LT3688 LINER [Linear Technology], LT3688 Datasheet
LT3688
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LT3688 Summary of contents
Page 1
... The LT3688 watchdog timer monitors for watchdog falling edges grouped too close together or too far apart. The LT3688 is available in 24-Pin TSSOP and 4mm × 4mm QFN packages, each with an exposed pad for low thermal resistance. BIAS BST2 0.22μ ...
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... For more information on lead free part marking, go to: For more information on tape and reel specifi cations, go to: 2 Operating Junction Temperature Range (Note 3) LT3688E, LT3688I ..............................–40°C to 125°C LT3688H ............................................–40°C to 150°C Maximum Junction Temperature LT3688E, LT3688I ............................................. 125°C LT3688H ........................................................... 150° ...
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... I = 2.5mA 0.6V SINK 100μ 0.6V SINK Set to 0.680V 1.2V WDE 2.5mA SINK 100μA SINK LT3688 MIN TYP MAX UNITS 3 3.5 3.8 V 0.01 1 μA 65 105 μA 235 310 μA 0.01 1 μA 155 200 μA –5 –20 μA 0.790 0.800 0.810 V 0 ...
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... Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: Absolute Maximum Voltage at the V , CONFIG and EN/UVLO pins IN is 36V for continuous operation. Note 3: The LT3688 is tested under pulsed load conditions such that The LT3688E is guaranteed to meet performance specifi cations J A from 0° ...
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... DUTY CYCLE (%) BST Pin Current 1000 0 200 400 600 800 SWITCH CURRENT (mA) LT3688 T = 25°C unless otherwise noted. A Maximum Load Current (5V 1MHz SW 1 15μ 10μ INPUT VOLTAGE (V) 3688 G05 Switch Current Limit vs Temperature 2 ...
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... LT3688 TYPICAL PERFORMANCE CHARACTERISTICS Switching Frequency 2.5 2.0 1.5 1.0 0 100 150 R (kΩ) T 3688 G13 EN/UVLO Pin Current PIN VOLTAGE (V) 3688 G17 Switching Waveforms, Burst Mode Operation I L 0.2A/DIV V SW 5V/DIV V OUT 10mV/DIV 3688 G20 5μ ...
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... G27 100000 10000 1000 100 10 0.1 1000 100000 0.001 (nF) 3688 G29 LT3688 T = 25°C unless otherwise noted. A Watchdog Window Mode Period vs Temperature 1000pF WDT 100 –50 – TEMPERATURE (° ...
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... RST pins to BIAS with a 100k resistor for a stronger pull-up. WDO (Pin 18/Pin 15): WDO will go low if the micropro- cessor fails to drive the WDI pin of the LT3688 with the appropriate signal. Tie the WDO pin to BIAS with a 100k resistor for a stronger pull-up. Keep capacitive loading on this pin below 1000pF ...
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... OSCILLATOR OSCILLATOR OSCILLATOR ERROR AMP + + – – 80mV – + – 3.4V CONFIGURATION LOGIC TRANSITION WATCHDOG DETECT TIMER 2μA 22μA WDE WDO C WDT LT3688 – + SWITCH LATCH BST2 SW2 S DISABLE DA2 Burst Mode OPERATION DETECT R SEN2 CLAMP FB2 – ...
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... Power-On Reset and Watchdog Timer Operation . An C The LT3688 has two power-on reset comparators that monitor the regulated output voltages below the regulation value, the RST pin is pulled low. Once the output voltage crosses over 90% of the regulation ...
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... TIMING DIAGRAMS t < t WDL WDI WDO Power-On Reset Timing V OUT RST RST Watchdog Timing t t WDTO WDU LT3688 t WDTO 3686 TD01 3688f 11 ...
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... LT3688 TIMING DIAGRAMS V OUT1 RST1 V OUT2 RST2 WDO WDI V OUT1 V OUT2 RST1 RST2 WDO WDI V OUT1 RST1 V OUT2 RST2 WDO WDI RST1 RST2 t WDU STARTUP TIMING (V = HIGH) CONFIG RST1 t WDU STARTUP TIMING (V = LOW) CONFIG RST1 ...
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... At frequencies higher than f no longer operates with constant frequency. The LT3688 enters pulse skip mode at frequencies higher than f because of the limitation on the LT3688’s minimum on time of 140ns (180ns for T is increased above f for shorter periods to maintain the same duty cycle. Delays associated with turning off the power switch dictate the minimum on-time of the part ...
