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19-2239; Rev 1; 12/01
KIT ATION EVALU BLE AVAILA
500kHz, 36V Output, SOT23, PWM Step-Up DC-DC Converters
General Description
The MAX5025-MAX5028 constant-frequency, pulsewidth modulating (PWM), low-noise boost converters are intended for low-voltage systems that often need a locally generated high voltage. These devices are capable of generating low-noise, high output voltages required for varactor diode biasing in TV tuners, set-top boxes, and PCI cable modems. The MAX5025- MAX5028 operate from as low as 3V and switch at 500kHz. The constant-frequency, current-mode PWM architecture provides for low output noise that is easy to filter. A 40V lateral DMOS device is used as the internal power switch, making the devices ideal for boost converters up to 36V. The MAX5025/MAX5026 adjustable versions require the use of external feedback resistors to set the output voltage. The MAX5027/MAX5028 offer a fixed 30V output. These devices are available in a small, 6pin SOT23 package. o Input Voltage Range: 3V to 11V (MAX5026/MAX5028) 4.5V to 11V (MAX5025/MAX5027) o Wide Output Voltage Range: VCC to 36V o Output Power: 120mW (max) o User-Adjustable Output Voltage with MAX5025/MAX5026 Using External Feedback Resistors o Fixed 30V Output Voltage: MAX5027/MAX5028 o Internal 1.3 (typ), 40V Switch o Constant PWM Frequency Provides Easy Filtering in Low-Noise Applications o 500kHz (typ) Switching Frequency o 1A (max) Shutdown Current o Small, 6-Pin SOT23 Package
Features
MAX5025-MAX5028
Applications
TV Tuner Power Supply Low-Noise Varactor Diode Biasing Set-Top Box Tuner Power Supply PCI Cable Modem Voice-Over-Cable LCD Power Supply Avalanche Photodiode Biasing
Ordering Information
PART MAX5025EUT-T MAX5026EUT-T MAX5027EUT-T MAX5028EUT-T TEMP. RANGE -40C to +85C -40C to +85C -40C to +85C -40C to +85C PINPACKAGE 6 SOT23-6 6 SOT23-6 6 SOT23-6 6 SOT23-6 TOP MARK AATJ AATK AATL AATM
Typical Operating Circuit
Selector Guide appears at end of data sheet.
VCC = 4.5V TO 11V (MAX5027) VCC = 3V TO 11V (MAX5028) L1 D1 VCC LX
VOUT 30V
Pin Configuration
TOP VIEW
PGND 1 6 LX
MAX5027 MAX5028 SHDN FB C1 PGND C2
GND 2 GND FB 3
MAX5025- MAX5028
5
VCC
4
SHDN
SOT23-6
________________________________________________________________ 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
500kHz, 36V Output, SOT23, PWM Step-Up DC-DC Converters MAX5025-MAX5028
ABSOLUTE MAXIMUM RATINGS
VCC to GND ............................................................-0.3V to +12V PGND to GND .......................................................-0.1V to +0.1V FB to GND (MAX5025/MAX5026)...............-0.3V to (VCC + 0.3V) FB to GND (MAX5027/MAX5028)...........................-0.3V to +40V SHDN to GND.............................................-0.3V to (VCC + 0.3V) LX to GND ..............................................................-0.3V to +45V Peak LX Current ................................................................600mA Operating Temperature Range ...........................-40C to +85C Continuous Power Dissipation (TA = +70C) 6-Pin SOT23 (derate 7.1mW/C above +70C)..........695.7mW 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
