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19-1183; Rev 0; 6/97
NUAL KIT MA UATION TA SHEET EVAL WS DA FOLLO
High-Efficiency, Step-Up DC-DC Converters for 1V Inputs
____________________________Features
o Built-In Synchronous Rectifier o 0.88V Guaranteed Start-Up o Ultra-Small MAX Package: 1.1mm High o 83% Efficiency o 4A Quiescent Supply Current into BATT Pin o 2A Logic-Controlled Shutdown (MAX1642) o Two Undervoltage Detectors (MAX1643) o 2V to 5.2V Output Range o 20mA Output Current at 1.2V Input o Reverse Battery Protection
_______________General Description
The MAX1642/MAX1643 are high-efficiency, low-voltage, step-up DC-DC converters intended for devices powered by a single alkaline cell. They feature low quiescent supply currents and are supplied in the ultra-small MAX package, which is only 1.1mm high. The guaranteed start-up voltage is 0.88V. Each device consists of an internal 1, N-channel MOSFET power switch; a built-in synchronous rectifier that acts as the catch diode; an oscillator; a reference; and pulse-frequency-modulation (PFM) control circuitry. Both devices feature an independent undervoltage comparator (PFI/PFO). The MAX1642 also includes a 2A logic-controlled shutdown mode. The MAX1643 offers a dedicated low-battery detector (BATTLO) in lieu of shutdown. The output voltage for each device is preset to 3.3V 4%, or can be adjusted from +2V to +5.2V using only two resistors.
MAX1642/MAX1643
______________Ordering Information
PART MAX1642C/D MAX1642EUA MAX1643C/D MAX1643EUA TEMP. RANGE 0C to +70C -40C to +85C 0C to +70C -40C to +85C PIN-PACKAGE Dice* 8 MAX Dice* 8 MAX
________________________Applications
Pagers Remote Controls Pointing Devices Personal Medical Monitors Single-Cell Battery-Powered Devices
*Dice are tested at TA = +25C. Note: To order these devices shipped in tape and reel, add a -T to the part number.
_________________Pin Configurations
TOP VIEW
BATT 1 8 OUT LX GND FB
__________Typical Operating Circuit
PFI 2 PFO 3 SHDN 4
MAX1642
7 6 5
INPUT 0.88V TO 1.65V 22F
100H LX OUT
OUTPUT 3.3V 22F BATT 1
MAX
MAX1642
BATT ON OFF SHDN PFI GND PFO FB
8
OUT LX GND FB
LOW-BATTERY DETECTOR INPUT
LOW-BATTERY DETECTOR OUTPUT
PFI 2 BATTLO 3 PFO 4
MAX1643
7 6 5
MAX ________________________________________________________________ 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 408-737-7600 ext. 3468.
High-Efficiency, Step-Up DC-DC Converters for 1V Inputs MAX1642/MAX1643
ABSOLUTE MAXIMUM RATINGS
BATT to GND ...........................................................-0.3V to 6.0V BATT Forward Current ..........................................................0.5A OUT to GND.............................................................-0.3V to 6.0V OUT, LX Current.......................................................................1A LX to GND................................................................-0.3V to 6.0V SHDN, FB, BATTLO, PFO to GND ...........................-0.3V to 6.0V PFI to GND ............................................................-0.3V to VBATT Reverse Battery Current (TA = +25C) (Note 1) ...............220mA Continuous Power Dissipation MAX (derate 4.1mW/C above 70C)..........................330mW Operating Temperature Range MAX1642EUA/MAX1643EUA ............................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +165C Lead Temperature (soldering, 10sec) .............................+300C
Note 1: The reverse battery current is measured from the Typical Operating Circuit's input terminal to GND when the battery is connected backward. A reverse current of 220mA will not exceed package dissipation limits but, if left for an extended time (more than 10 minutes), may degrade performance.
