MAX639C [MAXIM]
5V/3.3V/3V/Adjustable, High-Efficiency, Low IQ, Step-Down DC-DC Conver; 5V / 3.3V / 3V /可调，高效率，低IQ ，降压型DC- DC CONVER
| 型号： | MAX639C |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | 5V/3.3V/3V/Adjustable, High-Efficiency, Low IQ, Step-Down DC-DC Conver |
| 文件： | 总13页 (文件大小：773K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-4505; Rev 4; 7/05
5V/3.3V/3V/Adjustable, High-Efficiency,
Low IQ, Step-Down DC-DC Converters
_______________General Description
____________________________Features
♦ High Efficiency for a Wide Range of Load Currents
♦ 10µA Quiescent Current
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.
♦ Output Currents Up to 225mA
♦ Preset or Adjustable Output Voltage:
5.0V (MAX639)
3.3V (MAX640)
3.0V (MAX653)
The MAX639/MAX640/MAX653 input range is 4V to
11.5V, and the devices provide lower preset output volt-
ages 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
♦ Current-Limiting PFM Control Scheme
______________Ordering Information
The MAX639/MAX640/MAX653 have an internal 1A power
MOSFET switch, making them ideal for minimum-compo-
nent, 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.
PART
TEMP RANGE
0°C to +70°C
PIN-PACKAGE
8 Plastic DIP
8 SO
MAX639CPA
MAX639CSA
MAX639C/D
MAX639EPA
MAX639ESA
MAX639MJA
0°C to +70°C
0°C to +70°C
Dice*
-40°C to +85°C
-40°C to +85°C
-55°C to +125°C
8 Plastic DIP
8 SO
________________________Applications
9V Battery to 5V, 3.3V, or 3V Conversion
High-Efficiency Linear Regulator Replacement
Portable Instruments and Handy-Terminals
5V-to-3.3V Converters
8 CERDIP
Ordering Information continued on last page.
*Contact factory for dice specifications.
__________Typical Operating Circuit
__________________Pin Configuration
TOP VIEW
INPUT
5.5V TO 11.5V
OUTPUT
5V
V+
225mA
LX
VOUT
LBO
8
7
6
5
1
2
3
4
SHDN
VFB
MAX639
MAX640
MAX653
MAX639
SHDN
LBI
ON/OFF
VOUT
LBO
LBI
V+
LX
LOW-BATTERY
DETECTOR
OUTPUT
LOW-BATTERY
DETECTOR
INPUT
GND
DIP/SO
VFB
GND
________________________________________________________________ Maxim Integrated Products
1
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.
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
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
Continuous Power Dissipation (T = +70°C)
A
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
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, I
unless otherwise noted.)
= 0mA, T = T
to T
, typical values are at T = +25°C,
MAX A
LOAD
A
MIN
PARAMETER
Supply Voltage
CONDITIONS
MIN
TYP
MAX
11.5
20
UNITS
V
4.0
Supply Current
10
5.00
3.30
3.00
0.5
µA
SHDN = V+, no load
MAX639, V+ = 6.0V to 11.5V, 0mA < I
MAX640, V+ = 4.0V to 11.5V, 0mA < I
MAX653, V+ = 4.0V to 11.5V, 0mA < I
< 100mA
< 100mA
< 100mA
4.80
3.17
2.88
5.20
3.43
3.12
OUT
OUT
OUT
Output Voltage (Note 2)
Dropout Voltage
V
V
I
= 100mA, L = 100µH
OUT
I
I
I
I
I
I
= 100mA, L = 100µH
= 25mA, L = 470µH
= 100mA, L = 100µH
= 25mA, L = 470µH
= 100mA, L = 100µH
= 25mA, L = 470µH
91
OUT
OUT
OUT
OUT
OUT
OUT
MAX639
MAX640
MAX653
MAX639
MAX640
MAX653
MAX639
MAX640
MAX653
94
87
Efficiency
%
µs
µs
91
85
89
V+ = 9V, V
V+ = 6V, V
V+ = 9V, V
V+ = 4V, V
V+ = 9V, V
V+ = 4V, V
V+ = 9V, V
V+ = 6V, V
V+ = 9V, V
V+ = 4V, V
V+ = 9V, V
V+ = 4V, V
= 5V
10.6
14.2
7.5
12.5
16.7
8.8
14.4
19.2
10.1
82.1
9.5
OUT
OUT
OUT
OUT
OUT
OUT
OUT
OUT
OUT
OUT
OUT
OUT
= 3V
= 3.3V
= 3.3V
= 3V
Switch On-Time
Switch Off-Time
60.7
7.1
71.4
8.3
= 3V
42.5
9.0
50.0
11.7
19.5
15.6
15.6
17.2
17.2
57.5
13.5
22.4
17.9
17.9
19.8
19.8
= 5V
= 3V
16.6
13.3
13.3
14.6
14.6
= 3.3V
= 3.3V
= 3V
= 3V
2
_______________________________________________________________________________________
5V/3.3V/3V/Adjustable, High-Efficiency,
Low IQ, Step-Down DC-DC Converters
ELECTRICAL CHARACTERISTICS (continued)
(V+ = 9V for the MAX639, V+ = 5V for the MAX640/MAX653, I
unless otherwise noted.)
