19-2142; Rev 1; 9/02
3A, 1MHz, DDR Memory Termination Supply
General Description
The MAX1809 is a reversible energy flow, constant-off-
time, pulse-width modulated (PWM), step-down DC-DC
converter. It is ideal for use in notebook and subnote-
book computers that require 1.1V to 5V active
termination power supplies. This device features an
internal PMOS power switch and internal synchronous
rectifier for high efficiency and reduced component
count. The internal 90mΩ PMOS power switch and
70mΩ NMOS synchronous-rectifier switch easily deliver
continuous load currents up to 3A. The MAX1809 accu-
rately tracks an external reference voltage, produces
an adjustable output from 1.1V to V
IN
, and achieves
efficiencies as high as 93%.
The MAX1809 uses a unique current-mode, constant-
off-time, PWM control scheme that allows the output to
source or sink current. This feature allows energy to
return to the input power supply that otherwise would
be wasted. The programmable constant-off-time archi-
tecture sets switching frequencies up to 1MHz, allowing
the user to optimize performance trade-offs between
efficiency, output switching noise, component size, and
cost. The MAX1809 features an adjustable soft-start to
limit surge currents during startup, a 100% duty-cycle
mode for low-dropout operation, and a low-power shut-
down mode that disables the power switches and
reduces supply current below 1µA. The MAX1809 is
available in a 28-pin QFN with an exposed backside
pad, a 28-pin thin QFN, or a 16-pin QSOP.
o
Source/Sink 3A
o
±1% Output Accuracy
o
Up to 1MHz Switching Frequency
o
93% Efficiency
o
Internal PMOS/NMOS Switches
90mΩ/70mΩ On-Resistance at V
IN
= 4.5V
110mΩ/80mΩ On-Resistance at V
IN
= 3V
o
1.1V to V
IN
Adjustable Output Voltage
o
3V to 5.5V Input Voltage Range
o
<1µA Shutdown Supply Current
o
Programmable Constant-Off-Time Operation
o
Thermal Shutdown
o
Adjustable Soft-Start Inrush Current Limiting
o
Output Short-Circuit Protection
Features
MAX1809
Ordering Information
PART
MAX1809EGI*
MAX1809EEE
MAX1809ETI
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
28 QFN
16 QSOP
28 Thin QFN
Applications
DDR Memory Termination
Active Termination Buses
*Contact
factory for availability.
Pin Configurations
SHDN
N.C.
LX
LX
Typical Operating Circuit
V
IN
IN
MAX1809
V
CC
SHDN
V
SET
EXTREF
TOFF
REF
SS
LX
PGND
V
OUT
TOP VIEW
28
N.C.
27
26
25
24
N.C.
23
N.C.
IN
LX
IN
22
N.C.
1
2
3
4
5
6
7
10
11
12
13
14
8
9
21
20
19
PGND
PGND
LX
LX
PGND
V
CC
GND
GND
N.C.
MAX1809
18
17
16
15
FB
SS
EXTREF
N.C.
N.C.
N.C.
TOFF
THIN QFN
Pin Configurations continued at end of data sheet.
________________________________________________________________
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.
GND
REF
FB
3A, 1MHz, DDR Memory Termination Supply
MAX1809
ABSOLUTE MAXIMUM RATINGS
V
CC
, IN to GND ........................................................-0.3V to +6V
IN to V
CC
.............................................................................±0.3V
GND to PGND.....................................................................±0.3V
SHDN,
SS, FB, T
OFF
, R
REF
,
EXTREF to GND.......................................-0.3V to (V
CC
+ 0.3V)
LX Current (Note 1).............................................................±4.7A
REF Short Circuit to GND Duration ............................Continuous
Continuous Power Dissipation (T
A
= +70°C)
28-Pin QFN (derate 20mW/°C above +70°C;
part mounted on 1in
2
of 1oz copper) ..............................1.6W
16-Pin QSOP (derate 12.5mW/°C above +70°C;
part mounted on 1in
2
of 1oz copper) .................................1W
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
Note 1:
LX has clamp diodes to PGND and IN. If continuous current is applied through these diodes, thermal limits must be
observed.
