_______________General Description
The MAX649/MAX651/MAX652 BiCMOS, step-down DC-
DC switching controllers provide high efficiency over
three decades of load current. A unique, current-limited
pulse-frequency-modulated (PFM) control scheme gives
these devices the benefits of pulse-width-modulation
(PWM) converters (high efficiency at heavy loads), while
using only 100µA of supply current (vs. 2mA to 10mA for
PWM converters). The result is high efficiency over loads
ranging from 10mA to more than 2.5A.
These devices use miniature external components.
Their high switching frequency (up to 300kHz) allows
for less than 9mm diameter surface-mount inductors.
The MAX649/MAX651/MAX652 have dropout voltages
less than 1V and accept input voltages up to 16.5V.
Output voltages are preset at 5V (MAX649), 3.3V
(MAX651), and 3V (MAX652). These controllers can
also be adjusted to any voltage from 1.5V to the input
voltage by using two resistors.
These step-down controllers drive external P-channel
MOSFETs at loads greater than 10W. If less power is
required, use the MAX639/MAX640/MAX653 step-down
converters with on-chip FETs, which allow up to a
225mA load current.
________________________Applications
5V-to-3.3V Green PC Applications
High-Efficiency Step-Down Regulation
Minimum-Component DC-DC Converters
Battery-Powered Applications
____________________________Features
o
More than 90% Efficiency (10mA to 1.5A Loads)
o
More than 12.5W Output Power
o
100µA Max Quiescent Supply Current
o
5µA Max Shutdown Supply Current
o
Less than 1.0V Dropout Voltage
o
16.5V Max Input Voltage
o
5V (MAX649), 3.3V (MAX651), 3V (MAX652),
or Adjustable Output Voltage
o
Current-Limited Control Scheme
o
Up to 300kHz Switching Frequency
______________Ordering Information
Ordering Information continued at end of data sheet.
* Dice are tested at T
A
= +25°C.
**Contact factory for availability and processing to MIL-STD-883.
MAX649/MAX651/MAX652
5V/3.3V/3V or Adjustable, High-Efficiency,
Low I
Q
, Step-Down DC-DC Controllers
________________________________________________________________
Maxim Integrated Products
1
1
2
3
4
8
7
6
5
GND
EXT
CS
V+
REF
SHDN
FB
OUT
DIP/SO
TOP VIEW
MAX649
MAX651
MAX652
__________________Pin Configuration
__________Typical Operating Circuit
19-0225; Rev 3; 9/97
PART
TEMP. RANGE
PIN-PACKAGE
MAX649
CPA
0°C to +70°C
8 Plastic DIP
MAX649CSA
0°C to +70°C
8 SO
MAX649C/D
0°C to +70°C
Dice*
MAX649EPA
-40°C to +85°C
8 Plastic DIP
MAX649ESA
-40°C to +85°C
8 SO
MAX649MJA
-55°C to +125°C
8 CERDIP**
MAX651
V+
CS
SHDN
FB
GND
ON/OFF
P
EXT
REF
OUT
OUTPUT
3.3V
INPUT
4V TO 16.5V
EVALUATION KIT
AVAILABLE
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.
For small orders, phone 1-800-835-8769.
MAX649/MAX651/MAX652
5V/3.3V/3V or Adjustable, High-Efficiency,
Low I
Q
, Step-Down DC-DC Controllers
2
_______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(V+ = 5V, T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25°C.)
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.