= 0mA, T = T
to T
, typical values are at T = +25°C,
MAX A
LOAD
A
MIN
PARAMETER
CONDITIONS
V+ = 9V, T = +25°C, MAX639/MAX640/MAX653
MIN
TYP
MAX
1.5
UNITS
0.8
A
LX Switch On-Resistance
V+ = 6V, T = T
to T
to T
, MAX639
2.5
Ω
A
MIN
MIN
MAX
MAX
V+ = 4V, T = T
, MAX640/MAX653
2.8
A
T
= +25°C
0.003
1.0
A
A
LX Switch Leakage
V+ = 11.5V, V = 0V
LX
µA
T
= T
to T
30.0
15.0
MIN
MAX
VFB Bias Current
VFB = 2V
4.0
50
nA
VFB Dual-Mode Trip Point
mV
MAX6_ _C
1.26
1.24
1.28
1.28
2
1.30
1.32
10
VFB Threshold
LBI Bias Current
LBI Threshold
V
nA
V
MAX6_ _E/M
V
LBI
= 2V
MAX6_ _C
1.26
1.24
0.8
1.28
1.28
2.5
1.30
1.32
MAX6_ _E/M
MAX639
MAX640/MAX653
LBO Sink Current
V
LBO
= 0.4V
mA
0.4
1.2
LBO Leakage Current
LBO Delay
V
= 11.5V
0.001
25
0.1
µA
µs
V
LBO
50mV overdrive
0.80
0.10
1.15
0.20
2.00
0.40
SHDN Threshold
SHDN Pull-Up Current
µA
SHDN = 0V
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, T = +25°C, unless otherwise noted.)
A
EFFICIENCY vs.
OUTPUT CURRENT
EFFICIENCY vs.
OUTPUT CURRENT
EFFICIENCY vs.
OUTPUT CURRENT
100
100
100
L = 470µH
L = 100µH
V+ = 9V
L = 470µH
V+ = 9V
90
80
70
60
90
80
70
60
90
80
70
60
MAX639, V+ = 6V
MAX640, V+ = 4.3V
MAX653, V+ = 4V
MAX639
MAX640
MAX653
MAX639
MAX640
MAX653
50
50
50
1m
10m
1m
10m
10µ
100µ
100m
1m
10m
100m
10µ
100µ
100m
10µ
100µ
1
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
_______________________________________________________________________________________
3
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, T = +25°C, unless otherwise noted.)
A
EFFICIENCY vs.
EFFICIENCY vs.
EFFICIENCY vs.
INPUT VOLTAGE
INPUT VOLTAGE
OUTPUT CURRENT
100
100
95
100
I
= 100mA
L = 470µH
OUT
L = 100µH
I
= 25mA
OUT
90
80
70
60
MAX639
MAX639
95
90
MAX639, V+ = 6V
MAX640, V+ = 4.3V
MAX653, V+ = 4V
90
MAX640
MAX640
85
80
85
80
MAX653
MAX653
50
3
4
5
6
7
8
9
10 11 12
3
4
5
6
7
8
9
10 11 12
1m
10m
100m
10µ
100µ
1
V+ (V)
V+ (V)
OUTPUT CURRENT (A)
MAX639
OUTPUT VOLTAGE RIPPLE vs.
INPUT VOLTAGE
MAXIMUM OUTPUT CURRENT vs.
INPUT VOLTAGE
MAXIMUM OUTPUT CURRENT vs.
