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Электронный компонент: MAX887

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_______________General Description
The MAX887 high-efficiency, step-down DC-DC con-
verter provides an adjustable output from 1.25V to
10.5V. It accepts inputs from 3.5V to 11V and delivers
600mA. Operation to 100% duty cycle minimizes
dropout voltage (300mV typ at 500mA). Synchronous
rectification reduces output rectifier losses, resulting in
efficiency as high as 95%.
Fixed-frequency pulse-width modulation (PWM)
reduces noise in sensitive communications applica-
tions. Using a high-frequency internal oscillator allows
tiny surface-mount components to reduce PC board
area, and eliminates audio-frequency interference. A
SYNC input allows synchronization to an external clock
to avoid interference with sensitive RF and data-
acquisition circuits.
The MAX887 features current-mode operation for supe-
rior load/line-transient response. Cycle-by-cycle current
limiting protects the internal MOSFET and rectifier. A
low-current (2.5A typ) shutdown mode conserves bat-
tery life.
________________________Applications
Portable Instruments
Cellular Phones and Radios
Personal Communicators
Distributed Power Systems
Computer Peripherals
____________________________Features
o
95% Efficiency
o
600mA Output Current
o
Cycle-by-Cycle Current Limiting
o
Low-Dropout, 100% Duty-Cycle Operation,
300mV at 500mA
o
Internal 0.6
(typ) MOSFET
o
Internal Synchronous Rectifier
o
High-Frequency Current-Mode PWM
o
External SYNC or Internal 300kHz Oscillator
o
Guaranteed 260kHz to 340kHz Internal Oscillator
Frequency Limits
o
2.5A Shutdown Mode
MAX887
100% Duty Cycle, Low-Noise,
Step-Down, PWM DC-DC Converter
________________________________________________________________
Maxim Integrated Products
1
1
2
8
7
V+
LX
SYNC
GND
SHDN
FB
REF
VL
MAX887
SO
TOP VIEW
3
4
6
5
__________________Pin Configuration
MAX887
REF
R1
165k
R2
100k
0.047
F
2.2
F
47
F
47
F
C1
100pF
0.33
F
33
H
V+
LX
FB
GND
SYNC
VL
SHDN
V
OUT
= 3.3V
V
OUT
= 1.25V (R1/R2 + 1)
V
IN
= 3.5V to 11V
ON
OFF
__________Typical Operating Circuit
19-1142 Rev 0; 9/96
PART
MAX887HC/D
MAX887HESA
-40C to +85C
0C to +70C
TEMP. RANGE
PIN-PACKAGE
Dice*
8 SO
EVALUATION KIT MANUAL
AVAILABLE
______________Ordering Information
*
Contact factory for availability. Dice are tested at T
A
= +25C.
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800
MAX887
100% Duty Cycle, Low-Noise,
Step-Down, PWM DC-DC Converter
2
_______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(V+ = +7V, PGND = GND = 0V,
SHDN = V+,
(T
A
= 0C to T
MAX
)
, unless otherwise noted.)
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.
REF, FB, SYNC, VL to GND..................................... -0.3V to +6V
V+ to GND ............................................................. -0.3V to +12V
SHDN, LX to GND ....................................... -0.3V to (V+ + 0.3V)
PGND to GND ...................................................... -0.3V to +0.3V
Continuous Power Dissipation (T
A
= +70C)
SO (derate 9.09mW/C above +70C) .........................471mW
Operating Temperature Ranges
MAX887HC/D.......................................................0C to +70C
MAX887HESA ...................................................-40C to +85C
Storage Temperature Range ........................... -65C to +165C
Lead Temperature (soldering, 10sec) ............................ +300C
SYNC = GND or 3V
I
OUT
= 0mA, SYNC = GND
V+ rising
I
OUT
= 0mA, SYNC = 3.0V
V+ falling
V+ = floating, LX = 5V,
