IZ1937 LT1937 - Datasheet Archive

 

White LED Step-Up Converter (Functional equvalent of LT1937 Linear Technology Corporation) Description The IZ1937 is a step-up

 

IZ1937 IZ1937 White LED Step-Up Converter (Functional equvalent of LT1937 LT1937 Linear Technology Corporation) Description The IZ1937 IZ1937 is a step-up DC/DC converter specifically designed to drive white LEDs with a constant current. The device can drive two, three or four LEDs in series from a Li-Ion battery. Series connection of the LEDs provides identical LED currents resulting in uniform brightness and eliminating the need for ballast resistors. The IZ1937 IZ1937 operates at 1.2MHz, allowing the use of tiny external components. The output capacitor can be as small as 0.22uF, saving space and cost versus alternative solutions. A low 95mV feedback voltage minimizes power loss in the current setting resistor for better efficiency. The device can used in mobile phones, PDAs, Handheld Computers, calculators, digital cameras, MP3-players, GPS-receivers. Features · Internally determined LED current · High Efficiency: 84% Typical · Drives Up to 4 LEDs from a 3.2V Supply · Drives Up to 6 LEDs from a 5V Supply · 36V rugged bipolar switch · Fast 1.2MHz switching frequency · Uses tiny 1mm Tall Inductors · Requires only 0.22uF output capacitor ICs are available for shipment in chip form on unsawn wafers Tab 1. Contact Pad Description Contact pad number Symbol Description 01 SW 02 GND 03 VIN 04 SHDN Shutdown pad (pin) 05 GND Common pad (pin) 06 FB Feedback pad (pin) Switch pad (Pin) Common pad (pin) Input supply pad (pin) 1 Ver.1.0/9.02.2008 IZ1937-TSe.doc IZ1937 IZ1937 VIN FB SW 03 06 01 A1 Reference voltage source A3 - R1 + R3 + R2 A2 C1 A5 RS -flip-flops VT1 A4 + R4 Sawtooth voltage generator 02,05 GND SHDN 04 Oscilator A1 ­ error amplifier; A2 ­ addrer; A3 ­ PWM ­ comprator; A4 ­ comparator; A5 ­driver; C1 ­ capacitor; R1 ­ R4 ­ resistor; VT1 ­ transistor Te device contain, switch on/off circuit; output current overrising protection unit, driver-buffer, output switch. Fig.1 Block Diagram 2 Ver.1.0/9.02.2008 IZ1937-TSe.doc IZ1937 IZ1937 Table 2 ­Absolute maximum ratings Symbol UIN USW UFB U SHDN TJ stg Parameter Absolute maximum ratings Min. Max. 10 36 10 10 150 -60 150 Recommended operating mode Min. Max. 2,5 10 125 Input voltage SW pin Voltage FB pin Voltage SHDN pin Voltage Storage Temperature Junction Temperature Unit Unit V V V V o C o C Table 3 ­ Recommended operating mode Symbol UIN TJ Parameter Input voltage Storage Temperature V C o Table 4 Electric Parameters Parameter, unit Minimum input voltage, V Maximum input voltage, V Symbol UIN MIN UIN MAX Feedback Voltage, mV Supply Current, IFB 10 10 100 150 UIN = 3,0 V, U SHDN = 3,0 V, ISW = 100 mA Duty Cycle 66 % UIN = 3,0 V, U SHDN = 3,0 V 2,5 3,75 1,0 2,0 1,6 1,8 UIN = 3,0 V, U SHDN = 3,0 V UIN = 3,0 V, U SHDN = 0 V UIN = 3,0 V, U SHDN = 3,0 V - UIN = 3,0 V, U SHDN = 3,0 V UIN = 3,0 V, U SHDN =3,0V, USW = 5,0 V - uA fS 0,8 0,6 DCMAX 85 80 - Switching Frequency, MHz Switch Leakage Current, uA ILSW Ambient temperature, °C U SHDN = 3,0 V IQ mA Maximum Duty Cycle, % Testing mode - UFB FB pad Bias Current, nA Value Min. Max. 2,5 2,5 10 10 86 104 76 114 3 5,0 7,5 25 ± 10 -40 . +125 Ver.1.0/9.02.2008 IZ1937-TSe.doc IZ1937 IZ1937 Table 4 Electric Parameters (continued) Parameter, unit Symbol SHDN Voltage High, V SHDN Voltage Low , V UIH UIL Value Min. Max. 1,5 1,5 0,4 0,4 Testing mode UIN = 3,0 V Note 1 UIN = 3,0 V Note 1 Ambient temperature, °C 25 ± 10 -40 . +125 Notes 1 During UIH & UIL measurements threthhold voltage is tested, which has to be within range from 0,4 to 1,5 V (see fig. 2). 