Rainbow Electronics MAX1655 User Manual

19-0305; Rev 2; 9/95

Low-Dropout, Step-Down DC-DC Controllers

5V/3.3V or Adjustable, High-Efficiency,

_______________General Description

The MAX1649/MAX1651 BiCMOS, step-down, DC-DC
switching controllers provide high efficiency over loads
ranging from 1mA to more than 2.5A. A unique, current­limited 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). Dropout performance down
to 300mV is provided by a high switch duty cycle (96.5%)
and a low current-sense threshold (110mV).

A high switching frequency (up to 300kHz) allows these
devices to use miniature external components.

The MAX1649/MAX1651 have dropout voltages less
than 0.3V at 500mA and accept input voltages up to
16V. Output voltages are preset at 5V (MAX1649), or

3.3V (MAX1651). They 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 12.5W. 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

PDAs
High-Efficiency Step-Down Regulation
5V-to-3.3V Green PC Applications
Battery-Powered Applications

____________________________Features

♦ More than 90% Efficiency (10mA to 1.5A Loads)
♦ More than 12.5W Output Power
♦ Less than 0.3V Dropout Voltage at 500mA
♦ 100µA Max Quiescent Supply Current
♦ 5µA Max Shutdown Supply Current
♦ 16V Max Input Voltage
♦ 5V (MAX1649), 3.3V (MAX1651), or Adjustable

Output Voltage

♦ Current-Limited Control Scheme
♦ Up to 300kHz Switching Frequency
♦ Up to 96.5% Duty Cycle

______________Ordering Information

PART TEMP. RANGE PIN-PACKAGE

MAX1649CPA

MAX1649CSA 0°C to +70°C 8 SO
MAX1649C/D 0°C to +70°C Dice*
MAX1649EPA -40°C to +85°C 8 Plastic DIP
MAX1649ESA -40°C to +85°C 8 SO
MAX1651CPA
MAX1651CSA 0°C to +70°C 8 SO
MAX1651C/D 0°C to +70°C Dice*
MAX1651EPA -40°C to +85°C 8 Plastic DIP
MAX1651ESA -40°C to +85°C 8 SO

* Dice are tested at TA= +25°C.

0°C to +70°C 8 Plastic DIP

0°C to +70°C 8 Plastic DIP

MAX1649/MAX1651

__________Typical Operating Circuit

INPUT

3.6V TO 16V

V+

ON/OFF

REF

MAX1651

FB GND

CSSHDN

EXT

OUT

________________________________________________________________

P

OUTPUT

3.3V

__________________Pin Configuration

TOP VIEW

OUT

1

FB

2

SHDN

REF

MAX1649

3

MAX1651

4

DIP/SO

Maxim Integrated Products

Call toll free 1-800-998-8800 for free samples or literature.

8

GND
EXT

7

CS

6
5

V+

1

5V/3.3V or Adjustable, High-Efficiency,
Low-Dropout, Step-Down DC-DC Controllers

ABSOLUTE MAXIMUM RATINGS

Supply Voltage, V+ to GND.......................................-0.3V, +17V

REF, SHDN, FB, CS, EXT, OUT.......................-0.3V, (V+ + 0.3V)

Continuous Power Dissipation (T

Plastic DIP (derate 9.09mW/°C above +70°C) .............727mW

SO (derate 5.88mW/°C above +70°C)..........................471mW

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.

= +70°C)

A

ELECTRICAL CHARACTERISTICS

(V+ = 5V, TA= T

PARAMETER SYMBOL MIN TYP MAX UNITS

V+ Input Voltage Range V+ 3.0 16 V

Supply Current

MAX1649/MAX1651

FB Trip Point

FB Input Current I

Output Voltage V

Reference Voltage V
REF Load Regulation mV410

Output Voltage
Line Regulation

Output Voltage
Load Regulation

Efficiency

SHDN Input Current V+ = 16V, SHDN = 0V or V+ 1 µA
SHDN Input Voltage High V
SHDN Input Voltage Low V

MIN

to T

, unless otherwise noted. Typical values are at TA= +25°C.)

