19-1142 Rev 0; 9/96
AN
N KIT M
LUATIO ABLE
EVA
AVAIL
UAL
100% Duty Cycle, Low-Noise,
Step-Down, PWM DC-DC Converter
____________________________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 0.6Ω (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
2.5µA Shutdown Mode
_______________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 (2.5µA typ) shutdown mode conserves bat-
tery life.
MAX887
________________________Applications
Portable Instruments
Cellular Phones and Radios
Personal Communicators
Distributed Power Systems
Computer Peripherals
______________Ordering Information
PART
MAX887HC/D
MAX887HESA
TEMP. RANGE
0°C to +70°C
-40°C to +85°C
PIN-PACKAGE
Dice*
8 SO
*Contact
factory for availability. Dice are tested at T
A
= +25°C.
__________Typical Operating Circuit
V
IN
= 3.5V to 11V
V+
47µF
ON
0.33µF
LX
R1
165kΩ
47µF
33µH
V
OUT
= 3.3V
__________________Pin Configuration
TOP VIEW
SHDN
1
FB
2
REF
3
8
V+
LX
SYNC
GND
MAX887
SHDN
SYNC
VL
REF
C1
100pF
OFF
MAX887
7
6
5
FB
R2
100kΩ
VL
4
GND
2.2µF
0.047µF
V
OUT
= 1.25V (R1/R2 + 1)
SO
________________________________________________________________
Maxim Integrated Products
1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800
100% Duty Cycle, Low-Noise,
Step-Down, PWM DC-DC Converter
MAX887
ABSOLUTE MAXIMUM RATINGS
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
= +70°C)
SO (derate 9.09mW/°C above +70°C) .........................471mW
Operating Temperature Ranges
MAX887HC/D.......................................................0°C to +70°C
MAX887HESA ...................................................-40°C to +85°C
Storage Temperature Range ........................... -65°C to +165°C
Lead Temperature (soldering, 10sec) ............................ +300°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.
ELECTRICAL CHARACTERISTICS
(V+ = +7V, PGND = GND = 0V,
SHDN
= V+,
(T
A
= 0°C to T
MAX
),
unless otherwise noted.)
PARAMETER
Supply Range
Quiescent Supply Current
(PWM Mode)
Quiescent Supply Current
(PFM Mode)
Shutdown Supply Current
Output Voltage Range
Load Regulation
Line Regulation
PWM FB Feedback Threshold
FB Input Current
SYNC Frequency
SYNC Pulse Width High or Low
PWM Maximum Duty Cycle
PWM Switching Frequency
High-Side Current Limit
LX On-Resistance
LX Leakage Current
LX Reverse Leakage Current,
Regulator Off
Undervoltage Lockout
Startup Voltage
SYNC Input High Voltage
SYNC Input Low Voltage
SYNC Input Current
SHDN
Input High Voltage
SHDN
Input Low Voltage
SHDN
Input Current, Sinking
SHDN
Input Capacitance
VL Output Voltage
REF Output Voltage
V
FB
I
FB
f
SYNC
SYNC, PW
PWM, DUTY
f
OSC
I
LIM+
R
ON, LX
I
LXLKG
I
LXLKGR
V
+, UVLO
V
+, START
V
IH, SYNC
V
IL, SYNC
I
IN, SYNC
V
IH,
SHDN
V
IL,
SHDN
I
IN-,
SHDN
C
IN,
SHDN
V
L
V
REF
SHDN
= GND or V+
(Note 1)
I
VL
= 0mA to 1mA
0µA to 30µA
3.3
1.25
SYNC = GND or 3V
2.4
0.8
±1
10
I
LX
= ±100mA
V+ = 12V, LX = GND to 12V
V+ = floating, LX = 5V,
SHDN
= GND
V+ falling
V+ rising
2.5
0.5
±1
-10
SYNC = 3.0V, FB = 1.18V
SYNC = 3.0V
SYMBOL
V+
I
V+, PWM
I
V+, PFM
I
V+, SHDN
V
OUT, RANGE
I
OUT
= 0mA, SYNC = 3.0V
I
OUT
= 0mA, SYNC = GND
SHDN
= GND
Circuit of Figure 2
I
OUT
= 0mA to 500mA
V
IN
= 4V to 11V, PWM mode
SYNC = 3.0V, PWM duty cycle = 50%
FB = 1.30V
25
500
100
260
0.75
300
1.0
0.6
1.0
1.0
3.0
3.1
10
20
3.3
3.5
340
1.40
1.225
1.25
0.005
0.2
1.250
1.275
±0.10
440
CONDITIONS
MIN
3.5
2.7
0.2
2.5
TYP
MAX
11.0
4.0
0.5
5
10.50
UNITS
V
mA
mA
µA
V
%/mA
%/V
V
µA
kHz
ns
%
kHz
A
Ω
µA
µA
V
V
V
V
µA
V
V
µA
pF
V
V
Note 1:
Guaranteed by design and not production tested.