PARAMETER
SYMBOL
MIN
TYP
MAX
UNITS
1.455
1.5
1.545
1.4625
1.5
1.5375
FB Trip Point
1.470
1.5
1.530
V
I
Q
2
5
FB Input Current
I
FB
±50
nA
±70
±90
Output Voltage
V
OUT
4.80
5.0
5.20
V
Supply Current
V+ Input Voltage Range
V+
4.0
16.5
V
80
100
µA
4
3.17
3.3
3.43
2.88
3.0
3.12
Reference Voltage
V
REF
1.470
1.5
1.530
V
1.4625
1.5
1.5375
1.455
1.5
1.545
REF Load Regulation
4
10
mV
4
15
CONDITIONS
MAX649M, MAX65_M
Circuit of
Figure 1
MAX649E, MAX65_E
MAX649C, MAX65_C
V+ = 10V, SHDN
≥
1.6V (shutdown)
MAX649C, MAX65_C
MAX649E, MAX65_E
MAX649C, MAX65_C, I
REF
= 0
MAX649E, MAX65_E, I
REF
= 0
MAX649M, MAX65_M
MAX649M, MAX65_M, I
REF
= 0
V+ = 16.5V, SHDN
≤
0.4V (operating, switch off)
V+ = 16.5V, SHDN
≥
1.6V (shutdown)
Supply Voltage, V+ to GND.......................................-0.3V, +17V
REF, SHDN, FB, CS, EXT, OUT .......................-0.3V, (V+ + 0.3V)
Continuous Power Dissipation (T
A
= +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
MAX649C_A, MAX65_C_A ..................................0°C to +70°C
MAX649E_A, MAX65_E_A ................................-40°C to +85°C
MAX649MJA, MAX65_MJA ............................-55°C to +125°C
Storage Temperature Range .............................-65°C to +160°C
Lead Temperature (soldering, 10sec) .............................+300°C
MAX649, V+ = 6V to 16.5V
MAX651, V+ = 4V to 16.5V
MAX652, V+ = 4V to 16.5V
MAX649C/E, MAX65_C/E
MAX649M, MAX65_M
0
≤
I
REF
≤
100µA,
sourcing only
4V
≤
V+
≤
16.5V
REF Line Regulation
40
100
µV/V
2.6
mV/V
1.7
1.9
Output Voltage
Line Regulation
Circuit of
Figure 1
MAX649, 6V
≤
V+
≤
16V,
I
LOAD
= 1A
MAX651, 4.5V
≤
V+
≤
16V,
I
LOAD
= 1A
MAX652, 4V
≤
V+
≤
16V,
I
LOAD
= 1A
MAX649/MAX651/MAX652
5V/3.3V/3V or Adjustable, High-Efficiency,
Low I
Q
, Step-Down DC-DC Controllers
_______________________________________________________________________________________
3
ELECTRICAL CHARACTERISTICS (continued)
(V+ = 5V, T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
SYMBOL
MIN
TYP
MAX
-45
UNITS
V+ = 16.5V, SHDN = 0V or V+
-45
SHDN Input Current
1
µA
Output Voltage
Load Regulation
-47
mV/A
CONDITIONS
Circuit of
Figure 1
MAX649, 0
≤
I
LOAD
≤
1.5A,
V
IN
= 10V
MAX651, 0
≤
I
LOAD
≤
1.5A,
V
IN
= 5V
MAX652, 0
≤
I
LOAD
≤
1.5A,
V
IN
= 5V
MAX649, V+ = 10V,
I
LOAD
= 1A
MAX651, V+ = 5V,
I
LOAD
= 1A
89
MAX652, V+ = 5V,
I
LOAD
= 1A
88
Efficiency
92
%
Circuit of
Figure 1
4V
≤
V+
≤
16.5V
SHDN Input Voltage High
1.6
V
V
IH
4V
≤
V+
≤
16.5V
0.4
V
V
IL
SHDN Input Voltage Low
4V
≤
V+
≤
16.5V
CS Input Current
±1
µA
V+ = 12V
12
16
20
µs
t
ON
(max)
Switch Maximum
On-Time
C
EXT
= 0.001µF, V+ = 12V
EXT Rise Time
50
ns
C
EXT
= 0.001µF, V+ = 12V
EXT Fall Time
50
ns
V+ = 12V
Switch Minimum
Off-Time
1.8
2.3
2.8
µs
t
OFF
(min)
MAX649C/E, MAX65_C/E
Current-Limit Trip
Level (V+ to CS)
180
210
240
mV
V
CS
MAX649M, MAX65_M
160
210
260
4V
≤
V+
≤
16.5V
MAX649/MAX651/MAX652
5V/3.3V/3V or Adjustable, High-Efficiency,
Low I
Q
, Step-Down DC-DC Controllers
4
_______________________________________________________________________________________
__________________________________________Typical Operating Characteristics
(T
A
= +25°C, unless otherwise noted.)