SHDN = GND
V+ = 12V, LX = GND to 12V
I
LX
= 100mA
SYNC = 3.0V
FB = 1.30V
SYNC = 3.0V, PWM duty cycle = 50%
SHDN = GND
Circuit of Figure 2
I
OUT
= 0mA to 500mA
V
IN
= 4V to 11V, PWM mode
SYNC = 3.0V, FB = 1.18V
CONDITIONS
V
2.4
V
IH,
SHDN
SHDN Input High Voltage
A
1
I
IN, SYNC
SYNC Input Current
V
0.5
V
IL, SYNC
SYNC Input Low Voltage
V
2.5
V
IH, SYNC
SYNC Input High Voltage
V
3.1
3.5
V
+, START
Startup Voltage
V
3.0
3.3
V
+, UVLO
Undervoltage Lockout
A
1.0
20
I
LXLKGR
LX Reverse Leakage Current,
Regulator Off
A
-10
1.0
10
I
LXLKG
LX Leakage Current
0.6
R
ON, LX
LX On-Resistance
A
0.75
1.0
1.40
I
LIM+
High-Side Current Limit
kHz
260
300
340
f
OSC
PWM Switching Frequency
SHDN Input Low Voltage
V
IL,
SHDN
%
100
PWM, DUTY
PWM Maximum Duty Cycle
mA
0.2
0.5
I
V+, PFM
Quiescent Supply Current
(PFM Mode)
mA
2.7
4.0
I
V+, PWM
V
3.5
11.0
V+
Supply Range
Quiescent Supply Current
(PWM Mode)
ns
500
SYNC, PW
SYNC Pulse Width High or Low
kHz
25
440
f
SYNC
SYNC Frequency
A
0.10
I
FB
FB Input Current
V
1.225
1.250
1.275
V
FB
PWM FB Feedback Threshold
A
2.5
5
I
V+, SHDN
Shutdown Supply Current
V
1.25
10.50
V
OUT, RANGE
Output Voltage Range
%/mA
0.005
Load Regulation
%/V
0.2
Line Regulation
UNITS
MIN
TYP
MAX
SYMBOL
PARAMETER
0.8
V
SHDN Input Current, Sinking
I
IN-,
SHDN
SHDN = GND or V+
1
A
SHDN Input Capacitance
C
IN,
SHDN
(Note 1)
10
pF
VL Output Voltage
V
L
I
VL
= 0mA to 1mA
3.3
V
REF Output Voltage
V
REF
0A to 30A
1.25
V
Note 1:
Guaranteed by design and not production tested.
MAX887
100% Duty Cycle, Low-Noise,
Step-Down, PWM DC-DC Converter
_______________________________________________________________________________________
3
Note 2:
Specifications from 0C to -40C are guaranteed by design and not production tested.
I
OUT
= 0mA, SYNC = GND
V+ rising
I
OUT
= 0mA, SYNC = 3.0V
V+ falling
SYNC = 3.0V
FB = 1.30V
SYNC = 3.0V, PWM duty cycle = 50%
SHDN = GND
Circuit of Figure 2
CONDITIONS
V
3.1
3.5
V
+, START
Startup Voltage
V
3.0
3.3
V
+, UVLO
Undervoltage Lockout
A
0.75
1.00
1.50
I
LIM+
High-Side Current Limit
kHz
250
300
350
f
OSC
PWM Switching Frequency
mA
0.2
0.6
I
V+, PFM
Quiescent Supply Current
(PFM Mode)
mA
2.7
4.0
I
V+, PWM
V
3.5
11.0
V+
Supply Range
Quiescent Supply Current
(PWM Mode)
A
0.10
I
FB
FB Input Current
V
1.222
1.250
1.278
V
FB
PWM FB Feedback Threshold
A
2.5
5
I
V+, SHDN
Shutdown Supply Current
V
1.25
10.50
V
OUT, RANGE
Output Voltage Range
UNITS
MIN
TYP
MAX
SYMBOL
PARAMETER
ELECTRICAL CHARACTERISTICS
(V+ = +7V, PGND = GND = 0V,
SHDN = V+,
(T
A
= -40C to +85C)
, unless otherwise noted.) (Note 2)
__________________________________________Typical Operating Characteristics
(Circuit of Figure 2, T
A
= +25C, unless otherwise noted.)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0
200
400
600
800
1000
LOAD CURRENT (mA)
DROPOUT VOLTAGE
vs. LOAD CURRENT
MAX887-01
DROPOUT VOLTAGE (V)
3.3V SETTING
V
OUT
= 3.135V
5V SETTING
V
OUT
= 4.75V
0
10
20
30
40
50
60
70
80
90
100
0.0001
0.001
0.01
0.1
0.6
EFFICIENCY (%)
OUTPUT CURRENT (A)
EFFICIENCY vs. OUTPUT CURRENT
MAX887-02
PWM MODE
(SYNC = VL)
V
OUT
= 3.3V
V
IN
= 4V
V
IN
= 5V
V
IN
= 7V
V
IN
= 11V
V
IN
= 9V
0
10
20
30
40
50
60
70
80
90
100
0.0001
0.001
0.01
0.1
0.6
EFFICIENCY (%)
OUTPUT CURRENT (A)
EFFICIENCY vs. OUTPUT CURRENT
MAX887-03
PWM MODE
(SYNC = VL)
V
OUT
= 5V
V
IN
= 9V
V
IN
= 5.5V
V
IN
= 11V
V
IN
= 7V
MAX887
100% Duty Cycle, Low-Noise,
Step-Down, PWM DC-DC Converter
4
_______________________________________________________________________________________
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 2, T
A
= +25C, unless otherwise noted.)