(VCC = 5V, SHDN = VCC, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER SUPPLY VOLTAGE Input Voltage Range Undervoltage Lockout Supply Current Shutdown Current BOOST CONVERTER Switching Frequency fSW MAX5025/MAX5027 MAX5026/MAX5028, VCC = 3.3V MAX5025/MAX5027, ILOAD = 2mA, VCC = 4.5V to 11V, VOUT = 30V Line Regulation MAX5026/MAX5028, ILOAD = 0.5mA, VCC = 3V to 11V, VOUT = 30V MAX5025/MAX5027, VCC = 5V, ILOAD = 0 to 4mA, VOUT = 30V Load Regulation MAX5026/MAX5028, VCC = 3.3V, ILOAD = 0 to 1mA, VOUT = 30V Thermal Shutdown Thermal Shutdown Hysteresis 1.0 140 2 C C 0.25 345 410 500 500 0.25 %/V 1000 670 kHz VCC VUVLO ICC ISHDN MAX5026/MAX5028 MAX5025/MAX5027 Rise/fall, hysteresis = 3mV MAX5025/MAX5026, FB = 1.4V MAX5027/MAX5028, FB = 35V SHDN = GND 3.0 4.5 2.25 2.65 350 0.01 11 11 2.95 1000 1 V V A A SYMBOL CONDITIONS MIN TYP MAX UNITS
2.0 %
2
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500kHz, 36V Output, SOT23, PWM Step-Up DC-DC Converters
ELECTRICAL CHARACTERISTICS (continued)
(VCC = 5V, SHDN = VCC, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER SYMBOL CONDITIONS MAX5025, VCC = 4.5V to 11V FB Set Point VFB MAX5027, VCC = 4.5V to 11V MAX5026, VCC = 3.3V to 11V MAX5028, VCC = 3.3V to 11V FB Input Bias Current Output Voltage Adjustment Range LX OUTPUT MAX5026/MAX5028, VCC = 3V VCC = 5V VCC = 11V Switch Current Limit ILIM Note 2 MAX5025/MAX5026, VFB = 1.4V MAX5027/MAX5028, VFB = 35V 0.8 2.4 -1 1 V V A 2.0 1.3 1.0 260 4.0 3.0 2.5 mA IFB MAX5025/MAX5026, FB = 1V MAX5027/MAX5028, FB = 30V MAX5025/MAX5026 VCC + 1 MIN 1.19 28.5 1.212 29.0 TYP 1.25 30.0 1.25 30 110 100 MAX 1.31 31.5 1.288 31 310 170 36 nA A V V UNITS
MAX5025-MAX5028
LX On-Resistance
RON
ILX = 40mA
LX Leakage Current
VLX = 40V
0.01
10
A
LOGIC INPUT: SHDN Input Low Level Input High Level Input Bias Current VIL VIH
Note 1: All devices are 100% production tested at TA = +25C. All temperature limits are guaranteed by design. Note 2: Switch current-limit accuracy is typically 20% and is a function of the input voltage. ILIM = (VIN/5) (260mA).
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3
500kHz, 36V Output, SOT23, PWM Step-Up DC-DC Converters MAX5025-MAX5028
Typical Operating Characteristics
(VCC = 5V, VOUT = 30V, TA = +25C, unless otherwise noted.)
EFFICIENCY vs. LOAD CURRENT (VOUT = 12V)
MAX5025-28 toc01
EFFICIENCY vs. LOAD CURRENT (VOUT = 15V)
MAX5025-28 toc02
EFFICIENCY vs. LOAD CURRENT (VOUT = 24V)
70 60 EFFICIENCY (%) 50 40 30 20 10 0 8 0 1 2 MAX5026 VCC = 5V, VOUT = 24V CIRCUIT OF FIGURE 2. R1 = 147k, R2 = 8.07k 3 4 5
MAX5025-28 toc03
90 80 70 EFFICIENCY (%) 60 50 40 30 20 10 0 0 2 4 6 8 MAX5026 VCC = 5V, VOUT = 12V CIRCUIT OF FIGURE 2. R1 = 147k, R2 = 16.2k
