lt3645 Linear Technology Corporation, lt3645 Datasheet
lt3645
Available stocks
Related parts for lt3645
lt3645 Summary of contents
Page 1
... Other features of the LT3645 include a <2μA shutdown, short circuit protection, soft-start and thermal shutdown. The LT3645 is available in the thermally enhanced 16-lead (3mm × 3mm) QFN package 12-lead MSE package. L, LT, LTC, LTM, Linear Technology, Burst Mode and the Linear logo are registered trademarks of Linear Technology Corporation ...
Page 2
... For more information on tape and reel specifi cations, go to: 2 EN2, NPG Voltages .................................... –0.3V to 16V Operating Junction Temperature Range (Note 2) LT3645E ............................................ –40°C to 125°C LT3645I ............................................. –40°C to 125°C LT3645H ............................................ –40°C to 150°C Storage Temperature Range .................. –65°C to 150°C Lead Temperature (Soldering, 10 sec)…… ........... 300°C NC ...
Page 3
... LOAD I = 10mA LOAD I = 200mA LOAD I = 200mA LOAD I = 200mA LOAD Rising Falling I = 1mA 850mV NPG FB FB2 V = 16V 750mV NPG FB FB2 V = 800mV, V Rising FB FB2 LT3645 = 3.3V, OUT2 = 1.8V unless CC2 MIN TYP MAX UNITS l 3 3 0.79 0.8 0.81 l 0.785 0.8 0.813 l 20 300 l 0.015 %/V 1 0.01 2 ...
Page 4
... Specifi cations over the –40°C to 125°C operating temperature range are assured by design, characterization and correlation with statistical process controls. The LT3645I is guaranteed over the full –40°C to 125°C operating temperature range. The LT3645H is guaranteed over the full – ...
Page 5
... TEMPERATURE (°C) LDO Dropout Voltage 350 300 250 200 150 100 50 0 200 –60 –40 – 100 120 TEMPERATURE (°C) LT3645 Undervoltage Lockout 3.8 3.7 3.6 3.5 3.4 3.3 3.2 150 –50 –30 – TEMPERATURE (°C) 3645 G08 LDO Power Transistor Current Limit 340 320 ...
Page 6
... LT3645 TYPICAL PERFORMANCE CHARACTERISTICS EN/UVLO Pin Current 120 100 EN/UVLO PIN VOLTAGE EN2 Threshold Voltage 1.5 1.4 1.3 1.2 1.1 1.0 0.9 FALLING 0.8 0.7 0.6 0.5 – TEMPERATURE (°C) 6 EN/UVLO PIN Threshold Voltage 1.26 1.25 1.24 1.23 1.22 1.21 1.20 1. –50 3645 G16 750 740 RISING 730 720 710 700 ...
Page 7
... See Frequency Compensation (LDO) section for more details. FB2 (Pin 10/Pin 16): The FB2 pin programs the LDO output voltage. The LT3645 regulates the FB2 pin to 0.797V. The feedback resistor divider tap should be connected to this pin. The output voltage is programmed according to the ...
Page 8
... LT3645 BLOCK DIAGRAM 8 3645f ...
Page 9
... OPERATION The LT3645 includes a constant frequency, current mode step-down buck switching regulator together with a low- dropout regulator (LDO). If EN/UVLO is less than ~0.7V, both the buck and LDO are off, the output is disconnected and the input current is less than 2μA. The buck turns on when EN/UVLO is greater than 1 ...
Page 10
... D As the input voltage is increased, the part is required to switch for shorter periods of time. Delays associated with turning off the power switch dictate the minimum on time of the part. The minimum on time for the LT3645 100ns. Figure 2 illustrates the switching waveforms when ...
Page 11
... A ceramic input capacitor combined with trace or cable inductance forms a high quality (underdamped) tank cir- cuit. If the LT3645 circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the LT3645’s voltage rating. This situation can easily be avoided ...
Page 12
... Output Capacitor The output capacitor has two essential functions. Along with the inductor, it fi lters the square wave generated by the LT3645 to produce the DC output. In this role it determines the output ripple so low impedance at the switching frequency is important. The second function is to store energy in order to satisfy transient loads and stabilize the LT3645’ ...
Page 13
... APPLICATIONS INFORMATION boost circuit. If the input voltage is ramped slowly the LT3645 is turned on with the EN/UVLO pin when the output is already in regulation, then the boost capacitor might not be fully charged. Because the boost capacitor is charged with the energy stored in the inductor, the circuit will rely on some minimum load current to get the boost circuit running properly ...