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
(VBATT = V SHDN = 1.3V, ILOAD = 0mA, FB = GND, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER Minimum Operating Input Voltage Maximum Operating Input Voltage Start-Up Voltage (Note 2) Start-Up Voltage Tempco Output Voltage Output Voltage Range FB Set Voltage N-Channel On-Resistance P-Channel On-Resistance P-Channel Catch-Diode Voltage On-Time Constant Off-Time Tracking Ratio (Note 3) Quiescent Current into OUT Quiescent Current into BATT Shutdown Current into OUT Shutdown Current into BATT Efficiency FB Input Current PFI Trip Voltage PFI Input Current PFO, BATTLO Low Output Voltage PFO, BATTLO Leakage Current BATTLO Trip Voltage SHDN Input Low Voltage SHDN Input High Voltage SHDN Input Current VIL VIH VOL K RATIO IQOUT IQBATT ISHDN,OUT ISHDN,BATT VOUT = 3.5V (MAX1642) VBATT = 1.0V (MAX1642) ILOAD = 20mA VFB = 1.3V Falling PFI, hysteresis = 1% VPFI = 650mV VPFI = 0V, VOUT = 3.3V, ISINK = 1mA VPFI = 650mV, V PFO = 6V VOUT = 3.3V, hysteresis = 2% (MAX1643) % of VBATT (MAX1642) % of VBATT (MAX1642) (MAX1642) 80 10 0.96 1.0 590 614 VFB VOUT VFB < 0.1V External feedback External feedback VOUT = 3.3V VOUT = 3.3V IDIODE = 100mA, P-channel switch off 0.9V < VBATT < 1.5V (tON = K / VBATT) 0.9V < VBATT < 1.5V, VOUT = 3.3V VOUT = 3.5V 17 1 11 4 0.1 2 80 10 632 10 0.4 1 1.04 20 3.16 2.0 1.18 1.225 1 1.5 0.8 25 35 1.5 18 6.5 1 3.5 A A A A % nA mV nA V A V % % nA RL = 3k, TA = +25C 0.88 -2 3.30 3.44 5.2 1.27 1.5 2.2 SYMBOL VBATT(MIN) CONDITIONS MIN TYP 0.7 1.65 MAX UNITS V V V mV/C V V V V V-s
2
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High-Efficiency, Step-Up DC-DC Converters for 1V Inputs
ELECTRICAL CHARACTERISTICS
(VBATT = V SHDN = 1.3V, ILOAD = 0mA, FB = GND, TA = -40C to +85C, unless otherwise noted.) (Note 4) PARAMETER Output Voltage FB Set Voltage N-Channel On-Resistance P-Channel On-Resistance On-Time Constant Quiescent Current into OUT Quiescent Current into BATT Shutdown Current into OUT Shutdown Current into BATT PFI Trip Voltage BATTLO Trip Voltage K IQOUT IQBATT ISHDN,OUT ISHDN,BATT VOUT = 3.5V (MAX1642) VBATT = 1.0V (MAX1642) Falling PFI, hysteresis = 1% Falling VBATT, VOUT = 3.3V, hysteresis = 2% (MAX1643) 550 0.93 SYMBOL VOUT VFB VFB < 0.1V External feedback VOUT = 3.3V VOUT = 3.3V 0.9V < VBATT < 1.5V (tON = K / VBATT) VOUT = 3.5V 12.4 CONDITIONS MIN 2.99 1.11 MAX 3.56 1.32 1.5 2.2 38.2 18 6.5 1 3.5 662 1.06 UNITS V V V-s A A A A mV V
MAX1642/MAX1643
Note 2: Start-up guaranteed by correlation to measurements of device parameters (i.e., switch on-resistance, on-times, off-times, and output voltage trip points). Note 3:
t x VBATT tOFF = ON x RATIO. This guarantees discontinuous conduction. VOUT - VBATT
Note 4: Specifications to -40C are guaranteed by design, not production tested.
