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LT1612 датащи(PDF) 5 Page - Linear Technology |
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LT1612 датащи(HTML) 5 Page - Linear Technology |
5 / 8 page 5 LT1612 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 Layout Hints The LT1612 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 for a buck (step-down) converter. Follow this closely in your PC layout. Note the direct path of the switching loops. Input capacitor C1 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. The ground terminal of input capacitor C1 should tie close to Pin 4 of the LT1612. Doing this reduces dI/dt in the ground copper which keeps high frequency spikes to a minimum. The DC/DC converter ground should tie to the PC board ground plane at one place only, to avoid intro- ducing dI/dt in the ground plane. OPERATIO Figure 3. Output Voltage Ripple is 20mVP-P for the Circuit of Figure 1 Burst Mode Operation Defeat To maintain high efficiency at light loads, the LT1612 will automatically shift into Burst Mode operation (MODE = 0V or floating). In this mode of operation the oscillator and switch drive circuitry is alternately turned on and off, reducing quiescent current to 160 µA. This reduces power consumption but also adds low frequency voltage ripple to the output. Figure 3 shows switching waveforms for a 5V to 3.3V converter running in Burst Mode operation. Output voltage ripple is approximately 20mVP-P. If the MODE pin is pulled high, Burst Mode operation will be inhibited and the oscillator runs continuously with no low frequency ripple at the output. See Figures 4 and 5. Figure 4. Transient Response for the Circuit of Figure 1 with the MODE Pin Tied to Ground or Floating Figure 5. With the MODE Pin Tied High, Low Frequency Output Voltage Ripple Is No Longer Present 1612 F03 VOUT 20mV/DIV AC COUPLED IL 200mA/DIV 5 µs/DIV 1612 F04 VOUT 200mV/DIV AC COUPLED ILOAD 10mA TO 310mA 0.1ms/DIV IL 200mA/DIV 1612 F05 VOUT 200mV/DIV AC COUPLED ILOAD 10mA TO 300mA 0.1ms/DIV IL 200mA/DIV 1 2 8 7 3 4 6 5 L1 C2 R1 C3 LT1612 VOUT VIN GND SHDN 1612 F02 MODE MULTIPLE VIAs C1 R2 RC CC |
Аналогичный номер детали - LT1612 |
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Аналогичное описание - LT1612 |
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