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LTC1159CN-3.3 Datasheet(PDF) 11 Page - Linear Technology |
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LTC1159CN-3.3 Datasheet(HTML) 11 Page - Linear Technology |
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11 / 20 page  11 LTC1159/LTC1159-3.3/LTC1159-5 APPLICATIO S I FOR ATIO 2. EXTVCC Connected Directly to VOUT. This is the normal connection for a 5V regulator and provides the highest efficiency. 3. EXTVCC Connected to an Output-Derived Boost Net- work. For 3.3V and other low voltage regulators, effi- ciency gains can still be realized by connecting EXTVCC to an output-derived voltage which has been boosted to greater than 4.5V. This can be done either with the inductive boost winding shown in Figure 5a or the capacitive charge pump shown in Figure 5b. The charge pump has the advantage of simple magnetics and gen- erally provides the highest efficiency at the expense of a slightly higher parts count. 4. EXTVCC Connected to an External Supply. If an external supply is available in the 5V to 12V range, it may be used to power EXTVCC providing it is compatible with the MOSFET gate drive requirements. There are no restric- tions on the EXTVCC voltage relative to VIN. EXTVCC may be higher than VIN providing EXTVCC does not exceed the 15V absolute maximum rating. When driving standard threshold MOSFETs, the exter- nal supply must always be present during operation to prevent MOSFET failure due to insufficient gate drive. The LTC1149 family should also be considered for applications which require the use of standard threshold MOSFETs. Important Information About LTC1159 Adjustable Applications When an output voltage other than 3.3V or 5V is required, the LTC1159 adjustable version is used with an external resistive divider from VOUT to the VFB pin (Figure 6). The regulated voltage is determined by: VOUT = 1.25V ) )1+ R2 R1 The VFB pin is extremely sensitive to pickup from the inductor switching node. Care should be taken to isolate the feedback network from the inductor, and the 100pF capacitor should be connected between the VFB and S-GND pins next to the package. In LTC1159N and LTC1159S applications with VOUT > 5.5V, the VCC pin may self-power through the Sense pins when SHDN2 is taken high, preventing shutdown. In these applications, a pull-down must be added to the Sense– pin as shown in Figure 6. This pull-down effectively takes the place of the SHDN1 pin, ensuring complete shutdown. Note: For versions in which both the SHDN1 and SHDN2 pins are available (LTC1159G and all fixed output ver- sions), the two pins are simply connected to each other and driven together to guarantee complete shutdown. The Figure 6 circuit cannot be used to regulate a VOUT which is greater than the maximum voltage allowed on the LTC1159 Sense pins (13V). In applications with VOUT > 13V, RSENSE must be moved to the ground side of the output capacitor and load. This operates the current sense VIN P-DRIVE LTC1159-3.3 P-GATE N-CH VIN 1N4148 • • P-CH + + + CIN RSENSE COUT 1 µF VOUT LTC1159 • F05a N-GATE P-GND EXTVCC L 1:1 Figure 5a. Inductive Boost Circuit for EXTVCC Figure 5b. Capacitive Charge Pump for EXTVCC VIN P-DRIVE LTC1159-3.3 P-GATE N-CH BAT85 0.22 µF 1 µF BAT85 BAT85 VN2222LL VIN P-CH + CIN RSENSE + COUT + VOUT LTC1159 • F05b N-GATE P-GND EXTVCC L |
Similar Part No. - LTC1159CN-3.3 |
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Similar Description - LTC1159CN-3.3 |
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