Datasheet LT3471 (Analog Devices) - 10
| Manufacturer | Analog Devices |
| Description | Dual 1.3A, 1.2MHz Boost/Inverter in 3mm × 3mm DFN |
| Pages / Page | 16 / 10 — APPLICATIONS INFORMATION. DIODE SELECTION. Compensation—Theory. LAYOUT … |
| File Format / Size | PDF / 307 Kb |
| Document Language | English |
APPLICATIONS INFORMATION. DIODE SELECTION. Compensation—Theory. LAYOUT HINTS. Figure 6. Boost Converter Equivalent Model
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LT3471
APPLICATIONS INFORMATION DIODE SELECTION Compensation—Theory
A Schottky diode is recommended for use with the Like all other current mode switching regulators, the LT3471. For high effi ciency, a diode with good thermal LT3471 needs to be compensated for stable and effi cient characteristics at high currents should be used such as operation. Two feedback loops are used in the LT3471: a the On Semiconductor MBRM120. This is a 20V diode. fast current loop which does not require compensation, Where the switch voltage exceeds 20V, use the MBRM140, and a slower voltage loop which does. Standard Bode a 40V diode. These diodes are rated to handle an average plot analysis can be used to understand and adjust the forward current of 1.0A. In applications where the average voltage feedback loop. forward current of the diode is less than 0.5A, use the As with any feedback loop, identifying the gain and phase Philips PMEG 2005, 3005, or 4005 (a 20V, 30V or 40V contribution of the various elements in the loop is critical. diode, respectively). Figure 6 shows the key equivalent elements of a boost con- verter. Because of the fast current control loop, the power
LAYOUT HINTS
stage of the IC, inductor and diode have been replaced by the equivalent transconductance amplifi er g The high speed operation of the LT3471 demands care- mp. gmp acts as a current source where the output current is proportional ful attention to board layout. You will not get advertised to the V performance with careless layout. Figure 5 shows the C voltage. Note that the maximum output current of g recommended component placement. mp is fi nite due to the current limit in the IC. CONTROL 1 CONTROL 2 – CSS1 CSS2 RSS1 RSS2 gmp V GND GND GND OUT + CPL R R ESR L C4 C C1 OUT VOUT2 + 1.00V V REFERENCE C g L1 L2 ma R1 L3 RC RO VCC • – VOUT1 D1 C5 • C R2 C SW1 SW2 3471 F06 10 9 8 7 6 C D2 C: COMPENSATION CAPACITOR C3 SHDN/SS1 SHDN/SS2 COUT: OUTPUT CAPACITOR CPL: PHASE LEAD CAPACITOR GND GND gma: TRANSCONDUCTANCE AMPLIFIER INSIDE IC gmp: POWER STAGE TRANSCONDUCTANCE AMPLIFIER RC: COMPENSATION RESISTOR LT3471 RL: OUTPUT RESISTANCE DEFINED AS VOUT DIVIDED BY ILOAD(MAX) PIN 11 GND RO: OUTPUT RESISTANCE OF gma R1, R2: FEEDBACK RESISTOR DIVIDER NETWORK RESR: OUTPUT CAPACITOR ESR FB1N FB1P VREF FB2P FB2N
Figure 6. Boost Converter Equivalent Model
1 2 3 4 5 R4 R2 R3 R1 VOUT1 VOUT2 C2 3471 F05
Figure 5. Suggested Layout Showing a Boost on SW1 and an Inverter on SW2. Note the Separate Ground Returns for All High Current Paths (Using a Multilayer Board)
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APPLICATIONS INFORMATION DIODE SELECTION Compensation—Theory
A Schottky diode is recommended for use with the Like all other current mode switching regulators, the LT3471. For high effi ciency, a diode with good thermal LT3471 needs to be compensated for stable and effi cient characteristics at high currents should be used such as operation. Two feedback loops are used in the LT3471: a the On Semiconductor MBRM120. This is a 20V diode. fast current loop which does not require compensation, Where the switch voltage exceeds 20V, use the MBRM140, and a slower voltage loop which does. Standard Bode a 40V diode. These diodes are rated to handle an average plot analysis can be used to understand and adjust the forward current of 1.0A. In applications where the average voltage feedback loop. forward current of the diode is less than 0.5A, use the As with any feedback loop, identifying the gain and phase Philips PMEG 2005, 3005, or 4005 (a 20V, 30V or 40V contribution of the various elements in the loop is critical. diode, respectively). Figure 6 shows the key equivalent elements of a boost con- verter. Because of the fast current control loop, the power
LAYOUT HINTS
stage of the IC, inductor and diode have been replaced by the equivalent transconductance amplifi er g The high speed operation of the LT3471 demands care- mp. gmp acts as a current source where the output current is proportional ful attention to board layout. You will not get advertised to the V performance with careless layout. Figure 5 shows the C voltage. Note that the maximum output current of g recommended component placement. mp is fi nite due to the current limit in the IC. CONTROL 1 CONTROL 2 – CSS1 CSS2 RSS1 RSS2 gmp V GND GND GND OUT + CPL R R ESR L C4 C C1 OUT VOUT2 + 1.00V V REFERENCE C g L1 L2 ma R1 L3 RC RO VCC • – VOUT1 D1 C5 • C R2 C SW1 SW2 3471 F06 10 9 8 7 6 C D2 C: COMPENSATION CAPACITOR C3 SHDN/SS1 SHDN/SS2 COUT: OUTPUT CAPACITOR CPL: PHASE LEAD CAPACITOR GND GND gma: TRANSCONDUCTANCE AMPLIFIER INSIDE IC gmp: POWER STAGE TRANSCONDUCTANCE AMPLIFIER RC: COMPENSATION RESISTOR LT3471 RL: OUTPUT RESISTANCE DEFINED AS VOUT DIVIDED BY ILOAD(MAX) PIN 11 GND RO: OUTPUT RESISTANCE OF gma R1, R2: FEEDBACK RESISTOR DIVIDER NETWORK RESR: OUTPUT CAPACITOR ESR FB1N FB1P VREF FB2P FB2N
Figure 6. Boost Converter Equivalent Model
1 2 3 4 5 R4 R2 R3 R1 VOUT1 VOUT2 C2 3471 F05
Figure 5. Suggested Layout Showing a Boost on SW1 and an Inverter on SW2. Note the Separate Ground Returns for All High Current Paths (Using a Multilayer Board)
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