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19-4778; Rev 0a; 8/98
MAX668 Evaluation Kit
General Description
The MAX668 evaluation kit (EV kit) combines a constant-frequency, pulse-width-modulation (PWM) stepup controller with an external N-channel MOSFET and Schottky diode to provide a regulated output voltage. The EV kit accepts a +3V to VOUT input and converts it to a +12V output for currents up to 1A, with greater than 90% conversion efficiency. The EV kit operates at 500kHz, allowing the use of small external components. The MAX668 EV kit is a fully assembled and tested surface-mount circuit board. This EV kit can also be configured for the application circuits listed in the EV Kit Application Circuit Capabilities table. For input voltages below 3V and down to 1.8V, replace the MAX668 with a MAX669. The MAX669 must always operate in bootstrapped mode (JU2 shunt across pins 1 and 2). o +12V or Adjustable Output Voltage o Output Current Up to 1A o N-Channel External MOSFET o 4A IC Shutdown Current o 500kHz Switching Frequency o Surface-Mount Components o Fully Assembled and Tested
Features
o +3V to VOUT Input Range (as shipped)
Evaluates: MAX668/MAX669
Component List
DESIGNATION QTY C1 1 DESCRIPTION 68F, 20V, low-ESR tantalum cap Sprague 593D686X0020E2W or AVX TPSE686M020R0150 120F, 20V, low-ESR tantalum cap Sprague 594D127X0020R2T 0.1F ceramic capacitor 0.22F ceramic capacitor 1F ceramic capacitors 220pF ceramic capacitor Not installed 3A Schottky diode Hitachi HRF302A or Motorola MBRS340T3 4.7H power inductor Sumida CDRH104-4R7 (shielded), Coiltronics UP2B-4R7, or Coilcraft DO3316P-472 N-channel MOSFET Fairchild FDS6680 or International Rectifier IRF7801 0.020, 1%, 1/2W resistor Dale WSL-2010-R020F or IRC LR2010-01-R020F 218k, 1% resistor 24.9k, 1% resistor 100k, 1% resistor MAX668EUB 3-pin headers 2-pin header Shunts (JU1, JU2) MAX668/MAX669 PC board MAX668/MAX669 data sheet 1
Ordering Information
C5 PART MAX668EVKIT TEMP. RANGE 0C to +70C IC PACKAGE 10 MAX C2 C3 C4, C8 C7 C6 1 1 2 1 0 1 1
Note: To evaluate the MAX669, request a MAX669EUB free sample with the MAX668EVKIT.
EV Kit Application Circuit Capabilities
VIN(MIN) (V) 1.8 1.8 2.5 3 3 3 12 VOUT (V) 12 24 12 5 12 36 24 IOUT (A) 0.4 0.1 0.65 3 1 0.02 0.5
D1
L1
1
N1
1
R1 R2 R3 R4 U1 JU1, JU2 JU3 None None None
1 1 1 1 1 2 1 2 1 1
Note: Design information for these applications is included. The shaded row shows EV kit configuration as shipped.
________________________________________________________________ Maxim Integrated Products
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.
MAX668 Evaluation Kit Evaluates: MAX668/MAX669
Component Suppliers
SUPPLIER AVX CoilCraft Coiltronics Dale-Vishay Fairchild Hitachi International Rectifier IRC Motorola Siliconix Sprague Sumida Vishay/Vitramon PHONE 803-946-0690 708-639-6400 561-241-7876 402-564-3131 408-721-2181 888-777-0384 310-322-3331 512-992-7900 602-303-5454 408-988-8000 603-224-1961 708-956-0666 203-268-6261 FAX 803-626-3123 708-639-1469 561-241-9339 402-563-6418 408-721-1635 650-244-7947 310-322-3332 512-992-3377 602-994-6430 408-970-3950 603-224-1430 708-956-0702 203-452-5670
Note: Please indicate that you are using the MAX668 when contacting these component suppliers.