0
10
20
30
40
50
60
70
80
90
100
0.0001 0.001
0.01
0.1
0.6
EFFICIENCY (%)
OUTPUT CURRENT (A)
EFFICIENCY vs. OUTPUT CURRENT
MAX887-04
IDLE MODE
(SYNC = GND)
V
OUT
= 3.3V
V
IN
= 5V
V
IN
= 7V
V
IN
= 9V
V
IN
= 11V
V
IN
= 4V
0
10
20
30
40
50
60
70
80
90
100
0.0001
0.001
0.01
0.1
0.6
EFFICIENCY (%)
OUTPUT CURRENT (A)
EFFICIENCY vs. OUTPUT CURRENT
MAX887-05
IDLE MODE
(SYNC = GND)
V
OUT
= 5V
V
IN
= 5.5V
V
IN
= 9V
V
IN
= 7V
V
IN
= 11V
0
200
400
600
800
1000
1200
3
5
7
9
11
13
15
17
MAXIMUM OUTPUT CURRENT (mA)
SUPPLY VOLTAGE (V)
MAXIMUM OUTPUT CURRENT
vs. SUPPLY VOLTAGE
MAX887-06
GUARANTEED OUTPUT CURRENT
OF FIGURE 2 IS 600mA
3.3V SETTING, V
OUT
= 3.135V
5V SETTING, V
OUT
= 4.75V
0
200
400
600
800
1000
1200
0
100
200
300
400
500
600
MAXIMUM OUTPUT CURRENT (mA)
SYNC FREQUENCY (kHz)
MAXIMUM OUTPUT CURRENT
vs. SYNC FREQUENCY
MAX887-07
C2, C3 = 47F
L1 = 33H
V
IN
= 5V
V
OUT
= 3.3V
V
OUT
= -5% at I
OUT(MAX)
250
260
270
280
290
300
310
320
330
340
350
0
2
4
6
8
10
12
14
16
18
SWITCHING FREQUENCY (kHz)
SUPPLY VOLTAGE (V)
SWITCHING FREQUENCY
vs. SUPPLY VOLTAGE
MAX887-10
V
OUT
= 3.3V
0
0.5
1.5
2.5
3.5
3.0
2.0
1.0
QUIESCENT CURRENT (mA)
SUPPLY VOLTAGE (V)
QUIESCENT SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX887-08
A
A
A: V
OUT
= 3.3V, PWM MODE
B: V
OUT
= 3.3V, PFM MODE
0
2
4
6
8
10
12
14
16
18
C
B
0
0.5
1.0
1.5
2.0
2.5
3.0
-60 -40 -20 0
20 40 60 80 100 120 140
QUIESCENT CURRENT (mA)
TEMPERATURE (C)
QUIESCENT CURRENT
vs.TEMPERATURE
MAX887-09
PWM MODE
V
IN
= 5.3V
V
OUT
= 3.3V
PFM MODE
250
260
270
280
290
300
310
320
330
340
350
FREQUENCY (kHz)
TEMPERATURE (C)
SWITCHING FREQUENCY
vs. TEMPERATURE
MAX887-11
V
OUT
= 3.3V
-60 -40 -20
0
20 40 60 80 100 120 140
4
-1
10k
10M
OUTPUT RIPPLE AND HARMONICS
0
2
3
1
MAX887 TOC-20
FREQUENCY (Hz)
OUTPUT NOISE (mV)
100k
1M
V
IN
= 5V
V
OUT
= 3.3V
I
OUT
= 500mA
PWM MODE
MAX887
100% Duty Cycle, Low-Noise,
Step-Down, PWM DC-DC Converter
_______________________________________________________________________________________
5
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 2, T
A
= +25C, unless otherwise noted.)
V
IN
= 5V, V
OUT
= 3.3V, LOAD = 500mA
A: LX, 5V/div
B: V
OUT
, 20mV/div, AC COUPLED
C: INDUCTOR CURRENT, 500mA/div
1
s/div
HEAVY-LOAD, PWM-MODE
SWITCHING WAVEFORMS
A
B
C
0mA
MAX887-12
V
IN
= 5V, V
OUT
= 3.3V, LOAD = 0mA
A: LX, 5V/div
B: V
OUT
, 20mV/div, AC COUPLED
C: INDUCTOR CURRENT, 500mA/div
1
s/div
LIGHT-LOAD, PWM-MODE
SWITCHING WAVEFORMS
A
B
C
MAX887-13
V
IN
= 5V, V
OUT
= 3.3V, LOAD = 0mA
A: LX, 5V/div
B: V
OUT
, 20mV/div, AC COUPLED
C: INDUCTOR CURRENT, 200mA/div
1
s/div
LIGHT-LOAD, PFM-MODE
SWITCHING WAVEFORMS
A
B
C
MAX887-14
V
IN
= 5V, V
OUT
= 3.3V, LOAD = 70mA
A: LX, 5V/div
B: V
OUT
, 20mV/div, AC COUPLED
C: INDUCTOR CURRENT, 200mA/div
10
s/div
MEDIUM-LOAD, PFM-MODE
SWITCHING WAVEFORMS
A
B
C
MAX887-15