__________________________________________Typical Operating Characteristics
(Circuit of Figure 4, VBATT = 1.2V, R1 + R2 = 1M, TA = +25C, unless otherwise noted.)
EFFICIENCY vs. OUTPUT CURRENT (VOUT = 2.4V)
MAX1642/43 TOC01A
EFFICIENCY vs. OUTPUT CURRENT (VOUT = 2.4V)
MAX1642/43 TOC01B
EFFICIENCY vs. OUTPUT CURRENT (VOUT = 3.3V)
90 80 EFFICIENCY (%) 70 60 50 40 30 20 VIN = 1.0V VIN = 0.85V L1 = 100H SUMIDA CD54-101 0.01 0.1 1 10 100 VIN = 1.2V VIN = 1.6V
MAX1642/43 TOC02A
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 0.01 0.1 1 10 L1 = 100H SUMIDA CD54-101 VIN = 0.85V VIN = 1.0V VIN = 1.2V VIN = 1.6V
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 L1 = 150H TDK NLC565050T-151K 0.01 0.1 1 10 VIN = 1.0V VIN = 0.85V VIN = 1.2V VIN = 1.6V
100
10 0 100
100
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
_______________________________________________________________________________________
3
High-Efficiency, Step-Up DC-DC Converters for 1V Inputs MAX1642/MAX1643
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 4, VBATT = 1.2V, R1 + R2 = 1M, TA = +25C, unless otherwise noted.)
EFFICIENCY vs. OUTPUT CURRENT (VOUT = 3.3V)
MAX1642/43 TOC02B
EFFICIENCY vs. OUTPUT CURRENT (VOUT = 5.0V)
MAX1642/43 TOC03a
EFFICIENCY vs. OUTPUT CURRENT (VOUT = 5.0V)
90 80 EFFICIENCY (%) 70 60 50 40 30 20 VIN = 1.2V VIN = 0.85V VIN = 1.6V VIN = 1.0V
MAX1642/43 TOC03b
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 0.01 0.1 1 10 L1 = 150H TDK NLC565050T-151K VIN = 1.0V VIN = 0.85V VIN = 1.2V VIN = 1.6V
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 L1 = 100H SUMIDA CD54-101 0.01 0.1 1 10 VIN = 1.2V VIN = 0.85V VIN = 1.6V VIN = 1.0V
100
10 0 100 0.01
L1 = 150H TDK NLC565050T-151K 0.1 1 10 100
100
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
NO-LOAD BATTERY CURRENT vs. INPUT VOLTAGE
MAX1642/43 TOC04
NO-LOAD BATTERY CURRENT vs. TEMPERATURE
MAX1642/43 TOC05
BATT AND OUT PIN QUIESCENT CURRENTS vs. TEMPERATURE
VBATT = 1.2V VOUT = 3.6V
MAX1642/43 TOC06
10,000
140 120 QUIESCENT CURRENT (A) 100 80 60 40 20 0 VBATT = 1.2V VOUT = 3.3V
30 25 QUIESCENT CURRENT (A) 20 15 IOUT 10 5 0
QUIESCENT CURRENT (mA)
1000 VOUT = 5.0V 100
VOUT = 2.5V OR 3.3V 10 0.8 1.0 1.2 1.4 1.6 1.8 INPUT VOLTAGE (V)
IBATT
-40
-20
0
20
40
60
80
100
-40
-20
0
20
40
60
80
100
TEMPERATURE (C)
TEMPERATURE (C)
MINIMUM START-UP INPUT VOLTAGE vs. OUTPUT CURRENT
MAX1642/43 TOC07a
MINIMUM START-UP INPUT VOLTAGE vs. OUTPUT CURRENT
1.5 START-UP INPUT VOLTAGE (V) 1.4 1.3 1.2 1.1 1.0 0.9 0.8 0.7 0.6 VOUT = 2.4V, 3.3V VOUT = 5V L1 = 150H TDK NLC565050T-151K
MAX1642/43 TOC07b
1.6 1.5 START-UP INPUT VOLTAGE (V) 1.4 1.3 1.2 1.1 1.0 0.9 0.8 0.7 0.6 0 5 10 15 20 VOUT = 2.4V, 3.3V L1 = 100H SUMIDA CD54-101 VOUT = 5V
1.6
25
0
2
4
6
8
10
12
14
16
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
4
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High-Efficiency, Step-Up DC-DC Converters for 1V Inputs
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 4, VBATT = 1.2V, R1 + R2 = 1M, TA = +25C, unless otherwise noted.)
