19-1454; Rev 2; 7/01
KIT
ATION
EVALU
BLE
AVAILA
Low-Noise, 14V Input, 1A, PWM
Step-Down Converters
General Description
Features
o
Up to 96% Efficiency
o
1A Guaranteed Output Current
o
100% Duty Cycle in Dropout
o
2.7V to 14V Input Range (15V Absolute Max)
o
±1% Accurate Reference Output
o
0.24Ω P-Channel On-Resistance
o
Synchronizable Switching Frequency
o
Fixed-Frequency PWM Operation
300kHz (MAX1684)
600kHz (MAX1685)
o
150µA Normal-Mode Quiescent Current
o
25µA Low-Power Mode Quiescent Current
o
2µA Shutdown Current
o
Dual Mode™ Fixed 3.3V (±1%) Output or
Adjustable Output (1.25V to V
IN
)
o
Small 16-QSOP Package
o
Auxiliary Output (CVL): 3V/5mA
MAX1684/MAX1685
The MAX1684/MAX1685 are high-efficiency, internal-
switch, pulse-width modulation (PWM) step-down switch-
ing regulators intended to power cellular phones,
communicating PDAs, and handy-terminals. These
devices deliver a guaranteed 1A output current from two
lithium-ion (Li+) batteries. Their wide-input voltage range
of 2.7V to 14V gives design flexibility and allows batteries
to charge from a wall cube, since the ICs operate at the
higher voltages that occur when the battery is removed.
The output voltage is preset to 3.3V or can be externally
adjusted from 1.25V to V
IN
.
The low on-resistance power switch and built-in synchro-
nous rectifier provide high efficiencies of up to 96%.
There are four modes of operation: fixed-frequency, nor-
mal, low-power, and shutdown. The fixed-frequency
PWM mode of operation offers excellent noise character-
istics. The normal mode maintains high efficiency at all
loads. The low-power mode is used to conserve power in
standby or when full load is not required. The shutdown
mode is used to power down the device for minimal cur-
rent draw.
The MAX1684 runs at 300kHz for applications that
require highest efficiency. The MAX1685 runs at
600kHz to allow the use of smaller external compo-
nents. These devices can also be synchronized to an
external clock. Other features include a 100% duty
cycle for low-dropout applications, an auxiliary 3V/5mA
output, and a 1% accurate reference.
Both devices are available in a space-saving 16-QSOP
package. An evaluation kit is also available to help
speed designs. For a similar device in a 10-pin µMAX
package with lower input voltage requirements (5.5V
max), refer to the MAX1692 data sheet.
Ordering Information
PART
MAX1684EEE
MAX1685EEE
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
16 QSOP
16 QSOP
Typical Operating Circuit
Applications
Cellular Phones
Two-Way Radios and Walkie-Talkies
Computer Peripherals
Personal Communicators
PDAs and Handy-Terminals
INPUT
2.7V TO 14V
+
IN
AIN
SHDN
CVH
CVL
STBY
SYNC/PWM
BOOT
LX
OUTPUT
3.3V AT 1A
+
MAX1684
MAX1685
GND
Pin Configuration appears at end of data sheet.
FB
CC
REF
Dual Mode is a trademark of Maxim Integrated Products, Inc.
________________________________________________________________
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.
Low-Noise, 14V Input, 1A, PWM
Step-Down Converters
MAX1684/MAX1685
ABSOLUTE MAXIMUM RATINGS
AIN to AGND ............................................................-0.3 to +15V
IN to PGND ................................................-0.3V to (V
AIN
+ 0.3V)
LX to PGND .................................................-0.5V to (V
IN
+ 0.3V)
PGND to AGND ..................................................................±0.3V
SHDN
to AGND .........................................-0.3V to (V
AIN
+ 0.3V)
ILIM/SS, FB, CC, BOOT, REF to AGND ....-0.3V to (V
CVL
+ 0.3V)
CVH to IN..................................................................-6V to +0.3V
CVL,
STBY,
SYNC/PWM to AGND............................-0.3V to +6V
Reference Current ..............................................................±1mA
CVL Current .......................................................-1mA to +10mA
LX Peak Current (Internally Limited) .....................................2.3A
Continuous Power Dissipation (T
A
= +70°C)
16-Pin QSOP (derate 8.3mW/°C above +70°C)............667mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+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
IN
= V
SHDN
= 6V,
STBY
= SYNC/PWM = CVL, V
BOOT
= V
OUT
, FB = AGND, circuit of Figure 1,
T
A
= 0°C to +85°C,
unless otherwise
noted. Typical values are at T
A
= +25°C.)
