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19-1971; Rev 2; 10/01
MAX1856 Evaluation Kit SLIC Power Supply
General Description
The MAX1856 evaluation kit (EV kit) is a fully assembled and tested surface-mount circuit board that contains an inverting transformer flyback DC-DC converter. The circuit is configured for two output voltages simultaneously: a -72V that can supply up to 100mA and a -24V that can supply up to 400mA. The input voltage may range from +8V to +24V. The circuit can be configured for -48V, and supply up to 200mA. When operating from a +5V input supply, the circuit can deliver up to 7.2W output power in either configuration. The MAX1856 EV kit switching frequency is set at 250kHz but can range from 100kHz to 500kHz or may be driven by an external clock. The MAX1856 EV kit demonstrates low quiescent current and high efficiency (over 80%). The MAX1856 comes in the 10-pin MAX package. o +8V to +24V Input Range o +5V Input Range at Up to 7.2W Output Power o Output Voltages VOUT1 = -72V at 100mA VOUT2 = -24V at 400mA o Configurable for -48V at 200mA Output o 100kHz to 500kHz Switching Frequency o External Frequency Control o Low-Cost Minimum Components with Flyback Design o Fully Assembled and Tested
Features
Evaluates: MAX1856
Ordering Information
PART MAX1856EVKIT TEMP RANGE 0C to +70C IC PACKAGE 10 MAX
Component List
DESIGNATION C1 QTY 1 DESCRIPTION 22F, 100V aluminum electrolytic capacitor (8 x 11.5) Sanyo 100MV22AX 100F, 35V aluminum electrolytic capacitor (8 x 11.5) Sanyo 35MV100AX 10F 10%, 25V X5R ceramic capacitors (1812) Taiyo Yuden TMK432BJ106KM 100pF 10%, 200V COG ceramic capacitor (0805) Murata GRM40COG101K200 Not installed 470pF 10%, 200V X7R ceramic capacitor (0805) Murata GRM40X7R471K200 1F 10%, 25V X7R ceramic capacitor (1206) Taiyo Yuden TMK316BJ105KL T1 1 D2 0 DESIGNATION C10, C13 QTY 2 DESCRIPTION 1000pF 5%, 50V NP0 ceramic capacitors (0805) AVX 0805-5A-102-JAT-2A 1F 10%, 10V X7R ceramic capacitor (0805) Taiyo Yuden LMK212BJ105KG 2.2F 10%, 10V ceramic capacitor (1206) Murata GRM42-6X7R225K010AD 1A, 400V, ultra-fast-recovery diode (SMB) Central Semiconductor Corp CMR1U-04 Not installed 1A, 200V, ultra-fast-recovery diode (SMB) Central Semiconductor Corp CMR1U-02 22H, 1:2:2:2, 6.7A transformer Coiltronics CTX01-14853 or ICE Components ICA-0635
C2
1
C11
1
C3, C4
2
C12
1
C5 C6, C7 C8
1 0 1
D1
1
D3
1
C9
1
________________________________________________________________ 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.
MAX1856 Evaluation Kit SLIC Power Supply Evaluates: MAX1856
Component List (continued)
DESIGNATION N1 R1 R2, R3 R4, R5 R6 R7 R8 R9 R10 R11 R12 R13 U1 JU1 None None None None QTY 1 1 0 2 1 1 1 1 1 1 1 0 1 1 1 1 1 1 DESCRIPTION 3.8A, 55V, N-channel MOSFET (SOT223) International Rectifier IRLL2705 200 5% resistor (2512) Not installed 10 5% resistors (1206) 0.033 1% resistor (2010) IRC LRC-LRF2010-01-R033-F or Dale WSL 2010 0.033 1% 100 5% resistor (0805) 200k 1% resistor (0805) 5.11k 1% resistor (0805) 681k 1% resistor (0805) 174k 1% resistor (0805) 100k 5% resistor (0805) Not installed MAX1856EUB (10-pin MAX) 2-pin header Shunt (JU1) MAX1856 PC board MAX1856 data sheet MAX1856 EV kit data sheet
Quick Start
The MAX1856 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:
Output VOUT1 and VOUT2
1) Verify that a shunt is across pins 1 and 2 of jumper JU1 (SYNC/SHDN). 2) Connect a voltmeter to the VOUT1 pad. 3) Connect a +8V to +24V DC power supply to the VIN pad, with the voltage set to 0. 4) Connect the supply ground to the GND pad. 5) Turn on the power supply and gradually increase the input voltage through the +8V to +24V range. 6) Verify that VOUT1 is -72V throughout the +8V to +24V input voltage range. 7) Verify that VOUT2 is -24V throughout the +8V to +24V input voltage range. Note: Exercise caution when measuring the -72V. For instructions on reconfiguring VOUT1 to -48V, see Evaluating -48V Output.
