LT3472 LINER

Document overview

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Technical content

■ CCD Bias ■ TFT LCD Bias ■ OLED Bias ■ ± Rail Generation for Op Amps ■ Generates 15V at 20mA, –8V at 50mA from a Li-Ion Cell ■ Internal Schottky Diodes ■ VIN Range: 2.2V to 16V ■ Output Voltages Up to ±34V ■ Capacitor-Programmable Soft-Start ■ Sequencing: Positive Output Reaches 88% of Final Value Before Negative Output Begins ■ Requires Only One Resistor to Set Output Voltage ■ Constant Switching Frequency Ensures Low Noise Outputs ■ Available in a 10-Lead (3mm × 3mm) DFN Package Boost and Inverting DC/DC Converter for CCD Bias The LT 3472 dual channel switching regulator generates positive and negative outputs for biasing CCD imagers. The device delivers up to –8V at 50mA and 15V at 20mA from a lithium-ion cell, providing bias for many popular CCD imagers. Switching at 1.1MHz, the LT3472 uses tiny, low profile capacitors and inductors and generates low noise outputs that are easy to filter. Schottky diodes are internal and the output voltages are set with one resistor per channel, reducing external component count. The entire solution is less than 1mm profile and occupies just 50mm Internal sequencing circuitry disables the negative chan- nel until the positive channel has reached 88% of its final value, ensuring that the sum of the two outputs is always positive. Separate soft-start capacitors for each output allow the ramp of each output to be independently controlled. The LT3472 is available in a low profile (0.75mm) 10-pin 3mm × 3mm DFN package. , LTC and LT are registered trademarks of Linear Technology Corporation. SWP V IN SWN SSP GND SSN VPOS FBP SHDN FBN DN LT3472 2.2µF 2.2µF 2.2µF100nF 47µH 100nF 550k 320k 1µF22µH4 7 µH SHDN VIN 3V TO 4.2V VPOS 15V 20mA VNEG –8V 50mA

3472 TA01a

4.7pF 10pF Conversion Efficiency LOAD CURRENT (mA) EFFICIENCY (%) 20 40 50

3472 TA01b

Operating Temperature Range ORDER PART NUMBER DFN PART MARKING TJMAX = 125°C, θJA = 43°C/W, θJC = 3°C/W EXPOSED PAD IS GND (PIN 11) MUST BE SOLDERED TO PCB LBGC LT3472EDD ABSOLUTE AXI U RATI GSW WW U PACKAGE/ORDER I FOR ATIOUU W (Note 1) ELECTRICAL CHARACTERISTICSThe ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 3V, SHDN = 3V unless otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS Minimum Operation Voltage 2.2 V Maximum Operation Voltage 16 V Supply Current SHDN = 3V, Not Switching 2.8 mA SHDN = 0V 0.1 1 µA SHDN Voltage High ● 0.8 V SHDN Voltage Low ● 0.3 V SHDN Pin Bias Current SHDN = 3V 35 µA Positive Feedback Voltage ● 1.2 1.25 1.3 V Negative Feedback Voltage ● –5 0 5 mV Positive Feedback Voltage Line Regulation 0.01 %/V Negative Feedback Voltage Line Regulation 0.008 mV/V FBP Current FBP = V FBP ● 24.5 25 25.3 µA FBN Current FBN = V FBN ● 24.5 25 25.3 µA FBP to Start Negative Channel 1.02 1.1 1.18 V Switching Frequency 0.9 1.1 1.4 MHz Maximum Duty Cycle (Both Channels) ● 88 92 % Positive Channel Switch Current Limit ● 250 350 mA Negative Channel Switch Current Limit ● 300 400 mA Positive Channel Switch VCESAT ISWP = 200mA 245 mV Negative Channel Switch VCESAT ISWN = 200mA 400 mV Switch Leakage Current (Both Channels) V SW = 5V 0.01 5 µA Schottky DP Forward Drop I DP = 150mA 700 950 mV Schottky DN Forward Drop I DN = 150mA 750 1000 mV Schottky Leakage Current (Both Channels) V R = 36V 4 µA Consult LTC Marketing for parts specified with wider operating temperature ranges. TOP VIEW DD PACKAGE 10-LEAD (3mm × 3mm) PLASTIC DFN

1 VPOS

V IN SHDN SWN DN Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LT3472E is guaranteed to meet specified performance from 0°C to 70°C. Specifications over the –40°C to 85°C operating range are assured by design, characterization and correlation with statistical process controls.