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... Unlike many fi xed frequency regulators, the LT3688 can extend its duty cycle by remaining on for multiple cycles. The LT3688 will not switch off at the end of each clock cycle if there is suffi cient voltage across the boost capacitor (C3 in the Block Diagram). Eventually, the voltage on the boost capacitor falls and requires refreshing ...
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... L www.toko.com where f is the switching frequency of the LT3688 and L is the value of the inductor. The peak inductor and switch current is www.sumida.com I SW(PK) To maintain output regulation, this peak current must be less than the LT3688’s switch current limit I least 1 ...
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... Output Capacitor and Output Ripple The output capacitor has two essential functions. Along with the inductor, it fi lters the square wave generated by the LT3688 to produce the DC output. In this role it determines the output ripple, and low impedance at the switching frequency is important. The second function is to store energy in order to satisfy transient loads and stabilize the LT3688’ ...
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... The LT3688 uses current mode control to regulate the output, which simplifi es loop compensation. In particular, the LT3688 does not require the ESR of the output capaci- tor for stability, allowing the use of ceramic capacitors to achieve low output ripple and small circuit size. Figure 3 shows an equivalent circuit for the LT3688 control loop. The error amp is a transconductance amplifi ...
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... LT3688 operates in sleep mode increases and the average input current is greatly reduced, resulting in high effi ciency even at very low loads (see Figure 5). At higher output loads the LT3688 will be running at the frequency programmed by the R and will be operating in standard PWM mode. The transi- tion between PWM and low ripple Burst Mode operation is seamless, and will not disturb the output voltage ...
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... If the input voltage is ramped slowly, or the LT3688 is turned on with its EN/UVLO pin when the output is already in regulation, then the boost capacitor may not be fully charged. Because the boost capacitor is charged ...
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... Shutdown and Undervoltage Lockout Figure 8 shows how to add undervoltage lockout (UVLO) to the LT3688. Typically, UVLO is used in situations where the input supply is current limited, or has a relatively high source resistance. A switching regulator draws constant power from the source, so source current increases as source voltage drops ...
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... Each channel’s output voltage must be above 90% of the programmed value for RST not to be asserted (refer to the Timing Diagram). The LT3688 will assert RST during power-up, power-down and brownout conditions. Once the output voltage rises above the RST threshold, the adjustable reset timer is started and RST is released after the reset timeout period ...
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... LT3688 APPLICATIONS INFORMATION If WDO is low and RST goes low, then WDO will go high. The WDE pin allows the user to turn on and off the watchdog function. Leaving this pin open is okay and will automatically enable the watchdog. It has an internal weak pull-down to ground. The WDI pin has an internal weak pull-up that keeps the WDI pin high ...
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... There is another situation to consider in systems where pin unconnected POR the output will be held high when the input to the LT3688 is absent. This may occur in battery charging applications or in battery backup systems where a battery or some other supply is diode ORed with the LT3688’s output. If the V pin is allowed to fl ...
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... LFPM airfl ow, this resistance can fall by another 25%. Further increases in airfl ow will lead to lower thermal re- sistance. Because of the large output current capability of the LT3688 possible to dissipate enough heat to raise the junction temperature beyond the absolute maximum of 125°C (150°C for H Grade). When operating at high ambient temperatures, the maximum load current should be derated as the ambient temperature approaches 125° ...
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... FB1 FB2 C8 C9 1nF 1nF RUN/SS2 RUN/SS1 WDE C WDT C POR1 μP I/O WDI C POR2 WDO I/O RT RESET RST1 SYNC RST2 GND f LT3688 L2 C3 12μH V 0.22μF OUT2 3.3V 800mA 316k 10pF C5 R4 22μF 100k C10 4.7nF C12 C11 1nF 4.7nF R5 110k 3688 TA02 = 500kHz ...
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... WDI C POR2 WDO I/O RT RESET RST1 RST2 SYNC GND f = 2MHz: 8V < 4.7μ EN/UVLO BIAS BST1 BST2 L1 C2 0.22μF SW1 SW2 LT3688 D1 DA1 DA2 FB1 FB2 C8 1nF CONFIG RUN/SS1 RUN/SS2 C WDE WDT C POR1 μP WDI C I/O POR2 WDO RT RST1 RESET RST2 SYNC ...
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... 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, IF PRESENT 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 LT3688 3.25 (.128 ...
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... Linear Technology Corporation 28 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 ● C1 4.7μ EN/UVLO BIAS BST1 BST2 C2 C3 0.22μF 0.22μF SW1 SW2 D1 LT3688 D2 DA1 DA2 FB1 FB2 C8 C9 CONFIG 1nF 1nF RUN/SS2 RUN/SS1 C WDE WDT C POR1 I/O WDI C POR2 ...