Linear Technology LT3695 Series Скачать руководство пользователя страница 26 | Manualshive

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LT3695 Series

26

3695fa

Fully Tolerant 3.3V Step-Down Converter with Soft-Start

V

IN

BD

LT3695

RUN/SS

V

C

0.22μF

D1
B140

D2

B140

V

OUT

3.3V
0.9A, V

IN

> 5V

1A, V

IN

> 6.5V

f = 800kHz

100k

0.36Ω

17.8k

56.2k

L

10μH

10μF

3695 TA02

470pF

2.2μF

V

IN

5V TO 28.5V

TRANSIENT TO 36V

RT

PG

40.2k

14k

0.22μF

47Ω

324k

SYNC

BOOST

SW

DA

FB

GND

PGND

1.8V Step-Down Converter

V

IN

BD

LT3695

RUN/SS

V

C

0.22μF

D1
B140

V

OUT

1.8V
1A

102k

f = 500kHz

127k

L1

6.8μH

22μF

3695 TA03

330pF

4.7μF

V

IN

3.6V TO 25V

RT

PG

71.5k

17.4k

SYNC

BOOST

ON OFF

SW

DA

FB

GND

PGND

TYPICAL APPLICATIONS

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Содержание LT3695 Series

Страница 1: ...back and thermal shutdown provide additional protection The LT3695 series is available in a thermally enhanced 16 pin MSOP package 5V Step Down Converter FEATURES APPLICATIONS n Wide Input Range Operation from 3 6V to 36V Overvoltage Lockout Protects Circuits Through 60V Transients n FMEA Fault Tolerant Output Stays at or Below Regulation Voltage During Adjacent Pin Short or When a Pin Is Left Flo...

Страница 2: ... Consult LTC Marketing for parts speciﬁed with wider operating temperature ranges The temperature grade is identiﬁed by a label on the shipping container Consult LTC Marketing for information on non standard lead based ﬁnish parts For more information on lead free part marking go to http www linear com leadfree For more information on tape and reel speciﬁcations go to http www linear com tapeandre...

Страница 3: ... 0V Not Switching l 35 0 01 55 0 0 5 100 5 μA μA μA Quiescent Current from OUT1 2 Pins LT3695 3 3 VRUN SS 0 2V VRUN SS 10V VOUT1 2 3 3V Not Switching l 5 43 10 65 15 112 μA μA LT3695 5 VRUN SS 0 2V VRUN SS 10V VOUT1 2 5V Not Switching l 5 43 10 65 15 112 μA μA Minimum BD Pin Voltage LT3695 2 8 3 V Feedback Voltage LT3695 l 792 785 800 800 808 815 mV mV FB Pin Bias Current LT3695 FB Pin Voltage 800...

Страница 4: ...ended periods may affect the device reliability and lifetime Note 2 Positive currents ﬂow into pins negative currents ﬂow out of pins Minimum and maximum values refer to absolute values Note 3 Absolute maximum voltage at VIN and RUN SS pins is 60V for nonrepetitive 1 second transients and 36V for continuous operation Note 4 The LT3695E regulators are guaranteed to meet performance speciﬁcations fr...

Страница 5: ... 1 25 1 00 0 75 1 50 40 3695 G06 0 50 0 25 10 15 20 30 35 25 1 75 TYPICAL MINIMUM VOUT 3 3V L 10μH f 800kHz SYNC 0V SYNC 3 3V INPUT VOLTAGE V 5 LOAD CURRENT A 1 00 0 75 1 25 40 3682 G07 0 50 0 25 10 15 20 30 35 25 1 50 TYPICAL MINIMUM VOUT 5V L 10μH f 800kHz SYNC 0V SYNC 5V INPUT VOLTAGE V 8 LOAD CURRENT A 1 00 1 25 20 3695 G08 0 50 0 75 0 25 10 12 14 16 18 1 50 TYPICAL MINIMUM VOUT 5V L 4 7μH f 2...