2 Symbol descriptions : - U SHDN - Shutdown pad voltage (contact pad 04); - UFB ­ Feedback Voltage pad voltage (contact pad 06); - USW ­ Switch pad voltage (contact pad 01); - ISW ­ Switch pad current (contact pad 01). UI, V IC is switched on IC is switched off UIH=1,5V UIL=0,4V USHDN, V Fig.2 Switching on/off diagramm 4 Ver.1.0/9.02.2008 IZ1937-TSe.doc IZ1937 IZ1937 Table 5 ­Typical Electric Parameters Symbol ICL UCESAT ISHDN Parameter, unit Testing mode Output transistor saturation voltage SHDN pad (pin) bias current Unit UIN = 3,0 V, U SHDN = 3,0 V UIN = 3,0 V, U SHDN = 3,0 V, ISW = 250 UIN = 3,0 V, U SHDN = 3,0 V Output transistor current limit Typ.value 320 mA 350 mV 65 uA OPERATION DESCRIPTION The IZ1937 IZ1937 consist of following units: voltage switch on/off circuit, sawtooth generator, rectangular pulse generator PWM ­comparator RS-latch, error amplifier, output buffer, output switch, currentlimit circuit for output switch. The IZ1937 IZ1937 uses a constant frequency, current mode control scheme to provide excellent line and load regulation. At the start of each oscillator cycle, signal from oscillator applied to S-pin of the RS-latch, the latch output high level voltage is set. This voltage through buffer turns on the power switch (transistor VT1). A voltage proportional to the switch current is added to a stabilizing sawtooth voltage and the resulting sum is applied to the positive terminal of the PWM comparator A3. When this voltage exceeds the level at the negative input of A3, the SR latch is reset turning off the power switch VT1. The level at the negative input of A3 is set by the error amplifier A1, and is simply an amplified version of the difference between the feedback voltage and the reference voltage of 95mV. In this way, the error amplifier A1 contols the peak current level to keep the output in regulation. If the error amplifier's output increases, more current is delivered to the output; if it decreases, less current is delivered. 5 Ver.1.0/9.02.2008 IZ1937-TSe.doc IZ1937 IZ1937 L1 22uHn VIN 3 to 5 V VD1 C1 1 C2 0,22uF VD2 VIN SW VD3 IZ1937 IZ1937 OFF ON FB SHDN GND 15 mA VD4 R1 6,34Ohm VD1 ­ Shottki diode; VD2 ­ VD4 - diodes Fig. 3 ­ Typical application diagramm (3 white LED driver supplied by Li-ion battery) 6 Ver.1.0/9.02.2008 IZ1937-TSe.doc IZ1937 IZ1937 Fig. 4­ Chip diagramm Table 5 ­ Contact pads coordinates Coordinates (ref. left bottom corner), mm Y 01 0.0825 0.564 02 0.237 0.385 03 0.0985 0.1645 04 0.711 0.139 05 0.7165 0.360 06 0.711 0.5905 Notes­ Size of contact pads 100 × 100 um by the layer «passivation». Coordinates of the contact pads are indicated by the layer «passivation» Contact pad number 7 Ver.1.0/9.02.2008 IZ1937-TSe.doc