19-2547; Rev 0; 7/02
Smallest 1A, 1.4MHz Step-Down Regulators
General Description
The MAX1973/MAX1974 are constant-frequency
1.4MHz pulse-width-modulated (PWM) current-mode
step-down regulators. The output voltage can be set as
low as 0.75V using an external voltage-divider, or it can
be set to preset outputs of 1V, 1.5V (MAX1974), 1.8V,
or 2.5V (MAX1973) without requiring external resistors.
The MAX1973 also includes a voltage-margining fea-
ture that offsets the output voltage up or down 4% to
facilitate board-level production testing.
A fixed 1.4MHz operating frequency ensures operation
outside the DSL frequency band, provides fast transient
response, and allows the use of small external compo-
nents. Only 4.7µF input and output ceramic capacitors
are needed for 1A applications. Forced PWM operation
ensures a constant switching frequency over all load
conditions.
Output voltage accuracy is ±1% over load, line, and
temperature operating ranges. The MAX1973 features
voltage margining; the MAX1974 provides a POK out-
put to indicate when the output has reached 90% of its
nominal regulation voltage. Both devices are available
in small 10-pin µMAX packages.
o
Tiny Circuit Footprint of 0.19in
2
o
Ultra-Low Circuit Height of 1.8mm
o
4.7µF Ceramic Input and Output Capacitors
o
2.6V to 5.5V Input Voltage
o
1A Output Current
o
1% Accurate
o
Built-In ±4% Logic-Controlled Voltage Margining
(MAX1973)
o
Preset 1V, 1.5V, 1.8V, 2.5V, or 0.75V to V
IN
Adjustable Output
o
Fixed-Frequency PWM Current-Mode Operation
o
1.4MHz Switching Frequency, Operate Outside
DSL Band
o
100% Duty-Cycle Dropout Capability
o
Small External Components
Features
MAX1973/MAX1974
Applications
Network Equipment
Cellular Base Stations
DSL and Wireless Modems/Routers
Optical Modules
Central-Office DSL and Telecom
DSP/ASIC Core and IO supplies
Selector Guide appears at end of data sheet.
TOP VIEW
FBSEL
1
COMP
FB
INPUT
2.6V TO 5.5V
IN
COMP
FB
FBSEL
MAX1973
SS
GND
CTL1
CTL2
PGND
VOLTAGE
MARGINING
ON/OFF
FBSEL
1
COMP
FB
SS
GND
MAX1974 OUTPUT DOWN TO 0.75V
2
3
4
5
LX
OUTPUT
1.25V TO V
IN
1A
SS
GND
2
3
4
5
Ordering Information
PART
MAX1973EUB
MAX1974EUB
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
10 µMAX
10 µMAX
Pin Configurations
Typical Operating Circuit
10
CTL1
9
IN
LX
PGND
CTL2
MAX1973
8
7
6
µMAX
10
ON
9
IN
LX
PGND
POK
MAX1974
8
7
6
µMAX
________________________________________________________________
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.
Smallest 1A, 1.4MHz Step-Down Regulators
MAX1973/MAX1974
ABSOLUTE MAXIMUM RATINGS
IN, POK, CTL1, CTL2, FBSEL, ON to GND ..............-0.3V to +6V
COMP, FB, SS to GND ................................-0.3V to (V
IN
+ 0.3V)
PGND to GND .......................................................-0.3V to +0.3V
LX Current (Note 1) ...............................................-2.4A to +2.4A
Continuous Power Dissipation (T
A
= +70°C)
10-Pin µMAX (derate 5.6mW/°C above +70°C) .......... 444mW
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Note 1:
LX has internal clamp diodes to IN and PGND. Applications that forward bias these diodes should take care not to exceed
the IC package power dissipation limit.
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
CTL_
= 3.3V, FB = OUT,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
IN
IN Voltage Range
IN Undervoltage Lockout
Threshold
Supply Current
Supply Current in Dropout
Shutdown Supply Current
FB
Output Voltage Range
MAX1973
MAX1974
FBSEL not connected
MAX1973
FB Regulation Voltage
MAX1974
FBSEL = GND
FBSEL = IN
FBSEL not connected
FBSEL = GND
FBSEL = IN
FB Regulation Voltage
Positive Voltage Margining
FB Regulation Voltage
Negative Voltage Margining
FB Input Resistance to GND in
Preset Output Modes
FB Input Bias Current
SS (REFERENCE OUTPUT)
SS Voltage
MAX1974
MAX1973
0.75
1.25
V
FBSEL not connected
MAX1973, CTL1 = GND, CTL2 = IN
1.25
0.75
1.2375
1.7820
2.4750
0.7425
0.99
1.485
+3
1.25
1.8
2.5
0.75
1.00
1.500
+4
V
IN
V
IN
1.2625
1.8180
2.5250
0.7575
1.01
1.515
+5
%
V
V
Rising and falling, hysteresis is 25mV (typ)
Switching with no load
V
OUT
set for 3.6V
V
IN
= 5.5V
2.6
2.2
2.35
4.0
3
0.1
5.5
2.5
7.5
5
10
V
V
mA
mA
µA
CONDITIONS
MIN
TYP
MAX
UNITS
MAX1973, CTL1 = IN, CTL2 = GND
-3
-4
-5
%
10
-0.1
30
0.01
70
+0.1
kΩ
