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LT1308 Datasheet(PDF) 5 Page - Linear Technology |
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LT1308 Datasheet(HTML) 5 Page - Linear Technology |
5 / 8 page 5 LT1308 PIN FUNCTIONS SW (Pin 5): Switch Pin. Connect inductor/diode here. Minimize trace area at this pin to keep EMI down. VIN (Pin 6): Supply Pin. Must have local bypass capacitor right at the pin, connected directly to ground. LBI (Pin 7): Low-Battery Detector Input. 200mV refer- ence. Voltage on LBI must stay between ground and 700mV. Low-battery detector does not function with SHDN pin grounded. If not used, float LBI pin. LBO (Pin 8): Low-Battery Detector Output. Open collec- tor, can sink 10 µA. A 1MΩ pullup is recommended. LBO is high impedance when SHDN is grounded. BLOCK DIAGRAM – + – + – + – + + + Σ COMPARATOR RAMP GENERATOR R BIAS VC gm Q2 ×10 Q1 FB FB ENABLE 200mV A = 3 FF A2 A1 ERROR AMPLIFIER A4 0.03 Ω DRIVER SW GND 1308 BD Q3 Q S 600kHz OSCILLATOR 5 LBO LBI SHDN SHUTDOWN 3 7 1 4 R6 40k R5 40k R1 (EXTERNAL) R3 30k R4 140k 2 VIN VIN VOUT 6 8 R2 (EXTERNAL) LAYOUT HINTS The LT1308 switches current at high speed, mandating careful attention to layout for proper performance. You will not get advertised performance with careless layouts. Figure 2 shows recommended component placement. Follow this closely in your PC layout. Note the direct path of the switching loops. Input capacitor CIN must be placed close (< 5mm) to the IC package. As little as 10mm of wire or PC trace from CIN to VIN will cause problems such as inability to regulate or oscillation. A 10 µF ceramic bypass capacitor is the only input capacitance required provided the battery has a low inductance path to the circuit. The battery itself provides the bulk capacitance the device requires for proper operation. If the battery is located some APPLICATIONS INFORMATION Figure 2. Recommended Component Placement. Traces Carrying High Current Are Direct. Trace Area at FB Pin and VC Pin is Kept Low. Lead Length to Battery Should Be Kept Short. Ground Plane Should Be Placed Under All Components 1 2 3 4 8 7 6 5 L CIN COUT D LT1308 VOUT VIN GND MULTIPLE VIAs GROUND PLANE 1308 F02 |
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Similar Description - LT1308 |
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