Datasheet LT1316 (Analog Devices) - 10

LT1316
U U W U APPLICATIONS INFORMATION
VOUT V 100mV/DIV OUT 100mV/DIV AC COUPLED AC COUPLED IL I 100mA/DIV L 100mA/DIV 1316 F07 1316 F08 100µs/DIV 50µs/DIV
Figure 7. Switching Waveforms for the Circuit Figure 8. By Adding C1, Output Ripple Voltage Shown in Figure 7 Without C1. The Output Ripple is Reduced to Less Than 80mVP-P Voltage is Approximately 140mVP-P Layout/Input Bypassing
1µF ceramic capacitor acts to smooth voltage spikes at switch turn-on and turn-off. If the power source is far away The LT1316’s high speed switching mandates careful from the IC, inductance in the power source leads results attention to PC board layout. Suggested component place- in high impedance at high frequency. A local high capaci- ment is shown in Figure 9. The input supply must have low tance bypass is then required to restore low impedance at impedance at AC and the input capacitor should be placed the IC. as indicated in the figure. The value of this capacitor depends on how close the input supply is to the IC. In
Low-Battery Detector
situations where the input supply is more than a few inches away from the IC, a 47 The LT1316 contains an independent low-battery detector µF to 100µF solid tantalum bypass capacitor is required. If the input supply is close to that remains active when the device is shut down. This the IC, a 1 detector, actually a hysteretic comparator, has an open µF ceramic capacitor can be used instead. The LT1316 switches current in pulses up to 0.5A, so a low collector output that can sink up to 500µA. The compara- impedance supply must be available. If the power source tor also operates below the switcher’s undervoltage lock- (for example, a 2 AA cell battery) is within 1 or 2 inches of out threshold, operating until VIN reaches approximately the IC, the battery itself provides bulk capacitance and the 1.4V. 1 8 2 LT1316 7 3 6 V L IN 4 5 RSET + CIN GND D COUT + 1316 F09 VOUT
Figure 9. Suggested PC Layout
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