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LTC1159-5 数据表(PDF) 12 Page - Linear Technology |
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LTC1159-5 数据表(HTML) 12 Page - Linear Technology |
12 / 20 page 12 LTC1159/LTC1159-3.3/LTC1159-5 APPLICATIO S I FOR ATIO Figure 6. High Efficiency Adjustable Regulator with 5.5V < VOUT < 13V 0.15 µF VIN CAP P-DRIVE P-GND EXTVCC VFB LTC1159 ITH CT P-GATE VCC VCC SHDN2 SENSE– SENSE+ IRFZ34 VN2222LL 0.1 µF 100pF 5M 1N4148 VIN IRF9Z34 1N5819 0.01 µF 100 Ω 100 Ω + 100 µF 50V + 150 µF 16V OS-CON + 1 µF 0V = NORMAL >3V = SHUTDOWN 3300pF CT 390pF 1k N-GATE S-GND VOUT R1 24.9k LTC1159 • F06 R2 215k VOUT = () 1 + R2 R1 VALUES SHOWN FOR VOUT = 12V/2.5A 100 µH RSENSE 0.039 Ω 1.25 comparator at 0V common mode, increasing the off-time approximately 40% and requiring the use of a smaller timing capacitor CT. Inverting Regular Applications The LTC1159 can also be used to obtain negative output voltages from positive inputs. In these inverting applica- tions, the current sense resistor connects to ground while the LTC1159 and N-channel MOSFET connections, which would normally go to ground, instead ride on the negative output. This allows the negative output voltage to be set by the same process as in conventional applications, using either the internal divider (LTC1159-3.3, LTC1159-5) or an external divider with the adjustable version. Figure 15 in the Typical Applications shows a synchronous 12V to –12V converter which can supply up to 1A with better than 85% efficiency. By grounding the EXTVCC pin in the Figure 15 circuit, the entire 12V output voltage is placed across the driver and control circuits since the LTC1159 ground pins are at –12V. During start-up or short-circuit conditions, operating power is supplied by the internal 4.5V regulator. The shutdown signal is level-shifted to the negative output rail by Q3, and Q4 ensures that Q1 and Q2 remain off during the entire shutdown sequence. Efficiency Considerations The percent efficiency of a switching regulator is equal to the output power divided by the input power times 100%. It is often useful to analyze individual losses to determine what is limiting the efficiency and which change would produce the most improvement. Percent efficiency can be expressed as: %Efficiency = 100 – (L1 + L2 + L3 + ...) where L1, L2, etc., are the individual losses as a percentage of input power. Although all dissipative elements in the circuit produce losses, four main sources usually account for most of the losses in LTC1159 circuits: 1) LTC1159 VIN current, 2) LTC1159 VCC current, 3) I 2R losses, and 4) P-channel transition losses. 1. LTC1159 VIN current is the DC supply current given in the electrical characteristics which excludes MOSFET driver and control currents. VIN current results in a small (< 1%) loss which increases with VIN. 2. LTC1159 VCC current is the sum of the MOSFET driver and control circuit currents. The MOSFET driver current results from switching the gate capacitance of the power MOSFETs. Each time a MOSFET gate is switched from |
类似零件编号 - LTC1159-5 |
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类似说明 - LTC1159-5 |
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