CAT4238AEVB CAT4238 10-LED Boost Converter Evaluation Board User's Manual http://onsemi.com EVAL BOARD USER’S MANUAL Introduction CAT4237EVAL2 Board Hardware This document describes the CAT4238AGEVB Evaluation Board for the ON Semiconductor CAT4238 High Efficiency 10-LED Boost Converter. The functionality and major parameters of the CAT4238 can be evaluated with the CAT4238AGEVB board. The CAT4238 is a high voltage CMOS constant-current DC/DC converter that has been designed to drive with high efficiency white or other high brightness LEDs. The high-voltage output stage allows driving up to 10 white LEDs in series. A single external resistor sets the LED current between 5 mA and 40 mA. LED current can be adjusted using either a pulse width modulated (PWM) signal or a DC voltage. Detailed descriptions and electrical characteristics are in the CAT4238 data sheet. The evaluation board contains a CAT4238 DC-DC boost converter in a typical application circuit. As configured, the board circuit is set to drive up to 10 white LEDs in series. The user can chose to connect the CAT4238 output to the on-board LEDs string or to an external LEDs string from an application. The board provides the option to connect a different number of LEDs available on board, 8, 9 or 10, using a jumper shunt for one of the J2 to J4 connectors. The board schematic is shown in Figure 1. VIN LQ1 T1 C1 4.7 mF S1 GND GEN/DC GND FB SGND T2 J1 T3 R4 200 kW T4 T5 R5 10 kW SW T9 47 mH 5 1 VIN SW CAT4238 SHDN 3 4 FB GND 2 U1 C2 0.22 mF R3 1 kW T8 VOUT T7 D1 GND L1 LED T10 L2 L3 R2 100 W L4 L5 R1 6.81 W T6 L6 L7 J2 J3 J4 L8 L9 L10 Figure 1. CAT4238AEVB Board Schematic Semiconductor Components Industries, LLC, 2011 September, 2011 − Rev. 3 1 Publication Order Number: EVBUM2019/D CAT4238AEVB PWM signal or a DC voltage. Resistors R3 and R5 (R5 – soldered on board by the user) are used to adjust the LED current using the dimming control with an external applied DC voltage on the FB pin. The ON/OFF operation and dimming control can be selected using the jumper options for the J1 connector. Test points T1 to T10 are available to apply the external voltages/signal generator or to measure the output voltages/signals provided by CAT4238. The component placement is shown in Figure 2. Table 1 presents the component list for this evaluation board. The board is powered from an external voltage applied to the VIN (T1) pad. The circuit is delivered with no LEDs soldered on board. The user can solder his white LEDs on the CAT4138 board (8 to 10 LED string pads layout provided) or he can choose to connect the LEDs from his application between VOUT (T7) and LED (T10) test points. The LED current is set through the external resistors connected to the FB pin (R1, R2). Using the variable resistor R2, the LED current can be set from 3 mA to 40 mA. Most white LEDs are driven at a maximum current between 15 mA and 20 mA to ensure a pure “white” light. The board also demonstrates the CAT4238 shutdown mode and LED brightness control by using an external Figure 2. CAT4238AEVB Board Table 1. CAT4238AGEVB BOARD LIST OF COMPONENTS Name Manufacturer U1 ON Semiconductor C1 Taiyo Yuden (or Panasonic) C2 Taiyo Yuden (or Kemet) L1 Sumida D1 Central Semi R1 Yageo R2 R3 Description Part Number Units CMOS White LED Driver, TSOT23 - 5pin CAT4238TD-G 1 Ceramic Capacitor 4.7 mF/6.3 V, X5R, Size 0805 JMK212BJ475 (or Digi-Key PCC2315CT-ND) 1 Ceramic Capacitor 0.22 mF/50 V, X5R(X7R) UMK212BJ224KG (Digi-Key 587-1287-1-ND) 1 Inductor 47 mH, Low DCR, High Current CDC5D23B-470 (or CDR6D23MN-470) 1 Schottky Diode, Low VF, 40 V, 500 mA, SOD-323 CMDSH05-4 1 SMT Resistor 1/16 W, 6.81 W, 0603 Digi-Key 311-6.81HCT-ND 