Страница 6: ...TAGE mV 0 FREQUENCY kHz 1000 900 3695 G17 800 600 400 200 0 100 200 300 400 600 700 800 500 1200 RRT 29 4k TEMPERATURE C 50 FEEDBACK VOLTAGE mV 810 790 800 780 770 0 50 25 25 100 3695 G14 150 75 125 TEMPERATURE C 50 FREQUENCY MHz 1 20 1 15 1 10 1 05 1 00 0 80 0 85 0 90 0 95 0 50 25 25 100 3695 G16 150 75 125 RT 29 4k TEMPERATURE C 50 SWITCH CURRENT LIMIT A 1 9 1 7 1 5 1 3 1 1 0 5 0 7 0 9 0 50 25 2...

Страница 7: ...T LIMIT A 1 4 0 8 1 0 1 2 1 6 1 8 3 5 3695 G21 0 4 0 2 0 6 0 0 5 1 0 1 5 2 0 3 0 2 5 2 0 SYNC 0 3V BOOST DIODE CURRENT A 0 BOOST DIODE V F V 1 0 0 8 1 2 1 3695 G23 0 4 0 2 0 6 0 0 25 0 5 0 75 1 4 Minimum Input Voltage TEMPERATURE C 50 MINIMUM SWITCH ON TIME ns 120 100 80 60 40 0 20 0 50 25 25 100 3695 G20 150 75 125 IOUT 1A Error Ampliﬁer Output Current LT3695 3 3 Frequency Foldback LT3695 5 FREQU...

Страница 8: ...DIV VOUT 5V DIV VIN 20V DIV VIN 12V FRONT PAGE APPLICATION ILOAD 500mA 3695 G33 5μs DIV VSW 5V DIV VOUT 20mV DIV IL 0 2A DIV VIN 12V FRONT PAGE APPLICATION ILOAD 5mA 3695 G34 1μs DIV VSW 5V DIV VOUT 20mV DIV IL 0 2A DIV 3695 G35 VIN 12V FRONT PAGE APPLICATION ILOAD 55mA 1μs DIV VSW 5V DIV VOUT 20mV DIV IL 0 5A DIV 3695 G36 VIN 12V FRONT PAGE APPLICATION ILOAD 500mA Maximum VIN for Full Frequency M...

Страница 9: ...shouldhave rise and fall times faster than 1μs Note that the maximum load current depends on which mode is chosen See the Applications Information section for more information VIN Pin 8 Pin 8 The VIN pin supplies current to the internal regulator and to the internal power switch This pin must be locally bypassed VC Pin 9 Pin 9 The VC pin is the output of the internal error ampliﬁer The voltage on ...

Страница 10: ...8 6 R1 R2 FB GND OVLO SLOPE COMP R S Q DA PGND SW BOOST BD VC CC C3 L1 D1 C2 CF RC 3695 BDa 1 PGND 17 14 VIN VIN VOUT C1 RT PG RUN SS SYNC RT INTERNAL 0 8V REF SOFT START 0 720V ERROR AMP OSCILLATOR 250kHz TO 2 2MHz DISABLE SYNC OUT OUTB Burst Mode DETECT THERMAL SHUTDOWN VC CLAMP 2 4 14 16 9 5 7 11 8 6 R1 R2 GND OVLO SLOPE COMP R S Q DA PGND SW BOOST OUT1 13 OUT2 VC CC C3 L1 D1 C2 CF RC 3695 BD 1...

Страница 11: ...heBOOSTpin Anexternalcapacitorandtheinternalboost diode are used to generate a voltage at the BOOST pin that is higher than the input supply This allows the driver to fully saturate the internal bipolar NPN power switch for efﬁcient operation To further optimize efﬁciency the LT3695 regulators au tomatically switch to Burst Mode operation in light load situations Between bursts all circuitry assoc...

Страница 12: ... voltage and higher dropout voltage The highest acceptable switching frequency fSW MAX for a given application can be calculated as follows f V V t V V V SW MAX OUT D ON MIN IN SW D where VIN is the typical input voltage VOUT is the output voltage VD is the catch diode drop 0 5V and VSW is the internal switch drop 0 5V at max load This equation shows that lower switching frequency is necessary to ...