MAX1642/MAX1643
MAXIMUM OUTPUT CURRENT vs. INPUT VOLTAGE
MAX1642/43 TOC08b
MAXIMUM OUTPUT CURRENT vs. INPUT VOLTAGE
MAX1642/43 TOC08c
SWITCHING WAVEFORMS
MAX1642/43 TOC09
35 MAXIMUM OUTPUT CURRENT (mA) 30 25 20 15 VOUT = 3.3V 10 5 0 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 L1 = 100H SUMIDA CD54-101 VOUT = 5V VOUT = 2.4V
20 18 MAXIMUM OUTPUT CURRENT (mA) 16 14 12 10 8 6 4 2 0 L1 = 150H TDK NLC565050T-151K 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 VOUT = 5V VOUT = 3.3V VOUT = 2.4V
A
B
C
1.6
1.6
10ms/div VOUT = 3.3V, VIN = 1.2V, IOUT = 12mA A: LX, 2V/div, L1 = TDK NLC565050T-151K B: OUT, 20mV/div, 3.3V DC OFFSET C: INDUCTOR CURRENT, 100mA/div
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
LOAD-TRANSIENT RESPONSE
MAX1642/43 TOC10
LINE-TRANSIENT RESPONSE
MAX1642/43 TOC11
SHUTDOWN RESPONSE AND INDUCTOR CURRENT
MAX1642/43 TOC12
A A A
B B B C
400s/div VOUT = 3.3V, VBATT = 1.2V A: OUT, 20mV/div, 3.3V DC OFFSET B: LOAD, 2mA to 20mA, 10mA/div
400s/div VOUT = 3.3V, LOAD = 15mA A: OUT, 50mV/div, 3.3V DC OFFSET B: VBATT, 1V to 1.5V, 500mV/div
10ms/div VOUT = 3.3V, VBATT = 1.2V, IOUT = 5mA A: OUT, 1V/div B: INDUCTOR CURRENT, 200mA/div C: SHDN, 2V/div
_______________________________________________________________________________________
5
High-Efficiency, Step-Up DC-DC Converters for 1V Inputs MAX1642/MAX1643
______________________________________________________________Pin Description
PIN MAX1642 1 2 -- 3 4 5 6 7 8 MAX1643 1 2 3 4 -- 5 6 7 8 NAME BATT PFI BATTLO PFO SHDN FB GND LX OUT FUNCTION IC Battery-Power Input. Sense input for BATTLO comparator (MAX1643 only). Power-Fail Input. When the voltage on PFI drops below 614mV, PFO sinks current. Open-Drain Battery-Low Output. When the voltage at BATT drops below 1V, BATTLO sinks current. Open-Drain Power-Fail Output. Sinks current when PFI drops below 614mV. Active-Low Shutdown Input. Connect to BATT for normal operation. Feedback Input for adjustable-output operation. Connect FB to an external resistor voltage divider between OUT and GND. Connect to GND for fixed-output operation. Ground N-Channel MOSFET Switch Drain and P-Channel Synchronous-Rectifier Drain Power Output. Feedback input for fixed 3.3V operation and IC power input. Connect filter capacitor close to OUT.
