19-1737; Rev 0; 7/00
External Four-Input Feedback Integrator for
Power Supplies
General Description
The MAX1804 feedback integrator is designed to
improve voltage regulation in power-supply systems.
The device corrects line- and load-regulation problems,
and can be used to compensate for voltage drops in
power-management distribution lines.
The regulation set point is determined by an external
reference voltage applied at the ADJ pin. The differ-
ence between that reference and MAX1804 feedback is
integrated, and a correction current is applied to the
voltage regulator’s feedback.
The MAX1804’s four inputs allow voltage monitoring in
several local and remote locations to correct for distribu-
tion losses caused by long traces, connectors, and
switches. This eliminates the wasteful practice of perma-
nently adjusting the regulator’s output voltage high
enough to correct for worst-case voltage drops. This is
especially helpful in systems where the load current
varies widely and portions of the load are often shut down
or disconnected (for example, in notebook computers).
If a load switch is opened and the output voltage
sensed at one input falls, the MAX1804 automatically
disables that input and adjusts the regulator’s output
voltage to the lowest of remaining active inputs. If all
inputs are disabled, the OUT pin is in a high-imped-
ance state and makes no output voltage correction.
When
SHDN
is low, the MAX1804 draws less than 1µA
and its inputs and output are high impedance. The
MAX1804 is available in a 10-pin µMAX package, about
half the size of an 8-pin SOIC.
o
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o
o
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Features
High Precision (±1% max Error)
Low Power (25µA Supply Current)
Automatic Input Disable
Shutdown (1µA max Supply Current)
Inputs and Outputs High Impedance in Shutdown
or When V+ = 0
+2.7V to +5.5V Supply Range
2.8V to 5.5V Regulation Adjust Range
Parallelable for More than Four Inputs
10-Pin µMAX Package
MAX1804
Ordering Information
PART
MAX1804EUB
TEMP. RANGE
-40°C to +85°C
PIN-PACKAGE
10
µMAX
Pin Configuration appears at end of data sheet.
Applications
Remote Feedback Regulators
High-Accuracy Regulators
Desktop/Notebook Computers
Servers and Workstations
Subnotebooks and PDAs
Typical Operating Circuit
V
IN
DH
SYSTEM
SUPPLY
V
OUT
A
DL
V
OUT
B
RTOP
REF
FB
V
OUT
C
R
OUT
R
BOTTOM
OUT
ADJ
MAX1804
COMP
GND
V+
SHDN
IN1
IN2
IN3
IN4
V
OUT
D
________________________________________________________________
Maxim Integrated Products
1
For free samples and the latest literature, visit www.maxim-ic.com or phone 1-800-998-8800.
For small orders, phone 1-800-835-8769.
External Four-Input Feedback Integrator for
Power Supplies
MAX1804
ABSOLUTE MAXIMUM RATINGS
V+, IN1, IN2, IN3, IN4, OUT, ADJ,
SHDN
to GND...…-0.3V, +6V
COMP to GND ....................................................-0.3V, V+ +0.3V
Continuous Power Dissipation (T
A
= +70°C)
10-Pin µMAX (derate 8.3mW/°C above +70°C) ..........667mW
Operating Temperature Extended Range ...........-40°C to +85°C
Junction Temperature ..................…………………………+150°C
Storage Temperature Range .……...……………-65°C to +165°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
(T
A
= 0°C to +85°C,
V
V
+ = 3.3V, V
ADJ
= 1.2V, V
OUT
= 2V, C
V
+ = 0.1µF, C
COMP
= 470pF. Typical values are at T
A
= +25°C, unless
otherwise noted.)
PARAMETER
Supply Voltage Range (V+)
Shutdown Supply Current (V+)
Quiescent Supply Current (V+)
UVLO Threshold, Rising
UVLO Threshold, Falling
INTEGRATOR INPUTS IN1–IN4
IN_ Voltage Range
IN_ Offset
IN_ Scale Factor
IN_ Transconductance
IN_ Bias Current
IN_ Shutdown Current
IN_ Leakage Current
IN_ Disable Threshold
IN_ Disable Threshold Hysteresis
ADJ INPUT
ADJ Voltage Range
ADJ Bias Current
ADJ Shutdown Current
ADJ Leakage Current
COMP OUTPUT
COMP Source Current
COMP Sink Current
COMP Output Voltage Low
COMP Output Voltage High
OUT OUTPUT
OUT Output Voltage Low
OUT Output Leakage Current
OUT Transconductance
I
OUT
= 10
µA,
V
IN_
= 4.6V
V
SHDN
= 0
V
V+
= 0
V
IN_
= 5.0V
V
COMP
= 1V to 2V
4
10
0.2
0.1
0.1
0.1
22
µS
µA
V
V
COMP
= 1.3V, V
IN_
= 4.6V
V
COMP
= 1.3V, V
IN_
= 5.0V
Sink 1µA, V
IN_
= 5.0V
Source 1µA, V
IN_
= 4.6V
2.4
1.6
1.6
2.0
2.0
2.4
2.4
0.2
µA
µA
V
V
SHDN
= GND
V
V+
= 0, V
SHDN
= 0
0.7
-20
1.4
20
0.2
0.2
V
nA
µA
µA
V
V+
= 2.7V to 5.5V
V
ADJ
= 0.7V to 1.4V
V
IN_
= 4.75V to 4.85V, V
COMP
= 1.3V
V
IN_
= 4.8V
SHDN
= GND
V
V+
= 0, V
SHDN
= 0
V
ADJ
= 0.7V to 1.4V, V
ADJ
x 4, falling edge
V
ADJ
= 0.7V to 1.4V, rising edge
87
90
50
0
-15
3.988
12
4.000
30
1.5
5.5
15
4.016
48
2.7
0.2
0.2
93
V
mV
V/V
µS
µA
µA
µA
%
mV
2.3
SHDN
= GND
SHDN
= V+
CONDITIONS
MIN
2.7
0.01
25
2.5
2.4
TYP
MAX
5.5
1
35
2.6
UNITS
V
µA
µA
V
V
2
_______________________________________________________________________________________
External Four-Input Feedback Integrator for
Power Supplies
MAX1804
ELECTRICAL CHARACTERISTICS (continued)
(T
A
= 0°C to +85°C,
V
V
+ = 3.3V, V
ADJ
= 1.2V, V
OUT
= 2V, C
V
+ = 0.1µF, C
COMP
= 470pF. Typical values are at T
A
= 25°C, unless oth-
erwise noted.)