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
= 3.3V, V
EXTREF
= 1.1V,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
Input Voltage
Feedback Voltage Accuracy
(V
FB
- V
EXTREF
)
Feedback Load Regulation Error
External Reference Voltage
Range
Reference Voltage
Reference Load Regulation
PMOS Switch
On-Resistance
NMOS Switch
On-Resistance
Current-Limit Threshold
Switching Frequency
No Load Supply Current
Shutdown Supply Current
Thermal-Shutdown Threshold
Undervoltage Lockout Threshold
FB Input Bias Current
Off-Time
Startup Off-Time
On-Time
t
ON
(Note 3)
0.35
I
FB
t
OFF
R
PMOS
R
NMOS
I
LIMIT
f
SW
I
CC
I
IN
I
SHDN
∆V
FB
V
EXTREF
V
REF
I
REF
= -1µA to +10µA
I
LX
= 0.5A
I
LX
= 0.5A
V
IN
> V
LX
(Note 3)
f
SW
= 500kHz
f
SW
= 500kHz
SHDN
= GND, I
CC
+ I
IN
Hysteresis = 15°C
V
CC
falling, hysteresis = 90mV
V
FB
= V
EXTREF
+ 0.1V
R
TOFF
= 30.1kΩ
R
TOFF
= 110kΩ
R
TOFF
= 499kΩ
2.5
0
0.24
0.9
3.8
1
16
<1
160
2.6
60
0.30
1.0
4.5
4 x t
OFF
2.7
250
0.37
1.1
5.2
µs
µs
µs
15
V
IN
= 4.5V
V
IN
= 3V
V
IN
= 4.5V
V
IN
= 3V
3.5
SYMBOL
V
IN
,V
CC
V
IN
= V
CC
= 3V to 5.5V, I
LOAD
= 0,
V
EXTREF
= 1.25V (Note 2)
I
LOAD
= -3A to +3A, V
EXTREF
= 1.25V
V
IN
= V
CC
= 3V to 5.5V
V
REF
-
0.01
1.078
1.100
0.5
90
110
70
80
4.1
CONDITIONS
MIN
3.0
-12
20
V
IN
-
1.7
1.122
2.0
200
250
150
200
4.7
1
TYP
MAX
5.5
+12
UNITS
V
mV
mV
V
V
mV
mΩ
mΩ
A
MHz
mA
µA
°C
V
nA
2
_______________________________________________________________________________________
3A, 1MHz, DDR Memory Termination Supply
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= V
CC
= 3.3V, V
EXTREF
= 1.1V,
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
SHDN
Input Current
SHDN
Logic Levels
Maximum Output RMS Current
V
IL
V
IH
I
OUT(RMS)
2
3.1
SYMBOL
I
SS
I
SS
V
SS
= 1V
V
SHDN
= 0, V
CC
CONDITIONS
MIN
4
1
-1
TYP
5
50
+1
0.8
MAX
6
UNITS
µA
mA
µA
V
A
RMS
MAX1809
ELECTRICAL CHARACTERISTICS
(V
IN
= V
CC
= 3.3V, V
EXTREF
= 1.1V,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 4)
PARAMETER
Input Voltage
Feedback Voltage Accuracy
(V
FB
- V
EXTREF
)
External Reference Voltage
Range
Reference Voltage
PMOS Switch
On-Resistance
NMOS Switch
On-Resistance
Current-Limit Threshold
FB Input Bias Current
Off-Time
V
EXTREF
V
REF
R
PMOS
R
NMOS
I
LIMIT
I
FB
t
OFF
I
LX
= 0.5A
I
LX
= 0.5A
V
IN
> V
LX
V
FB
= V
EXTREF
+ 0.1V
R
TOFF
= 110kΩ
0.85
V
IN
= 4.5V
V
IN
= 3V
V
IN
= 4.5V
V
IN
= 3V
3.3
SYMBOL
V
IN
, V
CC
V
IN
= V
CC
= 3V to 5.5V, I
LOAD
= 0,
V
EXTREF
= 1.25V
V
IN
= V
CC
= 3 V to 5.5V
CONDITIONS
MIN
3.0
-24
V
REF
-
0.01V
1.067
TYP
MAX
5.5
+24
V
IN
-
1.9V
1.133
200
250
150
200
4.9
300
1.15
UNITS
V
mV
V
V
mΩ
mΩ
A
nA
µs
Note 2:
The output voltage will have a DC-regulation level lower than the feedback error comparator threshold by 50% of the ripple.
Note 3:
Recommended operating frequency, not production tested.
Note 4:
Specifications from 0°C to -40°C are guaranteed by design, not production tested.
_______________________________________________________________________________________
3
3A, 1MHz, DDR Memory Termination Supply
MAX1809
Typical Operating Characteristics
(Circuit of Figure 1, V
OUT
= 1.25V, for V
IN
= 5V: L = 1µH, R
TOFF
= 130kΩ; for V
IN
= 3.3V: L = 0.68µH, R
TOFF
= 73.2kΩ.)