µA
2
_______________________________________________________________________________________
Smallest 1A, 1.4MHz Step-Down Regulators
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= V
CTL_
= 3.3V, FB = OUT,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
SS Source Current
SS Sink Current
SS to GND Resistance in
Shutdown
FBSEL
Low Input Threshold
High Input Threshold
Input Bias Current
COMP
Transconductance from FB to
COMP
COMP to GND Resistance in
Shutdown
Clamp Voltage Low
Clamp Voltage High
LX
On-Resistance High
On-Resistance Low
Current-Sense Transresistance
Positive Current-Limit Threshold
Negative Current-Limit Threshold
LX Shutdown Leakage Current
Switching Frequency
CTL1, CTL2 (MAX1973), ON (MAX1974)
Logic-Low Input Threshold
Logic-High Input Threshold
Logic Input Current
POK (MAX1974 only)
Output Low Voltage
Output Valid Threshold for POK
POK sinking 1mA
Percentage of nominal
regulation voltage
Rising
Falling
90
88
10
92.5
90
100
95
92
mV
%
-1
0.6
1.6
+1
V
V
µA
V
LX
= V
IN
= 5.5V
LX = GND, V
IN
= 5.5V
-20
1.2
1.4
1.6
V
IN
= 3.3V
V
IN
= 3.3V
0.275
1.1
-1.2
0.23
0.16
0.335
1.6
-0.8
0.46
0.32
0.425
1.75
-0.4
20
Ω
Ω
V/A
A
A
µA
MHz
40
5
0.6
1.35
60
40
0.9
1.75
80
100
1.2
2.15
µS
Ω
V
V
FBSEL = GND or IN, V
IN
= 5.5V
-20
10
0.3
V
IN
-
0.3
+20
V
V
µA
CONDITIONS
MIN
-25
10
5
TYP
-20
20
40
MAX
-15
35
100
UNITS
µA
µA
Ω
MAX1973/MAX1974
3
_______________________________________________________________________________________
Smallest 1A, 1.4MHz Step-Down Regulators
MAX1973/MAX1974
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= V
CTL_
= 3.3V, FB = OUT,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
THERMAL SHUTDOWN
Thermal-Shutdown Threshold
Thermal-Shutdown Hysteresis
+170
20
°C
°C
CONDITIONS
MIN
TYP
MAX
UNITS
ELECTRICAL CHARACTERISTICS
(V
IN
= V
FB
= V
CTL_
= 3.3V,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 2)
PARAMETER
IN
IN Voltage Range
IN Undervoltage Lockout
Threshold
Supply Current
Supply Current in Dropout
Shutdown Supply Current
FB
Output Voltage Range
MAX1973
MAX1974
FBSEL not connected
MAX1973
FB Regulation Voltage
MAX1974
FB Regulation Voltage
Positive Voltage Margining
FB Regulation Voltage
Negative Voltage Margining
FB Input Resistance to GND in
Preset Output Modes
FB Input Bias Current
SS (REFERENCE OUTPUT)
SS Source Current
SS Sink Current
-25
10
-15
35
µA
µA
FBSEL not connected
FBSEL = GND
FBSEL = IN
FBSEL not connected
FBSEL = GND
FBSEL = IN
MAX1973, CTL1 = GND, CTL2 = IN
MAX1973, CTL1 = IN, CTL2 = GND
1.25
0.75
1.2375
1.7820
2.4750
0.7425
0.99
1.485
3
-3
10
-0.15
V
IN
V
IN
1.2625
1.8180
2.5250
0.7575
1.01
1.515
5
-5
70
+0.15
%
%
kΩ
µA
V
V
Rising and falling, hysteresis is 25mV (typ)
Switching with no load
V
OUT
set for 3.6V
V
IN
= 5.5V
2.6
2.2
5.5
2.5
7.5
5
10
V
V
mA
mA
µA
CONDITIONS
MIN
TYP
MAX
UNITS
4
_______________________________________________________________________________________
Smallest 1A, 1.4MHz Step-Down Regulators
ELECTRICAL CHARACTERISTICS
(V
IN
= V
CTL_
= 3.3V, FB = OUT,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 2)
PARAMETER
SS to GND Resistance
in Shutdown
FBSEL
Low Input Threshold
High Input Threshold
Input Bias Current
COMP
Transconductance
from FB to COMP
COMP to GND Resistance
in Shutdown
Clamp Voltage Low
Clamp Voltage High
LX
On-Resistance High
On-Resistance Low
Current-Sense Transresistance
Positive Current-Limit Threshold
Negative Current-Limit Threshold
LX Shutdown Leakage Current
Switching Frequency
CTL1, CTL2 (MAX1973), ON (MAX1974)
Logic-Low Input Threshold
Logic-High Input Threshold
Logic Input Current
POK (MAX1974 only)
Output Low Voltage
Output Valid Threshold
for POK
POK sinking 1mA
Percentage of nominal
regulation voltage
Rising
Falling
90
88
100
95
92
mV
%
-1
0.6
1.6
1
V
V
µA
V
LX
= V
IN
= 5.5V
LX = GND, V
IN
= 5.5V
-20
1.2
1.6
V
IN
= 3.3V
V
IN
= 3.3V
0.275
1.10
-1.20
0.46
0.32
0.425
1.85
-0.35
20
Ω
Ω
V/A
A
A
µA
MHz
40
5
0.6
1.3
80
100
1.2
2.2
µS
Ω
V
V
FBSEL = GND or IN, V
IN
= 5.5V
-20
0.3
V
IN
-
0.4
+20
V
V
µA
CONDITIONS
MIN
5
TYP
40
MAX
100
UNITS
Ω
MAX1973/MAX1974
Note 2:
Specifications to -40°C are guaranteed by design and not production tested.
_______________________________________________________________________________________
5
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