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19-1436; Rev 1; 9/99
UAL
IT MAN
TION K
A
SHEET
EVALU
S DATA
W
FOLLO
3A, Low-Voltage, Step-Down Regulator with
Synchronous Rectification and Internal Switches
General Description
The MAX1623 switch-mode buck regulator with syn-
chronous rectification provides local CPU and bus-ter-
mination power in notebook and desktop computers.
An internal 55mΩ (typ), 3A PMOS power switch and
60mΩ (typ), 3A NMOS synchronous-rectifier switch
deliver continuous load currents up to 3A from a 5V
supply with 95% typical efficiency. Output accuracy is
±1%, including line and load regulation.
The MAX1623 features constant-off-time, current-mode
pulse-width-modulation (PWM) control with switching
frequencies as high as 350kHz. An external resistor at
the TOFF pin sets the off-time, allowing optimum design
flexibility in terms of switching frequency, output switch-
ing noise, and inductor size. This device is available in
a space-saving 20-pin SSOP package.
____________________________Features
o
±1% Output Accuracy, Including Line and Load
Regulation
o
94% Efficiency
o
Internal Switches
55mΩ PMOS Power Switch
60mΩ NMOS Synchronous-Rectifier Switch
o
Guaranteed 3A Load Capability
o
Minimal External Components
o
Pin-Selectable Fixed 3.3V, 2.5V, or
Adjustable (1.1V to 3.8V) Output Voltage
o
+4.5V to +5.5V Input Voltage Range
o
400µA (typ) Supply Current
o
<1µA Shutdown Supply Current
o
o
o
o
o
Constant-Off-Time PWM Operation
Switching Frequencies Up to 350kHz
Idle Mode™ Operation at Light Loads
Thermal Shutdown Protection
Available in 20-Pin SSOP
MAX1623
________________________Applications
5V to 3.3V Conversion
Notebook Computer CPU I/O Supply
Desktop Computer Bus-Termination Supply
CPU Daughter Card Supply
DSP Supply
Ordering Information
PART
MAX1623EAP
TEMP. RANGE
-40°C to +85°C
PIN-PACKAGE
20 SSOP
Typical Operating Circuit
TOP VIEW
+5V
INPUT
+2.5V
OUTPUT
IN
LX
Pin Configuration
LX 1
IN 2
20 LX
19 PGND
18 LX
17 PGND
MAX1623
LX 3
V
CC
FBSEL
SHDN
TOFF
COMP
FB
GND
REF
PGND
IN 4
LX 5
IN 6
SHDN 7
FBSEL 8
TOFF 9
FB 10
MAX1623
16 LX
15 PGND
14 V
CC
13 COMP
12 REF
11 GND
SSOP
Idle Mode is a trademark of Maxim Integrated Products.
________________________________________________________________
Maxim Integrated Products
1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.
For small orders, phone 1-800-835-8769.
3A, Low-Voltage, Step-Down Regulator with
Synchronous Rectification and Internal Switches
MAX1623
ABSOLUTE MAXIMUM RATINGS
IN to PGND .....................................................................0V to 6V
V
CC
to GND ................................................................-0.3V to 6V
PGND to GND.....................................................................±0.5V
IN to V
CC
.............................................................................±0.5V
LX to PGND.................................................................-0.5V to 6V
SHDN
to GND .............................................................-0.3V to 6V
REF, FBSEL, COMP, FB, TOFF to GND .....-0.3V to (V
CC
+ 0.3V)
REF Short to GND ......................................................Continuous
Continuous Power Dissipation (T
A
= +70°C) (with part mounted
on 1 sq. inch of one ounce copper)
20-Pin SSOP (derate 22mW/°C above +70°C) ................1.3W
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature Range .............................-65°C to +150°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
IN
= V
CC
= +5V, FBSEL unconnected, R
TOFF
= 110kΩ,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
=
+25°C.)
