a8450 Allegro MicroSystems, Inc., a8450 Datasheet
a8450
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a8450 Summary of contents
Page 1
... The logic-level input, on the ENB pin, allows enable/disable by microcontroller or DSP signals. When disabled, the A8450 draws less than 10 μA of current. A POR (power-on-reset) block monitors the supply voltages and provides a reset signal, with an adjustable delay, for microcontroller or DSP resets. ...
Page 2
... C7, C8 0.1 μF, 100 V ceramic X7R (for 42 V applications) C10 0.22 μ X7R D1 Schottky (for 14 V applications) L1 100 μH, 1.2 A Q1, Q2 pass transistors npn transistor, h A8450KLB-DS, Rev. 2 Automotive Multioutput Voltage Regulator Functional Block Diagram D2 VIN C7 CIN VBB LX Buck Converter with 3 ...
Page 3
... V5D Current Limit I OUTV5DLIM V5A Current Limit I OUTV5ALIM Base Drive Output Current I Feedback Voltage V Feedback Input Bias Current Continued on next page A8450KLB-DS, Rev. 2 Automotive Multioutput Voltage Regulator –40ºC to 135° Test Conditions Enabled mode ENBAT ENB ...
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... PCB based on JEDEC high-conductance standard PCB (JESD51-7; High Effective Thermal Conductivity Test Board for Leaded Surface Mount Packages); data on other PCB types is provided on the Allegro Web site. A8450KLB-DS, Rev. 2 Automotive Multioutput Voltage Regulator –40ºC to 135°C, V ...
Page 5
... ENB ENBAT signals power-on Charge pump ramping Charge pump OK flag set V UVLOV33 V Slope of V (which controls REG Figure 1c. Power-on using ENBAT, followed by power-off using ENB A8450KLB-DS, Rev. 2 Automotive Multioutput Voltage Regulator Timing Diagrams V HYSV33 V UVLOV33 t POR A B from determined by I and output capacitor (C3, C4). ...
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... RISE t (0.2 μs/Div.) V5D Regulator t (50 μs/Div.) V5A Regulator t (50 μs/Div.) A8450KLB-DS, Rev. 2 Automotive Multioutput Voltage Regulator Load Transients Diagrams = 100 mA 25°C; ac-coupled; C1, C2, C3 and μF A 90% *For the adjustable regulator, the transient load response is improved as the voltage is reduced. This is due to the ability of the regulator to provide more base drive (V ADJBD ) because of more available voltage ...
Page 7
... Buck Converter with Switching Regulator. A cur- rent-mode, variable frequency buck dc-to-dc converter and switching regulator are integrated in the A8450, as shown in figure 2. This feature allows the device to efficiently handle power over a wide range of input supply levels. The dc-to-dc converter outputs 5.7 V typical, and has an overcurrent limit of 1 ...
Page 8
... When emerging from disabled mode, the buck converter switching regulator does not operate until the charge pump has stabilized (≈ 300 μs). Enabled Mode. When one or both of the signal input pins, ENBAT and ENB, are in the high state, the A8450 is enabled. 3.3 V and Adjustable Regulators Overcurrent Foldback 6 ...
Page 9
... ENBAT is an edge-triggered enable (logic 1 ≥ 2.7 V), which is used to enable the A8450 in response to a high-voltage signal, such as from an automobile ignition or battery switch. In this capacity, ENBAT is used only as a momentary switch to wake up the device. If there is no need for a high-voltage signal, ENBAT can be pulled low continuously. ...
Page 10
... RIPPLE(max) L1OFF where L (μH) is the inductance for the selected component, L1 and V is the voltage (V) through the inductor when the L1OFF A8450 is in the quiescent state L1OFF REG(max) D1 where V (V) is the voltage drop on diode D1 the total load current, and R ...
Page 11
... Packaged for sufficient power dissipation. In order to ensure appropriate thermal handling, the design of the ap- plication must take into consideration the thermal charac- teristics of the PCB where the A8450 and pass transistors are mounted, the ambient temperature, and the power dissipation characteristics of the transistor packages. In ...
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... OUT where – V – V DROP REG RCL A8450KLB-DS, Rev. 2 Automotive Multioutput Voltage Regulator Assume that V Assume also that T – V OUT the MPSW06 npn transistor, beta = 300 at 125˚C). In order to determine the resistance values for the current- limiting and drop resistors terms ...
Page 13
... PWM enabled. This occurs at V cycle, DC, of the A8450 can be forced to 100% until V VADJBD(max) high enough to allow the switch to begin operating normally. × (V – V – 0.7 V) REG ADJ The point at which normal switching begins is dependent on ambient temperature, T increase ...
Page 14
... Regulator Bypass Some applications may not require the use of all four regula- tors provided in the A8450. For the regulators that are not used, the corresponding external components are not needed. If either or both of the two 5 V regulators are not required by the application, bypass an unused regulator by not connect- ing its output terminal, V5D or V5A ...
Page 15
... The in for ma tion in clud ed herein is believed rate and reliable. How ev er, Allegro MicroSystems, Inc. assumes no re spon si bil i ty for its use; nor for any in fringe ment of patents or other rights of third parties which may result from its use. Copyright©2004 AllegroMicrosystems, Inc. A8450KLB-DS, Rev. 2 Automotive Multioutput Voltage Regulator 24-Pin SOIC 15 ...