INPUT VOLTAGE
75
250
200
150
L = 470µH
L = 100µH
I
= 25mA
OUT
125
100
75
65
55
45
L = 100µH
MAX640
MAX639
MAX640
MAX653
150
100
50
25
0
L = 220µH
MAX653
35
25
MAX639
L = 470µH
3
4
5
6
7
8
9
10 11 12
3
4
5
6
7
8
9
10 11 12
5
6
7
8
9
10
11
12
V+ (V)
V+ (V)
INPUT VOLTAGE (V)
MAX640
MAX653
OUTPUT VOLTAGE RIPPLE vs.
INPUT VOLTAGE
OUTPUT VOLTAGE RIPPLE vs.
INPUT VOLTAGE
150
150
I
= 25mA
I
= 25mA
OUT
LOAD
125
100
75
125
100
75
L = 100µH
L = 100µH
L = 220µH
L = 220µH
50
25
0
50
25
0
L = 470µH
L = 470µH
3
4
5
6
7
8
9
10 11 12
3
4
5
6
7
8
9
10 11 12
V+ (V)
V+ (V)
4
_______________________________________________________________________________________
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, T = +25°C, unless otherwise noted.)
A
MAX639
START-UP TIME vs.
OUTPUT CURRENT
MAX639
START-UP TIME vs.
OUTPUT CURRENT
MAX640/MAX653
START-UP TIME vs.
OUTPUT CURRENT
12
40
30
10
8
MEASURED FROM THE RISING EDGE OF V+
MEASURED FROM THE RISING EDGE
MEASURED FROM THE RISING EDGE
OR SHDN TO (V
= 3.3V)(MAX640) OR
OF V+ OR SHDN TO (V
= 5V).
OF V+ OR SHDN TO (V
= 5.0V)
OUT
OUT
OUT
10
8
(V
= 3.0V)(MAX653). THE START-UP
L = 470µH.
OUT
TIME DIFFERENCE BETWEEN THE
MAX640 AND THE MAX653
IS NEGLIGIBLE.
V+ = 5.5V
V+ = 5.5V
6
V+ = 9.0V
6
20
V+ = 5.0V
V+ = 9.0V
4
4
2
0
V+ = 9.0V
10
0
2
0
V+ = 11.5V
V+ = 11.5V
V+ = 11.5V
25
L = 100µH
0
5
10
15
20
30
0
10 20 30 40 50 60 70 80 90 100
OUTPUT CURRENT (mA)
0
10 20 30 40 50 60 70 80 90 100
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
MAX640/MAX653
START-UP TIME vs.
OUTPUT CURRENT
NO-LOAD SUPPLY CURRENT vs.
INPUT VOLTAGE
70
40
MEASURED FROM THE RISING EDGE OF
V+ OR SHDN TO (V = 3.3V)(MAX640)
OUT
60
50
OR (V
= 3.0V)(MAX653). THE
OUT
MAX639, V
= 5V
OUT
30 START-UP TIME DIFFERENCE BETWEEN
THE MAX640 AND THE MAX653 IS
NEGLIGIBLE.
L = 470µH
20
40
30
20
MAX653, V
= 3V
OUT
V+ = 5.0V
10
V+ = 9.0V
25
10
0
V+ = 11.5V
0
0
5
10
15
20
30
0
1
2
3
4
5
6
7
8
9 10 11 12
OUTPUT CURRENT (mA)
INPUT VOLTAGE (V)
_______________________________________________________________________________________
5
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, T = +25°C, unless otherwise noted.)
A
MAX639
LOAD-TRANSIENT RESPONSE
MAX653
LOAD-TRANSIENT RESPONSE
A
B
A
B
1ms/div
1ms/div
A: I
LOAD,
0mA TO 200mA, 100mA/div
A: I
LOAD,
0mA TO 100mA, 50mA/div
B: V , 100mV/div, AC COUPLED
OUT
B: V , 100mV/div, AC COUPLED
OUT
V
IN
= 9V, V
= 5V
OUT
V
IN
= 5V, V
= 3V
OUT
MAX639
LINE-TRANSIENT RESPONSE
MAX653
LINE-TRANSIENT RESPONSE
A
B
A
B
10ms/div
10ms/div
A: V 6V TO 11.5V, 2V/div
IN,
A: V 4V TO 8V, 2V/div
IN,
B: V , 100mV/div
OUT
B: V , 100mV/div
OUT
V
OUT
= 5V, I
= 100mA
LOAD
V
OUT
= 3V, I
= 100mA
LOAD
6
_______________________________________________________________________________________
5V/3.3V/3V/Adjustable, High-Efficiency,
Low IQ, Step-Down DC-DC Converters
______________________________________________________________Pin Description
PIN
1
NAME
FUNCTION
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.