90 80 70 EFFICIENCY (%) 60 50 40 30 20 10 0 MAX5026 VCC = 5V, VOUT = 12V CIRCUIT OF FIGURE 2. R1 = 147k, R2 = 13k 0 2 4 LOAD CURRENT (mA) 6
80
10
LOAD CURRENT (mA)
LOAD CURRENT (mA)
EFFICIENCY vs. LOAD CURRENT (VOUT = 30V)
MAX5025-28 toc04
MAX5026 MINIMUM STARTUP VOLTAGE vs. LOAD CURRENT
MAX5025-28 toc05
MAX5026/MAX5028 SUPPLY CURRENT vs. SUPPLY VOLTAGE
450 400 SUPPLY CURRENT (A) 350 300 250 200 150 100 50 0 CURRENT INTO VCC PIN DEVICE NOT SWITCHING 0 3 6 SUPPLY VOLTAGE (V) 9 12
MAX5025-28 toc06
70 60 50 EFFICIENCY (%) 40 30 20 10 0 0 1 2 LOAD CURRENT (mA) 3 4 MAX5026 VCC = 5V, VOUT = 30V CIRCUIT OF FIGURE 2. R1 = 147k, R2 = 6.34k
4.0 3.5 STARTUP VOLTAGE (V) 3.0 2.5 2.0 1.5 1.0 0.5 0 0 1 2 LOAD CURRENT (mA) 3 4
500
MAX5026 NO LOAD SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX5025-28 toc07
SUPPLY CURRENT vs. TEMPERATURE
MAX5025-28 toc08
MAX5026 SWITCHING FREQUENCY vs. TEMPERATURE
600 SWITCHING FREQUENCY (kHz) 550 500 450 400 350 300 250 200 -40 -20 0 20 40 60 80 VCC = 5V VOUT = 30V CIRCUIT OF FIGURE 2.
MAX5025-28 toc09
16 NO LOAD SUPPLY CURRENT (mA) 14 12 10 8 6 4 2 0 3 5 7 SUPPLY VOLTAGE (V) 9 CIRCUIT OF FIGURE 2 VOUT = 30V
850 750 SUPPLY CURRENT (A) 650 550 450 350 250 CURRENT INTO VCC PIN 150 VCC = 11V VCC = 9V VCC = 7V VCC = 5V VCC = 3V
650
11
-40
-20
0
20
40
60
80
TEMPERATURE (C)
TEMPERATURE (C)
4
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500kHz, 36V Output, SOT23, PWM Step-Up DC-DC Converters MAX5025-MAX5028
Typical Operating Characteristics (continued)
(VCC = 5V, VOUT = 30V, TA = +25C, unless otherwise noted.)
EXITING SHUTDOWN
OUTPUT VOLTAGE 20V/div 5V
MAX5025-28 toc10
ENTERING SHUTDOWN
MAX5025-28 toc11
30V 30V OUTPUT VOLTAGE 20V/div 5V
INDUCTOR CURRENT 50mA/div 5V SHUTDOWN VOLTAGE 5V/div 2ms/div MAX5026, VCC = 5V, VOUT = 30V, ILOAD = 1mA. CIRCUIT OF FIGURE 3
SHUTDOWN VOLTAGE 5V/div
5V 0V
100ms/div MAX5026, VCC = 5V, VOUT = 30V, ILOAD = 1mA. CIRCUIT OF FIGURE 3
LIGHT-LOAD SWITCHING WAVEFORM WITHOUT RC FILTER
MAX5025-28 toc12
LIGHT-LOAD SWITCHING WAVEFORM WITH RC FILTER
MAX5025-28 toc13
VOUT 2mV/div AC-COUPLED
VOUT 1mV/div AC-COUPLED
LX PIN 20V/div 0V
LX PIN 20V/div 0V
IL 100mA/div 1s/div MAX5026, VCC = 5V, VOUT = 30V, ILOAD = 0.1mA. CIRCUIT OF FIGURE 2
0mA
IL 100mA/div 1s/div MAX5026, VCC = 5V, VOUT = 30V, ILOAD = 0.1mA. CIRCUIT OF FIGURE 3
0mA
MEDIUM-LOAD SWITCHING WAVEFORM WITHOUT RC FILTER
MAX5025-28 toc14
MEDIUM-LOAD SWITCHING WAVEFORM WITH RC FILTER
MAX5025-28 toc15
VOUT 5mV/div AC-COUPLED
VOUT 1mV/div AC-COUPLED
LX PIN 20V/div 0V
LX PIN 20V/div 0V
IL 200mA/div 1s/div MAX5026, VCC = 5V, VOUT = 30V, ILOAD = 2mA. CIRCUIT OF FIGURE 2
0mA
IL 200mA/div 1s/div MAX5026, VCC = 5V, VOUT = 30V, ILOAD = 2mA. CIRCUIT OF FIGURE 3
0mA
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500kHz, 36V Output, SOT23, PWM Step-Up DC-DC Converters MAX5025-MAX5028
Typical Operating Characteristics (continued)
(VCC = 5V, VOUT = 30V, TA = +25C, unless otherwise noted.)