1 Bourns Trimmer Pot, 1/4”, 100 W 3329W-101-ND (or equiv) 1 Yageo SMT Resistor 1/16 W, 1.0 kW, 0603 Digi-Key 311-1.0KHCT-ND 1 R4 Yageo SMT Resistor 1/16 W, 200 kW, 0603 Digi-Key 311-200KHCT-ND 1 R5 Yageo Metal Film Resistor 1/16W, 10kW (Not Soldered on Board) Digi-Key 10.0KXBK-ND L1 to L10 Nichia White LED, SMT (Optional) NSCW100 or NSCW335 10 J1 6-pin Header Connector, 0.1”, Single Strip Digi_Key S1012-06-ND (or equiv) 1 J2 to J4 2-pin Header Connector, 0.1”, Single Strip (optional) Digi_Key S1012-02-ND (or equiv) 3 Pin Receptacle (Test Points) #0149-0-15-01-30-14-04-0 (or equiv) 10 T1 to T10 Mil-Max http://onsemi.com 2 CAT4238AEVB CAT4238 EVALUATION The CAT4238AGEVB gives the user a way to evaluate the CAT4238 in a typical application of driving multiple LEDs. The following steps are an example of how the user can evaluate the CAT4238 white LED driver: Monitor the voltage on FB (T5), VOUT (T7), and SW (T9) Verify the internal switch frequency (fSW = 1.0 MHz typically) using a scope probe connected on SW (T9) test point (GND = T8) Figure 3 shows the internal switch output, VSW (DC coupled, 5 V/div) and the regulated voltage on FB pin, VFB (DC, 500 mV/div) for VIN = 3.6 V, ILED = 20 mA, 10 LEDs in series connected to the CAT4238 output. Driving 10 LEDs in series and Shutdown Mode 1. Connect the 10-LED string to the CAT4238 output through J4 header pin connector 2. Set the R2 potentiometer to the middle position 3. Apply the external voltage supply, Vext (3.0 V < VIN < 5 V) between VIN (T1) and GND (T2) 4. The CAT4238 is in the shutdown mode (SHDN pin is connected to GND) if the J1 connector (Pin #1 – Pin #2) is not jumpered Connect a current meter between Vext and VIN pad to measure the shutdown current: ISD << 1 mA n this mode of operation the LEDs are disconnected from the output: LEDs are OFF 5. Connect SHDN pin of CAT4238 to VIN using a jumper shunt between Pin #1 and Pin #2 of J1 connector Observe that LEDs are ON LED Current Evaluation 1. Programming LED current Figure 3. Internal Switch Output and Regulated VFB Voltage Waveforms (ILED = 20 mA, VIN = 3.6 V) LED current is programmed using the external resistors, RSET = R1 + R2, connected to the FB pin. The voltage at the FB pin is internally regulated to the value VFB = 300 mV 15 mV. 2. Evaluating LED current regulation versus the input voltage, VIN Set the ILED to a programmed value using the R2 potentiometer (i.e. 10 mA, 20 mA, 30 mA for VIN = 3.6 V) For any ILED value vary the VIN voltage between 3.0 V and 5.5 V Observe the value of ILED measured by the current meter and VFB using a voltmeter. Figure 4 presents the ILED current versus VIN. Figure 5 shows the CAT4238 FB voltage versus input voltage. The current into the LED pin can be set according to the following equation: I LED(mA) + V FB(mV) V FB + R1 ) R2 RSET(W) Set the input voltage: ex. VIN = 3.6 V Disconnect the jumper from the J4, connector and ILED (mA) RSET (W) 5 59 10 29.8 15 20 20 15 25 12 30 10 CAT4238 LED Current versus Input Voltage (10 LEDs in series) 35 30 ILED (mA) insert a current meter between these pins to monitor the LED current, ILED Rotate the potentiometer R2 and observe the ILED value on the current meter. The current can be adjusted between 3 mA and 30 mA, approximately. Various LED current values and the associated RSET values are listed below: 25 20 15 10 5 0 3.00 3.50 4.00 4.50 5.00 5.50 VIN (V) RSET = 29.8 W RSET = 15 W RSET = 10 W Note: RSET = R1 + R2 Figure 4. LED Current Line Regulation http://onsemi.com 3 CAT4238AEVB Dimming Control CAT4238 FB Voltage versus Input Voltage VFB (mV) ILED = 10 mA 310 300 290 280 270 260 250 240 230 220 210 200 3.00 ILED = 20 mA 3.50 