PARAMETER
Input Voltage Range
Feedback Voltage
Output Voltage (3.3V Mode)
Output Load Regulation
Output Current Capability
Output Adjust Range
FB Input Current
On-Resistance, P-Channel
On-Resistance, N-Channel
Current Limit in PWM Mode
Pulse-Skipping Current Threshold
Current Limit in Low-Power
Mode
Current Limit, N-Channel
Zero Crossing Threshold
I
LIMLP
I
LIM
SYNC/PWM = low
STBY
= low
SYNC/PWM = high
SYNC/PWM = low
PWM mode,
SYNC/PWM = high,
V
BOOT
= 3.3V
(Note 2)
Quiescent Power Consumption
MAX1684
MAX1685
MAX1684
MAX1685
I
FB
V
FB
V
OUT
V
FB
= V
OUT
, I
LOAD
= 0 to 1A
FB = AGND, I
LOAD
= 0 to 1A
V
FB
= V
OUT
, I
LOAD
= 0 to 1A
V
IN
= 5V to 14V
BOOT = AGND (Note 1)
V
FB
= 1.4V
High-side switch,
I
LX
= 1A
V
IN
= 6V
V
IN
= 2.7V
1.2
285
285
0.15
-10
20
1
V
REF
-50
0.24
0.34
3
1.75
380
380
0.4
50
80
13
25
0.9
0.14
V
IN
50
0.5
0.8
8
2.3
475
475
0.9
100
130
33
65
mW
2
0.27
SYMBOL
CONDITIONS
MIN
2.7
1.238
3.296
1.251
3.333
0.01
TYP
MAX
14
1.264
3.368
UNITS
V
V
V
%
A
V
nA
Ω
Ω
A
mA
mA
A
mA
Low-side switch, V
IN
= 2.7V, I
LX
= 200mA
Normal mode, SYNC/PWM = low,
V
BOOT
= 3.3V (Note 2)
Low-power mode,
STBY
= low,
V
BOOT
= 3.3V (Note 2)
2
_______________________________________________________________________________________
Low-Noise, 14V Input, 1A, PWM
Step-Down Converters
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= V
SHDN
= 6V,
STBY
= SYNC/PWM = CVL, V
BOOT
= V
OUT
, FB = AGND, circuit of Figure 1,
T
A
= 0°C to +85°C,
unless otherwise
noted. Typical values are at T
A
= +25°C.)
PARAMETER
Quiescent Supply Current
in Dropout
Shutdown Supply Current
LX Leakage Current
Oscillator Frequency
SYNC Capture Range
Maximum Duty Cycle
Constant-Frequency Minimum
Duty Cycle
Reference Output Voltage
Reference Load Regulation
Reference Supply Regulation
CVL Regulator Output Voltage
CVL Dropout Voltage
CVL Undervoltage Lockout
Threshold
CVH with Respect to V
IN
BOOT Switchover Threshold
Thermal Shutdown Threshold
ILIM/SS Source Current
Logic Input High Voltage
Logic Input Low Voltage
Logic Input Current
SYNC/PWM Pulse Width
V
IH
V
IL
V
REF
(Note 3)
I
REF
= 0
-1µA < I
REF
< 50µA
2.7V < V
BOOT
< 5.5V
V
IN
= 3V to 14V, BOOT = AGND,
I
CVL
= 0 to 5mA
BOOT = AGND, I
CVL
= 5mA
BOOT = AGND, CVL falling edge,
typical hysteresis is 40mV
I
CVH
= -1mA
BOOT falling edge,
typical hysteresis is 0.1V
Typical hysteresis is +10°C (Note 4)
V
ILIM/SS
= 1.4V
SHDN, STBY,
SYNC/PWM
SHDN, STBY,
SYNC/PWM
High or low period
3.3
2
0.7
-1
500
1
2.35
-5.0
2.35
2.5
-4.6
2.5
160
4
4.65
2.7
MAX1684
MAX1685
1.238
I
LX
f
OSC
SYMBOL
CONDITIONS
STBY
= low, V
IN
= 2.7V
SHDN
= low
V
IN
= 14V, V
LX
= 0 or 14V,
SHDN
= low
MAX1684
MAX1685
MAX1684
MAX1685
260
520
180
360
100
10
20
1.251
4
0.2
3.0
1.264
15
5
3.15
120
2.6
-4.1
2.65
300
600
MIN
TYP
230
2