HEAVY-LOAD SWITCHING WAVEFORM WITHOUT RC FILTER
MAX5025-28 toc16
HEAVY-LOAD SWITCHING WAVEFORM WITH RC FILTER
MAX5025-28 toc17
VOUT 5mV/div AC-COUPLED
VOUT 1mV/div AC-COUPLED
LX PIN 20V/div 0V
LX PIN 20V/div 0V
IL 200mA/div 1s/div MAX5026, VCC = 5V, VOUT = 30V, ILOAD = 4mA. CIRCUIT OF FIGURE 2
0mA
IL 200mA/div 1s/div MAX5026, VCC = 5V, VOUT = 30V, ILOAD = 4mA. CIRCUIT OF FIGURE 3
0mA
LOAD TRANSIENT RESPONSE
MAX5025-28 toc18
LINE TRANSIENT RESPONSE
MAX5025-28 toc19
OUTPUT VOLTAGE 200mV/div AC-COUPLED
OUTPUT VOLTAGE 1mV/div AC-COUPLED 0mV 0mV INPUT VOLTAGE 100mV/div AC-COUPLED 0mV 1ms/div MAX5026, VCC = 5V, VOUT = 30V, ILOAD = 0 TO 4mA. CIRCUIT OF FIGURE 2 2ms/div MAX5026, VCC = 5V TO 5.2V, VOUT = 30V, ILOAD = 1mA. CIRCUIT OF FIGURE 2
LOAD CURRENT 10mA/div
0mA
MAX5026 FB PIN VOLTAGE vs. TEMPERATURE
MAX5025-28 toc20
MAX5028 FB PIN VOLTAGE vs. TEMPERATURE
30.4 30.2 FB PIN VOLTAGE (V) 30.0 29.8 29.6 29.4 29.2 29.0 VCC = 3V VCC = 11V
MAX5025-28 toc21
1.270 1.265 VCC = 11V 1.260 FB PIN VOLTAGE (V) VCC = 5V 1.255 1.250 1.245 1.240 1.235 1.230 -40 -20 40 TEMPERATURE (C) 0 20 60 80 VCC = 3V
VCC = 5V
-40
-20
0
20
40
60
80
TEMPERATURE (C)
6
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500kHz, 36V Output, SOT23, PWM Step-Up DC-DC Converters
Typical Operating Characteristics (continued)
(VCC = 5V, VOUT = 30V, TA = +25C, unless otherwise noted.)
