output
For operation at the preset output voltage, connect VFB
to GND; no external resistors are required. For other
output voltages, use an external voltage divider. Set the
output voltage using R3 and R4 as determined by the
following formula:
R3 = R4 [(VOUT / VFB Threshold) - 1]
where R4 is any resistance in the 10kΩ to 1MΩ range (typically 100kΩ), and the VFB threshold is typically 1.28V.
INPUT, +5.5V TO +11.5V (MAX639),
+3.8V TO +11.5V (MAX640), +3.5V TO +11.5V (MAX653)
8
SHDN
CIN
33µF
6
V+
LX
5V, 3.3V OR 3.0V
AT 100mA
5
L = 100µH
+1.28V
BANDGAP
REFERENCE
ERROR
COMPARATOR
1N5817
VARIABLE
FREQUENCY
AND
DUTY-CYCLE
OSCILLATOR
VOUT 1
R1
COUT
100µF
LOW-BATTERY
COMPARATOR
MODE-SELECT
COMPARATOR
3 LBI
2 LBO
50mV
MAX639
MAX640
MAX653
R2
VFB
7
GND
4
Figure 3. Block Diagram
8
_______________________________________________________________________________________
5V/3.3V/3V/Adjustable, High-Efficiency,
Low IQ, Step-Down DC-DC Converters
Shutdown Mode
Bringing SHDN below 0.8V places the MAX639/
MAX640/MAX643 in shutdown mode. LX becomes high
impedance, and the voltage at VOUT falls to zero. The
time required for the output to rise to its nominal regulated voltage when brought out of shutdown (start-up
time) depends on the inductor value, input voltage, and
load current (see the Start-Up Time vs. Output Current
graph in the Typical Operating Characteristics). The
low-battery comparator remains active in shutdown
mode.
__________Applications Information
Inductor Selection
When selecting an inductor, consider these four factors:
peak-current rating, inductance value, series resistance,
and size. It is important not to exceed the inductor’s
peak-current rating. A saturated inductor will pull excessive currents through the MAX639/MAX640/MAX653’s
switch, and may cause damage. Avoid using RF chokes
or air-core inductors since they have very low peak-current ratings. Electromagnetic interference must not upset
nearby circuitry or the regulator IC. Ferrite-bobbin types
work well for most digital circuits; toroids or pot cores
work well for EMI-sensitive analog circuits.
Recall that the inductance value determines IPEAK for all
input voltages (Equation 3). If there are no resistive losses and the diode is ideal, the maximum average current
that can be drawn from the MAX639/MAX640/MAX653
will be one-half IPEAK. With the real losses in the switch,
inductor, and diode taken into account, the real maximum output current typically varies from 90% to 50% of
the ideal. The following steps describe a conservative
way to pick an appropriate inductor.
Step 1: Decide on the maximum required output
current, in amperes: IOUTMAX.
Step 2: IPEAK = 4 x IOUTMAX.
Table 1. Component Suppliers
INDUCTORS — THROUGH HOLE
PART
NUMBER
SIZE
(inches)
VALUE
(µH)
IMAX
(A)
SERIES R
(Ω)
MAXL001*
0.65 x 0.33 dia.
100
1.75
0.2
7300-13**
0.63 x 0.26 dia.
100
0.89
0.27
7300-15**
0.63 x 0.26 dia.
150
0.72
0.36
7300-17**
0.63 x 0.26 dia.
220
0.58
0.45
7300-19**
0.63 x 0.26 dia.
330
0.47
0.58
7300-21**
0.63 x 0.26 dia.
470
0.39
0.86
7300-25**
0.63 x 0.26 dia.
1000
0.27
2.00
* Maxim Integrated Products
**Caddell-Burns
258 East Second Street
Mineola, NY 11501-3508
(516) 746-2310
INDUCTORS — SURFACE MOUNT
PART
NUMBER
SIZE
(mm)
VALUE
(µH)
IMAX
(A)
SERIES R
(Ω)
CD54
5.2 x 5.8 x 4.5
100
0.52
0.63
CD54
5.2 x 5.8 x 4.5
220
0.35
1.50
CDR74
7.1 x 7.7 x 4.5
100
0.52
0.51
CDR74
7.1 x 7.7 x 4.5
220
0.35
0.98
CDR105
9.2 x 10.0 x 5.0
100
0.80
0.35
CDR105
9.2 x 10.0 x 5.0
220
0.54
0.69
Sumida Electric (USA)
637 East Golf Road
Arlington Heights, IL 60005
(708) 956-0666
CAPACITORS — LOW ESR
PART
NUMBER
SIZE
(inches)
VALUE
(µF)
ESR
(Ω)
VMAX
(V)
MAXC001*
0.49 x 0.394 dia.
150
0.2
35
267 Series**
D SM packages
47
0.2
10
267 Series**
E SM packages
100
0.2
6.3
* Maxim Integrated Products
**Matsuo Electronics
2134 Main Street
Huntington Beach, CA 92648
(714) 969-2491
SCHOTTKY DIODES — SURFACE MOUNT
PART
NUMBER
SIZE
VF
(V)
IMAX
(A)
SE014
SOT89
0.55
1
SE024
SOT89
0.55
0.95
Collmer Semiconductor
14368 Proton Road
Dallas, TX 75244
(214) 233-1589
NOTE: This list does not constitute an endorsement by Maxim
Integrated Products and is not intended to be a comprehensive
list of all manufacturers of these components.