26.0 25.5 25.0 24.5 24.0 SHDN VOLTAGE (V) SHDN CURRENT (µA) 300 250 200 150 100 51 01 5 2 0

3472 G07

TEMPERATURE (°C) –50 QUIESCENT CURRENT (mA) 3.1 3.0 2.9 2.8 2.7 2.6 2.5 0 50 100 –50 0 50 100 –50 0 50 100

3472 G01

TEMPERATURE (°C) 1.13 1.12 1.11 1.10 1.09 1.08 1.07 1.06 1.05

3472 G02

VFB1 (V) TEMPERATURE (°C) FBP VOLTAGE (V)

3472 G03

1.30 1.28 1.26 1.24 1.22 1.20 TEMPERATURE (°C) –50 0 50 100 –50 0 50 100 –50 0 50 100

3472 G04

TEMPERATURE (°C)

3472 G05

TEMPERATURE (°C)

3472 G06

FBN VOLTAGE (mV) –10 FBP BIAS CURRENT (µA) 26.0 25.5 25.0 24.5 24.0 FBN BIAS CURRENT (µA) SWITCH CURRENT (mA) POSITIVE SWITCH SATURATION VOLTAGE (mV) 350 300 250 200 150 100 50 100 150 200

3472 G08

90°C 25°C –45°C TYPICAL PERFOR A CE CHARACTERISTICSUW Quiescent Current Minimum FBP Voltage to Enable Inverter FBN Voltage FBP Bias Current FBN Bias Current SHDN Pin Bias Current Positive Channel Switch VCESAT FBP Voltage

Negative Channel Switch VCESAT Positive Channel Schottky I-V Characteristic Negative Channel Schottky I-V Characteristic TYPICAL PERFOR A CE CHARACTERISTICS UW SCHOTTKY FORWARD DROP (V) POSITIVE SCHOTTKY FORWARD CURRENT (mA) 0.6 1.0

3472 G09

0.2 0.4 0.8 400 350 300 250 200 150 100 SWITCH CURRENT (mA) NEGATIVE SWITCH SATURATION VOLTAGE (mV) 600 500 400 300 200 100 50 100 150 200

3472 G10

SCHOTTKY FORWARD DROP (V) 350 300 250 200 150 100 0.6

3472 G11

0.2 0.4 0.8 1.0 NEGATIVE SCHOTTKY FORWARD CURRENT (mA) 90°C90°C 25°C 25°C –45°C –45°C 90°C 25°C –45°C

SWP (Pin 1): Switch Pin for Positive (Boost) Channel. Connect boost inductor here. with a X5R or X7R type ceramic capacitor. enable device, 0.3V or less to disable device. SWN (Pin 4): Switch Pin for Negative (Inverter) Channel. Connect inverter input inductor and flying capacitor here. DN (Pin 5): Anode of Internal Schottky for Inverter. VO2 = 1.25 • R2/50k. Pin voltage = 0V when regulated. pin is connected to 1.25V with a 50k resistor internally. pin is connected to 1.25V with a 50k resistor internally. optimum thermal performance. Figure 1. LT3472 Block Diagram

into the positive terminal of the PWM comparator A2. Table 1. The efficiency comparison of different inductors Figure 3. Efficiency Comparison of Different Inductors

3473 F02a

3472 F02a

3472 F02b

3472 FO4

Figure 2. Switching Waveforms

Table 1. Recommended Inductors Table 2. Recommended Ceramic Capacitor Manufacturers

  • – 4 2 ω α ω ω α ω α α ω where L is the inductance, r is the resistance of the inductor and C is the output capacitance. For low DCR inductors, which is usually the case for this application, the peak inrush current can be simplified as follows: I V L EXPP IN= ⎛
  • – •06 α ω π Table 3 gives inrush peak currents for some component selections. Note that inrush current is not a concern if the input voltage rises slowly.

Table 3. Inrush Peak Current

mended Schottky diodes are listed in Table 4. Table 4. Recommended Schottky Diodes preferred (1% is recommended). channel are shown in Figure 4. channel are shown in Figure 5.

3472 FO4b

3472 FO5a

3472 FO5b

3472 FO4a

Figure 7. Recommended Component Placement Figure 6. Start-Up Sequencing quencing is shown in Figure 6. paid to the PCB board layout and component placement.

3472 FO6

3472 F06

ommended component placement is shown in Figure 7.