4.00 4.50 The LED brightness control can be accomplished by using a PWM signal applied to the SHDN pin or to the FB pin. The other method is to use a variable DC voltage applied through a resistor to FB pin. 1. Dimming using a PWM signal on the SHDN pin ILED = 30 mA 5.00 The LEDs are turned off and on at the PWM frequency. The average current changes with the duty cycle. Increasing the duty cycle will increase the LED brightness. The peak current value sets the light spectrum. Connect the jumper shunt between Pin #2 and Pin #3 of the J1 connector Apply a pulse signal generator to the GEN/DC (T3) pad; Frequency = 200 Hz to 2 kHz; Amplitude 0 V to 3 V for VIN = 3.6 V Modify the duty cycle between 0% and 100% Observe the average current through LEDs measured by a current meter inserted at J4 connector. For 0% duty cycle, the ILED will be off (ILED = 0 mA); At the maximum duty cycle, the LED will be driven at the maximum current set by the R2 potentiometer Monitor the FB voltage compared with the PWM signal applied on SHDN input 5.50 VIN (V) Figure 5. VFB Voltage Line Regulation Efficiency Evaluation The efficiency is evaluated according to the following equation: Efficiency(%) + I LED I IN SVFi V IN 100 where SVFi = VOUT – VLED, VLED is the voltage measured on LED (T10) test point. 1. Insert a current meter, CM1, between input supply voltage, Vext, and VIN pad to monitor the input current, IIN (or use an embedded power supply current meter) 2. Set the input voltage for VIN = 3.6 V 3. Adjust the R2 potentiometer for the ILED = 5 mA. Observe the ILED current on the meter, CM2, inserted between Pin #1 and Pin #2 of J4 connector 4. Measure the IIN current on CM1 5. Monitor the output voltage on VOUT (T7) and VLED voltage on LED (T10) test points 6. Repeat steps 3 to 5 for ILED = 10 mA, 15 mA, 20 mA, 25 mA and 30 mA Figure 7 shows the voltage monitored on the FB pin, VFB (CH2) using a PWM signal applied to the SHDN pin (CH1). The frequency of the PWM signal is 2 kHz approximately. Figure 6 shows the efficiency measured for 2 values of input voltage, VIN = 3.6 V and VIN = 4.2 V, with 10 LEDs in series connected to the CAT4238 output. CAT4238 Efficiency (10 LEDs in series) VIN = 3.6 V VIN = 4.2 V Efficiency (%) 90% Figure 7. FB Voltage Waveform with PWM 85% 80% 2. Dimming using a DC voltage applied to the FB pin 75% TA variable external DC voltage is applied on FB pin to adjust the LED current. As the DC voltage is increased, the voltage drop on resistor R3 is increased and the voltage drop on RSET = R1+R2 is decreased, thus the LED current decreases. The external DC voltage is applied to FB pin through a series resistor, R5, which sets the maximum DC voltage. 70% 65% 5 10 15 20 25 30 ILED (mA) Figure 6. CAT4238 Efficiency Driving 10 LEDs in Series http://onsemi.com 4 CAT4238AEVB Also, a filtered PWM signal can be considered as a variable DC voltage. Connect the SHDN pin to VIN: jumper shunt between Pin #1 and Pin #2 of J1 connector Set the ILED current (i.e. ILED MAX = 20 mA) Connect the GEN/DC to FB pin through R5 resistor using one jumper between Pin #3 and Pin #4 and another jumper shunt between Pin #5 and Pin #6 of J1 connector Apply the variable DC voltage between GEN/DC (T3) and GND (T4) Increase the DC voltage value (from 0V to VMAX = 3.2 V) Observe the ILED current decreases from the ILED MAX (20 mA – previous set) to ILED MIN (0 mA for VMAX = 3.2 V with the existing resistors values, R3 = 1 kW, R5 = 10 kW). ON Semiconductor and are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC reserves the right to make changes without further notice to any products herein. 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