Document
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 difference 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 distribution losses caused by long traces, connectors, and switches. This eliminates the wasteful practice of permanently 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-impedance 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 o o o o o o o o
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
VIN DH SYSTEM SUPPLY VOUT A DL VOUT B RTOP
REF
FB VOUT C ROUT RBOTTOM
OUT ADJ MAX1804 COMP GND
V+ SHDN IN1 IN2 IN3 IN4
VOUT D
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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 (TA = +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
(TA = 0°C to +85°C, VV+ = 3.3V, VADJ = 1.2V, VOUT = 2V, CV+ = 0.1µF, CCOMP = 470pF. Typical values are at TA = +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 IOUT = 10 µA, VIN_ = 4.6V V SHDN = 0 VV+ = 0 VIN_ = 5.0V VCOMP = 1V to 2V 4 10 0.2 0.1 0.1 0.1 22 µS µA V VCOMP = 1.3V, VIN_ = 4.6V VCOMP = 1.3V, VIN_ = 5.0V Sink 1µA, VIN_ = 5.0V Source 1µA, VIN_ = 4.6V 2.4 1.6 1.6 2.0 2.0 2.4 2.4 0.2 µA µA V V SHDN = GND VV+ = 0, V SHDN = 0 0.7 -20 1.4 20 0.2 0.2 V nA µA µA VV+ = 2.7V to 5.5V VADJ = 0.7V to 1.4V VIN_ = 4.75V to 4.85V, VCOMP = 1.3V VIN_ = 4.8V SHDN = GND VV+ = 0, V SHDN = 0 VADJ = 0.7V to 1.4V, VADJ x 4, falling edge VADJ = 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.