SWITCH ON-RESISTANCE vs. TEMPERATURE
MAX5025-28 toc22
MAX5025-MAX5028
LX LEAKAGE CURRENT vs. TEMPERATURE
0.045 LX LEAKAGE CURRENT (A) 0.040 0.035 0.030 0.025 0.020 0.015 0.010 CURRENT INTO LX PIN VLX = 40V
MAX5025-28 toc23
3.0 MAX5026 2.5 VCC = 3V RON () 2.0 VCC = 5V
0.050
1.5
1.0 VCC = 11V 0.5 -40 -20 0 20 40 60 80 TEMPERATURE (C)
0.005 0 -40 -20 0 20 40 60 80 TEMPERATURE (C)
LOAD REGULATION
MAX5025-28 toc24
MAX5026 MAXIMUM LOAD CURRENT vs. INPUT VOLTAGE
MAX5025-28 toc25
32 MAX5026 VCC = 5V OUTPUT VOLTAGE (V) 31 WITHOUT RC FILTER (CIRCUIT OF FIGURE 2)
100 MAXIMUM LOAD CURRENT (mA) A 10 C E 1 A: VOUT = 12V B: VOUT = 24V C: VOUT = 30V D: VOUT = 32V E: VOUT = 36V 3 5 7 INPUT VOLTAGE (V) 9 B D
30 WITH RC FILTER (CIRCUIT OF FIGURE 3)
29
28 0 1 2 3 4 5 LOAD CURRENT (mA)
0.1 11
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7
500kHz, 36V Output, SOT23, PWM Step-Up DC-DC Converters MAX5025-MAX5028
Pin Description
PIN MAX5025/ MAX5026 1 2 3 -- 4 5 6 MAX5027/ MAX5028 1 2 -- 3 4 5 6 NAME FUNCTION Power Ground. Connect directly to local ground plane. Use a star ground configuration for low noise. Ground. Connect directly to local ground plane. Feedback Pin. Reference voltage is approximately 1.25V. Connect resistive-divider tap here. Minimize trace area at FB. See Setting the Output Voltage section. Feedback Pin. Connect VOUT to FB for +30V. Internal resistors divide down the output voltage. Shutdown Pin. Connect to VCC to enable device. Connect to GND to shut down. Input Supply Voltage. Bypass with a 4.7F ceramic capacitor. Drain of Internal 40V N-Channel DMOS. Connect inductor/diode to LX. Minimize trace area at this pin to keep EMI down.
PGND GND FB FB SHDN VCC LX
Detailed Description
The MAX5025-MAX5028 current-mode PWM controllers operate in a wide range of DC-DC conversion applications including boost, flyback, and isolated output configurations. These converters provide lownoise, high output voltages making them ideal for varactor diode tuning applications as well as TFT LCD bias. Other features include shutdown, fixed 500kHz PWM oscillator, and a wide input range: 3V to 11V for MAX5026/MAX5028 and 4.5V to 11V for MAX5025/ MAX5027. The MAX5025-MAX5028 operate in discontinuous mode in order to reduce the switching noise at the output. Other continuous mode boost converters generate a large voltage spike at the output when the LX switch turns on because there is a conduction path between the output, diode, and switch to ground during the time needed for the diode to turn off. To reduce the output noise even further, the LX switch turns off by taking 40ns typically to transition from "ON" to "OFF." As a consequence, the positive slew rate of the LX node is reduced and the current from the inductor does not "force" the output voltage as hard as would be the case if the LX switch were to turn off more quickly.
is direct summing, lacking a traditional error amplifier and its associated phase shift. The direct summing configuration approaches ideal cycle-by-cycle control over the output voltage since there is no conventional error amp in the feedback path. The device operates in PWM mode using a fixed-frequency, current-mode operation. The current-mode feedback loop regulates peak inductor current as a function of the output error signal.
SHDN Input
The SHDN pin provides shutdown control. Connect SHDN to V CC for normal operation. To disable the device, connect SHDN to GND.
Design Procedure
The MAX5025-MAX5028 can operate in a number of DC-DC converter configurations including step-up, single-ended primary inductance converter (SEPIC), and flyback. The following design discussions are limited to step-up, with a complete circuit shown in the Application Circuits section.
