View MAX1804_314621.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

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 1A and its inputs and output are high impedance. The MAX1804 is available in a 10-pin MAX 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 (25A Supply Current) Automatic Input Disable Shutdown (1A 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 MAX Package
MAX1804
Ordering Information
PART MAX1804EUB TEMP. RANGE -40C to +85C PIN-PACKAGE 10 MAX
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
________________________________________________________________ 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 (TA = +70C) 10-Pin MAX (derate 8.3mW/C above +70C) ..........667mW Operating Temperature Extended Range ...........-40C to +85C Junction Temperature ................................................+150C Storage Temperature Range .........................-65C to +165C Lead Temperature (soldering, 10s) .................................+300C
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 = 0C to +85C, VV+ = 3.3V, VADJ = 1.2V, VOUT = 2V, CV+ = 0.1F, CCOMP = 470pF. Typical values are at TA = +25C, 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 A, 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 S A V VCOMP = 1.3V, VIN_ = 4.6V VCOMP = 1.3V, VIN_ = 5.0V Sink 1A, VIN_ = 5.0V Source 1A, VIN_ = 4.6V 2.4 1.6 1.6 2.0 2.0 2.4 2.4 0.2 A A V V SHDN = GND VV+ = 0, V SHDN = 0 0.7 -20 1.4 20 0.2 0.2 V nA A A 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 S A A A % 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 A A V V
2
_______________________________________________________________________________________
External Four-Input Feedback Integrator for Power Supplies MAX1804
ELECTRICAL CHARACTERISTICS (continued)
(TA = 0C to +85C, VV+ = 3.3V, VADJ = 1.2V, VOUT = 2V, CV+ = 0.1F, CCOMP = 470pF. Typical values are at TA = 25C, unless otherwise noted.)
PARAMETER SHDN INPUT Logic Input Voltage High Logic Input Voltage Low Logic Input Current VV+ = 2.7V to 5.5V VV+ = 2.7V to 5.5V -1 2.0 0.6 1 V V A CONDITIONS MIN TYP MAX UNITS
ELECTRICAL CHARACTERISTICS
(TA = -40C to +85C, VV+ = 3.3V, VADJ = 1.2V, VOUT = 2V, CV+ = 0.1F, CCOMP = 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 VCOMP = 1.3V, VIN_ = 4.6V VCOMP = 1.3V, VIN_ = 5.0V Sink 1A, VIN_ = 5.0V Source 1A, VIN_ = 0.6V IOUT = 10A, VIN_ = 4.6V V SHDN = 0 VV+ = 0 VIN = 5.0V VCOMP = 1V to 2V 3 2.4 0.2 0.1 0.1 0.1 23 S A 1.6 1.6 2.4 2.4 0.2 A A V V V SHDN = GND V V+ = 0, V SHDN = 0 0.7 -30 1.4 30 0.2 0.2 V nA A A 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 87 0 -20 3.98 12 5.5 20 4.02 60 2.7 0.2 0.2 93 V mV V/V S A A A % 2.3 SHDN = GND SHDN = V+ CONDITIONS MIN 2.7 TYP MAX 5.5 1 35 2.6 UNITS V A A V V
_______________________________________________________________________________________
3
External Four-Input Feedback Integrator for Power Supplies MAX1804
ELECTRICAL CHARACTERISTICS (continued)
(TA = -40C to +85C, VV+ = 3.3V, VADJ = 1.2V, VOUT = 2V, CV+ = 0.1F, CCOMP = 470pF.) (Note 1)
PARAMETER SHDN INPUT Logic Input Voltage High Logic Input Voltage Low Logic Input Current VV+ = 2.7V to 5.5V VV+ = 2.7V to 5.5V -1 2.0 0.6 1 V V A CONDITIONS MIN TYP MAX UNITS
Note 1: Specifications to -40C are guaranteed by design and not production tested.