_______________Detailed Description
The MAX1642/MAX1643 each consist of an internal 1, N-channel MOSFET power switch, a built-in synchronous rectifier that acts as the catch diode, an oscillator, a reference, and PFM control circuitry (Figure 1). These devices are optimized for applications with power-management features that operate from one alkaline cell, such as pagers, remote controls, and battery-powered instruments. They are designed to meet the specific demands of the operating states characteristic of such systems: 1) Primary battery is good and the load is active: In this state, the system draws tens of milliamperes, and the MAX1642/MAX1643 typically offer 80% efficiency. 2) Primary battery is good and the load is sleeping: In this state, the load is drawing hundreds of microamperes, and the DC-DC converter IC draws very low quiescent current. In many applications, the load is expected to be in this state most of the time.
Operating Principle
The MAX1642/MAX1643 employ a proprietary pulsefrequency-modulation (PFM) control scheme that combines the ultra-low quiescent current traditional of pulse-skipping PFM converters with the high-load efficiency of pulse-width-modulation (PWM) converters. The on-time and minimum off-times are varied as a function of the input and output voltages:
t ON =
K VBATT 1.2 x K VOUT - VBATT
t OFF(MIN) =
where K is typically 25V-s. This enables the MAX1642/MAX1643 to maintain high efficiency over a wide range of loads and input/output voltages. The DCDC converter is powered from the OUT pin.
6
_______________________________________________________________________________________
High-Efficiency, Step-Up DC-DC Converters for 1V Inputs
When the error comparator detects that the output voltage is too low, it turns on the internal N-channel MOSFET switch until the on-time is satisfied (see Figure 1 and the Standard Application Circuits, Figures 2 and 3). During the on-time, current ramps up in the inductor, storing energy in a magnetic field. When the MOSFET turns off, during the second half of each cycle, the magnetic field collapses, causing the inductor voltage to force current through the synchronous rectifier, transferring the stored energy to the output filter capacitor and load. The output filter capacitor stores charge while current from the inductor is high, then holds up the output voltage until the second half of the next switching cycle, smoothing power flow to the load. the P-channel synchronous rectifier remains off and either its body diode or an external diode is used as an output rectifier. Reduce the load as needed to allow start-up with input voltages below 2V (see Typical Operating Characteristics).
MAX1642/MAX1643
Shutdown (MAX1642)
Pulling SHDN low places the MAX1642 in shutdown mode (ISHDN = 2A typical). In shutdown, the internal switching MOSFET turns off, PFO goes highimpedance, and the synchronous rectifier turns off to prevent reverse current from flowing from the output back to the input. However, there is still a forward current path through the synchronous-rectifier body diode from the input to the output. Thus, in shutdown, the output remains one diode drop below the battery voltage (V BATT ). To disable the shutdown feature, connect SHDN (a logic input) to BATT.
Bootstrap DC-DC Block
The bootstrap block contains a low-voltage start-up oscillator. This oscillator pumps up the output voltage to approximately 1.7V, where the main DC-DC converter can operate. The oscillator is powered from the BATT input and drives an NPN switch. During start-up,
BATT TIMING 0.5REF TON TOFF PDRV NDRV P
OUT
EN PFI
LOGIC
MAX1642
LX
PFO
FB
REF
N
RFRDY REF
REF 0.5REF
START-UP OSCILLATOR
GND OUT SHDN 1.7V
Figure 1. MAX1642 Functional Diagram
_______________________________________________________________________________________ 7
High-Efficiency, Step-Up DC-DC Converters for 1V Inputs MAX1642/MAX1643
BATTLO (MAX1643)
The MAX1643 contains an on-chip comparator for lowbattery detection. If the voltage at BATT drops below 1V, BATTLO sinks current. BATTLO is an open-drain output. In combination with PFI/PFO, this allows monitoring of both the input and output voltages.
0.88V to 1.65V INPUT 22F 0.1F BATT OUT PFI LX OUT 3.3VOUT 0.1F 22F 100H, 350mA
Reverse-Battery Protection
The MAX1642/MAX1643 can sustain/survive single-cell battery reversal up to the package power-dissipation limit. An internal 5 resistor in series with a diode limits reverse current to less than 220mA, which prevents damage to the MAX1642/MAX1643. Prolonged operation above 220mA reverse-battery current can degrade the devices' performance.