If the minimum input voltage is below +3.0V, use the MAX669 with VCC bootstrapped from VOUT (Table 1). In bootstrapped mode, if VOUT is always less than +5.5V, then LDO may be shorted to V CC to eliminate the dropout voltage of the LDO regulator. This increases the gate drive to the MOSFET, which lowers the MOSFET on-resistance but increases the MAX668 supply current due to gate-charge loss. If VIN is greater than +3.0V, the MAX668's VCC can be powered from VIN. This will decrease quiescent power dissipation, especially when V OUT is large. If V IN is always less than +5.5V, LDO may be shorted to VCC to eliminate the dropout voltage of the LDO regulator. If VIN is in the range of +3V to +4.5V, then the user may still want to bootstrap from VOUT to increase gate drive to the MOSFET at the expense of power dissipation. If VIN is always greater than +4.5V, the VCC input should always be tied to VIN, since bootstrapping from VOUT will not increase the gate drive from LDO, but quiescent power dissipation will rise. Jumpers JU2 and JU3 control the VCC and LDO inputs (see MAX668/MAX669 data sheet).
Jumper Selection
_________________________Quick Start
The MAX668 EV kit is fully assembled and tested. Follow these steps to verify board operation. Do not turn on the power supply until all connections are completed. 1) Place the shunt on JU1 across pins 1 and 2. Verify that the shunt is across JU2 pins 2 and 3 (VCC is tied to VIN) and JU3 is open (LDO is open). 2) Connect a +5V supply to the V IN pad. Connect ground to the GND pad. 3) Connect a voltmeter to the VOUT pad. 4) Turn on the power supply and verify that the output voltage is 12V.
The 3-pin header JU1 selects shutdown mode. Table 1 lists the selectable jumper options. The 3-pin header JU2 selects bootstrapped mode. Table 2 lists the selectable jumper options. For VCC less than 5.5V, use the 2-pin header JU3 to short LDO to VCC. This eliminates the internal linear regulator (LDO) dropout voltage. For the MAX668, this allows operation with input voltages down to 2.7V. Table 3 lists the selectable jumper options.
Other Output Voltages
The MAX668 EV kit can also be used to evaluate other output voltages. Refer to the Output Voltage Selection section in the MAX668 data sheet for instructions on selecting the feedback resistors R2 and R3. For output voltages greater than 15V, replace C5 (20V) with a capacitor that has a higher voltage rating. In addition to the standard EV kit configuration of 3VIN to 12V OUT at 1A, the EV Kit Application Circuit Capabilities table listed several common Input/Output combinations. Table 4 lists the components recommended for these alternative circuits.
_______________Detailed Description
The MAX668 EV kit provides a regulated +12V output voltage from an input source as low as +3V. It drives loads up to 1A with greater than 90% conversion efficiency. This EV kit is shipped configured in the nonbootstrapped mode (VCC is tied to VIN). However, there are several methods of connecting V CC and LDO depending on the specific design including input and output voltage range, quiescent power dissipation, MOSFET selection, and load.
2
_______________________________________________________________________________________
MAX668 Evaluation Kit Evaluates: MAX668/MAX669
Table 1. Jumper JU1 Functions
SHUNT LOCATION 1 and 2 2 and 3 Not installed SYNC/SHDN PIN Connected to VCC Connected to GND Floating MAX668 OUTPUT MAX668 enabled, VOUT = 12V. MAX668 operates at internal frequency. Shutdown mode, VOUT = VIN - diode MAX668 can be externally synchronized when the SYNC/SHDN pad is clocked.
Table 2. Jumper JU2 Functions
SHUNT LOCATION 1 and 2 2 and 3 VCC PIN Connected to VOUT Connected to VIN MAX668 MODE Bootstrapped mode Non-bootstrapped mode
Table 3. Jumper JU3 Functions
SHUNT LOCATION On Off LDO PIN Connected to VCC Open
_______________________________________________________________________________________
3
MAX668 Evaluation Kit Evaluates: MAX668/MAX669
Table 4. Components for Alternate Application Circuits
VIN
(MIN)
(V)
VOUT IOUT (V) (A)
MAXIM PART NO.