Typical Operating Characteristics
(VV+ = V SHDN = 3.3V, VADJ = 1.2V, VOUT = 2V, CCOMP = 470pF, TA = +25C, 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 VIN_ = 4.85V TO 4.75V VCOMP = 1.3V -40 -20 0 20 40 60 80
MAX1804 toc03
29.0 28.5 QUIESCENT CURRENT (A) 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) VV+ = 3.3V VV+ = 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. VADJ = 1.4V VADJ = 1.2V VADJ = 0.7V
34
IN_TRANSCONDUCTANCE (S)
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 VOUT = 5V (NOMINAL) CCOMP = 470pF 0.001 0.01 0.1 1 10 MAX1804 OFF
MAX1804toc06
30 25 OUT CURRENT (A) 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)
(VV+ = V SHDN = 3.3V, VADJ = 1.2V, VOUT = 2V, CCOMP = 470pF, TA = +25C, 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
100s/div CH1 = ILOAD; 1.00A/div CH5 = VIN1; 500mV/div; AC-COUPLED (CCOMP = 1000pF) CH4 = VIN1; 500mV/div; AC-COUPLED (CCOMP = 470pF) CH3 = VIN1; 500mV/div; AC-COUPLED (CCOMP = 220pF) CH2 = VIN1; 500mV/div; AC-COUPLED (MAX1804 DISABLED) VIN (MAX1653) = 8V
400s/div CH1 = ILOAD; 500mA/div CH2 = VIN1; 500mV/div; AC-COUPLED (CCOMP = 0.047F) CHR4 = VIN1; 500mV/div; AC-COUPLED (CCOMP = 1000pF) CHR3 = VIN1; 500mV/div; AC-COUPLED (CCOMP = 2200pF) CHR2 = VIN1; 500mV/div; AC-COUPLED (CCOMP = 4700pF) CHR1 = VIN1; 500mV/div; AC-COUPLED (MAX1804 DISABLED) VIN (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 200s/div IN2 DISABLE
200s/div CH1 = SHDN, 2V/div CH2 = VIN2; 200mV/div; DC OFFSET = 4.7V ILOAD = 0.5A VIN (MAX1653) = 8V NOTE: Circuit of Figure 2.
CHR1 = VG(PFET); 5V/div CH1 = VIN1; 200mV/div; DC OFFSET = 4.8V CH2 = VIN2; 2V/div VIN (MAX1653) = 8V NOTE: Circuit of Figure 2.
_______________________________________________________________________________________
5
External Four-Input Feedback Integrator for Power Supplies MAX1804
Pin Description
NAME IN1 IN2 IN3 IN4 ADJ GND COMP PIN 1 2 3 4 5 6 7 FUNCTION Sense Input 1. Connect to one of up to four inputs to be monitored. If IN_ is the lowest active input, IN_ will be regulated at 4 x V ADJ. If IN_ is less than 90% of the regulation set point (4 x VADJ), it is automatically disabled. Sense Input 2 Sense Input 3 Sense Input 4 Regulation Adjustment Input. The voltage at this input adjusts the regulation set point of IN1-IN4.There is a 4x scale factor between V ADJ and the regulation set point. Ground Integrator Capacitor Connection. Connect a capacitor (>100pF) to GND to set the integrator time constant. See Integrator Gain-Bandwidth Product and Regulator Stability section. Open-Drain Output. Can sink at least 10A if any of the inputs remain below the regulation set point. Connect OUT to the feedback point of the regulator-divider resistors. If OUT is connected through a resistor, its value relative to the regulator's feedback-divider values sets the maximum positive adjustment range. See Setting the Maximum Regulator Output Adjustment Increase section. Shutdown Control Input. When SHDN is low, the device is off and the supply current is reduced to about 10nA. All inputs are in high-impedance state. When SHDN is high, the device is on. Power-Supply Input. Bypass with 0.1F capacitor to GND.
OUT
8
SHDN V+
9 10
Detailed Description
The MAX1804 is a precision external feedback integrator used for tight point-of-load regulation in power-management systems. The dynamic regulation of the output is still controlled by the power-supply regulator. The MAX1804 is used only to fine tune the output voltage, removing load- and line-regulation errors and voltage drops across switches and connectors that occur in the power-supply distribution line. The MAX1804 includes four remote-sense inputs and an output that connects to a voltage regulator's feedback divider. It can be used with any regulator or controller with a high-impedance feedback input. Its OUT pin sinks current to increase the regulator's set point so that the four IN_ inputs are at or above MAX1804's regulation set point, which is four times the voltage applied to the ADJ pin. The MAX1804 monitors the input signals and compares the lowest to the voltage set point. The error between the input signal and the set point is integrated. The MAX1804 output stage generates a current based on the integrator output to adjust the regulator's output voltage to meet the set point.