PF0
MAX1642
SHDN GND FB
________________Design Information
Output Voltage Selection
The MAX1642/MAX1643 operate with a 3.3V 4% or adjustable output. To select fixed-voltage operation, connect FB to GND. For an adjustable output between 2V and 5.2V, connect FB to a resistor voltage divider between OUT and GND (Figure 4). FB regulates to 1.23V. Since FB leakage is 10nA max, select feedback resistor R2 in the 100k to 1M range. R1 is given by:
V R1 = R2 OUT - 1 VREF
Figure 2. MAX1642 3.3V Standard Application Circuit
0.88V to 1.65V INPUT 100H, 350mA 22F 0.1F BATT OUT LX OUT 3.3VOUT 0.1F 22F PFI BATTLO PFO GND FB
MAX1643
where VREF = 1.23V.
Power-Fail Detection
The MAX1642/MAX1643 have an on-chip comparator for power-fail detection. This comparator can detect loss of power at the input or output. If the voltage at PFI falls below 614mV, the PFO output sinks current to GND. Hysteresis at the power-fail input is 1%. The power-fail monitor's threshold is set by two resistors: R3 and R4 (Figure 5). Set the threshold using the following equation:
V R3 = R4 TH - 1 VPFI
Figure 3. MAX1643 3.3V Standard Application Circuit
the battery voltage decreases below the start-up voltage (see Typical Operating Characteristics).
Inductor Selection
A 100H inductor is recommended for most applications. The use of lower inductor values (down to 68H) increases maximum output current. Higher values (up to 220H) reduce peak inductor current and consequent ripple and noise. The inductor's saturationcurrent rating must exceed the peak current limit synthesized by the MAX1642/MAX1643's timing algorithms: IPEAK = KMAX LMIN
where VTH is the desired threshold of the power-fail detector, and VPFI is the 614mV reference of the powerfail comparator. Since PFI leakage is 10nA max, select feedback resistor R4 in the 100k to 1M range.
Low-Battery Start-Up
The MAX1642/MAX1643 are bootstrapped circuits with a low-voltage start-up oscillator. They can start under low-load conditions at lower battery voltages than at full load. Once started, the output can maintain the load as
8
where KMAX = 35V-s. The maximum recommended IPEAK is 350mA. For best efficiency, inductor series resistance should be less than 1.
_______________________________________________________________________________________
High-Efficiency, Step-Up DC-DC Converters for 1V Inputs
Capacitor Selection
Choose input and output capacitors to service input and output peak currents with acceptable voltage ripple. A 22F, 6V, low-ESR, surface-mount tantalum output filter capacitor typically provides 60mV output ripple when stepping up from 1.3V to 3.3V at 20mA. The input filter capacitor (CIN) also reduces peak currents drawn from the battery and improves efficiency. Low equivalent series resistance (ESR) capacitors are recommended. Capacitor ESR is a major contributor to output ripple (usually more than 60%). Ceramic capacitors have the lowest ESR, but low-ESR tantalums represent a good balance between cost and performance. Low-ESR aluminum electrolytic capacitors are tolerable, and standard aluminum electrolytic capacitors should be avoided. Do not exceed tantalum capacitors' ripplecurrent ratings; select capacitors with a rating exceeding the peak inductor current (IPEAK).
