CAT4237TD-T3 ONSEMI | Alldatasheet
Document overview
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Technical content
Characteristics subject to change without notice
FEATURES
Drives 6 to 8 White LEDs in series from 3V Up to 87% Efficiency Low Quiescent Ground Current 0.6mA Adjustable Output Current (up to 40mA) High Frequency 1MHz Operation High Voltage Power Switch Shutdown current less than 1µA Open LED low power mode Automatic Shutdown at 1.9V (UVLO) Thermal shutdown protection RoHS-compliant Thin SOT23 5-Lead (1mm max height)
APPLICATIONS
Color LCD and keypad Backlighting Cellular Phones Handheld Devices Digital Cameras PDAs Portable Game Machine
ORDERING INFORMATION
CAT4237TD-T3 TSOT23-5 (1) 3000 LT CAT4237TD-GT3 TSOT23-5 (2) 3000 UD Notes: (1) Matte-Tin Plated Finish (RoHS-compliant). (2) NiPdAu Plated Finish (RoHS-compliant).
DESCRIPTION
The CAT4237 is a DC/DC step-up converter that delivers an accurate constant current ideal for driving LEDs. Operation at a constant switching frequency of 1MHz allows the device to be used with small value external ceramic capacitors and inductor. LEDs connected in series are driv en with a regulated current set by the external resistor R 1. LED currents up to 40mA can be supported over a wide range of input supply voltages from 2.8V to 5.5V, making the device ideal for battery-powered applications. The CAT4237 high- voltage output stage is perfect for driving six, seven or eight white LEDs in series with inherent current matching in LCD backlight applications. LED dimming can be done by using a DC voltage, a logic signal, or a pulse width modulation (PWM) signal. The shutdown input pin allows the device to be placed in power-down mode with “zero” quiescent current. In addition to thermal protection and overload current limiting, the device also enters a very low power operating mode during “Open LED” fault conditions. The device is housed in a low profile (1mm max height) 5-lead thin SOT23 package for space critical applications. For Ordering Information details, see page 13. PIN CONFIGURATION TYPI CAL APPLICATION CIRCUIT 5-Lead Thin SOT23 (1mm max height) Top View L: Sumida CDRH3D16-330 D: Central CMDSH05-4 (rated 40V) C2: Taiyo Yuden UMK212BJ224 (rated 50V) High Voltage CMOS Boost White LED Driver VIN FB SHDN SW GND VIN CAT4237 VIN LD V OUT 15Ω 20mAVFB = 300mV 4.7µF 3V to 4.2V C1 0.22µF FBSHDN SW GND ON 33µH OFF
Characteristics subject to change without notice ABSOLUTE MAXIMUM RATINGS Parameters Ratings Units VIN, FB voltage -0.3 to +7 V SHDN¯¯¯¯¯ voltage -0.3 to +7 V SW voltage -0.3 to 55 V Storage Temperature Range -65 to +160 ºC Junction Temperature Range -40 to +150 ºC Lead Temperature 300 ºC RECOMMENDED OPERATING CONDITIONS Typical application circuit with external components are shown on page 1. Parameters Range Units VIN 2.8 to 5.5 V SW pin voltage 0 to 30 V Ambient Temperature Range -40 to +85 ºC 6, 7 or 8 LEDs 1 to 40 mA Note: (1) Thin SOT23-5 package thermal resistance θJA = 135°C/W when mounted on board over a ground plane. DC ELECTRICAL CHARACTERISTICS VIN = 3.6V, ambient temperature of 25ºC (over recommended operating conditions unless specified otherwise). Symbol Parameter Conditions Min Typ Max Unit IQ Operating Current VFB = 0.2V VFB = 0.4V (not switching) 0.6 0.1 1.5 0.6 mA ISD Shutdown Current VSHDN¯¯¯¯¯ = 0V 0.1 1 µA VFB FB Pin Voltage 8 LEDs with I LED=20mA 285 300 315 mV IFB FB pin input leakage 1 µA ILED Programmed LED Current R1 = 10Ω R1 = 15Ω R1 = 20Ω 28.5 14.25 31.5 15.75 mA VIH VIL Enable Threshold Level Shutdown Threshold Level 0.4 0.8 0.7 1.5 V V FSW Switching Frequency 0.8 1.0 1.3 MHz ILIM Switch Current Limit 350 450 600 mA RSW Switch “On” Resistance I SW = 100mA 1.0 2.0 Ω ILEAK Switch Leakage Cu rrent Switch Off, V SW = 5V 1 5 µA Thermal Shutdown 150 ºC Thermal Hysteresis 20 ºC VUVLO Undervoltage Lockout (UVLO) Threshold 1.9 V VOV-SW Overvoltage Threshold 35 V