1k 1%
+10V
MAX400
1k 1%
-10V 1M 1% 3.3V 25k 1% 75k 1%
3.3V SHDN OUT
V+ IN1 IN2
MAX1804
ADJ
IN3 IN4 COMP
EXTERNAL REF
0.1F 470pF
Figure 1. Test Circuit for MAX1804 IN_ Regulation Set Point
6
_______________________________________________________________________________________
External Four-Input Feedback Integrator for Power Supplies MAX1804
VL VIN 4.5V TO 28V 4.7F 16V 10 C2 0.1F SHDN VL 3 JU2 2 1 2 SKIP DL 13 SYNC 2 JU4 3 5 SYNC PGND 12 3 C5 0.33F 100k 4 GND SS 1 C6 0.01F JU3 0.01F 100k 1M EXT REF COMP VL V+ SHDN ADJ OUT IN1 IN2 CSH 8 CSL 9 FB 7 RBOTTOM 100k 1% 2 1 3 JU1 2 6 V+ C3 D1 CMPSH-3 11 VL DH 16 BST 14 SHDN 3 4 3 C4 0.1F LX 15 8 7 N1A IRF7303 D2 MBR0530 L1 15H R1 0.033 1% C7 220F 10V VOUT 5V 5% PFET 6 5 N1B IRF7303 C1 22F 35V
1
2
U1 MAX1653
RTOP 91k 1%
ILOAD
REF
REF
562k
MAX1804
IN3 IN4
Figure 2. Application Circuit with Step-Down Regulator
The MAX1804 only sinks current at OUT (Figure 4). The maximum sink current and maximum regulator voltage increase are limited by the minimum guaranteed OUT current of 10A. The maximum regulator output voltage increase can be further limited by including a resistor between OUT and the feedback point of the regulator. If any of the IN_ inputs fall to 90% of the regulation set point, they are automatically disabled and OUT continues to regulate according to the lowest remaining active input. See Automatic Input Disable.
The total error in the MAX1804 regulation set point is: total percentage error = [(IN_scale factor x VADJ + IN_offset) / (4 x VADJ)] x 100% The maximum IN_ voltage is 5.5V. Use the MAX1804 for higher output voltages by using an external divider to divide down the desired output voltage at the IN1-IN4 pins. Since the IN_ input bias current is fairly high (1.5A typ), choose the resistive divider accordingly.
Automatic Input Disable
The MAX1804 has an input buffer stage that monitors the sense inputs (IN1-IN4) and connects the lowest to its internal integrator (Figure 4). Each input is compared to 90% of the set point. If the input falls below this value, the input buffer is disabled and the output voltage is adjusted according to the lowest of the remaining active inputs (see Automatic Input Disable in Typical Operating Characteristics). If all four sense
7
Adjusting the Regulation Set Point
The MAX1804 monitors the voltage at the IN1-IN4 sense inputs and regulates the lowest active input to four times the reference voltage at ADJ. The IN1-IN4 regulation set point is calculated as: VIN_ = 4 VADJ
_______________________________________________________________________________________
External Four-Input Feedback Integrator for Power Supplies MAX1804
5V TO 11V
10F
FDV 304P IN OFF OUT
10F
ILOAD
Place the regulator's feedback resistors and R OUT close to the regulator's feedback pin to reduce noise pickup at the regulator's feedback point, which can cause unstable switching in the regulator (Figure 5).
MAX603
0 TO 500mA RTOP 300k RTOP 600k
Shutdown Mode
SET
GND RBOTTOM 100k
SHDN is a logic input that, when held low, places the MAX1804 in its low-power shutdown mode, reducing the supply current to 10nA (typ). The IN1-IN4, OUT, and ADJ are high impedance when the MAX1804 is in shutdown or when V+ is removed. Connect SHDN to V+ for normal operation.
Undervoltage Lockout
1.25V REFERENCE
V+ ADJ
SHDN
SET IN1 IN2
MAX1804
COMP 2200pF GND
IN3 IN4
The MAX1804 has an undervoltage lockout (UVLO) feature that deactivates the device when the supply voltage at V+ goes below 2.4V; IN1-IN4, OUT, and ADJ go to high impedance and do not affect the regulator operation. Hysteresis holds the device in lockout until the supply voltage at V+ rises above 2.6V.
Integrator Gain-Bandwidth Product and Regulator Stability
The MAX1804 gain-bandwidth (GBW) product is set by the external capacitor on COMP: GBW = [4 x (IN_ transconductance)] / (2 CCOMP) The bandwidth is typically 40kHz with a 470pF capacitor on COMP. For system stability, the integrator GBW product is typically set below the regulator circuit's crossover frequency, if known. Switching regulators typically have crossover frequencies well below their switching frequencies. Setting the MAX1804's GBW product too high can cause regulator loop instability, typically evidenced by ringing after transients. Setting the GBW product unnecessarily low will slow the MAX1804's loop response to transients, although the regulator's loop transient response will remain unaffected (see Load Transient Response in Typical Operating Characteristics). Often the regulator's crossover frequency varies with load and is not easily found. If the regulator's crossover frequency is unknown, the MAX1804's gain-bandwidth product can be chosen empirically. Start with a fairly low capacitor value (470pF is a good starting point) and increase the value until the circuit is stable with all loads. Then increase the value further to ensure design margin. If transient response is unimportant, choose a large COMP capacitor value (such as 2200pF), thereby maximizing stability.
Figure 3. MAX1804 Used with Linear Regulator
inputs are disabled, OUT is high impedance. Connect any unused input to GND.