80
66
SUPPLY CURRENT vs. TEMPERATURE
68
78
I+ (mA)
76
74
-60
-20
60
140
MAX649-A01
TEMPERATURE (°C)
20
100
-40
0
80
40
120
72
70
V+ = 10V
V+ = 16.5V
V+ = 4V
4.0
0
SHUTDOWN CURRENT
vs. TEMPERATURE
0.5
3.5
I+ (mA)
3.0
2.5
-60
-20
60
140
MAX649-A02
TEMPERATURE (°C)
20
100
-40
0
80
40
120
2.0
1.5
V+ = 8V
V+ = 16.5V
V+ = 4V
1.0
2500
0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 1415
MAX649 MAXIMUM LOAD CURRENT
vs. SUPPLY VOLTAGE
500
2000
MAX649-A03
INPUT VOLTAGE (V)
MAXIMUM LOAD CURRENT (mA)
1500
1000
V
OUT
= 5V
CIRCUIT OF FIGURE 1
100
90
0
100
µ
1m
10m
100m
1
MAX649
EFFICIENCY vs. LOAD CURRENT
20
MAX649-A04
LOAD CURRENT (A)
EFFICIENCY (%)
40
60
80
70
50
30
10
V
IN
= 6V
V
IN
= 8V
V
IN
= 10V
V
IN
= 12V
V
IN
= 15V
V
OUT
= 5V
TOP TO BOTTOM:
17
15
SWITCH ON-TIME
vs. TEMPERATURE
t
ON
(ms)
-60 -40 -20
60
MAX649-A07
TEMPERATURE (°C)
0
20
40
80 100 120
16
V+ = 5V
100
90
0
100
µ
1m
10m
100m
1
MAX651
EFFICIENCY vs. LOAD CURRENT
20
MAX649-A05
LOAD CURRENT (A)
EFFICIENCY (%)
40
60
80
70
50
30
10
V
IN
= 4.3V
V
IN
= 5V
V
IN
= 8V
V
IN
= 10V
V
IN
= 12V
V
IN
= 15V
V
OUT
= 3.3V
TOP TO BOTTOM:
100
90
0
100
µ
1m
10m
100m
1
MAX652
EFFICIENCY vs. LOAD CURRENT
20
MAX649-A06
LOAD CURRENT (A)
EFFICIENCY (%)
40
60
80
70
50
30
10
V
IN
= 4.3V
V
IN
= 5V
V
IN
= 8V
V
IN
= 10V
V
IN
= 12V
V
IN
= 15V
V
OUT
= 3V
TOP TO BOTTOM:
2.5
1.5
SWITCH OFF-TIME
vs. TEMPERATURE
t
OFF
(ms)
MAX649-A08
TEMPERATURE (°C)
2.0
V+ = 5V
-60 -40 -20
60
0
20
40
80 100 120
8.0
6.0
SWITCH ON-TIME/OFF-TIME RATIO
vs. TEMPERATURE
6.4
7.6
t
ON
/t
OFF
RATIO
7.2
6.8
6.2
6.6
7.8
7.4
7.0
V+ = 5V
-60
-20
60
140
MAX649-A9
TEMPERATURE (°C)
20
100
-40
0
80
40
120
MAX649/MAX651/MAX652
5V/3.3V/3V or Adjustable, High-Efficiency,
Low I
Q
, Step-Down DC-DC Controllers
_______________________________________________________________________________________
5
130
20
EXT RISE AND FALL TIMES
vs. TEMPERATURE (1nF)
120
t
RISE
&
t
FALL
(ns)
110
90
-60
-20
60
140
MAX649-A10
TEMPERATURE (°C)
20
100
-40
0
80
40
120
V+ = 5V, t
RISE
100
80
70
60
40
50
30
V+ = 5V, t
FALL
V+ = 12V, t
RISE
V+ = 12V, t
FALL
C
EXT
= 1nF
500
50
EXT RISE AND FALL TIMES
vs. TEMPERATURE (5nF)
450
t
RISE
&
t
FALL
(ns)
400
350
-60
-20
60
140
MAX649-A11
TEMPERATURE (°C)
20
100
-40
0
80
40
120
V+ = 5V, t
RISE
300
250
150
200
100
V+ = 5V, t
FALL
V+ = 12V, t
RISE
C
EXT
= 5nF
V+ = 12V, t
FALL
1000
0
0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
DROPOUT VOLTAGE
vs. LOAD CURRENT
200
300
100
800
900
MAX649-A12
LOAD CURRENT (A)
DROPOUT VOLTAGE (mV)
600
500
700
400
MAX649, V
OUT
= 5V