PARAMETER
SHDN
INPUT
Logic Input Voltage High
Logic Input Voltage Low
Logic Input Current
V
V+
= 2.7V to 5.5V
V
V+
= 2.7V to 5.5V
-1
2.0
0.6
1
V
V
µA
CONDITIONS
MIN
TYP
MAX
UNITS
ELECTRICAL CHARACTERISTICS
(T
A
= -40°C to +85°C,
V
V
+ = 3.3V, V
ADJ
= 1.2V, V
OUT
= 2V, C
V
+ = 0.1µF, C
COMP
= 470pF.) (Note 1)
PARAMETER
Supply Voltage Range (V+)
Shutdown Supply Current (V+)
Quiescent Supply Current (V+)
UVLO Threshold, Rising
UVLO Threshold, Falling
INTEGRATOR INPUTS IN1–IN4
IN_ Voltage Range
IN_ Offset
IN_ Scale Factor
IN_ Transconductance
IN_ Bias Current
IN_ Shutdown Current
IN_ Leakage Current
IN_ Disable Threshold
ADJ INPUT
ADJ Voltage Range
ADJ Bias Current
ADJ Shutdown Current
ADJ Leakage Current
COMP OUTPUT
COMP Source Current
COMP Sink Current
COMP Output Voltage Low
COMP Output Voltage High
OUT Output Voltage Low
OUT Output Leakage Current
OUT Transconductance
V
COMP
= 1.3V, V
IN_
= 4.6V
V
COMP
= 1.3V, V
IN_
= 5.0V
Sink 1µA, V
IN_
= 5.0V
Source 1µA, V
IN_
= 0.6V
I
OUT
= 10µA, V
IN_
= 4.6V
V
SHDN
= 0
V
V+
= 0
V
IN
= 5.0V
V
COMP
= 1V to 2V
3
2.4
0.2
0.1
0.1
0.1
23
µS
µA
1.6
1.6
2.4
2.4
0.2
µA
µA
V
V
V
SHDN
= GND
V
V+
= 0, V
SHDN
= 0
0.7
-30
1.4
30
0.2
0.2
V
nA
µA
µA
V
V+
= 2.7V to 5.5V
V
ADJ
= 0.7V to 1.4V
V
IN_
= 4.75V to 4.85V, V
COMP
= 1.3V
V
IN_
= 4.8V
SHDN
= GND
V
V+
= 0, V
SHDN
= 0
V
ADJ
= 0.7V to 1.4V, V
ADJ
x 4, falling edge
87
0
-20
3.98
12
5.5
20
4.02
60
2.7
0.2
0.2
93
V
mV
V/V
µS
µA
µA
µA
%
2.3
SHDN
= GND
SHDN
= V+
CONDITIONS
MIN
2.7
TYP
MAX
5.5
1
35
2.6
UNITS
V
µA
µA
V
V
_______________________________________________________________________________________
3
External Four-Input Feedback Integrator for
Power Supplies
MAX1804
ELECTRICAL CHARACTERISTICS (continued)
(T
A
= -40°C to +85°C,
V
V
+ = 3.3V, V
ADJ
= 1.2V, V
OUT
= 2V, C
V
+ = 0.1µF, C
COMP
= 470pF.) (Note 1)
PARAMETER
SHDN
INPUT
Logic Input Voltage High
Logic Input Voltage Low
Logic Input Current
V
V+
= 2.7V to 5.5V
V
V+
= 2.7V to 5.5V
-1
2.0
0.6
1
V
V
µA
CONDITIONS
MIN
TYP
MAX
UNITS
Note 1:
Specifications to -40°C are guaranteed by design and not production tested.