JU2 BOOTSTRAPPED vs. NON-BOOTSTRAPPED
L1 (H)
R1 (m)
R2 R3 R4 (k) (k) (k)
D1
N1
C1
C5
C6
1.8
12
0.4
4.7 1&2 Sumida MAX669 Bootstrapped CDRH10 4-4R7 1.0 1&2 Coilcraft MAX669 Bootstrapped D03316102 4.7 Sumida 1&2 MAX669 Bootstrapped CDRH10 4-4R7 4.7 Sumida 1&2 MAX668 Bootstrapped CDRH12 7-4R7
20 Dale WSL- 218 24.9 100 2010R020F 15 Dale WSL- 454 24.9 200 2010R015F 20 Dale WSL- 218 24.9 100 2010R020F 15 Dale WSL2512R015F
Hitachi HRF302A
68F 120F International 20V 20V AVX Sprague Rectifier IRF7401 TPSE686M 594D127X 020R0150 0020R2T
Open
1.8
24
0.1
Hitachi HRF302A
68F 22F 22F 20V 35V 35V International AVX AVX AVX Rectifier TPSE686M TPSE226M TPSE226M IRF7401 020R0150 035R0300 035R0300 68F 120F International 20V 20V Rectifier AVX Sprague IRF7401 TPSE686M 594D127X 020R0150 0020R2T 330F 10V Kemet T510X337 M010
2.5
12
0.65
Hitachi HRF302A
Open
3
5
3
75
24.9 100
Hitachi HRF502A
Fairchild FDS6680
330F 330F 10V 10V Kemet Kemet T510X337 T510X337 M010 M010
3
36
0.020 MAX668
2&3 NonBootstrapped
4.7 Sumida CD434R7
100 Dale WSL- 398 24.9 100 1206R100F
Central Semiconductor CMPD914
Fairchild FDS5610
10F 2.2F 6.3V, X7R 50V, X7R Taiyo Kemet Yuden C1825C22 JMK325BJ1 5MR0RAC 06MN
Open
12
24
0.5
2&3 MAX668 NonBootstrapped
22 Sumida CD73220
50 Dale Motorola WSL- 453 24.9 100 MBRS140T3 2010R050F
Fairchild FDS6680
33F 22F 20V 35V AVX AVX TPSD336M TPSE226M 020R0200 035R0300
Open
Note: This table lists components recommended for building other application circuits using the MAX668 EV kit.
4
_______________________________________________________________________________________
VIN C1 68F 20V L1 4.7H
Figure 1. MAX668 EV Kit Schematic
LDO JU3 1 C4 1F
U1
D1 MBRS340T3 EXT N1 C5 120F 20V 8
MAX668
JU2 9 2 1 JU1 3 10 R1 0.02 PGND 4 REF 5 C3 0.22F FB 2 FREQ R4 100k 1% 7 SYNC/ SHDN VOUT 2 1 CS+ C2 0.1F 6 VCC 3 VCC
VOUT 12V, 1A C6 OPEN C8 1F
VCC
SYNC/ SHDN
R2 218k 1%
REF 1.25V
Evaluates: MAX668/MAX669
_______________________________________________________________________________________
GND 3 C7 220pF R3 24.9k 1%
MAX668 Evaluation Kit
5
MAX668 Evaluation Kit Evaluates: MAX668/MAX669
1.0"
Figure 2. MAX668 EV Kit Component Placement Guide-- Component Side
1.0"
Figure 3. MAX668 EV Kit PC Board Layout--Component Side
1.0"
Figure 4. MAX668 EV Kit PC Board Layout--Solder Side
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.
6 _____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 1998 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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