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ADP3207 Datasheet(PDF) 21 Page  ON Semiconductor 

ADP3207 Datasheet(HTML) 21 Page  ON Semiconductor 
21 / 29 page ADP3207 Rev. 1  Page 21 of 29  www.onsemi.com The following procedure and equations yield values for RCS1, RCS2, and RTH (the thermistor value at 25°C) for a given RCS value: 1. Select an NTC to be used based on type and value. Because there is no value yet, start with a thermistor with a value close to RCS. The NTC should also have an initial tolerance of better than 5%. 2. Based on the type of NTC, find its relative resistance value at two temperatures. Temperatures that work well are 50°C and 90°C. These are called Resistance Value A (A is RTH(50°C)/RTH(25°C)) and Resistance Value B (B is RTH(90°C)/RTH(25°C)). Note that the relative value of NTC is always 1 at 25°C. 3. Next, find the relative value of RCS that is required for each of these temperatures. This is based on the percentage of change needed, which is initially 0.39%/°C. These are called r1 and r2. () () 25 1 1 25 1 1 2 2 1 1 − × + = − × + = T TC r T TC r (9) where: TC = 0.0039 T1 = 50°C T2 = 90°C. 4. Compute the relative values for rCS1, rCS2, and rTH using () () () () () ( ) () 1 2 2 1 2 1 2 1 1 2 2 1 2 1 1 1 1 1 1 1 1 1 1 1 CS CS TH CS CS CS CS r r r r r A r A r B A r A B r B A r A B r B A r r B A r − − = − − − − = − − × − × − × − × × − × + × − × − × × − = (10) 5. Calculate RTH = RTH × RCS, then select the closest value of thermistor that is available. Also, compute a scaling factor k based on the ratio of the actual thermistor value relative to the computed one ) ( ) ( CALCULATED TH ACTUAL TH R R k = (11) 6. Finally, calculate values for RCS1 and RCS2 using () () () 2 2 1 1 1 CS CS CS CS CS CS r k k R R r k R R × + − × = × × = (12) This example starts with a thermistor value of 100 k Ω and uses a Vishay NTHS0603N04 NTC thermistor (a 0603 size thermistor) with A = 0.3359 and B = 0.0771. From this data, rCS1 = 0.359, rCS2 = 0.729 and rTH = 1.094. Solving for RTH yields 240 kΩ, so 220 kΩ is chosen, making k = 0.914. Finally, RCS1 and RCS2 are 72.3 kΩ and 166 kΩ. Choosing the closest 1% resistor values yields a choice of 71.5 kΩ and 165 kΩ. COUT SELECTION The required output decoupling for processors and platforms is typically recommended by Intel. The following guidelines can also be used if both bulk and ceramic capacitors in the system: • Select the total amount of ceramic capacitance. This is based on the number and type of capacitors to be used. The best location for ceramics is inside the socket; 20 pieces of Size 0805 being the physical limit. Additional capacitors can be placed along the outer edge of the socket. • Select the number of ceramics and find the total ceramic capacitance (CZ). Combined ceramic values of 200 μF to 300 μF are recommended and are usually made up of multiple 10 μF or 22 μF capacitors. • Note that there is an upper limit imposed on the total amount of bulk capacitance (CX) when considering the VID onthefly output voltage stepping (voltage step VV in time tV with error of VERR), and also a lower limit based on meeting the critical capacitance for load release at a given maximum load step ΔIO. For a stepoff load current, the current version of the IMVP6 specification allows a maximum VCORE overshoot (VOSMAX) of 10 mV, plus 1.5% of the VID voltage. For example, if the VID is 1.150 V, then the largest overshoot allowed is 27 mV. () ⎟ ⎟ ⎟ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎜ ⎜ ⎜ ⎝ ⎛ − × ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ Δ + × Δ × ≥ z VID O OSMAX O O MIN x C V I V R n I L C (13) z O V VID v VID V 2 O 2 MAX X C L nKR V V t V V R nK L C − ⎟ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎜ ⎝ ⎛ − ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ × + × × ≤ 1 1 2 ) ( (14) where: ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ − = V ERR V V n K 1 (15) To meet the conditions of these equations and transient response, the ESR of the bulk capacitor bank (RX) should be less than two times the droop resistance, RO. If the CX(MIN) is larger than CX(MAX), the system does not meet the VID onthefly and/or deeper sleep exit specification and can require a smaller inductor or more phases (the switching frequency can also have to be increased to keep the output ripple the same). 