MAX

CONDITIONS

V

< V+

OUT

V+ = 16V, SHDN ≤ 0.4V (operating, switch off)
V+ = 16V, SHDN ≥ 1.6V (shutdown)

I+

V+ = 10V, SHDN ≥ 1.6V (shutdown)
MAX1649C, MAX1651C
MAX1649E, MAX1651E
MAX1649C, MAX1651C

FB

MAX1649E, MAX1651E
Circuit of

OUT

Figure 1
MAX1649C, MAX1651C, I

REF

MAX1649E, MAX1651E, I
0µA ≤ I
3V ≤ V+ ≤ 16VREF Line Regulation 40 100 µV/V

Circuit of
Figure 1

Circuit of
Figure 1

Circuit of
Figure 1

3V ≤ V+ ≤ 16V 1.6 V

IH

3V ≤ V+ ≤ 16V 0.4 V

IL

≤ 100µA, sourcing only

REF

Operating Temperature Ranges

MAX1649C_A, MAX1651C_A ..............................0°C to +70°C

MAX1649E_A, MAX1651E_A............................-40°C to +85°C

Storage Temperature Range.............................-65°C to +160°C

Lead Temperature (soldering, 10sec).............................+300°C

78 100

2
15

1.470 1.5 1.530

1.4625 1.5 1.5375
±50
±70

MAX1649, V+ = 5.5V to 16V
MAX1651, V+ = 3.6V to 16V

= 0µA

REF

= 0µA

REF

MAX1649, 5.5V ≤ V+ ≤ 16V,
I

= 1A

LOAD

MAX1651, 3.6V ≤ V+ ≤ 16V,
I

= 1A

LOAD

MAX1649, 0A ≤ I
VIN= 10V

MAX1651, 0A ≤ I
VIN= 5V

MAX1649, V+ = 10V,
I

= 1A

LOAD

MAX1651, V+ = 5V,
I

= 1A

LOAD

LOAD

LOAD

≤ 1.5A,

≤ 1.5A,

4.80 5.0 5.20

3.17 3.3 3.43

1.470 1.5 1.530

1.4625 1.5 1.5375

2.6

1.7

-47

-45

90

90

µA

V

nA

V

V

mV/V

mV/A

%

2 _______________________________________________________________________________________

5V/3.3V or Adjustable, High-Efficiency,

Low-Dropout, Step-Down DC-DC Controllers

ELECTRICAL CHARACTERISTICS (continued)

(V+ = 5V, TA= T

PARAMETER

Current-Limit Trip Level
(V+ to CS)

Maximum Duty Cycle 95 96.5 %

MIN

to T

, unless otherwise noted. Typical values are at TA= +25°C.)

MAX

SYMBOL MIN TYP MAX UNITSCONDITIONS

3V ≤ V+ ≤ 16V 80 110 140

CS

3V ≤ V+ ≤ 16VCS Input Current ±1 µA
V+ = 12VSwitch Maximum On-Time 24 32 40 µstON(max)
V+ = 12VSwitch Minimum Off-Time 0.8 1.1 1.8 µst

(min)

OFF

C

= 0.001µF, V+ = 12VEXT Rise Time 25 ns

EXT

C

= 0.001µF, V+ = 12VEXT Fall Time 25 ns

EXT

t

ON

OFF

x 100%

tON+ t

mVV

__________________________________________Typical Operating Characteristics

(TA = +25°C, unless otherwise noted.)

SUPPLY CURRENT vs. TEMPERATURE

80

78

76

74

I+ (µA)

72

70

68

66

-60 -20 60 140

20 100-40 0 8040 120

TEMPERATURE (°C)

V+ = 16V

V+ = 10V

V+ = 4V

MAX1649-TOC06

SHUTDOWN CURRENT 

4.0

3.5

3.0

2.5

2.0

I+ (µA)

1.5

1.0

0.5
0

vs. TEMPERATURE

V+ = 16V

V+ = 8V

V+ = 4V

-60 -20 60 140

20 100-40 0 8040 120

TEMPERATURE (°C)

MAX1649-TOC05

(ns)

FALL

& t

RISE

t

EXT RISE AND FALL TIMES

60
55

50
45

40
35

30
25
20
15

vs. TEMPERATURE (1nF)

C

= 1nF

EXT

V+ = 5V, t

RISE

V+ = 5V, t

FALL

V+ = 15V, t

RISE

V+ = 15V, t

FALL

-60 -20 60 140

20 100-40 0 8040 120

TEMPERATURE (°C)

