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19-0221; Rev 3a; 11/97
MAX797 Evaluation Kit
_______________General Description
The MAX797 evaluation kit (EV kit) is a preassembled and tested demonstration board that embodies the standard 3.3V application circuit. The board comes configured to accept battery voltages between 4.5V and 28V, but can be reconfigured for voltages between 4.5V and 30V by substituting MOSFETs with higher breakdown voltage ratings. The standard board is guaranteed to deliver at least 3A of load current. To modify the load-current capability, change the sense-resistor (R1) value and re-size the external components according to Table 1 in the MAX796/MAX797/MAX799 data sheet. The main output voltage comes preset to 3.35V (nominal). To select 5V operation, move jumper J3 to position 1-2. For operation in adjustable mode, install resistors R4 & R5 and remove the jumper. There is a small PC trace jumper that shunts J3 on the board. This default jumper must be cut apart for either adjustable-mode or fixed 5V operation. Don't operate the circuit if a jumper or resistor divider has not been installed, as this will damage the IC due to output overvoltage. In addition to the standard components, the EV kit has some extra pull-up and pull-down resistors (R4-R8) to set default logic input levels. These resistors can usually be omitted in the final design.
____________________________Features
o Battery Range: 4.5V to 28V o Load Capability: 3.3V at 3A o Adjustable 2.5V to 6V Output (optional resistor divider) o Precision 2.505V Reference Output o Oscillator SYNC Input o Low-Noise Mode Control Input
Evaluates: MAX797
______________Ordering Information
EV KIT MAX797EVKIT-SO VOUT +3.3V or Adj BOARD TYPE Surface Mount
_____________________MAX797 EV Kit
________________________________________________________________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.
MAX797 Evaluation Kit Evaluates: MAX797
____________________Component List
DESIGNATION QTY C1, C11 2 DESCRIPTION 22F, 35V low-ESR capacitors AVX TPSE226M035R0300 Sprague 595D226X0035R2T Kemet T510 X 477(1) 006 AS 470F, 0.030 low-ESR capacitor 0.1F ceramic capacitors 4.7F, 16V tantalum capacitors Sprague 595D475X0016A2T 0.33F ceramic capacitor 0.01F ceramic capacitor Open 100mA, 30V Schottky diode Central Semiconductor CMPSH-3 Motorola MBR0530 1A, 40V Schottky diode Motorola MBRS140T3 Nihon EC10QS04 International Rectifier 10BQ040 2-pin headers Leave these sites open 10H, 2A inductor Sumida CDRH-125-100 (shielded) Coiltronics UP2-100 Coilcraft DO3316-103 5A, 30V logic-level N-channel MOSFETs Motorola MMSF5N03HD International Rectifier IRF7201 Siliconix Si9410 0.025 sense resistor Dale WSL-2010-R025-F IRC LR2010-R025-F Unused reference designators Leave these sites open 1M, 5% resistors 100k, 5% resistor Maxim MAX797CSE R8
_________________________Quick Start
1) Connect a stiff (20W or better) bench power supply to the VIN and GND pads found at the edge of the board. 2) Check that the jumpers are set correctly (J1 and J2 installed, J3 set to position 2-3, J4 set to 1-2). 3) Turn up the input voltage to somewhere between 4.75V and 28V. 4) Verify that the main output is regulating at 3.3V. Normal full-load regulation is -2.5% while keeping the output in tolerance. If the measured error is higher, there may be drops in the wiring or ground. 5) Ensure that the voltmeter is sensing directly at the output and ground pads of the PC board. To observe normal PWM switching action, place a 1A load on the main output and observe the switching node (device LX pin) with an oscilloscope while varying the input voltage. Without a load, the switching waveforms are intermittent and difficult to trigger on, and it may appear that the board is not working. Jumper J4 comes installed for 300kHz operation. Component values may need to be changed if 150kHz operation is selected; see the Design Procedure section in the MAX796/MAX797/MAX799 data sheet. The oscillator can be synchronized to an external clock signal by driving the SYNC pad with a pulse train of 5V amplitude.
C2 C3, C8 C4 C5 C6 C21 D1
1 2 1 1 1 0 1
D2 J1, J2 J3, J4
1 2 0
L1
1
Table 1. Pull-Up/Down Resistors
RESISTOR R4, R5 R6 R7 FUNCTION Adjustable-mode resistor dividers, not installed. VOUT = 2.505V (1 + R4/R5). 1M, low-noise-mode pull-up resistor, usually shorted out (SKIP to GND). 100k SYNC pull-up resistor, usually shorted out (SYNC to REF). 1M SHDN pull-down resistor, usually shorted out (SHDN to V+).
Q1, Q2
2
R1 R2, R3 R4, R5 R6, R8 R7 U1
1 0 0 2 1 1
Table 2. Jumper Connections
JUMPER J1 J2 J3 J4 FUNCTION On/off control. Remove to force shutdown mode. Low-noise mode select. Remove to force low-noise mode. Output voltage select. Install in position 1-2 for 5V, 2-3 for 3.3V. Frequency select. Install in position 1-2 for 300kHz, 2-3 for 150kHz.
See Table 2 in the MAX796/MAX797/MAX799 data sheet for component supplier phone/fax numbers.
2 ________________________________________________________________________________________
MAX797 Evaluation Kit Evaluates: MAX797
C11 22F, 35V C8 0.1F J1 ON/OFF TO REF R7 100k R8 1M
C1 22F, 35V
VIN = 4.75V TO 28V VL OUTPUT (+5V AT 5mA)
10 V+ 6 SHDN
11 VL BST DH 14 16
D1
C4 4.7F Q1
LX
15
C3 0.1F
L1 10H Q2 D2
R1 25m
+3.3V AT 3A
MAX797
DEFAULT J4 TO VL R6 1M SYNC LOW-NOISE CONTROL J2 C6 0.01F 2 SKIP SS 1 GND 4 3 REF 5 SYNC
DL PGND CSH CSL FB
13 12 8 9 7
C2 220F
C21 220F
R4 OPEN
TO VL
C5 0.33F REF OUTPUT (+2.505V AT 100A)
R5 OPEN
DEFAULT J3
Figure 1. MAX797 EV Kit Schematic
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MAX797 Evaluation Kit Evaluates: MAX797
Figure 2. MAX797 EV Kit Component Placement Guide-- Component Side
Figure 3. MAX797 EV Kit Component Placement Guide-- Solder Side
Figure 4. MAX797 EV Kit PC Board Layout--Component Side
Figure 5. MAX797 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.
4 _____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 1997 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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