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19-2176; Rev 1; 9/02
MAX1848 Evaluation Kit
General Description
The MAX1848 evaluation kit (EV kit) is a fully assembled and tested circuit board that contains a step-up switching-regulator current source powering three series-connected white LEDs. The circuit provides programmable LED current. The EV kit can be powered from a 2.6VDC to 5.5VDC source. The MAX1848 features programmable soft-start and LED brightness control. The MAX1848 EV kit demonstrates matching LED brightness with high converter efficiency (87%) to maximize battery life. Operation at 1.2MHz allows the use of tiny surface-mount components. o >87% Efficiency o 2.6V to 5.5V Input Voltage Range o Analog LED Intensity Control o Drives Up to Three Series White LEDs with Uniform Brightness o Small, Low-Profile External Components o 0.3A IC Shutdown Current (typ) o 1.2MHz Switching Frequency o 8-Pin SOT23 Package o Fully Assembled and Tested
Features
Evaluates: MAX1848
Component Suppliers
SUPPLIER Central Murata Taiyo Yuden PHONE 631-435-1110 770-436-1300 800-348-2496 FAX 631-435-1824 770-436-3030 847-925-0899 PART MAX1848EVKIT
Ordering Information
TEMP RANGE 0C to +70C IC PACKAGE 8 SOT23
Note: Please indicate that you are using the MAX1848 when contacting these component suppliers.
Component List
DESIGNATION C1 QTY 1 DESCRIPTION 3.3F, 6.3V X5R ceramic capacitor (0805) Taiyo Yuden JMK212BJ335MG 1.0F, 16V X5R ceramic capacitor (0805) Taiyo Yuden EMK212BJ105KG 0.22F, 10V X7R ceramic capacitor (0603) Taiyo Yuden LMK107BJ224KA 1000pF, 50V X7R ceramic capacitor (0603) Taiyo Yuden UMK107B102KZ 0.2A, 30V high-speed switching diode (SOD-323) Central Semiconductor Corp. CMDSH2-3 DESIGNATION D2, D3, D4 QTY 3 DESCRIPTION Right angle white LEDs (SMD 2.8mm x 1.2mm x 1mm) 47H, 170mA inductor (low cost) Murata LQH3C470K34 33H (optimum performance) 4.99 1% resistor (0805) MAX1848EKA (8-pin SOT23) MAX1848 PC board MAX1848 data sheet MAX1848 EV kit data sheet
L1 R1 U1 None None None
1 1 1 1 1 1
C2
1
C3
1
C4
1
D1
1
________________________________________________________________ Maxim Integrated Products
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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.
MAX1848 Evaluation Kit Evaluates: MAX1848
Quick Start
The MAX1848 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.
Soft-Start
The soft-start feature limits the inrush current during startup. Capacitor C3 determines the startup delay time for the EV kit. The delay time for the EV kit is set to 18.3ms. The following equation can be used to configure the EV kit for other startup times: t = (C3) x (1V) / (12A)
Recommended Equipment
* * One voltmeter Dual power supply 5V, 1A
Main Output
1) Connect a voltmeter to the VOUT pad. 2) Make sure both power supplies are set to 0V and off before connecting the power supplies to the circuit. 3) Connect a 5V supply to the VIN pad. Connect the power-supply ground to the GND pad. 4) Connect a 5V supply to the VCTRL pad. Connect the power-supply ground to the GND pad. 5) Turn on the VIN power supply and set it to 3.3V. 6) Turn on the VCTRL power supply, vary the VCTRL between 0 and 2V and observe the variation in brightness of the LEDs. 7) Verify that the output, VOUT is approximately 10V when the VCTRL power supply is 2V. 8) Vary the VIN power supply from 2.6V to 5.5V and verify that the LED brightness remains constant. 9) Verify that the LEDs are off when VCTRL drops below 100mV. ILED = VCTRL / (13.33 x R1) Adjusting the control voltage VCTRL varies the intensity of the LEDs. VCTRL can range from 250mV to 5.5V or (VIN + 2V), whichever is lower. However, with R1 = 4.99, VCTRL should not exceed +2V in order to keep the LED current below its absolute maximum rating of 30mA. where t = desired startup time delay
LED Current
The current through the LEDs is related to the currentsense resistor (R1) by the following equation:
Shutdown
The MAX1848 enters shutdown mode when V CTRL drops below 100mV. In shutdown mode, the MAX1848 quiescent current is reduced to 0.3A. The MAX1848 comes out of shutdown mode when VCTRL rises above 250mV.
Detailed Description
The MAX1848 EV kit contains a switching-regulator current-source circuit. The EV kit's circuit is configured to drive three series-connected LEDs. The EV kit can be powered by a 2.6V to 5.5V DC source. The MAX1848 EV kit features programmable LED brightness by controlling LED current, overvoltage protection, and up to 87% efficiency for maximum battery life.
Overvoltage Protection
Overvoltage protection occurs when V OUT is above 13.25V (typ). The EV kit comes out of the overvoltage protection when VOUT falls below 12.25V (typ). This protects the MAX1848 and white LEDs during a fault condition.
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MAX1848 Evaluation Kit Evaluates: MAX1848
L1 47H VIN 2.6V TO 5.5V C1 3.3F GND VCTRL C4 1000pF GND GND 1 COMP C3 0.22F CS U1 2 OUT
8
V+
LX
4
D1
VOUT
3
C2 1F D2
MAX1848
CTRL PGND
5
D3
6
D4 CS
7 R1 4.99 1%
Figure 1. MAX1848 EV Kit Schematic
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MAX1848 Evaluation Kit Evaluates: MAX1848
Figure 2. MAX1848 EV Kit Component Placement Guide-- Component Side
Figure 3. MAX1848 EV Kit PC Board Layout--Component Side
Figure 4. MAX1848 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) 2002 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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