Characteristics subject to change without notice PIN DESCRIPTION VIN is the supply input for the internal logic The device is compatible with supply voltages down to 2.8V and up to 5.5V. It is recommended that a small bypass ceramic capacitor (4.7µF) be placed between the VIN and GND pins near the device. If the supply voltage drops below 1.9V, the device stops switching. SHDN¯¯¯¯¯ is the shutdown logic input. When the pin is tied to a voltage lower than 0.4V, the device is in shutdown mode, drawing nearly zero current. When the pin is connected to a voltage higher than 1.5V, the device is enabled. GND is the ground reference pin. This pin should be connected directly to the ground place on the PCB. SW pin is connected to the drain of the internal CMOS power switch of the boost converter. The inductor and the Schottky diode anode should be connected to the SW pin. Traces going to the SW pin should be as short as possible with minimum loop area. An over- voltage detection circuit is connected to the SW pin. When the voltage reaches 35V, the device enters a low power operating mode preventing the SW voltage from exceeding the maximum rating. FB feedback pin is regulated at 0.3V. A resistor connected between the FB pin and ground sets the LED current according to the formula: I LED = 0.3V/R1 The lower LED cathode is connected to the FB pin. PIN DESCRIPTIONS Pin # Name Function 1 SW Switch pin. This is the dr ain of the internal power switch. 2 GND Ground pin. Connect the pin to the ground plane. 3 FB Feedback pin. Connect to the last LED cathode. 4 SHDN¯¯¯¯¯ Shutdown pin (Logic Low). Set high to enable the driver. 5 VIN Power Supply input. BLOCK DIAGRAM VIN VIN Enable Current Sense 300mV 15Ω LED Current 4.7µF RC N1 RS CC SHDN Thermal Shutdown & UVLO VREF 1MHz Oscillator Over Voltage Protection PWM & Logic Driver 0.22µF GND SW FB 33µH
Figure 1. Switching Waveform VIN = 4.2V,
Characteristics subject to change without notice TYPICAL CHARACTERISTICS VIN = 3.6V, CIN = 4.7μF, COUT = 0.22µF, L = 33µH with 8 LEDs at 20mA, TAMB = 25ºC, unless otherwise specified. Quiescent Current vs. VIN (Not Switching) 100 120 140 INPUT VOLTAGE [V] INPUT CURRENT [uA] VFB =0.4V (not switching) Quiescent Current vs. VIN (Switching) 0.0 0.5 1.0 1.5 2.0 INPUT VOLTAGE [V] SUPPLY CURRENT [mA] FB pin voltage vs. Supply Voltage 285 290 295 300 305 310 315 INPUT VOLTAGE [V] FEEDBACK [mV] 8LEDs at 20mA VOUT= 26V FB Pin Voltage vs. Output Current 285 290 295 300 305 310 315 0 5 10 15 20 25 30 OUTPUT CURRENT [mA] FB PIN VOLTAGE [mV]
8 LEDs
Switching Frequency vs. Supply Voltage Switching Waveforms 960 980 1000 1020 1040 INPUT VOLTAGE [V] FREQUENCY [kHz]
Characteristics subject to change without notice TYPICAL CHARACTERISTICS VIN = 3.6V, CIN = 4.7μF, COUT = 0.22µF, L = 33µH with 8 LEDs at 20mA, TAMB = 25ºC, unless otherwise specified. LED Current vs. Input Voltage (8 LEDS) INPUT VOLTAGE [V] LED CURRENT [mA] RFB = 10Ω RFB = 15Ω RFB = 20Ω LED Current Regulation (20mA) -1.0% -0.5% 0.0% 0.5% 1.0% INPUT VOLTAGE [V] CURRENT VARIATION [%] . 8 LED Efficiency vs. Load Current 5 1 01 52 02 53 0 LED CURRENT [mA] EFFICIENCY [%] VIN = 3.6V VIN = 4.2V VOUT ~ 27V at 20mA L = 33uH 8 LED Efficiency vs. Input Voltage INPUT VOLTAGE [V] EFFICIENCY [%] 15mA 20mA VOUT ~ 27V at 20mA L = 33uH 7 LED Efficiency vs. Load Current 5 1 01 52 02 53 0 LED CURRENT [mA] EFFICIENCY [%] VIN = 3.6V VIN = 4.2V
7 LEDs
VOUT ~ 23V at 20mA L = 33uH 6 LED Efficiency vs. Load Current 5 1 01 52 02 53 0 LED CURRENT [mA] EFFICIENCY [%] VIN = 3.6V VIN = 4.2V
6 LEDs
VOUT ~ 20V at 20mA L = 33uH
Characteristics subject to change without notice TYPICAL CHARACTERISTICS VIN = 3.6V, CIN = 4.7μF, COUT = 0.22µF, L = 33µH with 8 LEDs at 20mA, TAMB = 25ºC, unless otherwise specified. Power-up with 8 LEDs at 20mA Switch ON Resistance vs. Input Voltage 0.0 0.5 1.0 1.5 2.0 INPUT VOLTAGE [V] SWITCH RESISTANCE [ohm] FB pin voltage vs. Temperature 297 298 299 300 301 302 303 -50 0 50 100 150 TEMPERATURE [ºC] FEEDBACK VOLTAGE [mV] VIN=3.6V, 8LEDs ILED=20mA Shutdown Voltage vs. Input Voltage 0.2 0.4 0.6 0.8 1.0 INPUT VOLTAGE [V] SHUTDOWN VOLTAGE [V] 125°C 25°C 85°C -40°C Maximum Output Current vs. Input Voltage 100 120 140 INPUT VOLTAGE [V] MAX OUTPUT CURRENT [mA] VOUT = 15V VOUT = 20V
Characteristics subject to change without notice
APPLICATION INFORMATION