Страница 13: ...um operating input voltage Conversely a lower switching frequency will be necessary to achieve optimum operation at high input voltages Special attention must be paid when the output is in start up short circuit or other overload conditions Dur ing these events the inductor peak current might easily reach and even exceed the maximum current limit of the LT3695 regulators especially in those cases ...

Страница 14: ...nuous mode operation see Linear Technology s Application Note 44 Finally for duty cycles greaterthan50 VOUT VIN 0 5 aminimuminductance is required to avoid sub harmonic oscillations L V V f MIN OUT D SW 1 2 The current in the inductor is a triangle wave with an av erage value equal to the load current The peak inductor and switch current is I I I I SW PEAK L PEAK OUT MAX L Δ 2 where IL PEAK is the...

Страница 15: ...A 2 2μF capacitor is capable of this task but only if it is placed close to the LT3695 regulators see the PCB Layout section for more information A second precau tion regarding the ceramic input capacitor concerns the maximum input voltage rating of the LT3695 regulators A ceramic input capacitor combined with trace or cable inductance forms a high Q underdamped tank circuit If the LT3695 regulato...

Страница 16: ...oltage protection threshold This feature keeps the switch off for VIN VOVLO 39 9V maxi mum For inputs up to the maximum operating voltage of 36V use a diode with a reverse voltage rating greater APPLICATIONS INFORMATION Table 3 Capacitor Vendors VENDOR PHONE URL PART SERIES COMMANDS Panasonic 714 373 7366 www panasonic com Ceramic Polymer Tantalum EEF Series Kemet 864 963 6300 www kemet com Cerami...

Страница 17: ...f the circuits in this data sheet that is similar to your applica tion and tune the compensation network to optimize the performance Stability should then be checked across all operatingconditions includingloadcurrent inputvoltage and temperature The LT1375 data sheet contains a more thorough discussion of loop compensation and describes how to test the stability using a transient load Figure 1 sh...

Страница 18: ...on circuit will switch at full frequency at output loads higher than about 30mA ThemaximumloadcurrentthattheLT3695regulatorscan supply is reduced when SYNC is high BOOST Pin Considerations CapacitorC3andtheinternalboostSchottkydiode seethe Block Diagram are used to generate a boost voltage that is higher than the input voltage In most cases a 0 22μF capacitor will work well Figure 4 shows three wa...

Страница 19: ...8V VIN MIN 4 3V if VOUT 3V BD LT3695 VIN VIN C3 D1 D2 VOUT 3695 F04b BOOST SW DA GND PGND 4b For 2 5V VOUT 2 8V VIN MIN 4 3V BD LT3695 VIN VIN C3 D1 VOUT 3695 F04c BOOST SW DA GND PGND 4c For VOUT 2 5V VIN MAX 25V Figure 4 Three Circuits for Generating the Boost Voltage for the LT3695 the circuit in Figure 4a For higher output voltages make sure that there is no more than 8V at the BD pin either b...

Страница 20: ...00kHz to 2 2MHz range The RT resistor should be chosen to set theLT3695regulatorsswitchingfrequency20 belowthe lowestsynchronizationinput Forexample ifthesynchro nization signal is 360kHz the RT should be chosen for 300kHz To assure reliable and safe operation the LT3695 regulatorswillonlysynchronizewhentheoutputvoltageis near regulation as indicated by the PG ﬂag It is therefore necessary to choo...

Страница 21: ...aken during printed circuit board layout Figures 9 and 10 show the recommended component placement with trace ground plane and via locations Note that large switched currents ﬂow in the LT3695 regulators VIN SW and PGND pins the catch diode and the input capacitor CIN The loop formed by these components should be as small as possible These components along with the inductorandoutputcapacitor COUT ...

Страница 22: ...rorleaving onesinglepinﬂoatingdoesnotraiseVOUTorcausedamage to the LT3695 regulators However the application circuit must meet the requirements discussed in this section in order to achieve this tolerance level Tables 5 and 6 show the effects that result from shorting adjacent pins or from a ﬂoating pin respectively For the best fault tolerance to inadvertent adjacent pin shorts the RUN SS pin mus...