VOUT
Low-Battery Output. An open-drain N-channel MOSFET sinks current when the voltage at LBI drops
below 1.28V.
2
LBO
3
4
LBI
Low-Battery Input. When the voltage at LBI drops below 1.28V, LBO sinks current.
Ground
GND
Drain of a PMOS power switch that has its source connected to V+. LX drives the external inductor,
which provides current to the load.
5
6
LX
V+
Positive Supply-Voltage Input. Should not exceed 11.5V
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 volt-
age 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 shut-
down mode is not used.
7
8
VFB
SHDN
____________________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:
I
L
L
V
L
V
OUT
C
V+
OUT
(1) Capacitors: For the input and output filter capaci-
tors, 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.
Figure 1. Simplified Step-Down Converter
(3) Inductor: For the highest output current, choose a
100µH inductor with an incremental saturation cur-
rent rating of at least 600mA. To obtain the highest
efficiencies and smallest size, refer to the Inductor
Selection section.
I AT 200mA/div
L
_______________Detailed Description
Figure 1 shows a simplified, step-down DC-DC con-
verter. When the switch is closed, a voltage equal to
0A
0V
(V+ - V
) is applied to the inductor. The current
OUT
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.
V AT 5V/div
L
SWITCH ON
SWITCH ON
SWITCH OFF
SWITCH OFF
Figure 2. Simplified Step-Down Converter Operation
_______________________________________________________________________________________
7
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
When the output dips:
(1) The error comparator switches high.
V+ = 3/2 V
. The inductor current rises more slowly
OUT
(2) The internal oscillator starts (15µs start-up time)
and connects to the gate of the LX output driver.
than it falls because the magnitude of the voltage
applied during t is less than that applied during t
.
OFF
ON
Varying the duty cycle and switching frequency keeps
(3) LX turns on and off according to t
and t
,
OFF
ON
the peak current constant as input voltage varies. The
charging and discharging the inductor, and sup-
plying current to the output (as described above).
MAX639/MAX640/MAX653 control the switch (t
OFF
and
ON
t
) according to the following equations:
When the output voltage recovers:
(1) The comparator switches low.
(2) LX turns off.
Equation (1) t
Equation (2) t
Equation (3) I
= 50µsV / (V+ - V
)
OUT
ON
≥ 50µsV / V
OFF
PEAK
OUT
= 50µsV / L
(3) The oscillator shuts down to save power.
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.
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:
Figure 3 shows the MAX639/MAX640/MAX653 block dia-
gram 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:
R3 = R4 [(V
/ VFB Threshold) - 1]
OUT
where R4 is any resistance in the 10kΩ to 1MΩ range (typ-
ically 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
6
V+
5V, 3.3V OR 3.0V
AT 100mA
SHDN
LX
5
C
33µF
IN
L = 100µH
1N5817
+1.28V
BANDGAP
REFERENCE
VARIABLE
FREQUENCY
AND
DUTY-CYCLE
OSCILLATOR
ERROR
COMPARATOR
VOUT
1
R1
C
OUT
LOW-BATTERY
COMPARATOR
100µF
MODE-SELECT
COMPARATOR
3
2
LBI
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
Low-Battery Detector
Table 1. Component Suppliers
The low-battery detector compares the voltage on the
INDUCTORS — THROUGH HOLE
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 resis-
tors R1 and R2 (Figure 3) as determined by the follow-
ing formula:
PART
NUMBER
SIZE
(inches)
VALUE
(µH)
I
SERIES R
MAX
(A)
(Ω)
0.2
MAXL001* 0.65 x 0.33 dia.
100
100
150
220
330
470
1000
1.75
0.89
0.72
0.58
0.47
0.39
0.27
7300-13**
7300-15**
7300-17**
7300-19**
7300-21**
7300-25**
0.63 x 0.26 dia.
0.63 x 0.26 dia.
0.63 x 0.26 dia.
0.63 x 0.26 dia.
0.63 x 0.26 dia.
0.63 x 0.26 dia.
0.27
0.36
0.45
0.58
0.86
2.00
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.