MAX
430
6
20
340
680
350
700
UNITS
µA
µA
µA
kHz
kHz
%
%
V
mV
mV
V
mV
V
V
V
°C
µA
V
V
µA
ns
MAX1684/MAX1685
_______________________________________________________________________________________
3
Low-Noise, 14V Input, 1A, PWM
Step-Down Converters
MAX1684/MAX1685
ELECTRICAL CHARACTERISTICS
(V
IN
= V
SHDN
= 6V,
STBY
= SYNC/PWM = CVL, V
BOOT
= V
OUT
, FB = AGND, circuit of Figure 1,
T
A
= -40°C to +85°C,
unless other-
wise noted.) (Note 5)
PARAMETER
Input Voltage Range
Output Feedback Voltage
Output Voltage (3.3V Mode)
Output Current Capability
Output Adjust Range
FB Input Current
Current Limit in PWM Mode
Current Limit in Low-Power
Mode
I
FB
I
LIM
I
LIMLP
STBY
= low
Normal mode, SYNC/PWM = low,
V
BOOT
= 3.3V (Note 2)
Low-power mode,
STBY
= low,
V
BOOT
= 3.3V (Note 2)
SHDN
= low
f
OSC
MAX1684
MAX1685
I
REF
= 0
V
IN
= 3V to 14V, BOOT = AGND,
I
CVL
= 0 to 5mA
BOOT = AGND, CVL falling edge,
typical hysteresis is 40mV
I
CVH
= -1mA
BOOT falling edge, typical hysteresis is 0.1V
V
ILIM/SS
= 1.4V
V
IH
V
IL
SHDN, STBY,
SYNC/PWM
240
480
1.232
2.7
2.4
-5.0
2.35
3.1
2
0.7
V
FB
V
OUT
V
FB
= V
OUT
, I
LOAD
= 0 to 1A
FB = AGND, I
LOAD
= 0 to 1A
V
IN
= 6V to 14V
BOOT = AGND (Note 1)
V
FB
= 1.4V
SYMBOL
CONDITIONS
MIN
2.7
1.233
3.280
1
V
REF
-50
1.2
285
V
IN
50
2.3
475
2
mW
0.27
6
350
700
1.268
3.15
2.6
-4.1
2.65
4.7
µA
kHz
V
V
V
V
V
µA
V
MAX
14
1.269
3.382
UNITS
V
V
V
A
V
nA
A
mA
Quiescent Power Consumption
Shutdown Supply Current
Oscillator Frequency
Reference Output Voltage
CVL Regulator Output Voltage
CVL Undervoltage Lockout
Threshold
CVH with Respect to V
IN
BOOT Switchover Threshold
ILIM/SS Source Current
Logic Input High Voltage
Logic Input Low Voltage
Note 1:
The output adjust range with BOOT connected to V
OUT
is V
REF
to 5.5V. Connect BOOT to AGND for V
OUT
> 5.5V.
Note 2:
The quiescent power-consumption specifications include chip supply and gate-drive loss only. Divide these values by V
IN
(6V) to obtain quiescent currents. In normal and low-power modes, chip supply current dominates and quiescent power is
proportional to V
BOOT
(BOOT connected to OUT). In PWM mode, gate-drive loss dominates and quiescent power is propor-
tional to V
IN
✕
(V
IN
- V
CVH
). In addition, IR losses in power switches and external components typically increase PWM quies-
cent power consumption by 5mW to 10mW. Note that if the device is not bootstrapped, additional power is dissipated in the
CVL linear regulator.
Note 3:
When the duty factor (V
OUT
/ V
IN
) is less than this value, the switching frequency decreases in PWM mode to maintain
regulation.
Note 4:
Thermal shutdown is disabled in low-power mode (STBY = low) to reduce power consumption.
Note 5:
Specifications to -40°C are guaranteed by design, not production tested.