MAX652, V
OUT
= 3V
MAX651, V
OUT
= 3.3V
1100
600
DROPOUT VOLTAGE
vs. TEMPERATURE
700
1000
DROPOUT VOLTAGE (mV)
900
800
MAX651
-60
-20
60
140
MAX649-A13
TEMPERATURE (°C)
20
100
-40
0
80
40
120
I
LOAD
= 1A
CIRCUIT OF FIGURE 1
MAX649
MAX652
250
0
REFERENCE OUTPUT RESISTANCE
vs. TEMPERATURE
50
200
REFRENCE OUTPUT RESISTANCE (
Ω
)
150
100
-60
-20
60
140
MAX649-A16
TEMPERATURE (°C)
20
100
-40
0
80
40
120
I
REF
= 10
µ
A
I
REF
= 50
µ
A
I
REF
= 100
µ
A
235
185
CS TRIP LEVEL
vs. TEMPERATURE
195
225
CS TRIP LEVEL (mV)
215
205
-60
-20
60
140
MAX649-A14
TEMPERATURE (°C)
20
100
-40
0
80
40
120
190
200
230
220
210
1.506
1.492
REFERENCE OUTPUT VOLTAGE
vs. TEMPERATURE
1.494
1.504
REFRENCE OUTPUT (V)
1.502
1.500
-60
-20
60
140
MAX649-A15
TEMPERATURE (°C)
20
100
-40
0
80
40
120
1.498
1.496
____________________________Typical Operating Characteristics (continued)
(T
A
= +25°C, unless otherwise noted.)
MAX649/MAX651/MAX652
5V/3.3V/3V or Adjustable, High-Efficiency,
Low I
Q
, Step-Down DC-DC Controllers
6
_______________________________________________________________________________________
MAX649
LINE-TRANSIENT RESPONSE
250
µ
s/div
A
B
I
LOAD
= 1A
A: INPUT VOLTAGE (7V & 12V), 5V/div
B: 5V OUT, AC COUPLED, 100mV/div
_____________________________Typical Operating Characteristics (continued)
MAX649
LOAD-TRANSIENT RESPONSE
250
µ
s/div
A
B
A: LOAD CURRENT (100mA & 1A), 500mA/div
B: 5V OUTPUT VOLTAGE, AC COUPLED, 50mV/div
______________________________________________________________Pin Description
Positive power-supply input
V+
5
CS
6
Gate drive for external P-channel MOSFET. EXT swings between V+ and GND.
EXT
7
Ground
GND
8
1.5V reference output that can source 100µA. Bypass with 0.1µF.
REF
4
SHDN
3
PIN
FB
2
OUT
1
FUNCTION
NAME
Sense input for fixed 5V, 3.3V, or 3V output operation. OUT is internally connected to the on-chip voltage divider.
Although it is connected to the output of the circuit, the OUT pin does not supply current.
Feedback input. Connect to GND for fixed-output operation. Connect a resistor divider between OUT, FB,
and GND for adjustable-output operation. See
Setting the Output Voltage section.
Active-high TTL/CMOS logic-level input. Part is placed in shutdown when SHDN is driven high. In shutdown mode,
the reference and the external MOSFET are turned off, and OUT = 0V. Connect to GND for normal operation.
Current-sense input. Connect current-sense resistor between V+ and CS. When the voltage across the
resistor equals the current-limit trip level, the external MOSFET is turned off.