* Maxim Integrated Products
**Caddell-Burns
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 regu-
lated 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.
258 East Second Street
Mineola, NY 11501-3508
(516) 746-2310
INDUCTORS — SURFACE MOUNT
PART
NUMBER
SIZE
(mm)
VALUE
(µH)
I
SERIES R
MAX
(A)
(Ω)
CD54
5.2 x 5.8 x 4.5
5.2 x 5.8 x 4.5
7.1 x 7.7 x 4.5
7.1 x 7.7 x 4.5
9.2 x 10.0 x 5.0
9.2 x 10.0 x 5.0
100
220
100
220
100
220
0.52
0.35
0.52
0.35
0.80
0.54
0.63
1.50
0.51
0.98
0.35
0.69
CD54
CDR74
CDR74
CDR105
CDR105
__________Applications Information
Sumida Electric (USA)
637 East Golf Road
Arlington Heights, IL 60005
(708) 956-0666
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 exces-
sive 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-cur-
rent 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.
CAPACITORS — LOW ESR
PART
SIZE
VALUE
(µF)
ESR
(Ω)
0.2
0.2
0.2
V
MAX
(V)
NUMBER
(inches)
MAXC001* 0.49 x 0.394 dia.
267 Series** D SM packages
267 Series** E SM packages
150
47
35
10
100
6.3
* Maxim Integrated Products
**Matsuo Electronics
2134 Main Street
Huntington Beach, CA 92648
(714) 969-2491
Recall that the inductance value determines I
for all
PEAK
input voltages (Equation 3). If there are no resistive loss-
es and the diode is ideal, the maximum average current
that can be drawn from the MAX639/MAX640/MAX653
SCHOTTKY DIODES — SURFACE MOUNT
PART
NUMBER
V
(V)
I
F
MAX
(A)
SIZE
SOT89
SOT89
will be one-half I . With the real losses in the switch,
PEAK
SE014
0.55
1
inductor, and diode taken into account, the real maxi-
mum output current typically varies from 90% to 50% of
the ideal. The following steps describe a conservative
way to pick an appropriate inductor.
SE024
0.55
0.95
Collmer Semiconductor
14368 Proton Road
Dallas, TX 75244
(214) 233-1589
Step 1: Decide on the maximum required output
NOTE: This list does not constitute an endorsement by Maxim
current, in amperes: I
.
OUTMAX
Integrated Products and is not intended to be a comprehensive
list of all manufacturers of these components.
Step 2:
I
= 4 x I
.
PEAK
OUTMAX
_______________________________________________________________________________________
9
5V/3.3V/3V/Adjustable, High-Efficiency,
Low IQ, Step-Down DC-DC Converters
INPUT
+4.0V TO +11.5V
L = 100µH
OUTPUT
5
6
8
V+
LX
C
OUT
1N5817
SHDN
100µF
MAX639
MAX640
MAX653
C
IN
1
7
MAX639
MAX640
MAX653
R3
R4
VOUT
VFB
100µF
GND
4
LBI
3
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 / I
. L will be in µH. Do not use an
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.
PEAK
inductor of less than 100µH.
Step 4: Make sure that I
does not exceed 0.6A or
PEAK
the inductor’s maximum current rating,
whichever is lower.
With low-cost aluminum electrolytic capacitors, the
ESR-induced ripple can be larger than that caused by
the charge variation. Consequently, high-quality alu-
minum-electrolytic or tantalum filter capacitors will mini-
mize output ripple. Best results at reasonable cost are
typically achieved with an aluminum-electrolytic capac-
itor in the 100µF range, in parallel with a 0.1µF ceramic
capacitor (Table 1).
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 induc-
tor has low series resistance. Inductor and series
switch resistance form an LR circuit during t . If the
ON
ON
L/R time constant is less than the oscillator t , the
inductor’s peak current will fall short of the desired
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 high-
power circuits, or for maximum efficiency at low power.
1N5817 equivalent diodes are also available in surface-
mount packages (Table 1). Although the 1N4001 and
other general-purpose rectifiers are rated for high cur-
rents, they are unacceptable because their slow turn-
off times result in excessive losses.
I
.
PEAK
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 cur-
rents in the 600mA range do not need to be very large.
They are about the size of a 1W resistor, with surface-
mount versions less than 5mm in diameter. Table 1 lists
suppliers of inductors suitable for use with the
MAX639/MAX640/MAX653.