2
_______________________________________________________________________________________
100% Duty Cycle, Low-Noise,
Step-Down, PWM DC-DC Converter
ELECTRICAL CHARACTERISTICS
(V+ = +7V, PGND = GND = 0V,
SHDN
= V+,
(T
A
= -40°C to +85°C),
unless otherwise noted.) (Note 2)
PARAMETER
Supply Range
Quiescent Supply Current
(PWM Mode)
Quiescent Supply Current
(PFM Mode)
Shutdown Supply Current
Output Voltage Range
PWM FB Feedback Threshold
FB Input Current
PWM Switching Frequency
High-Side Current Limit
Undervoltage Lockout
Startup Voltage
SYMBOL
V+
I
V+, PWM
I
V+, PFM
I
V+, SHDN
V
OUT, RANGE
V
FB
I
FB
f
OSC
I
LIM+
V
+, UVLO
V
+, START
V+ falling
V+ rising
I
OUT
= 0mA, SYNC = 3.0V
I
OUT
= 0mA, SYNC = GND
SHDN
= GND
Circuit of Figure 2
SYNC = 3.0V, PWM duty cycle = 50%
FB = 1.30V
SYNC = 3.0V
250
0.75
300
1.00
3.0
3.1
1.25
1.222
1.250
CONDITIONS
MIN
3.5
2.7
0.2
2.5
TYP
MAX
11.0
4.0
0.6
5
10.50
1.278
±0.10
350
1.50
3.3
3.5
UNITS
V
mA
mA
µA
V
V
µA
kHz
A
V
V
MAX887
Note 2:
Specifications from 0°C to -40°C are guaranteed by design and not production tested.
__________________________________________Typical Operating Characteristics
(Circuit of Figure 2, T
A
= +25°C, unless otherwise noted.)
DROPOUT VOLTAGE
vs. LOAD CURRENT
MAX887-01
EFFICIENCY vs. OUTPUT CURRENT
MAX887-02
EFFICIENCY vs. OUTPUT CURRENT
90
80
PWM MODE
(SYNC = VL)
V
OUT
= 5V
V
IN
= 7V
V
IN
= 9V
MAX887-03
0.7
0.6
DROPOUT VOLTAGE (V)
0.5
0.4
0.3
0.2
0.1
0
0
200
400
600
800
LOAD CURRENT (mA)
5V SETTING
V
OUT
= 4.75V
3.3V SETTING
V
OUT
= 3.135V
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
PWM MODE
(SYNC = VL)
V
OUT
= 3.3V
V
IN
= 4V
V
IN
= 5V
V
IN
= 7V
V
IN
= 11V
V
IN
= 9V
100
EFFICIENCY (%)
70
60
50
40
30
20
10
V
IN
= 5.5V
V
IN
= 11V
1000
0.0001
0.001
0.01
0.1
OUTPUT CURRENT (A)
0.6
0
0.0001
0.001
0.01
0.1
0.6
OUTPUT CURRENT (A)
_______________________________________________________________________________________
3
100% Duty Cycle, Low-Noise,
Step-Down, PWM DC-DC Converter
MAX887
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 2, T
A
= +25°C, unless otherwise noted.)