_______________________________________________________________________________________
9
MAX639/MAX640/MAX653
Low-Battery Detector
The low-battery detector compares the voltage on the
LBI input with the internal 1.28V reference. LBO goes
low whenever the input voltage at LBI is less than
1.28V. Set the low-battery detection voltage with resistors R1 and R2 (Figure 3) as determined by the following formula:
R1 = R2 [(VLB / LBI Threshold) - 1]
where R2 is any resistance in the 10kΩ to 1MΩ range
(typically 100kΩ), the LBI threshold is typically 1.28V,
and VLB is the desired low-battery detection voltage.
The low-battery comparator remains active in shutdown
mode.
MAX639/MAX640/MAX653
5V/3.3V/3V/Adjustable, High-Efficiency,
Low IQ, Step-Down DC-DC Converters
INPUT
+4.0V TO +11.5V
6
8
CIN
100µF
LX
V+
L = 100µH
5
OUTPUT
COUT
100µF
1N5817
SHDN
MAX639 VOUT
MAX640
MAX653
1
R3
MAX639
MAX640
MAX653
VFB 7
GND
4
LBI
3
R4
Figure 4. Adjustable-Output Operation
Figure 5. Through-Hole PC Layout and Component Placement
Diagram for Standard Step-Down Application (Top-Side View)
Step 3: L = 50 / IPEAK. L will be in µH. Do not use an
inductor of less than 100µH.
Step 4: Make sure that IPEAK does not exceed 0.6A or
the inductor’s maximum current rating,
whichever is lower.
Inductor series resistance affects both efficiency and
dropout voltage. A high series resistance severely limits
the maximum current available at lower input voltages.
Output currents up to 225mA are possible if the inductor has low series resistance. Inductor and series
switch resistance form an LR circuit during tON. If the
L/R time constant is less than the oscillator tON, the
inductor’s peak current will fall short of the desired
IPEAK.
To maximize efficiency, choose the highest-value
inductor that will provide the required output current
over the whole range of your input voltage (see Typical
Operating Characteristics). Inductors with peak currents in the 600mA range do not need to be very large.
They are about the size of a 1W resistor, with surfacemount versions less than 5mm in diameter. Table 1 lists
suppliers of inductors suitable for use with the
MAX639/MAX640/MAX653.
It decreases with larger inductance, but increases as
the input voltage lessens. As a general rule, a smaller
amount of charge delivered in each pulse results in
less output ripple.
Output Filter Capacitor
The MAX639/MAX640/MAX653’s output ripple has two
components. One component results from the variation
in stored charge on the filter capacitor with each LX
pulse. The other is the product of the current into the
capacitor and the capacitor’s equivalent series resistance (ESR).
The amount of charge delivered in each oscillator pulse
is determined by the inductor value and input voltage.
10
With low-cost aluminum electrolytic capacitors, the
ESR-induced ripple can be larger than that caused by
the charge variation. Consequently, high-quality aluminum-electrolytic or tantalum filter capacitors will minimize output ripple. Best results at reasonable cost are
typically achieved with an aluminum-electrolytic capacitor in the 100µF range, in parallel with a 0.1µF ceramic
capacitor (Table 1).
External Diode
In most MAX639/MAX640/MAX653 circuits, the current
in the external diode (D1, Figure 3) changes abruptly
from zero to its peak value each time LX switches off.
To avoid excessive losses, the diode must have a fast
turn-on time. For low-power circuits with peak currents
less than 100mA, signal diodes such as the 1N4148
perform well. The 1N5817 diode works well for highpower circuits, or for maximum efficiency at low power.
1N5817 equivalent diodes are also available in surfacemount packages (Table 1). Although the 1N4001 and
other general-purpose rectifiers are rated for high currents, they are unacceptable because their slow turnoff times result in excessive losses.
Minimum Load
Under no-load conditions, because of leakage from the
PMOS power switch (see the LX Leakage Current vs.
Temperature graph in the Typical Operating
Characteristics) and from the internal resistor from V+
to VOUT, leakage current may be supplied to the output
______________________________________________________________________________________
5V/3.3V/3V/Adjustable, High-Efficiency,
Low IQ, Step-Down DC-DC Converters
SHDN
LX
5
MAX639
MAX640
1
MAX653 VOUT
L = 100µH
1N5817
COUT
100µF
GND
4
VFB
7
MAX639 FG02
CIN
100µF
MAXIMUM OUTPUT CURRENT (mA)
VIN
8
TA = +25°C
L = 100µH
MAX639
140
120
MAX639/MAX640/MAX653
160
6
V+
100
80
60
40
20
-5V
-3.3V
OR -3V
0
0
1
3
2
4
5
V+ (V)
Figure 7. Maximum Current Capability of Figure 6 Circuit
87.0
MAX639 FG02
capacitor, even when the switch is off. This will usually not
be a problem for a 5V output at room temperature, since
the diode’s reverse leakage current and the feedback
resistors’ current typically drain the excess. However, if
the diode leakage is very low (which can occur at low
temperatures and/or small output voltages), charge may
build up on the output capacitor, making VOUT rise above
its set point. If this happens, add a small load resistor
(typically 1MΩ) to the output to pull a few extra
microamps of current from the output capacitor.