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 resis-
tance (ESR).
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+
The amount of charge delivered in each oscillator pulse
is determined by the inductor value and input voltage.
to V
, leakage current may be supplied to the output
OUT
10 ______________________________________________________________________________________
5V/3.3V/3V/Adjustable, High-Efficiency,
Low IQ, Step-Down DC-DC Converters
160
T
= +25°C
A
6
8
140
C
L = 100µH
MAX639
IN
V
IN
V+
L = 100µH
SHDN
100µF
5
1
120
100
LX
1N5817
MAX639
MAX640
MAX653
80
60
40
VOUT
C
OUT
100µF
20
0
-5V
-3.3V
OR -3V
GND
4
VFB
7
0
1
2
3
4
5
V+ (V)
Figure 6. Inverting Configuration
Figure 7. Maximum Current Capability of Figure 6 Circuit
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
87.0
86.5
86.0
build up on the output capacitor, making V
rise above
OUT
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.
85.5
T
V
= +25°C
A
= -5V
OUT
85.0
L = 470µH
= 10mA
Layout
Several of the external components in a MAX639/
MAX640/MAX653 circuit experience peak currents up
to 600mA. Wherever one of these components con-
nects 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 capac-
itor’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 possi-
ble, preferably at the same point. Figure 5 shows a
suggested through-hole printed circuit layout that mini-
mizes ground bounce.
I
OUT
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 V
Other negative voltages can be generated by placing a
voltage divider across C and connecting the tap
point to VFB in the same manner as the normal step-
down configuration.
.
OUT
OUT
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 batter-
Inverter Configuration
ies. Connect the V ground point to your system’s input,
IN
and connect the output to your system’s ground input.
This configuration has the added advantage of reduced
Figure 6 shows the MAX639/MAX640/MAX653 in a
floating ground configuration. By tying what would nor-
mally be the output to the supply-voltage ground, the
IC’s GND pin is forced to a regulated -5V (MAX639),
on resistance, since the IC’s internal power FET has V
+
IN
V
of gate drive (Figures 7 and 8).
OUT
______________________________________________________________________________________ 11
5V/3.3V/3V/Adjustable, High-Efficiency,
Low IQ, Step-Down DC-DC Converters
_Ordering Information (continued)
___________________Chip Topography
PART
TEMP RANGE
0°C to +70°C
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
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
PIN-PACKAGE
8 Plastic DIP
8 SO
SHDN
VOUT
MAX640CPA
MAX640CSA
MAX640C/D
MAX640EPA
MAX640ESA
MAX640MJA
MAX653CPA
MAX653CSA
MAX653C/D
MAX653EPA
MAX653ESA
MAX653MJA
LBO
VFB
Dice*
8 Plastic DIP
8 SO
8 CERDIP
8 Plastic DIP
8 SO
0.083"
(2.108mm)
V+
LBI
Dice*
8 Plastic DIP
8 SO
8 CERDIP
GND
LX
*Contact factory for dice specifications.
0.072"
(1.828mm)
TRANSISTOR COUNT: 221
SUBSTRATE CONNECTED TO V+
12 ______________________________________________________________________________________
5V/3.3V/3V/Adjustable, High-Efficiency,
Low IQ, Step-Down DC-DC Converters
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.)
INCHES
MILLIMETERS
DIM
A
MIN
MAX
0.069
0.010
0.019
0.010
MIN
1.35
0.10
0.35
0.19
MAX
1.75
0.25
0.49
0.25
0.053
0.004
0.014
0.007
N
A1
B
C
e
0.050 BSC
1.27 BSC
E
0.150
0.228
0.016
0.157
0.244
0.050
3.80
5.80
0.40
4.00
6.20
1.27
E
H
H
L
VARIATIONS:
INCHES
1
MILLIMETERS
DIM
D
MIN
MAX
0.197
0.344
0.394
MIN
4.80
8.55
9.80
MAX
5.00
N
8
MS012
AA
TOP VIEW
0.189
0.337
0.386
D
8.75 14
10.00 16
AB
D
AC
D
C
A
B
0∞-8∞
e
A1
L
FRONT VIEW
SIDE VIEW
PROPRIETARY INFORMATION
TITLE:
PACKAGE OUTLINE, .150" SOIC
APPROVAL
DOCUMENT CONTROL NO.
REV.
1
21-0041
B
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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