LT1942 LINER [Linear Technology], LT1942 Datasheet
LT1942
Available stocks
Related parts for LT1942
LT1942 Summary of contents
Page 1
... LED currents if two strings of LEDs are used. Soft-start is built into the LED driver as well as the primary TFT supply. The LT1942 is available in a low profile (0.75mm) 24-lead QFN (4mm × 4mm) package. , LTC and LT are registered trademarks of Linear Technology Corporation. ...
Page 2
... FB1 Pin Voltage as a Percent of Nominal Voltage NFB2 Pin NFB2 Pin (Note 3) FB3 Pin FB3 Pin (Note 3) FB4 Pin 3.3V CTRL4 FB4 Pin (Note 3) FB4 Pin CTRL4 U W ORDER PART NUMBER LT1942EUF 18 LED1 17 LED2 FB4 14 FB1 UF PART 13 PGOOD MARKING ...
Page 3
... SW4 = SHDN SHDN CTRL4 CTRL4 V = 36V SWX I = 100mA (Note 5) SW1 I = 40mA (Note 5) SW2 I = 40mA (Note 5) SW3 I = 400mA (Note 5) SW4 0.5V SS LT1942 MIN TYP MAX UNITS µA ● 150 ...
Page 4
... Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LT1942 is guaranteed to meet performance specifications from 0°C to 70°C. Specifications over the –40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical controls ...
Page 5
... SW3 Saturation Voltage 400 T = 25°C A 350 300 250 200 150 100 SW3 CURRENT (mA) 1942 G10 LT1942 Oscillator Frequency 1200 1100 1000 900 800 700 600 –40 – 100 TEMPERATURE (°C) 1942 G06 SW1 Saturation Voltage 600 T = 25° ...
Page 6
... LT1942 W U TYPICAL PERFOR A CE CHARACTERISTICS LED1 to LED2 Current Matching 2 LED1 LED2 T = 85°C 1.5 A 1.0 0 25° –40°C A –0.5 –1.0 –1.5 –2 LED2 CURRENT (mA) 1942 G13 D4 Forward Voltage 1400 T = 25°C A 1200 1000 800 600 ...
Page 7
... LED2 (Pin 17): Second Input of Current Mirror for an LED String. Connect the negative end of second string of LEDs supply this pin. If not in use, leave floating. reaches DD LT1942 Switcher. Place a DD Switcher. Connect DD = 1.25(1 + R1/R2). OUT1 ) according to the following formula: LED ≥ ...
Page 8
... LT1942 CTIO S LED1 (Pin 18): First Input of Current Mirror for an LED String. Connect the negative end of first string of LEDs to this pin. If not in use, leave floating. SW4 (Pin 19): Switch Pin for LED Switcher. This is the collector of an internal NPN power switch. Minimize the metal trace area connected to this pin to minimize EMI ...
Page 9
... RAMP-PULSE GENERATOR V BOOST CONVERTER ON + COMPARATOR – FB3 – Σ RAMP-PULSE GENERATOR SS4 40V 12 SOFT-START COMPARATOR – – Σ RAMP-PULSE GENERATOR LT1942 SW1 AV BOOST CONVERTER 20 DD COMPARATOR DRIVER – PGND14 SW2 24 DRIVER – SW3 2 D3 DRIVER ...
Page 10
... ON switchers are boost type, while the V type. Power sequencing circuitry is integrated into the LT1942 to properly power up the TFT power supply. When the SHDN pin is driven above 1V initially, only the AV switcher is enabled. After the output of the AV reaches 97% of its final value, the PGOOD pin is driven low ...
Page 11
... The AV switching regulator provides a PGOOD pin used for an external output disconnect function. This pin can drive the gate of a PMOS device. When the LT1942 is first enabled, the AV switching regulator begins to DD charge up the output capacitor. Since PGOOD is still an ...
Page 12
... LT1942 U U APPLICATIO S I FOR ATIO SHUTDOWN START I < 1µA Q 5V/DIV V AVDD 5V/DIV V 10V/DIV 10V/DIV 10V/DIV V SHDN 1V/DIV > 1V SHDN AV ENABLED FB1 > (97% OF 1.25V) DD PGOOD GOES LOW V DISABLED OFF V DISABLED ON V < 0.4V SHDN TFT SUPPLY OUTPUT DISCONNECT SEQUENCE PNP TURNS ON COMPLETE Figure 1 ...
Page 13
... Proper layout techniques must be followed to achieve advertised performance of the part. Keep all SW and FB traces short and small. There are several power ground pins on the LT1942 and it is important to implement the grounding properly. PGND14 is the power ground pin for the AV and LED switchers. The output capacitor for both ...
Page 14
... SHDN 1V/DIV 2ms/DIV 22µH L3 22µ SW3 V SW1 698k CC FB3 FB1 R6 PGND14 100k PGND23 PGOOD V SW4 OUT3 LT1942 L4 33µH NFB2 D4 D2 LED1 C6 SW2 LED2 SHDN FB4 SGND/ CTRL4 AGND SS1 SS4 0.1µF 0.1µF C8 0.1µF Efficiency 90 AV ...
Page 15
... UF Package 24-Lead Plastic QFN (4mm × 4mm) (Reference LTC DWG # 05-08-1697) 0.70 ±0.05 PACKAGE OUTLINE 0.25 ±0.05 0.50 BSC 0.75 ± 0.05 4.00 ± 0.10 (4 SIDES) 2.45 ± 0.10 (4-SIDES) 0.200 REF 0.00 – 0.05 LT1942 BOTTOM VIEW—EXPOSED PAD 0.23 TYP R = 0.115 (4 SIDES) TYP 23 24 0.38 ± 0. (UF24) QFN 1103 0.25 ± 0.05 0.50 BSC ...
Page 16
... LT1942 RELATED PARTS PART NUMBER DESCRIPTION LT1613 550mA (I ), 1.4MHz High Efficiency Step-Up SW DC/DC Converter LT1615/LT1615-1 300mA/80mA (I ), Constant Off-Time, High Efficiency SW Step-Up DC/DC Converter LT1930/LT1930A 1.2MHz/2.2MHz High Efficiency Step-Up SW DC/DC Converter LT1932 Constant Current, 1.2MHz, High Efficiency White LED Boost Regulator LT1943 (Quad) Quad Output, 2 ...