2.2µF CIN: TAIYO YUDEN JMK107BJ225 COP: TAIYO YUDEN EMK316BJ225 CNF: TAIYO YUDEN EMK212BJ105 CON: TAIYO YUDEN LMK212BJ225 LP: MURATA LQH32CN220 LN1, LN2: MURATA LQH32CN470 CIN 2.2µF CON 2.2µF CSSP 100nF LN2 47µH CSSN 100nF RFBP 550k RFBN 320k CNF 1µFLP 22µH LN1 47µH SHDN VIN 3V TO 4.2V VPOS 15V 20mA VNEG –8V 50mA

3472 TA02

CFBP, 4.7pF CFBN 10pF VPOS 20mV/DIV IPOS 20µs/DIV

3472 TA04

50µs/DIV

3472 TA05

–30mA –20mA VPOS Load Step Response V NEG Load Step Response

3.00 ±0.10 (4 SIDES) NOTE: 1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2). CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 0.38 ± 0.10 BOTTOM VIEW—EXPOSED PAD 1.65 ± 0.10 (2 SIDES) 0.75 ±0.05 R = 0.115 TYP 2.38 ±0.10 (2 SIDES) 106 PIN 1 TOP MARK (SEE NOTE 6)

0.200 REF

0.00 – 0.05 (DD10) DFN 1103 0.25 ± 0.05 2.38 ±0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 1.65 ±0.05 (2 SIDES)2.15 ±0.05 0.50 BSC 0.675 ±0.05 3.50 ±0.05 PACKAGE OUTLINE 0.25 ± 0.05

0.50 BSC

10-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1699) Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

PART NUMBER DESCRIPTION COMMENTS LT1611 550mA (I SW), 1.4MHz, High Efficiency Micropower V IN: 1.1V to 10V, VOUT(MAX) = –34V, IQ = 3mA, ISD <1µA, Inverting DC/DC Converter ThinSOT Package LT1615/LT1615-1 300mA/80mA (I SW), High Efficiency V IN: 1V to 15V, VOUT(MAX) = 34V, IQ = 20µA, ISD <1µA, Step-Up DC/DC Converter ThinSOT Package LT1617/LT1617-1 350mA/100mA (I SW), High Efficiency Micropower V IN: 1.2V to 15V, VOUT(MAX) = –34V, IQ = 20µA, ISD <1µA, Inverting DC/DC Converter ThinSOT Package Step-Up DC/DC Converter ThinSOT Package LT1931/LT1931A 1A (I SW), 1.2MHz/2.2MHz, High Efficiency Micropower V IN: 2.6V to 16V, VOUT(MAX) = –34V, IQ = 5.8mA, ISD <1µA, Inverting DC/DC Converter ThinSOT Package LT1944/LT1944-1 Dual Output, 350mA/100mA (I SW), Constant V IN: 1.2V to 15V, VOUT(MAX) = 34V, IQ = 20µA, ISD <1µA, Off-Time, High Efficiency Step-Up DC/DC Converter MS10 Package LT1945(Dual) Dual Output, Boost/Inverter, 350mA (I SW), Constant V IN: 1.2V to 15V, VOUT(MAX) = ±34V, IQ = 40µA, ISD <1µA, Off-Time, High Efficiency Step-Up DC/DC Converter MS10 Package Step-Up DC/DC Converter MS8 Package LT3461/LT3461A 0.3A (I SW), Inverting 1.3MHz/3MHz High Efficiency V IN: 2.5V to 16V, VOUT(MAX) = 38V, IQ = 2.8mA, ISD <1µA, Step-Up DC/DC Converter with Integrated Schottky Diodes ThinSOT Package LT3462/LT3462A 300mA (I SW), Inverting 1.2MHz/2.7MHz DC/DC Converter V IN: 2.5V to 16V, VOUT(MAX) = –38V, IQ = 2.9mA, ISD <10µA, with Integrated Schottky Diodes ThinSOT Package LT3463/LT3463A Dual Output, Boost/Inverter, 250mA (I SW), Constant V IN: 2.3V to 15V, VOUT(MAX) = 40V, IQ = 40µA, ISD <1µA, Off-Time, High Efficiency Step-Up DC/DC Converter DFN Package with Integrated Schottkys LT3464 85mA (I SW), High Efficiency Step-Up DC/DC Converter V IN: 2.3V to 10V, VOUT(MAX) = 34V, IQ = 25µA, ISD <1µA, with Integrated Schottky and PNP Disconnect ThinSOT Package LT3467/LT3467A 1.1A, 1.3MHz/2.1MHz Step-Up DC/DC Converter with V IN: 2.4V to 16V, VOUT(MAX) = 40V, IQ = 1mA, ISD <1µA, Integrated Soft-Start in ThinSOT ThinSOT Package Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2004 LT/TP 0804 1K • PRINTED IN USA RELATED PARTS TYPICAL APPLICATIO U SWP V IN SWN SSP GND SSN VPOS FBP SHDN DN FBN LT3472 2.2µF 2.2µF 2.2µF100nF 47µH 100nF 550k 320k 1µF22µH4 7 µH SHDN VIN 3V TO 4.2V VPOS 15V 20mA VNEG –8V 50mA

3472 TA03

4.7pF 10pF