MAX649
SHUTDOWN RESPONSE TIME
1ms/div
A
B
I
LOAD
= 1A
A: SHDN INPUT VOLTAGE (0V & 5V), 2V/div
B: 5V OUTPUT VOLTAGE, 2V/div
MAX649/MAX651/MAX652
5V/3.3V/3V or Adjustable, High-Efficiency,
Low I
Q
, Step-Down DC-DC Controllers
_______________________________________________________________________________________
7
_______________Detailed Description
The MAX649/MAX651/MAX652 are BiCMOS, step-
down, switch-mode power-supply controllers that pro-
vide fixed outputs of 5V, 3.3V, and 3V, respectively.
Their unique control scheme combines the advantages
of pulse-frequency-modulation (low supply current)
and pulse-width-modulation (high efficiency at high
loads). An external P-channel power MOSFET allows
peak currents in excess of 3A, increasing the output
current capability over previous PFM devices. Figure 2
is the block diagram.
The MAX649/MAX651/MAX652 offer three main
improvements over prior solutions:
1) The converters operate with tiny (less than 9mm
diameter) surface-mount inductors, due to their
300kHz switching frequency.
2) The current-limited PFM control scheme allows
greater than 90% efficiencies over a wide range of
load currents (1.0mA to 1.5A).
3) The maximum supply current is only 100µA.
PFM Control Scheme
The MAX649/MAX651/MAX652 use a proprietary, cur-
rent-limited PFM control scheme. As with traditional
PFM converters, the external power MOSFET is turned
on when the voltage comparator senses that the output
is out of regulation. However, unlike traditional PFM
converters, switching is accomplished through the
combination of a peak current limit and a pair of one-
shots that set the maximum switch on-time (16µs) and
minimum switch off-time (2.3µs). Once off, the minimum
off-time one-shot holds the switch off for 2.3µs. After
this minimum time, the switch either 1) stays off if the
output is in regulation, or 2) turns on again if the output
is out of regulation.
The MAX649/MAX651/MAX652 also limit the peak induc-
tor current, which allows them to run in continuous-con-
duction mode and maintain high efficiency with heavy loads
(Figure 3a). This current-limiting feature is a key compo-
nent of the control circuitry. Once turned on, the switch
stays on until either 1) the maximum on-time one-shot turns
it off (16µs later), or 2) the current limit is reached.
To increase light-load efficiency, the current limit for
the first two pulses is set to half the peak current limit.
If those pulses bring the output voltage into regulation,
the voltage comparator holds the MOSFET off and the
current limit remains at half its peak. If the output vol-
tage is still out of regulation after two pulses, the
current limit for the next pulse is raised to its peak (Figure
3b). Calculate the peak current limit by dividing the
Current-Limit Trip Level (see
Electrical Characteristics)
by the value of the current-sense resistor.
Shutdown Mode
When SHDN is high, the MAX649/MAX651/MAX652 enter
shutdown mode. In this mode, the internal biasing circuit-
ry is turned off (including the reference) and the supply
current drops to less than 5µA. EXT goes high, turning off
the external MOSFET. SHDN is a TTL/CMOS logic-level
input. Connect SHDN to GND for normal operation.
Quiescent Current
In normal operation, the quiescent current is less than
100µA. However, this current is measured by forcing
the external transistor switch off. In an actual applica-
tion, even with no load, additional current is drawn to
supply external feedback resistors (if used) and the
diode and capacitor leakage currents. In the circuit of
Figure 1, with V+ at 5V and V
OUT
at 3.3V, the typical
quiescent current is 90µA.
EXT Drive Voltage Range
EXT swings from V+ to GND and provides the drive out-
put for an external P-channel power MOSFET.
Modes of Operation
When delivering high output currents, the MAX649/
MAX651/MAX652 operate in continuous-conduction
mode (CCM). In this mode, current always flows in the
MAX649
MAX651
MAX652
V+
CS
FB
GND
5
6
2
8
3
V
IN
C2
330
µ
F
7
1
EXT
OUT
SHDN
4
C3
0.1
µ
F
C4
0.1
µ
F
C1
100
µ
F
R1
0.1
Ω
D1
NSQ03A02L
L1
22
µ