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LT1310 Datasheet(PDF) 9 Page - Linear Technology |
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LT1310 Datasheet(HTML) 9 Page - Linear Technology |
9 / 12 page 9 LT1310 sn1310 1310fs 100mA to 200mA. Figure 3a shows the transient response with RC equal to 3k. The phase margin is poor as evi- denced by the excessive ringing in the output voltage and inductor current. In Figure 3b, the value of RC is increased to 6k, which results in a more damped response. Figure 3c shows the results when RC is increased further to 15k. The transient response is nicely damped and the compen- sation procedure is complete. Compensation—Theory Like all other current mode switching regulators, the LT1310 needs to be compensated for stable and efficient operation. Two feedback loops are used in the LT1310: a VOUT 100mV/DIV AC COUPLED IL 0.5A/DIV RC = 3k 200 µs/DIV 1310 F03a Figure 3a. Transient Response Shows Excessive Ringing VOUT 100mV/DIV AC COUPLED IL 0.5A/DIV RC = 6k 200 µs/DIV 1310 F03b Figure 3b. Transient Response is Better VOUT 100mV/DIV AC COUPLED IL 0.5A/DIV RC = 15k 200 µs/DIV 1310 F03b Figure 3c. Transient Response is Well Damped fast current loop which does not require compensation, and a slower voltage loop which does. Standard Bode plot analysis can be used to understand and adjust the voltage feedback loop. As with any feedback loop, identifying the gain and phase contribution of the various elements in the loop is critical. Figure 4 shows the key equivalent elements of a boost converter. Because of the fast current control loop, the power stage of the IC, inductor and diode have been replaced by the equivalent transconductance amplifier gmp. gmp acts as a current source where the output current is proportional to the VC voltage. Note that the maximum output current of gmp is finite due to the current limit in the IC. From Figure 4, the DC gain, poles and zeroes can be calculated as follows: Output Pole: P1= 2 2• • R Error Amp Pole: P2 = 1 2• • R Error Amp Zero: Z1= 1 2• • R DC Gain: A = 1.25 V L O C OUT π π π • • • •• • • C C C gR g R OUT C C ma O mp L In addition to the elements from Figure 4, current mode control aslo results in some other poles and zeroes. These are as follows: RHP Zero: Z2 = Output Zero: Z3 = Current Mode Pole: P3 > VR VL ESR C f IN L OUT OUT S 2 2 2 1 2 3 • •• • •• • π π The Current Mode zero is a right half plane zero which can be an issue in feedback control design, but is manageable with proper external component selection. APPLICATIO S I FOR ATIO |
Similar Part No. - LT1310_15 |
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Similar Description - LT1310_15 |
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