Страница 23: ...se VOUT may fall below regulation voltage Make sure that VIN VIN MAX see Input Voltage Range section for details and provide a bypass resistor at the DA pin See the following discussion DA VOUT may fall below regulation voltage Make sure that VIN VIN MAX see Input Voltage Range section for details and provide a bypass resistor See the following discussion SW VOUT will fall below regulation voltage...

Страница 24: ...5 3 3 and LT3695 5 the current through R3 must be drawn by RLOAD R4 and the OUT1 2 pins I V R R I R OUT LOAD OUT 3 12 4 Without load RLOAD and assuming the minimum current of 43μA into the OUT1 2 pins this leads to R V V V R µA OUT IN MAX OUT 4 3 43 as upper limit for R4 Depending on the required input voltage range R4 may be omitted Tables 7 and 8 show example values for common appli cations RSS ...

Страница 25: ... is shown in Figure 13 If SYNC is to be driven by an external circuitry RS may be used to isolate this circuitry from VIN CS must be used in this case to provide a low impedance path for the synchronization signal If SYNC is pulled low RS prevents VIN from being shorted to ground in case of an inadvertent short between SYNC and VIN If SYNC is pulled high to VIN then RS protects the RT pin during a...

Страница 26: ...00k 0 36Ω 17 8k 56 2k L 10μH 10μF 3695 TA02 470pF 2 2μF VIN 5V TO 28 5V TRANSIENT TO 36V RT PG 40 2k 14k 0 22μF 47Ω 324k SYNC BOOST SW DA FB GND PGND 1 8V Step Down Converter VIN BD LT3695 RUN SS VC 0 22μF D1 B140 VOUT 1 8V 1A 102k f 500kHz 127k L1 6 8μH 22μF 3695 TA03 330pF 4 7μF VIN 3 6V TO 25V RT PG 71 5k 17 4k SYNC BOOST ON OFF SW DA FB GND PGND TYPICAL APPLICATIONS ...

Страница 27: ...rant 5V Step Down Converter with Soft Start VIN LT3695 5 RUN SS VC 0 22μF D1 B140 VOUT 5V 0 9A f 2MHz 100k 0 36Ω 56 2k L 4 7μH 10μF 3695 TA04 680pF 2 2μF VIN 10V TO 16 5V TRANSIENT TO 36V RT PG 9 76k 13 3k 0 22μF 47Ω 365k SYNC BOOST SW DA OUT1 0UT2 GND PGND ...

Страница 28: ...EAD FLASH OR PROTRUSIONS INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0 152mm 006 PER SIDE 5 LEAD COPLANARITY BOTTOM OF LEADS AFTER FORMING SHALL BE 0 102mm 004 MAX 0 254 010 0o 6o TYP DETAIL A DETAIL A GAUGE PLANE 5 23 206 MIN 3 20 3 45 126 136 0 889 p 0 127 035 p 005 RECOMMENDED SOLDER PAD LAYOUT 0 305 p 0 038 0120 p 0015 TYP 0 50 0197 BSC BOTTOM VIEW OF EXPOSED PAD OPTION 2 845 p 0 102 112 p...

Страница 29: ...ever no responsibility is assumed for its use Linear Technology Corporation makes no representa tion that the interconnection of its circuits as described herein will not infringe on existing patent rights REVISION HISTORY REV DATE DESCRIPTION PAGE NUMBER A 11 09 All Sections Revised to Include LT3695 3 3 and LT3695 5 1 30 ...

Страница 30: ...e 2 4A 1 5A 1 5A IOUT with LDO Controller High Efﬁciency Step Down DC DC Converter VIN 4V to 36V VOUT MAX 0 8V IQ 7mA ISD 1μA 5mm 7mm QFN 38 Package LT3505 36V with Transient Protection to 40V 1 4A IOUT 3MHz High Efﬁciency Step Down DC DC Converter VIN 3 6V to 34V VOUT MAX 0 78V IQ 2mA ISD 2μA 3mm 3mm DFN 8 MSOP 8E Packages LT3500 36V 40VMAX 2A 2 5MHz High Efﬁciency Step Down DC DC Converter and L...

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