EFFICIENCY vs. OUTPUT CURRENT
(SOURCING)
MAX1809 toc01
EFFICIENCY vs. OUTPUT CURRENT
(SINKING)
MAX1809 toc02
NORMALIZED OUTPUT ERROR
vs. OUTPUT CURRENT
-0.2
NORMALIZED OUTPUT ERROR (%)
-0.6
-1.0
-1.4
-1.8
-2.2
-2.6
-3.0
V
IN
= 5V
V
IN
= 3.3V
MAX1809 toc03
100
95
90
EFFICIENCY (%)
85
80
75
70
65
60
55
50
0
1
2
OUTPUT CURRENT (A)
3
V
IN
= 5V,
V
OUT
= 2.5V
V
IN
= 3.3V,
V
OUT
= 1.25V
V
IN
= 5V,
V
OUT
= 1.25V
R
DROOP
= 0Ω
95
90
85
EFFICIENCY (%)
80
75
70
65
60
55
50
0
V
IN
= 5V,
V
OUT
= 2.5V
R
DROOP
= 0Ω
V
IN
= 5V,
V
OUT
= 1.25V
V
IN
= 3.3V,
V
OUT
= 1.25V
1
2
OUTPUT CURRENT (A)
3
-3
-2
-1
0
1
2
3
OUTPUT CURRENT (A)
NO-LOAD
SUPPLY CURRENT vs. SUPPLY VOLTAGE
NO-LOAD SUPPLY CURRENT (I
IN
+ I
CC
(mA))
24
20
16
12
8
4
0
0
1
2
3
V
IN
(V)
4
5
6
MAX1809 toc04
OFF-TIME vs. R
TOFF
4.5
4.0
3.5
t
OFF
(µs)
3.0
2.5
2.0
1.5
1.0
0.5
0
0
50 100 150 200 250 300 350 400 450 500
R
TOFF
(kΩ)
0
-3
-2
MAX1809 toc05
SWITCHING FREQUENCY
vs. OUTPUT CURRENT
V
IN
= 3.3V
MAX1809 toc06
5.0
1200
1000
FREQUECNY (kHz)
800
600
400
200
V
IN
= 5V
-1
0
1
OUTPUT CURRENT (A)
2
3
STARTUP AND SHUTDOWN
MAX1809 toc07
LOAD-TRANSIENT RESPONSE
I
IN
1A/div
R
DROOP
= 0Ω
MAX1809 toc08
V
OUT
(AC-COUPLED)
0A
V
SHDN
5V/div
V
OUT
1V/div
0V
0V
1ms/div
V
IN
= 3.3V, R
OUT
= 0.5Ω
V
SS
2V/div
10µs/div
V
EXTREF
= 1.25V, V
IN
= 3.3V, I
OUT
= -2A to +2A to -2A
0A
50mV/div
0V
0V
V(LX)
5V/div
I
OUT
5A/div
4
_______________________________________________________________________________________
3A, 1MHz, DDR Memory Termination Supply
Typical Operating Characteristics (continued)
(Circuit of Figure 1, V
OUT
= 1.25V, for V
IN
= 5V: L = 1µH, R
TOFF
= 130kΩ; for V
IN
= 3.3V: L = 0.68µH, R
TOFF
= 73.2kΩ.)
LOAD-TRANSIENT RESPONSE
R
DROOP
12mΩ
MAX1809 toc09
MAX1809
LINE-TRANSIENT RESPONSE
MAX1809 toc10
V
OUT
(AC-COUPLED)
V
OUT
(AC-COUPLED)
50mV/div
V
IN
2V/div
50mV/div
0V
V(LX)
5V/div
I
OUT
5A/div
0A
0V
10µs/div
V
EXTREF
= 1.25V, V
IN
= 3.3V, I
OUT
= -2A to +2A to -2A
20µs/div
I
OUT
= 2A, V
IN
= 5V to 3.3V to 5V
SWITCHING WAVEFORMS (SOURCING)
MAX1809 toc11
SWITCHING WAVEFORMS (SINKING)
MAX1809 toc12
V
OUT
(AC-COUPLED)
V
OUT
(AC-COUPLED)
50mV/div
50mV/div
I(LX)
2A/div
0A
0V
0A
I(LX)
2A/div
V(LX)
5V/div
400ns/div
I
OUT
= 2A, V
IN
= 5V
0V
400ns/div
I
OUT
= -2A, V
IN
= 5V
V(LX)
5V/div
_______________________________________________________________________________________
5
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