Page 14
... GND Figure 5. Diode D4 Prevents a Shorted Input from Discharging a Backup Battery Tied to the Output; It Also Protects the Circuit from a Reversed Input. The LT3645 Runs Only When the Input Is Present Frequency Compensation (Buck) The LT3645 uses current mode control to regulate the loop. This simplifi es loop compensation. In particular, the ...
Page 15
... Figure 7 shows the transient response of the LT3645 with a few output capacitor choices. The output is 3.3V. The load current is stepped from 0.25A to 0.5A and back to 0.25A, and the oscilloscope traces show the output voltage. The upper photo shows the recommended value ...
Page 16
... OUT2 come up as soon as possible. In this confi guration, pin IN EN/UVLO 20V/DIV OUT1 5V/DIV OUT2 2V/DIV 5V/DIV 3645 F10 Figure 11. OUT1 and OUT2 Come Up as Soon as Possible IN(MIN) 4.7μH SW LT3645 31.6K DA 10μF FB 10K V CC2 EN2 OUT2 OUT2 12.4k 2.2μF FB2 10k 3645 F11 NPG 500μ ...
Page 17
... Note that PFET 4.7μH BUCK OUTPUT SW LT3645 31. 10μF 10K V CC2 EN2 NPG OUT2 OUT2 12.4k FB2 2.2μF 10k 3645 F12 OUT2 2V/DIV NPG 5V/DIV 500μs/DIV Figure 12. OUT2 Comes Up Before OUT1 LT3645 – 300mV)/1mA P1 OUT1 R9 31.6K 0.1μF 3645f 17 ...
Page 18
... Figure 13 shows the recommended component placement with trace, ground plane, and via locations. Note that large, switched currents fl the LT3645’s V and SW pins, the catch diode (D1), and the input capacitor (C1). The loop formed by these components should be as small as possible and tied to system ground in only one place ...
Page 19
... FB2 GND 10k 3645 TA02 3.3V Step-Down Converter with 1.8V Logic Rail 0.1μF BOOST 10μH 12V 1μF LT3645 MBRM140 DA FB EN/UVLO EN2 NPG V CC2 OUT2 12.4k FB2 GND 10k LT3645 5V 300mA 52.3k 10μF 10k 3.3V 200mA 3.3V 300mA 31.6k 10μF 10k 1.8V 200mA 2.2μF 3645 TA03 3645f 19 ...
Page 20
... EN/UVLO EN2 V CC2 NPG OUT2 12.4k 2.2μF FB2 GND 10k 3645 TA04 2.5V Step-Down Converter with 1.2V Logic Rail BAT85 0.1μF BOOST 4.7μ 1μF LT3645 MBRM140 DA FB EN/UVLO EN2 NPG V CC2 OUT2 4.99k FB2 2.2μF GND 10k 3645 TA05 OUT1 3.3V 300mA 31.6K 0.1μF OUT2 1 ...
Page 21
... TYPICAL APPLICATIONS 12V ON OFF PGOOD 3.3V Step-Down Converter with 5V Logic Rail 0.1μF BOOST 6.8μ 1μF LT3645 MBRM140 DA FB EN/UVLO NPG EN2 V CC2 5V OUT2 50mA 52.3k 2.2μF FB2 GND 10k 3645 TA06 LT3645 3.3V 450mA 31.6k 10μF 10k 5.5V 0.1μF 3645f 21 ...
Page 22
... LT3645 PACKAGE DESCRIPTION 2.845 0.102 (.112 .004) 5.23 (.206) MIN 0.42 0.038 (.0165 .0015) TYP RECOMMENDED SOLDER PAD LAYOUT DETAIL “A” 0.254 (.010) GAUGE PLANE 0.18 (.007) NOTE: 1. DIMENSIONS IN MILLIMETER/(INCH) 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. ...
Page 23
... UD Package 16-Lead Plastic QFN (3mm × 3mm) (Reference LTC DWG # 05-08-1691) 0.70 0.05 PACKAGE OUTLINE 0.25 0.05 0.50 BSC BOTTOM VIEW—EXPOSED PAD R = 0.115 0.75 0.05 TYP 1.45 0.10 (4-SIDES) 0.200 REF 0.00 – 0.05 LT3645 PIN 1 NOTCH R = 0.20 TYP OR 0.25 45 CHAMFER 15 16 0.40 0. (UD16) QFN 0904 0.25 0.05 0.50 BSC 3645f 23 ...
Page 24
... High Effi ciency Step-Down DC/DC Converter Linear Technology Corporation 24 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 ● 1.8V Step-Down Converter with 0.8V Logic Rail 0.1μF BOOST 4.7μ LT3645 12.4k MBRM140 DA 10μF FB EN/UVLO 10k EN2 NPG V CC2 OUT2 2.2μF FB2 ...