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LTC4210-3 Datasheet(PDF) 9 Page - Linear Technology |
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LTC4210-3 Datasheet(HTML) 9 Page - Linear Technology |
9 / 16 page 9 LTC4210-3/LTC4210-4 421034fa APPLICATIO S I FOR ATIO Calculating Current Limit For a selected RSENSE, the nominal load current is given by Equation 1. The minimum load current is given by Equation 2: I V R mV R LIMIT MIN CB MIN SENSE MAX SENSE () () () ( == 44 M MAX) (2) where RR R SENSE MAX SENSE TOL () • =+ ⎛ ⎝⎜ ⎞ ⎠⎟ 1 100 The maximum load current is given by Equation 3: I V R mV R LIMIT MAX CB MAX SENSE MIN SENSE () () () ( == 56 M MIN) (3) where RR R SENSE MIN SENSE TOL () •– = ⎛ ⎝⎜ ⎞ ⎠⎟ 1 100 If a 7m Ω sense resistor with ±1% tolerance is used for current limiting, the nominal current limit is 7.14A. From Equations 2 and 3, ILIMIT(MIN) = 6.22A and ILIMIT(MAX) = 8.08A. For proper operation, the minimum current limit must exceed the circuit maximum operat- ing load current with margin. The sense resistor power rating must exceed VCB(MAX)2/RSENSE(MIN). Frequency Compensation A compensation circuit should be connected to the GATE pin for current limit loop stability. Method 1 The simplest frequency compensation network consists of RC and CC (Figure 2a). The total GATE capacitance is: CGATE = CISS + CC (4) Generally, the compensation value in Figure 2a is suffi- cient for a pair of input wires less than a foot in length. Applications with longer input wires may require the RC or CC value to be increased for better fault transient perfor- mance. For a pair of three foot input wires, users can start with CC = 47nF and RC = 100Ω. Despite the wire length, the general rule for AC stability required is CC ≥ 8nF and RC ≤ 1k Ω. Method 2 The compensation network in Figure 2b is similar to the circuitry used in method 1 but with an additional gate resistor RG. The RG resistor helps to minimize high frequency parasitic oscillations frequently associated with the power MOSFET. In some applications, the user may find that RG helps in short-circuit transient recovery as well. However, too large of an RG value will slow down the turn-off time. The recommended RG range is between 5Ω and 500 Ω. RG limits the current flow into the GATE pin’s internal zener clamp during transient events. The recom- mended RC and CC values are the same as method 1. The parasitic compensation capacitor CPisrequiredwhen0.2µF < load capacitance CL < 9µF, otherwise it is optional. Parasitic MOSFET Oscillation There are two possible parasitic oscillations when the MOSFET operates as a source follower when ramping at Figure 2. Frequency Compensation Q1 Si4410DY VCC SENSE RSENSE 0.007 Ω RG 200 Ω CP** 2.2nF VIN 12V VOUT 65 4 RC 100 Ω CC 10nF 4210 F02 GATE LTC4210* (2b) Method 2 CL + *ADDITIONAL DETAILS OMITTED FOR CLARITY **USE CP IF 0.2µF < CL < 9µF, OTHERWISE NOT REQUIRED VCC SENSE RSENSE 0.007 Ω Q1 Si4410DY VIN 5V *ADDI OMIT **USE OTHE 65 CL 4 RC 100 Ω CC 10nF GATE LTC4210* (2a) Method 1 VOUT + |
Similar Part No. - LTC4210-3_15 |
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Similar Description - LTC4210-3_15 |
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