PARAMETER
Input Voltage Range
FBSEL = unconnected
Output Voltage
Output Adjustment Range
Reference Output Voltage
Reference Load Regulation
Current-Limit Threshold
PMOS Switch On-Resistance
NMOS Switch On-Resistance
Maximum Switching Frequency
Idle Mode Threshold (Note 2)
No-Load Supply Current
Shutdown Supply Current
LX Leakage Current
Thermal Shutdown Threshold
Undervoltage Lockout Threshold
FB Input Bias Current
Error-Amplifier Gain Bandwidth
Off-Time Adjustment Range
Off-Time Default Period
AC Output Load Regulation
SHDN
Input Current
SHDN
Input Low Voltage
SHDN
Input High Voltage
2
FBSEL = GND
FBSEL = REF
SHDN
= GND or V
CC
-1
V
CC
falling, 100mV hysteresis
FBSEL = GND, adjustable output mode, V
FB
= 1.2V
(Note 1)
4.1
-25
500
0.5
0.85
1.00
1
2
0.03
1
0.8
4
1.15
Does not include switching losses
SHDN
= GND
V
IN
= 5.5V, V
LX
= 5.5V or 0
145
4.2
4.3
25
V
IN
= 4.5V
V
IN
= 4.5V
I
LOAD
≥
1.5A (Note 1)
1
1.25
400
0.5
V
IN
= 4.5V to 5.5V,
I
LOAD
= 0 to 3A
FBSEL = V
CC
FBSEL = GND or REF
CONDITIONS
MIN
4.5
3.296
2.49
1.089
V
REF
1.089
3.65
55
60
1.100
3.330
2.525
1.100
TYP
MAX
5.5
3.366
2.550
1.110
3.80
1.110
1
4.65
100
100
350
1.5
525
10
±20
V
V
mV
A
mΩ
mΩ
kHz
A
µA
µA
µA
°C
V
nA
kHz
µs
µs
%
µA
V
V
V
UNITS
V
FBSEL = GND or REF (Note 1)
I
REF
= 0
I
REF
= -1µA to 10µA
2
_______________________________________________________________________________________
3A, Low-Voltage, Step-Down Regulator with
Synchronous Rectification and Internal Switches
ELECTRICAL CHARACTERISTICS
(V
IN
= V
CC
= +5V, FBSEL unconnected, R
TOFF
= 110kΩ,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 3)
PARAMETER
Input Voltage Range
FBSEL = unconnected
Output Voltage
Output Adjustment Range
Reference Output Voltage
Current-Limit Threshold
PMOS Switch On-Resistance
NMOS Switch On-Resistance
No-Load Supply Current
Shutdown Supply Current
LX Leakage Current
Undervoltage Lockout Threshold
FB Input Bias Current
Off-Time Adjustment Range
Off-Time Default Period
SHDN
Input Current
SHDN
Input Low Voltage
SHDN
Input High Voltage
2.2
SHDN
= GND or V
CC
V
IN
= 4.5V
V
IN
= 4.5V
Does not include switching losses
SHDN
= GND
V
IN
= 5.5V, V
LX
= 5.5V or 0
V
CC
falling, 100mV hysteresis
FBSEL = GND, adjustable output mode, V
FB
= 1.2V
-20
4.0
-50
0.55
0.85
-1
V
IN
= 4.5V to 5.5V,
I
LOAD
= 0 to 3A
FBSEL = V
CC
FBSEL = GND or REF
CONDITIONS
MIN
4.5
3.234
2.450
1.075
V
REF
1.075
3.5
TYP
MAX
5.5
3.366
2.550
1.110
3.8
1.110
4.75
0.1
0.1
600
10
20
4.3
50
4
1.25
1
0.8
V
V
A
Ω
Ω
µA
µA
µA
V
nA
µs
µs
µA
V
V
V
UNITS
V
MAX1623
FBSEL = GND or REF (Note 1)
I
REF
= 0
Note 1:
Guaranteed by design, not production tested.
Note 2:
Idle Mode threshold is defined as the transition point in the load-current range between Idle Mode and constant-off-time
operation.
Note 3:
Specifications to -40°C are guaranteed by design, not production tested.
_______________________________________________________________________________________
3
3A, Low-Voltage, Step-Down Regulator with
Synchronous Rectification and Internal Switches
MAX1623
__________________________________________Typical Operating Characteristics
(Circuit of Figure 2, T
A
= +25°C, unless otherwise noted.)
SWITCH OFF-TIME vs.