Detailed Description
The MAX1856 EV kit is an inverted flyback DC-DC converter configured for two output voltages simultaneously. The transformer has a 1:2:2:2 turns ratio. The secondary has three taps to provide three different ratios of 1:2, 1:4, and 1:6. VOUT1 is connected to the 1:6 tap, providing -72V, which can supply up to 100mA. VOUT2 is connected to the 1:2 tap, providing -24V, which can supply up to 400mA. VOUT1 may be connected to the 1:4 tap to provide -48V and supply up to 200mA. The input voltage can range from +8V to +24V. The output voltage is determined by the following equation:
Component Suppliers
SUPPLIER AVX Central Semiconductor Coiltronics Dale Electronics Inc. ICE Components International Rectifier IRC Murata Sanyo USA Taiyo Yuden PHONE 803-946-0690 631-435-1110 561-241-7876 650-526-8333 703-257-7740 310-322-3331 650-367-9000 814-237-1431 619-661-6835 408-573-4150 FAX 803-626-3123 631-435-3388 561-241-9339 650-965-1644 703-257-7547 310-322-3332 650-367-7158 814-238-0490 619-661-1055 408-573-4159
|VOUT| = VIN x (N2 / N1) x D/(1 - D)
where (N2 / N1) is the secondary/primary turns ratio of the transformer, and D is the duty cycle of the pulsewidth-modulating (PWM) switching signal. For a fixed turns ratio, the duty cycle (D), will vary to compensate for the variation in VIN to maintain a constant output voltage. For example, for (N2 / N1) = 6:1, as VIN varies from +8V to +24V, D will vary from 60% to 33% to keep VOUT constant at -72V.
Note: Please indicate that you are using the MAX1856 when contacting these component suppliers.
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_______________________________________________________________________________________
MAX1856 Evaluation Kit SLIC Power Supply
When the input voltage drops to +5V, the total output power will fall to about 7.2W. The MAX1856 EV kit switches at 250kHz but can be varied from 100kHz to 500kHz by the internal oscillator in combination with resistor R8 (ROSC). The operating frequency may also be controlled by an external clock at the SYNC/SHDN pad. The external source must be a TTL level, and its maximum duty cycle may not exceed 45% for the 100kHz to 500kHz frequency range.
Table 1. Jumper JU1 Functions
SHUNT LOCATION SYNC/SHDN PIN MAX1856 OUTPUT MAX1856 enabled, VOUT1 = -72V, VOUT2 = -24V
Evaluates: MAX1856
1-2
Connected to VIN
Jumper Selection
Shutdown Mode The MAX1856 EV kit features a shutdown mode that reduces the MAX1856 quiescent current. The 2-pin jumper (JU1) selects the shutdown mode for the MAX1856. Table 1 lists the selectable jumper options.
None
No external frequency source connected to SYNC/SHDN pad External frequency source* connected to SYNC/SHDN pad
Shutdown mode, VOUT1 = VOUT2 = 0
None
MAX1856 enabled, VOUT1 = -72V, VOUT2 = -24V
Sync Mode
The MAX1856 EV kit features a synchronous mode that enables the operating frequency to be controlled by an external clock. To utilize the sync mode, remove the shunt on jumper JU1, and connect an external frequency source to the SYNC/SHDN pad. Select R8 as: R8 (ROSC ) = 1.15 x 50M x kHz CLOCK (kHz)
*External frequency source must have a duty cycle within the 20% to 45% range.
Evaluating -48V Output
The MAX1856 EV kit's -72V (VOUT1) output may be reconfigured for -48V and supply up to 200mA of current. To configure the -72V (VOUT1) output to -48V, remove diode D1 and install diode D2 (Central Semiconductor CMR1U-02 recommended). Remove capacitor C5 and install capacitor C6 (100pF, 200V). Remove resistor R1 and install resistor R2 (470, 0.5W). Replace resistor R10 with a 196k 1%, surface-mount (0805) resistor. Remove D3 and R11.
The external frequency source must be a TTL level and have a 20% to 45% duty cycle.
_______________________________________________________________________________________
3
Evaluates: MAX1856
MAX1856 Evaluation Kit SLIC Power Supply
Figure 1. MAX1856 EV Kit Schematic
C5 100pF 200V -72V VOUT1 C1 22F 100V T1 4 D1 R1 200 1W 5% 9 1 5 R4 10 5% 8 12 11 6 4 2 N1 7 3 JU1 10 SYNC/SHDN U1 MAX1856 1 LDO FB R9 5.11k 1% 4 REF FREQ GND 3 PGND 7 2 R8 200k 1% C12 2.2F C11 1F 10V REF 5 C13 1000pF REF VOUT2 C10 1000pF 50V R6 0.033 R10 681k 1% R11 174k 1% C7 OPEN R3 OPEN CS 6 R7 100 5% 1 D3 -24V VOUT2 R5 10 5% 9 VCC EXT 8 R13 SHORT (PC TRACE) C9 1F 25V SYNC/SHDN R12 100k 5% C6 OPEN R2 OPEN C8 470pF 200V 2 D2 OPEN GND C2 100F 35V GND VOUT1
4
+8V TO +24V/+5V* VIN
C3 10F 25V
C4 10F 25V
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GND
*TOTAL OUTPUT POWER LIMITED TO 7.2W FOR +5V VIN.
MAX1856 Evaluation Kit SLIC Power Supply Evaluates: MAX1856
1.0"
1.0"
Figure 2. MAX1856 EV Kit Component Placement Guide-- Component Side
Figure 3. MAX1856 EV Kit PC Board Layout--Component Side
1.0"
Figure 4. MAX1856 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.
5 _____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2001 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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