Setting the Output Voltage
The output voltage of the MAX5027/MAX5028 is fixed at 30V. The output voltage of the MAX5025/MAX5026 is set by two external resistors (R1 and R2, Figure 2 and Figure 3). First select the value of R2 in the 5k to 50k range. R1 is then given by:
PWM Controller
The heart of the MAX5025-MAX5028 current-mode PWM controllers is a BiCMOS multi-input comparator that simultaneously processes the output-error signal and switch current signal. The main PWM comparator
8
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500kHz, 36V Output, SOT23, PWM Step-Up DC-DC Converters
Determining the Inductor Value
ULVO OSCILLATOR THERMAL SHUTDOWN
MAX5025-MAX5028
3
FB REF
-A +A +C
MAIN PWM COMPARATOR CONTROL LOGIC
SHDN
4
LX
6
2
GND
-C
CURRENTLIMIT COMPARATOR
5
VCC
N PGND 1
47H is the recommended inductor value when the output voltage is 30V and the input voltage is 5V. In general, the inductor should have a current rating greater than the current-limit value. For example, the inductor's current rating should be greater than 150mA to support a 4mA output current. Equivalent series resistance (ESR) should be below 1 for reasonable efficiency. Due to the MAX5025-MAX5028's high switching frequency, inductors with a ferrite core or equivalent are recommended. Powdered iron cores are not recommended due to their high losses at frequencies over 500kHz. Table 1 shows a list of vendors and 47H inductor parts. For 4mA output current and output voltages other than 30V, the inductor can be simply scaled in value according to the following formula: L=
(47H) (VOUT - VIN ) (25V)
MAX5025 MAX5026
Figure 1. Functional Diagram
Use the following formula to calculate the upper bound of the inductor value at different output voltages and output currents. This is the maximum inductance value for discontinuous mode operation. LUPPER =
2 VIN (VOUT - VIN ) TS 2 2 IOUT VOUT
V R1 = R2 OUT - 1 VREF where VREF is 1.25V
Determining Peak Inductor Current
If the boost converter remains in the discontinuous mode of operation, then the approximate peak inductor current, ILPEAK, is represented by the formula below: ILPEAK = 2 TS ( VOUT - VIN ) IOUT L
Calculate the lower bound, LLOWER, for the acceptable inductance value using the following formula, which will allow the maximum output current to be delivered without reaching the peak current limit: LLOWER = 2 TS ( VOUT - VIN ) IOUT V IN (260mA) 5
2
where TS is the period, VOUT is the output voltage, VIN is the input voltage, IOUT is the output current, and is the efficiency of the boost converter.
Notice that the switch current limit, (VIN/5)(260mA), is a function of the input voltage, VIN. The current rating of the inductor should be greater than the switch current limit.
Table 1. Inductor Vendors
VENDOR Coilcraft Sumida Toko PHONE 847-639-6400 847-545-6700 847-297-0070 FAX 847-639-1469 847-545-6720 847-699-7864 PART NUMBER OF 47H INDUCTOR DT1608C-473 CDRH4D28-470 A915BY-470M
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9
500kHz, 36V Output, SOT23, PWM Step-Up DC-DC Converters MAX5025-MAX5028
For a design in which VIN = 5V, VOUT = 30V, IOUT = 4mA, = 0.5, and TS = 2s, LUPPER = 87H and LLOWER = 12H. For a worst-case scenario in which VIN = 4.75V, VOUT = 29V, IOUT = 4.4mA, = 0.5, and TS = 1.25s, LUPPER = 46H and LLOWER = 9H. The choice of 47H as the recommended inductance value is reasonable given the worst-case scenario above. In general, the higher the inductance, the lower the switching noise. Load regulation is also better with higher inductance.
Capacitor Selection
Output Filter Capacitor The output filter capacitor should be 1F or greater. To achieve low output ripple, a capacitor with low ESR, low ESL, and high capacitance value should be selected. For very low output ripple applications, the output of the boost converter can be followed by an RC filter to further reduce the ripple. Figure 3 shows a 100, 1F filter used to reduce the switching output ripple to 1mVp-p. X7R ceramic capacitors are better for this boost application because of their low ESR and tighter tolerance over temperature than the Y5V ceramic capacitors. Table 3 below lists manufacturers of recommended capacitors. Input Capacitor Bypass VCC with a 4.7F ceramic capacitor as close to the IC as is practical.
Diode Selection
The MAX5025-MAX5028's high switching frequency demands a high-speed rectifier. Schottky diodes are recommended for most applications because of their fast recovery time and low forward-voltage drop. Ensure that the diode's peak current rating is greater than or equal to the peak inductor current. Also, the diode reverse breakdown voltage must be greater than VOUT. Table 2 lists diode vendors.
