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SP6691EB 数据表(PDF) 2 Page - Sipex Corporation |
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SP6691EB 数据表(HTML) 2 Page - Sipex Corporation |
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2 / 6 page  2 USING THE EVALUATION BOARD 1) Powering Up the SP6691EB Circuit The SP6691EB Evaluation Board can be powered from inputs from a +1.2V to +5.0V. Connect with short leads directly to the “VIN” and “GND” posts. Monitor the Output Voltage and connect the Load between the “VOUT” post and the “GND” post. 2) Using the J1 Jumper: Enabling the SP6691EB Output and using the Shutdown Mode The SP6691EB output will be enabled if the J1 Jumper is in the bottom or pin 1 to 2 position. If J1 is in the pin 2 to 3 or top position, the Shutdown pin is brought to GND, which puts the SP6691EB in the low quiescent Shutdown Mode. 3) Using the Posts Since the part might get damaged when the output is open loop, two divider resistors (R1=1M, R2=64.9K) are used to provide the feedback loop and set the output voltage. For the white LEDs application, these two resistors (R1, R2) need to be removed from the evaluation board first to avoid over- voltage and then plug the white LED module between “VOUT” and “FB” posts. The bias resistor Rb should also be installed on the board. 4) Inductor Selection For SP6691EB, the internal switch will be turned off only after the inductor current reaches the typical dc current limit (ILIM=450mA). However, there is typically propagation delay of 200nS between the time when the current limit is reached and when the switch is actually turned off. During this 200nS delay, the peak inductor current will increase, exceeding the current limit by a small amount. The peak inductor current can be estimated by: nS 200 L V I I (max) in LIM pk ⋅ + = The larger the input voltage and the lower the inductor value, the greater the peak current. In selecting an inductor, the saturation current specified for the inductor needs to be greater than the SP6691EB peak current to avoid saturating the inductor, which would result in a loss in efficiency and could damage the inductor. Choosing an inductor with low DCR decreases power losses and increase efficiency. Refer to Table 1 for some suggested low ESR inductors. Table 1. Suggested Low ESR inductor MANUFACTURE PART NUMBER DCR ( Ω) Current Rating (mA) MURATA 770-436-1300 LQH32CN100K11 (10uH) 0.3 450 TDK 847-803-6100 NLC453232T-100K (22uH) 0.55 500 5) Diode Selection A schottky diode with a low forward drop and fast switching speed is ideally used here to achieve high efficiency. In selecting a Schottky diode, the current rating of the schottky diode should be larger than the peak inductor current. Moreover, the reverse breakdown voltage of the schottky diode should be larger than the output voltage. 6) Capacitor Selection Ceramic capacitors are recommended for their inherently low ESR, which will help produce low peak to peak output ripple, and reduce high frequency spikes. For the typical application, 4.7uF input capacitor and 2.2uF output capacitor are sufficient. The input and output ripple could be further reduced by increasing the value of the input and output capacitors. Place all the capacitors as close to the SP6691EB as possible for layout. For use as a voltage source, to reduce the output ripple, a small feedforward (47pF) across the top feedback resistor can be used to provide sufficient overdrive for the error comparator, thus reducing the output ripple. Refer to Table 2 for some suggested low ESR capacitors. |
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