4
_______________________________________________________________________________________
Low-Noise, 14V Input, 1A, PWM
Step-Down Converters
Typical Operating Characteristics
(Circuit of Figure 1, T
A
= +25°C, unless otherwise noted.)
MAX1684
EFFICIENCY vs. LOAD CURRENT
(V
IN
= 3.3V, V
OUT
= 1.8V, 2.5V)
MAX1684/85 toc01
MAX1684/MAX1685
MAX1684
EFFICIENCY vs. LOAD CURRENT
(V
OUT
= 3.3V)
MAX1684/85 toc02
MAX1684
EFFICIENCY vs. LOAD CURRENT
(V
OUT
= 3.3V, PWM MODE)
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
1
10
100
A: V
IN
= 4V
B: V
IN
= 5V
C: V
IN
= 9V
D: V
IN
= 12V
1000
10,000
A
D
B
C
MAX1684/85 toc03
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.1
1
C
B
A
D
E
A: V
OUT
= 2.5V LP MODE
B: V
OUT
= 1.8V LP MODE
C: V
OUT
= 2.5V NORM MODE
D: V
OUT
= 1.8V NORM MODE
E: V
OUT
= 2.5V PWM MODE
F: V
OUT
= 1.8V PWM MODE
10
100
1000
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.1
1
10
100
1000
A: V
IN
= 4V LP MODE
B: V
IN
= 12V LP MODE
C: V
IN
= 4V NORMAL MODE
D: V
IN
= 12V NORMAL MODE
B
A
D
C
100
F
10,000
10,000
LOAD CURRENT (mA)
LOAD CURRENT (mA)
LOAD CURRENT (mA)
MAX1684
EFFICIENCY vs. LOAD CURRENT
(V
OUT
= 5V)
MAX1684/85 toc04
MAX1684
EFFICIENCY vs. LOAD CURRENT
(V
OUT
= 5V, PWM MODE)
D
MAX1684/85 toc05
MAX1685
EFFICIENCY vs. LOAD CURRENT
(V
OUT
= 3.3V, PWM MODE)
90
80
EFFICIENCY (%)
70
60
50
40
30
V
IN
= 9V
V
IN
= 12V
V
IN
= 5V
V
IN
= 4V
MAX1684/85 toc06
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
0.1
1
A: V
IN
= 6V LP MODE
B: V
IN
= 9V LP MODE
C: V
IN
= 12V LP MODE
D: V
IN
= 6V NORMAL MODE
E: V
IN
= 9V NORMAL MODE
F: V
IN
= 12V NORMAL MODE
10
100
1000
B
A
C
F
E
E
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
1
10
100
1000
A: V
IN
= 6V
B: V
IN
= 9V
C: V
IN
=12V
B
C
A
100
20
10
0
1
10,000
10,000
10
100
1000
10,000
LOAD CURRENT (mA)
LOAD CURRENT (mA)
LOAD CURRENT (mA)
MAX1685
EFFICIENCY vs. LOAD CURRENT
(V
OUT
= 3.3V)
MAX1684/85 toc07
MAX1685
EFFICIENCY vs. LOAD CURRENT
(V
OUT
= 5V PWM MODE)
MAX1684/85 toc08
MAX1685
EFFICIENCY vs. LOAD CURRENT
(V
OUT
= 5V)
90
80
EFFICIENCY (%)
70
60
50
40
30
A: V
IN
= 6V LP MODE
B: V
IN
= 9V LP MODE
C: V
IN
= 12V LP MODE
D: V
IN
= 6V NORMAL MODE
E: V
IN
= 9V NORMAL MODE
F: V
IN
=12V NORMAL MODE
0.1
1
10
100
1000
10,000
LOAD CURRENT (mA)
A
B
E
D
MAX1684/85 toc09
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.1
1
B
D
A
100
90
80
EFFICIENCY (%)
70
60
50
40
30
V
IN
=12V
V
IN
= 6V
V
IN
= 9V
100
C
C
F
A: V
IN
= 4V LP MODE
B: V
IN
= 12V LP MODE
C: V
IN
= 4V NORMAL MODE
D: V
IN
= 12V NORMAL MODE
10
100
1000
10,000
20
10
0
1
20
10
0
10
100
1000
10,000
LOAD CURRENT (mA)
LOAD CURRENT (mA)
_______________________________________________________________________________________
5
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