Applications Information
Layout Considerations
The MAX5025-MAX5028 switch at high speed, mandating careful attention to layout for optimum performance. Protect sensitive analog grounds by using a star ground configuration. Minimize ground noise by connecting GND, PGND, the input bypass-capacitor ground lead, and the output-filter ground lead to a single point (star ground configuration). Also, minimize
Table 2. Schottky Diode Vendors
VENDOR Comchip Panasonic ST-Microelectronics Vishay-Telefunken Zetex PHONE 510-657-8671 408-942-2912 602-485-6100 402-563-6866 631-360-2222 FAX 510-657-8921 408-946-9063 602-486-6102 402-563-6296 631-360-8222 PART NUMBERS CDBS1045 MA2Z785 TMMBAT48 BAS382 ZHCS500
Table 3. Capacitor Table
COMPANY Murata Taiyo Yuden TDK PHONE 814-237-1431 408-573-4150 847-803-6100 FAX 814-238-0490 408-573-4159 847-803-6296 PART NUMBERS GRM42-2X7R105K050AD (1F capacitor) GRM32-1210R71C475R (4.7F capacitor) UMK325BJ105KH (1F capacitor) EMK316BJ475ML (4.7F capacitor) C3225X7R1H155K (1.5F capacitor) C3225X7R1H105K (1F capacitor)
10
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500kHz, 36V Output, SOT23, PWM Step-Up DC-DC Converters
trace lengths to reduce stray capacitance, trace resistance, and radiated noise. The trace between the output voltage-divider (MAX5025/MAX5026) and the FB pin must be kept short, as well as the trace between GND and PGND. Inductor Layout The shielded drum type inductors have a small air gap around the top and bottom periphery. The incident fringing magnetic field from this air gap to the copper plane on the PC board tends to reduce efficiency. This is a result of the induced eddy currents on the copper plane. To minimize this effect, avoid laying out any copper planes under the mounting area of these inductors.
30V Boost Application Circuit
Figures 2 and 3 show the MAX5025/MAX5026 operating in a 30V boost application. Figure 3 has an RC filter to reduce noise at the output. These circuits provide output currents greater than 4mA with an input voltage of 5V or greater. They are designed by following the Design Procedure section. Operating characteristics of these circuits are shown in the Typical Operating Characteristics section.
MAX5025-MAX5028
____________________Chip Information
TRANSISTOR COUNT: 365 PROCESS: BiCMOS
VCC = 4.5V TO 11V (MAX5025) VCC = 3V TO 11V (MAX5026) C1 4.7F
VCC
L1 TOKO 47H INDUCTOR 47H A915BY-470M ZETEX SCHOTTKY DIODE D1 ZHCS500 VOUT LX +30V R1 147k C2 1F R2 6.34k
MAX5025 MAX5026 SHDN FB PGND GND
Figure 2. Adjustable 30V Output Circuit
L1 TOKO 47H INDUCTOR 47H A915BY-470M ZETEX SCHOTTKY DIODE R3 100 D1 ZHCS500 LX R1 147k C2 1F R2 6.34k C3 1F
VCC = 4.5V TO 11V (MAX5025) VCC = 3V TO 11V (MAX5026) C1 4.7F
VCC
VOUT +30V
MAX5025 MAX5026 SHDN FB PGND GND
Figure 3. Adjustable 30V Output Circuit with RC Filter
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11
500kHz, 36V Output, SOT23, PWM Step-Up DC-DC Converters MAX5025-MAX5028
Selector Guide
PART MAX5025 MAX5026 MAX5027 MAX5028 OUTPUT Adjustable Adjustable Fixed 30V Fixed 30V FREQUENCY TOLERANCE -31% to +100% -18% to +34% -31% to +100% -18% to +34% FB SET POINT TOLERANCE 5% 3% 5% 3% INPUT VOLTAGE 4.5V to 11V 3V to 11V 4.5V to 11V 3V to 11V
12
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500kHz, 36V Output, SOT23, PWM Step-Up DC-DC Converters
Package Information
6LSOT.EPS
MAX5025-MAX5028
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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 13 (c) 2001 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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