0.88V to 1.65V INPUT 22F 0.1F BATT PFI OUT LX OUT 100pF* R1 100H
MAX1642/MAX1643
VOUT = 2V TO 5.2V
MAX1642
PF0 SHDN GND *OPTIONAL COMPENSATION FB
R2
Figure 4. Adjustable-Output Circuit
PC Board Layout and Grounding
High switching frequencies and large peak currents make PC board layout an important part of design. Poor design can result in excessive EMI on the feedback paths and voltage gradients in the ground plane. Both of these factors can result in instability or regulation errors. The OUT pin must be bypassed directly to GND as close to the IC as possible (within 0.2 in. or 5mm). Place power components--such as the MAX1642/ MAX1643, inductor, input filter capacitor, and output filter capacitor--as close together as possible. Keep their traces short, direct, and wide (50 mil or 1.25mm), and place their ground pins close together in a star-ground configuration. Keep the extra copper on the board and integrate it into ground as a pseudo-ground plane. On multilayer boards, route the star ground using component-side copper fill, then connect it to the internal ground plane using vias. Place the external voltage-feedback network very close to the FB pin (within 0.2 in. or 5mm). Noisy traces, such as from the LX pin, should be kept away from the voltagefeedback network and separated from it using grounded copper. The evaluation kit manual shows an example PC board layout, routing, and pseudo-ground plane.
VTH
MAX1642 MAX1643
PFI
R3
R4
Figure 5. Power-Fail Detection Circuit
2) Use a closed-core inductor, such as toroid or shielded bobbin, to minimize fringe magnetic fields. 3) Choose the largest inductor value that satisfies the load requirement to minimize peak switching current and resulting ripple and noise. 4) Use low-ESR input and output filter capacitors. 5) Follow sound circuit-board layout and grounding rules (see the PC Board Layout and Grounding section). 6) Where necessary, add LC pi filters, linear post-regulators such as the MAX8863 and MAX8864 (SOT23 package), or shielding. The LC pi filter's cutoff frequency should be at least a decade or two below the DC-DC converter's switching frequency for the specified load and input voltage.
Noise and Voltage Ripple
EMI and output voltage ripple can be minimized by following a few simple design rules. 1) Place the DC-DC converter and digital circuitry on an opposite corner of the PC board, away from sensitive RF and analog input stages.
_______________________________________________________________________________________
9
High-Efficiency, Step-Up DC-DC Converters for 1V Inputs MAX1642/MAX1643
Table 1. Component Suppliers
SUPPLIER AVX Coilcraft Coiltronics Dale Nichicon Sanyo Sprague Sumida TDK USA USA USA USA USA Japan USA Japan USA USA Japan USA PHONE (803) 946-0690 (800) 282-4975 (847) 639-6400 (561) 241-7876 (605) 668-4131 (847) 843-7500 81-7-5231-8461 (619) 661-6835 81-7-2070-6306 (603) 224-1961 (847) 956-0666 81-3-3607-5111 (847) 390-4373 FAX (803) 626-3123 (847) 639-1469 (561) 241-9339 (605) 665-1627 (847) 843-2798 81-7-5256-4158 (619) 661-1055 81-7-2070-1174 (603) 224-1430 (847) 956-0702 81-3-3607-5144 (847) 390-4428
__________________ Chip Information
TRANSISTOR COUNT: 594 SUBSTRATE CONNECTED TO GND
Table 2. Surface-Mount Inductor Information
INDUCTOR SPECIFICATION INDUCTANCE (H) VENDOR/PART Coilcraft DO1608-683 Sumida CD54-680 Coilcraft DO1608-104 100 Sumida CD54-101 TDK NLC565050T-101K Coilcraft DO1608-154 150 Sumida CD54-151 TDK NLC565050T-151K 220 Coilcraft DO1608-224 Sumida CD54-221 RESISTANCE () 0.75 0.46 1.1 0.7 1.6 1.7 1.1 2.2 2.3 1.57 ISAT (mA) 400 610 310 520 250 270 400 210 220 350
68
10
______________________________________________________________________________________
High-Efficiency, Step-Up DC-DC Converters for 1V Inputs
________________________________________________________Package Information
8LUMAXD.EPS
MAX1642/MAX1643
______________________________________________________________________________________
11
High-Efficiency, Step-Up DC-DC Converters for 1V Inputs MAX1642/MAX1643
NOTES
12
______________________________________________________________________________________

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