External Component Selection Capacitors The CAT4237 only requires small ceramic capacitors of 4.7µF on the input and 0.22µF on the output. Under normal condition, a 4.7µF input capacitor is sufficient. For applications with higher output power, a larger input capacitor of 10µF may be appropriate. X5R and X7R capacitor types are ideal due to their stability across temperature range. Inductor A 33µH inductor is recommended for most of the CAT4237 applications. In cases where the efficiency is critical, inductances with lower series resistance are preferred. Inductors with current rating of 300mA or higher are recommended for most applications. Sumida CDRH3D16-330 33µH inductor has a rated current of 320mA and a series resistance (D.C.R.) of 520mΩ typical. Schottky Diode The current rating of the Schottky diode must exceed the peak current flowing through it. The Schottky diode performance is rated in terms of its forward voltage at a given current. In order to achieve the best efficiency, this forward voltage should be as low as possible. The response time is also critical since the driver is operating at 1MHz. Central Semiconductor Schottky diode CMDSH05-4 (500mA rated) is recom– mended for most applications. LED Current Setting The LED current is set by the external resistor R connected between the feedback pin (FB) and ground. The formula below gives the relationship between the resistor and the current: R 1 = 0.3V/LED current Table 1. Resistor R1 and LED current
Characteristics subject to change without notice OPEN LED PROTECTION In the event of an “Open LED” fault condition, the CAT4237 will continue to boost the output voltage with maximum power until the output voltage reaches approximately 35V. Once the output exceeds this level, the internal circuitry immediately places the device into a very low power mode where the total input power is limited to about 4mW (about 1mA input current with a 3.6V supply). The SW pin clamps at a voltage below its maximum rating of 60V. There is no need to use an external zener diode between Vout and the FB pin. A 50V rated C 2 capacitor is required to prevent any overvoltage damage in the open LED condition. Open LED Protection without Zener VIN CAT4237 VIN L Schottky 100V (Central CMSH1-100) VOUT 15Ω V FB = 300mV 4.7µF 0.22µF FBSHDN SW GND OFF ON 33µH Open LED Switching waveforms without Zener Open LED Supply Current vs. VIN without Zener 0.0 0.5 1.0 1.5 2.0 INPUT VOLTAGE [V] SUPPLY CURRENT [mA] Open LED Output Voltage vs. VIN without Zener INPUT VOLTAGE [V] OUTPUT VOLTAGE [V]
The CAT4237 is a high-frequency switching regulator. order to minimize EMI, ripple and noise in general. Figure 3. Closed-switch Current Loop Figure 4. Open-switch Current Loop
Characteristics subject to change without notice PACKAGE OUTLINE DRAWING TSOT-23 5-Lead (TD) (1)(2) Notes: (1) All dimensions are in millimeters. Angles in degrees. (2) Complies with JEDEC standard MO-229. For current Tape and Reel information, download the PDF file from: http://www.catsemi.com/documents/tapeandreel.pdf. θ E1 E e b D c A TOP VIEW SIDE VIEW END VIEW L SYMBOL MIN NOM MAX A1 . 0 0 A1 0.01 0.05 0.10 A2 0.80 0.87 0.90 b 0.30 0.45 c 0.12 0.15 0.20 D2 . 9 0 B S C E2 . 8 0 B S C E1 1.60 BSC e0 . 9 5 T Y P L 0.30 0.40 0.50 L1 0.60 REF L2 0.25 BSC θ 0º 8º
Characteristics subject to change without notice EXAMPLE OF ORDERING INFORMATION1 Notes: (1) All packages are RoHS-compliant (Lead-free, Halogen-free). (2) The standard lead finish is NiPdAu. (3) The device used in the above exampl e is a CAT4237TD–GT3 (TSOT-23, NiPdAu Plated Finish, Tape & Reel 3000). (4) For Matte-Tin package option, please contac t your nearest ON Semiconductor Sales office. Prefix Device # Suffix CAT 4237 TD – G T3 Product Number 4237 Tape & Reel T: Tape & Reel 3: 3000/Reel Lead Finish G: NiPdAu Blank: Matte-Tin (4) Package TD: TSOT-23 Optional Company ID
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REVISION HISTORY
Date Rev. Description 13-Dec-05 00 Initial Issue 31-Jan-07 A Update Absolute Maximum Ratings Update Recommended Operating Conditions Change document number from 25094 to 5013, Rev. A 07-Jan-08 B Add NiPdAu lead finish Add Extended Temperature range Update Package Outline Drawing Add Example of Ordering Information Add “MD-“ to Document Number 19-Nov-08 C Change logo and fine print to ON Semiconductor