MAX1649/MAX1651

MAX1649/51-01

EXT RISE AND FALL TIMES

vs. TEMPERATURE (5nF)

240

C

= 5nF

EXT

220
200
180

V+ = 5V, t

(ns)

160

FALL

140

& t

120

RISE

t

100

80
60
40

-60 -20 60 140

V+ = 5V, t

RISE

FALL

V+ = 15V, t

V+ = 15V, t

20 100-40 0 8040 120

TEMPERATURE (°C)

_______________________________________________________________________________________ 3

RISE

FALL

MAX1649/51-02

vs. LOAD CURRENT (V

100

V

OUT

CIRCUIT OF 
FIGURE 1

90

80

70

EFFICIENCY (%)

60

50

40

0.1

EFFICIENCY

= 5V)

OUT

= 5V

TOP TO 
BOTTOM:

= 6V

V

IN

= 8V

V

IN

= 10V

V

IN

= 12V

V

IN

= 15V

V

IN

1 10 10k

LOAD CURRENT (mA)

100 1k

MAX1649/51-A1

vs. LOAD CURRENT (V

100

V

OUT

CIRCUIT OF 
FIGURE 1

90

80

70

EFFICIENCY (%)

60

50

40

0.1

EFFICIENCY

= 3.3V)

OUT

= 3.3V

TOP TO 
BOTTOM:

= 4.3V

V

IN

= 5V

V

IN

= 8V

V

IN

= 10V

V

IN

= 12V

V

IN

= 15V

V

IN

1 10 10k

LOAD CURRENT (mA)

100 1k

MAX1649/51-A2

5V/3.3V or Adjustable, High-Efficiency,
Low-Dropout, Step-Down DC-DC Controllers

____________________________Typical Operating Characteristics (continued)

(TA = +25°C, unless otherwise noted.)

SWITCH ON-TIME

vs. TEMPERATURE

34.0

33.5

33.0

32.5

(µs)

32.0

ON

t

31.5

31.0

30.5

30.0

-60 -20 60 140

MAX1649/MAX1651

20 100-40 0 8040 120

TEMPERATURE (°C)

MAX1649/51-03

(µs)

OFF

t

CS TRIP LEVEL

vs. TEMPERATURE

120

115

110

105

CS TRIP LEVEL (mV)

100

95

-60 -20 60 140

20 100-40 0 8040 120

TEMPERATURE (°C)

1.5

1.4

1.3

1.2

1.1

1.0

0.9

0.8

0.7

0.6

0.5

-60 -20 60 140

MAX1649/51-06

SWITCH OFF-TIME
vs. TEMPERATURE

20 100-40 0 8040 120

TEMPERATURE (°C)

MAXIMUM DUTY CYCLE

100

99

MAX1649/51-04

98

97
96

DUTY CYCLE (%)

95

94

93

-60 -20 60 140

DROPOUT VOLTAGE

vs. LOAD CURRENT

600

CIRCUIT OF 
FIGURE 1

500

400

V

= 4.80V

OUT

300

200

DROPOUT VOLTAGE (mV)

100

0

0 0.5 1.0 1.5 2.0

V

= 3.17V

OUT

LOAD CURRENT (A)

vs. TEMPERATURE

20 100-40 0 8040 120

TEMPERATURE (°C)

MAX1649/51-05

MAX1649/51-A3

REFERENCE OUTPUT RESISTANCE

250

200

150

100

50

REFERENCE OUTPUT RESISTANCE (Ω)

0

vs. TEMPERATURE

I

REF

I

REF

-60 -20 60 140

20 100-40 0 8040 120

TEMPERATURE (°C)

= 10µA

I

REF

= 100µA

MAX1649-TOC07

= 50µA

REFERENCE OUTPUT VOLTAGE (V)

REFERENCE OUTPUT VOLTAGE

1.506

1.504

1.502

1.500

1.498

1.496

1.494

1.492

vs. TEMPERATURE

I

REF

-60 -20 60 140

20 100-40 0 8040 120

TEMPERATURE (°C)

= 10µA

4 _______________________________________________________________________________________

MAX1649-TOC01