EFFICIENCY vs. OUTPUT CURRENT
MAX887-04
EFFICIENCY vs. OUTPUT CURRENT
MAX887-05
MAXIMUM OUTPUT CURRENT
vs. SUPPLY VOLTAGE
MAXIMUM OUTPUT CURRENT (mA)
3.3V SETTING, V
OUT
= 3.135V
1000
800
600
400
200
0
GUARANTEED OUTPUT CURRENT
OF FIGURE 2 IS 600mA
3
5
7
9
11
13
15
17
5V SETTING, V
OUT
= 4.75V
MAX887-06
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.0001
0.001
0.01
0.1
V
IN
= 9V
IDLE MODE
(SYNC = GND)
V
OUT
= 3.3V
V
IN
= 4V
V
IN
= 5V
V
IN
= 11V
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
V
IN
= 5.5V
V
IN
= 11V
1200
V
IN
= 9V
V
IN
= 7V
IDLE MODE
(SYNC = GND)
V
OUT
= 5V
0.001
0.01
0.1
0.6
V
IN
= 7V
0.6
0
0.0001
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
SUPPLY VOLTAGE (V)
MAXIMUM OUTPUT CURRENT
vs. SYNC FREQUENCY
MAX887-07
QUIESCENT SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX887-08
QUIESCENT CURRENT
vs.TEMPERATURE
V
IN
= 5.3V
V
OUT
= 3.3V
PWM MODE
2.0
1.5
1.0
0.5
PFM MODE
0
-60 -40 -20 0 20 40 60 80 100 120 140
TEMPERATURE (°C)
MAX887-09
1200
MAXIMUM OUTPUT CURRENT (mA)
1000
800
600
400
200
0
0
100
200 300 400 500
SYNC FREQUENCY (kHz)
C2, C3 = 47µF
L1 = 33µH
V
IN
= 5V
V
OUT
= 3.3V
V
OUT
= -5% at I
OUT(MAX)
3.5
A
3.0
QUIESCENT CURRENT (mA)
2.5
2.0
1.5
1.0
0.5
0
C
B
0
2
4
6 8 10 12 14 16
SUPPLY VOLTAGE (V)
A: V
OUT
= 3.3V, PWM MODE
B: V
OUT
= 3.3V, PFM MODE
A
3.0
2.5
600
18
SWITCHING FREQUENCY
vs. SUPPLY VOLTAGE
MAX887-10
SWITCHING FREQUENCY
vs. TEMPERATURE
MAX887-11
QUIESCENT CURRENT (mA)
OUTPUT RIPPLE AND HARMONICS
V
IN
= 5V
V
OUT
= 3.3V
I
OUT
= 500mA
PWM MODE
MAX887 TOC-20
350
340
SWITCHING FREQUENCY (kHz)
330
V
OUT
= 3.3V
350
340
330
FREQUENCY (kHz)
320
310
300
290
280
270
260
250
V
OUT
= 3.3V
4
3
OUTPUT NOISE (mV)
-60 -40 -20
0 20 40 60 80 100 120 140
TEMPERATURE (°C)
320
310
300
290
280
270
260
250
0
2
4
6 8 10 12 14 16
SUPPLY VOLTAGE (V)
18
2
1
0
-1
10k
100k
1M
10M
FREQUENCY (Hz)
4
_______________________________________________________________________________________
100% Duty Cycle, Low-Noise,
Step-Down, PWM DC-DC Converter
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 2, T
A
= +25°C, unless otherwise noted.)
MAX887
HEAVY-LOAD, PWM-MODE
SWITCHING WAVEFORMS
MAX887-12
LIGHT-LOAD, PWM-MODE
SWITCHING WAVEFORMS
MAX887-13
A
A
B
C
0mA
1µs/div
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
B
C
1µs/div
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
LIGHT-LOAD, PFM-MODE
SWITCHING WAVEFORMS
MAX887-14
MEDIUM-LOAD, PFM-MODE
SWITCHING WAVEFORMS
MAX887-15
A
A
B
B
C
1µs/div
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
C
10µs/div
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
_______________________________________________________________________________________
5
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