Design and Implementation of On-board Electrical Power ... - OUFTI-1
Design and Implementation of On-board Electrical Power ... - OUFTI-1 Design and Implementation of On-board Electrical Power ... - OUFTI-1
R KR >1.45V100mA − 1.3A35= 23.07Ω.The minimum cathode current for regulation is 1mA. When the regulation starts, theEmitter-Base voltage of the transistor V EB is around 0.6V. If there is no base current (I B = 0),the TL1431 is supplied through resistor KR:I KR > 1mA,The chosen value for R KR is 560Ω.R KR < V EB1mA = 600Ω.SCRA and SCRBThe intern reference of the TL1431 V I (ref) is equal to 2.5V.The ratio SCRB/SCRA is given by:V I (ref)4.2V − V I (ref) = 1.47.The resistances must not be too high or the reference input current (up to 3µA) can diruptthe regulation voltage. If they are too low, some power will be dissipated in the scaler.The chosen values are SCRA = 10kΩ and SCRB = 14.7kΩ.SHRFor the regulation, the transistor must be in linear mode. The Emitter-Collector voltagemust be superior to the Emitter-Collector saturation voltage (V E C(sat) = 0.75V when I C =2.5A, it will be less when I C = 1.3A ). We haveV E C = 4.2V − I C R S HR > V E C(sat),R S HR
Figure 5.40: Dissipated power in the transistor and in the resistor.5.5 Design of the protection circuits5.5.1 DescriptionThe protection circuit was chosen in [3]. It is the MAX890L. It can operate with an inputvoltage of 2.7 to 5.5V. It can thus be used for all systems supplied by 3.3V and 5V busses.It is a current-limiting circuit. A threshold current (I thr ) can be chosen between 240mAand 1,200mA. The threshold depends on the value of the resistor R set . It is possible to choosea threshold under 240mA, but the circuit will operate with less precision. When the currentat the output becomes higher than the threshold, the MAX890L starts to decrease the outputvoltage. The voltage falls to zero when the output current reach 1.5 times the threshold.The circuit has a thermal shut-down. When the junction temperature exceeds 135 ◦ C, theswitch turns off. It turns back on at 125 ◦ C. In case of high dV DSdton the output (short-circuit),the switch turns off too. It is then slowly tuned back on with the output current limited to1.5 × I thr .The circuit provides a “F AULT ′′ signal. It is an open-drain output that goes low whenI thr is reached or when the thermal shut-down is activated. There is a “ON/OF F ′′ input.When this input is set to high, the power output is disconnected from the power input.5.5.2 ComponentsThe value of R set depends on the desired I thr . Here is the formula to choose R set : R set =1,380I thr. The protection circuit of the EPS has a R set of 10kΩ (I thr = 138mA). It protects themeasurement system and their total consumption is very low (less than 10mA).A capacitor of 1µF is used on the input of the circuit and a capacitor of 0.1µF on theoutput. A pull-up resistor of 100kΩ and a decoupling capacitor of 100pF are used on the“ON/OF F ′′ input.83
- Page 32 and 33: Parameter SLPB723870H4 SLPB554374HN
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- Page 40 and 41: Chapter 4The Power Budget4.1 Introd
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- Page 66 and 67: Figure 5.14: Simplified schematics
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- Page 90 and 91: PrefixX7X5Y5Z5SuffixTemperature ran
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Figure 5.40: Dissipated power in the transistor <strong>and</strong> in the resistor.5.5 <strong>Design</strong> <strong>of</strong> the protection circuits5.5.1 DescriptionThe protection circuit was chosen in [3]. It is the MAX890L. It can operate with an inputvoltage <strong>of</strong> 2.7 to 5.5V. It can thus be used for all systems supplied by 3.3V <strong>and</strong> 5V busses.It is a current-limiting circuit. A threshold current (I thr ) can be chosen between 240mA<strong>and</strong> 1,200mA. The threshold depends on the value <strong>of</strong> the resistor R set . It is possible to choosea threshold under 240mA, but the circuit will operate with less precision. When the currentat the output becomes higher than the threshold, the MAX890L starts to decrease the outputvoltage. The voltage falls to zero when the output current reach 1.5 times the threshold.The circuit has a thermal shut-down. When the junction temperature exceeds 135 ◦ C, theswitch turns <strong>of</strong>f. It turns back on at 125 ◦ C. In case <strong>of</strong> high dV DSdton the output (short-circuit),the switch turns <strong>of</strong>f too. It is then slowly tuned back on with the output current limited to1.5 × I thr .The circuit provides a “F AULT ′′ signal. It is an open-drain output that goes low whenI thr is reached or when the thermal shut-down is activated. There is a “ON/OF F ′′ input.When this input is set to high, the power output is disconnected from the power input.5.5.2 ComponentsThe value <strong>of</strong> R set depends on the desired I thr . Here is the formula to choose R set : R set =1,380I thr. The protection circuit <strong>of</strong> the EPS has a R set <strong>of</strong> 10kΩ (I thr = 138mA). It protects themeasurement system <strong>and</strong> their total consumption is very low (less than 10mA).A capacitor <strong>of</strong> 1µF is used on the input <strong>of</strong> the circuit <strong>and</strong> a capacitor <strong>of</strong> 0.1µF on theoutput. A pull-up resistor <strong>of</strong> 100kΩ <strong>and</strong> a decoupling capacitor <strong>of</strong> 100pF are used on the“ON/OF F ′′ input.83
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