Typical Operating Characteristics
(V
V
+ = V
SHDN
= 3.3V, V
ADJ
= 1.2V, V
OUT
= 2V, C
COMP
= 470pF, T
A
= +25°C, unless otherwise noted.)
QUIESCENT CURRENT vs.
TEMPERATURE
MAX1804 toc01
IN_REGULATION SET-POINT ERROR
vs. TEMPERATURE
MAX1804 toc02
IN_ (TO COMP) TRANSCONDUCTANCE
vs. TEMPERATURE
32
30
28
26
24
22
20
∆V
IN_
= 4.85V TO 4.75V
V
COMP
= 1.3V
-40
-20
0
20
40
60
80
MAX1804 toc03
29.0
28.5
QUIESCENT CURRENT (µA)
28.0
27.5
27.0
26.5
26.0
25.5
25.0
24.5
24.0
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
V
V+
= 3.3V
V
V+
= 5V
0.050
IN_REGULATION SET-POINT ERROR (%)
0.045
0.040
0.035
0.030
0.025
0.020
0.015
0.010
0.005
0
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
NOTE:
Circuit of Figure 1.
V
ADJ
= 1.4V
V
ADJ
= 1.2V
V
ADJ
= 0.7V
34
IN_TRANSCONDUCTANCE (µS)
TEMPERATURE (°C)
OUT CURRENT vs. COMP VOLTAGE
MAX1804toc04
IN_SCALE FACTOR vs. ADJ VOLTAGE
MAX1804toc05
CHANGE IN OUTPUT VOLTAGE
vs. OUTPUT CURRENT
0
CHANGE IN OUTPUT VOLTAGE (mV)
-50
-100
-150
-200
MAX1804 ON
-250
-300
V
OUT
= 5V (NOMINAL)
C
COMP
= 470pF
0.001
0.01
0.1
1
10
MAX1804 OFF
MAX1804toc06
30
25
OUT CURRENT (µA)
20
15
10
5
0
0
0.5
1.0
1.5
2.0
2.5
3.0
4.05
4.00
IN_SCALE FACTOR
3.95
3.90
3.85
3.80
3.75
3.5
0.4
0.6
0.8
1.0
1.2
1.4
COMP VOLTAGE (V)
ADJ VOLTAGE (V)
NOTE:
Circuit of Figure 1.
OUTPUT CURRENT (A)
NOTE:
Application Circuit of Figure 2.
4
_______________________________________________________________________________________
External Four-Input Feedback Integrator for
Power Supplies
Typical Operating Characteristics (continued)
(V
V
+ = V
SHDN
= 3.3V, V
ADJ
= 1.2V, V
OUT
= 2V, C
COMP
= 470pF, T
A
= +25°C, unless otherwise noted.)
LOAD TRANSIENT RESPONSE
(APPLICATION CIRCUIT OF FIGURE2)
MAX1804toc07
MAX1804
LOAD TRANSIENT RESPONSE
MAX1804toc08
CH1
CH1
CH2
0.5
0.01
CH5
CH4
CH3
CH2
CHR4
CHR3
CHR2
CHR1
100µs/div
CH1 = I
LOAD
; 1.00A/div
CH5 = V
IN1
; 500mV/div; AC-COUPLED (C
COMP
= 1000pF)
CH4 = V
IN1
; 500mV/div; AC-COUPLED (C
COMP
= 470pF)
CH3 = V
IN1
; 500mV/div; AC-COUPLED (C
COMP
= 220pF)
CH2 = V
IN1
; 500mV/div; AC-COUPLED (MAX1804 DISABLED)
V
IN
(MAX1653) = 8V
400µs/div
CH1 = I
LOAD
; 500mA/div
CH2 = V
IN1
; 500mV/div; AC-COUPLED (C
COMP
= 0.047µF)
CHR4 = V
IN1
; 500mV/div; AC-COUPLED (C
COMP
= 1000pF)
CHR3 = V
IN1
; 500mV/div; AC-COUPLED (C
COMP
= 2200pF)
CHR2 = V
IN1
; 500mV/div; AC-COUPLED (C
COMP
= 4700pF)
CHR1 = V
IN1
; 500mV/div; AC-COUPLED (MAX1804 DISABLED)
V
IN
(MAX603) = 8V
NOTE:
Circuit of Figure 3.
STARTUP/SHUTDOWN WAVEFORM
MAX1804toc09
AUTOMATIC INPUT DISABLE WAVEFORM
CHR1
MAX1804toc10
CH1
CH1
IN2 ENABLE
CH2
CH2
IN2 DISABLE
200µs/div
IN2 DISABLE
200µs/div
CH1 = SHDN, 2V/div
CH2 = V
IN2
; 200mV/div; DC OFFSET = 4.7V
I
LOAD
= 0.5A
V
IN
(MAX1653) = 8V
NOTE:
Circuit of Figure 2.
CHR1 = V
G(PFET)
; 5V/div
CH1 = V
IN1
; 200mV/div; DC OFFSET = 4.8V
CH2 = V
IN2
; 2V/div
V
IN
(MAX1653) = 8V
NOTE:
Circuit of Figure 2.
_______________________________________________________________________________________
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