OFF-TIME RESISTANCE
MAX1623 TOC01
MAX1623 TOC02
EFFICIENCY
vs. OUTPUT CURRENT
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.001
0.01
0.1
1
10
0
0
1
V
OUT
= 3.3V, R
TOFF
= 110kΩ
t
OFF
(µs)
V
OUT
= 2.5V, R
TOFF
= 180kΩ
V
OUT
= 1.1V, R
TOFF
= 280kΩ
3
5
SUPPLY CURRENT
vs. INPUT VOLTAGE
MAX1623 TOC03
1000
4
100
SUPPLY CURRENT (µA)
SHDN = IN
10
2
1
SHDN = GND
0.1
0.01
100
200
300
R
TOFF
(kΩ)
400
500
600
0
1
2
3
4
5
6
INPUT VOLTAGE (V)
OUTPUT CURRENT (A)
SWITCHING FREQUENCY
vs. LOAD CURRENT
MAX1623 TOC04
SWITCHING FREQUENCY
vs. INPUT VOLTAGE
350
SWITCHING FREQUENCY (kHz)
300
250
200
150
100
50
V
IN
= 5V, V
OUT
= 3.3V,
R
TOFF
= 110kΩ
V
IN
= 5V, V
OUT
= 2.5V,
R
TOFF
= 180kΩ
MAX1623 TOC05
350
300
SWITCHING FREQUENCY (kHz)
V
OUT
= 1.1V, R
TOFF
= 280kΩ
400
250
V
OUT
= 2.5V, R
TOFF
= 180kΩ
200
150
100
50
0
V
OUT
= 3.3V, R
TOFF
= 110kΩ
0
500
1000
1500
2000
2500
3000
0
4.5
4.7
4.9
5.1
5.3
5.5
LOAD CURRENT (mA)
INPUT VOLTAGE (V)
REFERENCE LOAD REGULATION ERROR
vs. REFERENCE LOAD CURRENT
MAX1623 TOC06
LOAD REGULATION ERROR
vs. LOAD CURRENT
-0.05
LOAD REGULATION ERROR (%)
-0.10
-0.15
-0.20
-0.25
-0.30
-0.35
-0.40
-0.45
V
OUT
= 2.5V, R
TOFF
= 180kΩ
V
OUT
= 3.3V, R
TOFF
= 110kΩ
MAX1623 TOC07
0
REFERENCE LOAD REGULATION ERROR (%)
-0.01
-0.02
-0.03
T
A
= -40°C
-0.04
T
A
= +85°C
-0.05
-0.06
0
5
10
15
20
T
A
= +25°C
0
25
-0.50
0.001
0.01
0.1
LOAD CURRENT (A)
1
10
REFERENCE LOAD CURRENT (µA)
4
_______________________________________________________________________________________
3A, Low-Voltage, Step-Down Regulator with
Synchronous Rectification and Internal Switches
____________________________ Typical Operating Characteristics (continued)
(Circuit of Figure 2, T
A
= +25°C, unless otherwise noted.)
LOAD-TRANSIENT RESPONSE
(FBSEL = REF)
MAX1623 TOC09
MAX1623 TOC10
MAX1623
START-UP AND SHUTDOWN TRANSIENT
MAX1623 TOC08
START-UP AND SHUTDOWN TRANSIENT
A
A
I
LOAD
0 to 3A
B
B
V
OUT
50mV
AC-COUPLED
f = 300kHz
1ms/div
V
IN
= 5V, V
OUT
= 3.3V, I
LOAD
= 2A,
WAVEFORM AVERAGED
A: V
OUT
, 2V/div
B: I
IN
, 1A/div
C: V
SHDN
, 5V/div
20µs/div
C
1ms/div
V
IN
= 5V, V
OUT
= 3.3V, I
LOAD
= 3A,
WAVEFORM AVERAGED
A: V
OUT
, 2V/div
B: I
IN
, 1A/div
C: V
SHDN
, 5V/div
C
LOAD-TRANSIENT RESPONSE
(FBSEL = REF)
MAX1623 TOC11
LINE-TRANSIENT RESPONSE
MAX1623 TOC12
LINE-TRANSIENT RESPONSE
MAX1623 TOC13
V
IN
= 4.5V
to 5.5V
AC-COUPLED
(1V/div)
V
IN
= 4.5V
to 5.5V
AC-COUPLED
(1V/div)
I
LOAD
0 to 2A
V
OUT
50mV
AC-COUPLED
f = 300kHz
20µs/div
V
OUT
= 3.3V
AC-COUPLED
I
OUT
= 1.5A
(20mV/div)
V
OUT
= 3.3V
AC-COUPLED
I
OUT
= 100mA
(20mV/div)
20µs/div
20µs/div
_______________________________________________________________________________________
5

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