Setting the Maximum Regulator Output Voltage Increase
The ratio between the maximum guaranteed OUT current of 10A and the current in the regulator's feedback resistive divider determines the maximum increase. The maximum increase in the regulator output voltage depends on the regulator's upper feedback resistor (RTOP) and the sink current into OUT: VOUT(MAX) = IOUT(MAX) x RTOP The maximum adjust current IOUT(MAX) can be further limited with a resistor (ROUT) between OUT and the feedback point of the regulator (see Typical Operating Circuit): IOUT(MAX) = VFB / ROUT where VFB is the voltage at the regulator's feedback point. Therefore: VOUT(MAX) = VFB x RTOP / ROUT and: ROUT = VFB x RTOP / VOUT(MAX)
8
_______________________________________________________________________________________
External Four-Input Feedback Integrator for Power Supplies MAX1804
VBATT V+ +5V SYSTEM SUPPLY SYSTEM DC/DC FB3 GND ONB 51k 390k ONC FB5 47k ONA
OND 0.1F
SHDN
V+
MAX1804
SHUTDOWN LOGIC UVLO EN 3R 1R IN1
SHDN
OUT EN EN 3R 1R IN2
SHDN
EN 3R 1R
IN3
SHDN
EN 470pF COMP EN 3R gm = 120S 1R IN4
SHDN ADJ
GND
1R
9R
Figure 4. MAX1804 Functional Block Diagram _______________________________________________________________________________________ 9
External Four-Input Feedback Integrator for Power Supplies MAX1804
RTOP ROUT
Choose feedback resistors (RTOP and RBOTTOM) for about 25A current in the resistive divider for noise immunity.
TO
Therefore: (RTOP + RBOTTOM) = 4.8V / 25A = 192k For the MAX1653, the voltage at its feedback point VFB = 2.5V. Choose R TOP = 91k and therefore, R BOTTOM = 100k. If the desired adjustment range is +400mV, max OUT current (MAX1804) is given by: IOUT(MAX) = 0.4V / 91k = 4.4A
MAX1653
FB RBOTTOM GND
MAX1804
SHORT COMPACT PLACEMENT OF FEEDBACK RESISTORS REDUCES NOISE PICKUP
Figure 5. Proper Layout of Feedback Resistors for Regulator
Applications Information
Layout Information
Proper layout is essential due to high current levels and switching waveforms that generate noise. Place the regulator's feedback resistors and ROUT (from the regulator feedback point to OUT of MAX1804) close to the regulator's feedback point to prevent noise pickup (Figure 5). Minimize leakage of the COMP capacitor and traces around COMP because they cause IN_ set-point errors according to the IN_ transconductance. A leakage of ICOMP at COMP will result in an error given by: IN_ error voltage = ICOMP / (IN_ transconductance) For a typical value of IN_ transconductance of 30S, a leakage of 0.1A will result in an IN_ error voltage of 3mV in the set point.
ROUT = VFB / IOUT(MAX) = 2.5V / 4.4A = 562k To guarantee that the output will not go below the target of 4.75V, including all error sources, set the MAX1804 nominal regulation point to 4.85V. Since: IN_scale factor = 4 x VADJ, VADJ = 1.2125V Divide the reference voltage down and bypass as required if using the MAX1653 reference voltage as shown in Figure 2. Assuming 0.1% resistor accuracy and using the MAX1653 reference, the error budget can be calculated as: Reference Accuracy ADJ Divider Accuracy Scale Factor Error -1.6% -0.2% -0.4%
Design Example (Step-Down Converter Application)
Figure 2 is an example of an application circuit using the MAX1804 for point-of-load regulation when using a step-down controller (MAX1653). Use the following design procedure to optimize the basic schematic. Begin the design by establishing the following: * Input voltage to the MAX1653 controller (7V to 20V) * Typical output voltage and accuracy of MAX1653 (5V 5%) This gives a target of: VOUT, min = 5V - 5% = 4.75V To minimize power dissipation, set regulator output VOUT, R = 4.8V with MAX1653 feedback resistors.
IN_ Offset Voltage (-15mV) -0.3% Total -2.5% This gives a worst-case output voltage of 4.73V, which is below the target of 4.75V. The most-significant error source is the MAX1653 reference. Therefore, use a better reference, if available, in the system or increase the VADJ to increase the worst-case output voltage to 4.75V. The MAX1653 works well with the MAX1804's GBW product set at 40kHz, so use a 470pF capacitor on COMP.
Chip Information
TRANSISTOR COUNT: 636
10
______________________________________________________________________________________
External Four-Input Feedback Integrator for Power Supplies
Package Information
MAX1804
Note: MAX1804 does not feature exposed pads
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
11 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2000 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

▲Up To Search▲

Price & Availability of MAX1804

	To Download MAX1804 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .