LT1766 Linear Technology, LT1766 Datasheet
LT1766
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LT1766 Summary of contents
Page 1
... A shutdown pin reduces supply current and the device can be externally synchronized from 228kHz to 700kHz with logic level inputs. The LT1766/LT1766-5 are available in a 16-pin fused-lead SSOP package or a TSSOP package with exposed backside for improved thermal performance. , LTC and LT are registered trademarks of Linear Technology Corporation. ...
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... V Switching Threshold C V High Clamp Operating Junction Temperature Range LT1766EFE/LT1766EFE-5/LT1766EGN/ LT1766EGN-5 (Note 8,10) ................. – 125 C LT1766IFE/LT1766IFE-5/ LT1766IGN/LT1766IGN-5 (Note 8,10) – 125 C Storage Temperature Range ................ – 150 C Lead Temperature (Soldering, 10 sec)................. 300 ORDER PART TOP VIEW NUMBER GND ...
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... Note 7: Switch on resistance is calculated by dividing V the forced current (1.5A). See Typical Performance Characteristics for the graph of switch voltage at other currents. Note 8: The LT1766EGN, LT1766EGN-5, LT1766EFE and LT1766EFE-5 are guaranteed to meet performance specifications from 125 C junction temperature. Specifications over the – 125 C operating junction temperature range are assured by design, characterization and correlation with statistical process controls ...
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... LT1766/LT1766 TYPICAL PERFOR A CE CHARACTERISTICS Switch Peak Current Limit 2 TYPICAL 2.0 GUARANTEED MINIMUM 1.5 1 100 DUTY CYCLE (%) 1766 G01 Lockout and Shutdown Thresholds 2.4 LOCKOUT 2.0 1.6 1.2 0.8 START-UP 0.4 SHUTDOWN 0 –50 – 100 125 JUNCTION TEMPERATURE ( C) 1766 G04 Error Amplifier Transconductance ...
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... NPN switch. This pin is driven up to the input pin voltage during switch on time. Inductor current drives the switch pin negative during switch off time. Negative volt- age is clamped with the external catch diode. Maximum negative switch voltage allowed is – 0.8V. NC (Pins 13): No Connection. LT1766/LT1766-5 BOOST Pin Current ...
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... W BLOCK DIAGRA The LT1766 is a constant frequency, current mode buck converter. This means that there is an internal clock and two feedback loops that control the duty cycle of the power switch. In addition to the normal error amplifier, there is a current sense amplifier that monitors switch current on a cycle-by-cycle basis ...
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... LC resonant frequency. This makes it much easier to frequency compensate the feedback loop and also gives much quicker transient response. Most of the circuitry of the LT1766 operates from an internal 2.9V bias line. The bias regulator normally draws power from the regulator input pin, but if the BIAS pin is ...
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... U U APPLICATIO S I FOR ATIO FEEDBACK PIN FUNCTIONS The feedback (FB) pin on the LT1766 is used to set output voltage and provide several overload protection features. The first part of this section deals with selecting resistors to set output voltage and the remaining part talks about foldback frequency and current limiting created by the FB pin ...
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... H to 100 H. Lower values are chosen to reduce physical size of the inductor. Higher values allow more output current because they reduce peak current seen by the LT1766 switch, which has a 1.5A limit. Higher values also reduce output ripple voltage. When choosing an inductor you will need to consider output ripple voltage, maximum load current, peak induc- tor current and fault current in the inductor ...
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... Choosing a smaller inductor with lighter loads may result in discontinuous operation but the LT1766 is designed to work well in both continu- ous or discontinuous mode. Peak Inductor Current and Fault Current To ensure that the inductor will not saturate, the peak inductor current should be calculated knowing the maxi- mum load current ...
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... Applica- tion Note 19.) The LT1766 is able to maintain peak switch current limit over the full duty cycle range by using patented circuitry* to cancel the effects of slope compensation on peak switch current without affecting the frequency compensation it provides ...
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... When choosing small inductor values, however, discon- tinuous mode will occur at much higher output load currents. The limit to the smallest inductor value that can be chosen is set by the LT1766 peak switch current (I and the maximum output load current required, given by ...
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... To get low ESR takes volume , so physically smaller capacitors have high ESR. The ESR range for typical LT1766 applications is 0. typical output capacitor is an AVX type TPS, 100 F at 10V, with a guaranteed ESR less than 0.1 . This is a “D” size surface mount solid tantalum capacitor ...
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... The rise and fall times of these pulses are very fast. The input capacitor is required to reduce the voltage ripple this causes at the input of LT1766 and force the switching current into a tight local loop, thereby minimiz- ing EMI. The RMS ripple current can be calculated from: ...
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... W U SHUTDOWN FUNCTION AND UNDERVOLTAGE LOCKOUT Figure 4 shows how to add undervoltage lockout (UVLO) to the LT1766. Typically, UVLO is used in situations where the input supply is current limited , or has a relatively high to drive the output IN source resistance. A switching regulator draws constant power from the source, so source current increases as source voltage drops ...
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... At switch off, this parasitic in- ductance produces a flyback spike across the LT1766 switch. When operating at higher currents and input volt- ages, with poor layout, this spike can generate voltages across the LT1766 that may exceed its absolute maximum V is being clamped by the FB pin (see C ...
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... Board layout also has a significant effect on thermal resistance. Pins and 16, GND, are a continuous copper plate that runs under the LT1766 die. This is the best thermal path for heat out of the package. Reducing the thermal resistance from Pins and 16 onto the board will reduce die temperature and increase the power capability of the LT1766 ...
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... THERMAL CALCULATIONS Power dissipation in the LT1766 chip comes from four sources: switch DC loss, switch AC loss, boost circuit current, and input quiescent current. The following formu- las show how to calculate each of these losses. These ...
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... (1) (0.1) = 0.1W INDUCTOR Only a portion of the temperature rise in the external inductor and diode is coupled to the junction of the LT1766. Based on empirical measurements the thermal effect on LT1766 junction temperature due to power dissipation in the external inductor and catch diode can be calculated as: T (LT1766 ...
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... OUT V = Schottky diode forward drop switching frequency OSC A potential controllability problem arises if the LT1766 is called upon to produce an on time shorter than it is able to W produce. Feedback loop action will lower then reduce the exceeds 3. DROOP achievable in IN ...
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... For these reasons important that a final stability check is made with produc- tion layout and components. The LT1766 uses current mode control. This alleviates many of the phase shift problems associated with the inductor. The basic regulator loop is shown in Figure 10. ...
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... C In systems with a primary and backup supply, for ex- ample, a battery powered device with a wall adapter input, the output of the LT1766 can be held up by the backup pin enough to cause supply with the LT1766 input disconnected. In this condi- tion, the SW pin will source current into the V ...
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... It differs from the standard approach in the way the IC chip derives its feedback signal because the LT1766 accepts only positive feedback sig- nals. The ground pin must be tied to the regulated negative output. A resistor divider to the FB pin then provides the proper feedback voltage for the chip ...
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... Output current where continuous mode is needed: I CONT Minimum inductor discontinuous mode: = 12V MIN Minimum inductor continuous mode: L MIN † For a 40V to –12V converter using the LT1766 with peak switch current of 1.5A and a catch diode of 0.63V: R1 44. 100 F CONT 25V TANT R2 4.99k OUTPUT** For a load current of 0.25A, this says that discontinuous – ...
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... IN(MAX) To increase usable V can be achieved by placing a zener diode V C2+) in series with D2. Note: A maximum limit on V ensure a minimum V ) capacitor; referred to as “V Characteristics OUT )( V ) OUT LT1766/LT1766-5 (GND pin – GNDPIN C2 – (D1 –12V. Absolute maximum ratings should OUT = 12V ...
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... LT1766/LT1766-5 PACKAGE DESCRIPTIO 6.60 0.10 4.50 0.10 SEE NOTE 4 RECOMMENDED SOLDER PAD LAYOUT 4.30 – 4.50* (.169 – .177) 0.09 – 0.20 (.018 – .030) (.0036 – .0079) NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS 2. DIMENSIONS ARE IN 3. DRAWING NOT TO SCALE Package 16-Lead Plastic TSSOP (4.4mm) (Reference LTC DWG # 05-08-1663, Exposed Pad Variation BB) 3 ...
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... TYP .015 .004 45 .053 – .068 (0.38 0.10) (1.351 – 1.727) 0 – 8 TYP .008 – .012 (0.203 – 0.305) LT1766/LT1766-5 .189 – .196* (4.801 – 4.978) .009 (0.229 REF .150 – .157** (3.810 – 3.988) ...
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... OUT Step-Down DC/DC Converter LT1676 60V, 440mA (I ), 100kHz, High Efficiency OUT Step-Down DC/DC Converter LT1765 25V, 2.75A (I ), 1.25MHz, High Efficiency OUT Step-Down DC/DC Converter LT1766 60V, 1. 200kHz, High Efficiency OUT Step-Down DC/DC Converter LT1767 25V, 1. 1.25MHz, High Efficiency OUT Step-Down DC/DC Converter LT1776 40V, 550mA (I ), 200kHz, High Efficiency ...
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