86.5
EFFICIENCY (%)
Figure 6. Inverting Configuration
86.0
85.5
TA = +25°C
VOUT = -5V
L = 470µH
IOUT = 10mA
85.0
Layout
Several of the external components in a MAX639/
MAX640/MAX653 circuit experience peak currents up
to 600mA. Wherever one of these components connects to ground, there is a potential for ground bounce.
Ground bounce occurs when high currents flow
through the parasitic resistances of PC board traces.
What one component interprets as ground can differ
from the IC’s ground by several millivolts. This may
increase the MAX639/MAX640/MAX653’s output ripple,
since the error comparator (which is referenced to
ground) will generate extra switching pulses when they
are not needed. It is essential that the input filter capacitor’s ground lead, the MAX639/MAX640/MAX653’s
GND pin, the diode’s anode, and the output filter
capacitor’s ground lead are as close together as possible, preferably at the same point. Figure 5 shows a
suggested through-hole printed circuit layout that minimizes ground bounce.
Inverter Configuration
Figure 6 shows the MAX639/MAX640/MAX653 in a
floating ground configuration. By tying what would normally be the output to the supply-voltage ground, the
IC’s GND pin is forced to a regulated -5V (MAX639),
84.5
84.0
1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
V+ (V)
Figure 8. Efficiency of Figure 6 Circuit
-3.3V (MAX640), or -3V (MAX653). Avoid exceeding the
maximum differential voltage of 11.5V from V+ to VOUT.
Other negative voltages can be generated by placing a
voltage divider across COUT and connecting the tap
point to VFB in the same manner as the normal stepdown configuration.
Two AA Batteries to 5V, 3.3V, or 3V
For battery-powered applications, where the signal
ground does not have to correspond to the power-supply
ground, the circuit in Figure 6 generates 5V (MAX639),
3.3V (MAX640), or 3V (MAX653) from a pair of AA batteries. Connect the VIN ground point to your system’s input,
and connect the output to your system’s ground input.
This configuration has the added advantage of reduced
on resistance, since the IC’s internal power FET has VIN +
VOUT of gate drive (Figures 7 and 8).
______________________________________________________________________________________
11
MAX639/MAX640/MAX653
5V/3.3V/3V/Adjustable, High-Efficiency,
Low IQ, Step-Down DC-DC Converters
_Ordering Information (continued)
PART
TEMP RANGE
PIN-PACKAGE
MAX640CPA
0°C to +70°C
8 Plastic DIP
MAX640CSA
MAX640C/D
MAX640EPA
MAX640ESA
MAX640MJA
MAX653CPA
0°C to +70°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
-55°C to +125°C
0°C to +70°C
8 SO
Dice*
8 Plastic DIP
8 SO
8 CERDIP
8 Plastic DIP
MAX653CSA
MAX653C/D
MAX653EPA
MAX653ESA
MAX653MJA
0°C to +70°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
-55°C to +125°C
8 SO
Dice*
8 Plastic DIP
8 SO
8 CERDIP
*Contact factory for dice specifications.
___________________Chip Topography
VOUT
SHDN
LBO
VFB
LBI
0.083"
(2.108mm)
V+
GND
LX
0.072"
(1.828mm)
TRANSISTOR COUNT: 221
SUBSTRATE CONNECTED TO V+
12
______________________________________________________________________________________
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages.)
DIM
A
A1
B
C
e
E
H
L
N
E
H
INCHES
MILLIMETERS
MAX
MIN
0.069
0.053
0.010
0.004
0.014
0.019
0.007
0.010
0.050 BSC
0.150
0.157
0.228
0.244
0.016
0.050
MAX
MIN
1.35
1.75
0.10
0.25
0.35
0.49
0.19
0.25
1.27 BSC
3.80
4.00
5.80
6.20
0.40
SOICN .EPS
MAX639/MAX640/MAX653
5V/3.3V/3V/Adjustable, High-Efficiency,
Low IQ, Step-Down DC-DC Converters
1.27
VARIATIONS:
1
INCHES
TOP VIEW
DIM
D
D
D
MIN
0.189
0.337
0.386
MAX
0.197
0.344
0.394
MILLIMETERS
MIN
4.80
8.55
9.80
MAX
5.00
8.75
10.00
N MS012
8
AA
14
AB
16
AC
D
A
B
e
C
0∞-8∞
A1
L
FRONT VIEW
SIDE VIEW
PROPRIETARY INFORMATION
TITLE:
PACKAGE OUTLINE, .150" SOIC
APPROVAL
DOCUMENT CONTROL NO.
21-0041
REV.
B
1
1
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.
13 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2005 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products, Inc.
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