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SM72445 Fiches technique(PDF) 9 Page - Texas Instruments |
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SM72445 Fiches technique(HTML) 9 Page - Texas Instruments |
9 / 20 page SM72445 www.ti.com SNVS795 – MARCH 2012 CONFIGURABLE SETTINGS A/D pins A0, A2, A4, and A6 are used to configure the behavior of the SM72445 by adjusting the voltage applied to them through resistor dividers as shown in Figure 2, where RT1 to RT4 should be in the range of 20 k Ω. The voltages of the configuration pins are read and the operating mode is then set at start-up and after each reset of the device. Three different frequencies for the PWM operation of the H-bridge as well as two different implementations of the Panel Mode switch can be set on the ADC input channel 2 (pin A2). The table below lists the different conditions that a user can select on pin A2. Each frequency has a different associated dead time for the operation of the synchronous switches. When dedicated PM switch modes are used, the unit will stop switching the converter upon entering PM mode and the PM_OUT pin will switch at a high frequency to provide activation of a dedicated Panel Mode switch. When the H-bridge modes are used, the unit will keep the H-bridge switching at half the operating frequency (to reduce switching losses) and with a total input to output ratio of 1. The dead times are unchanged during this phase. Table 1. Programmable Settings on Pin A2 A2 PWM Frequency setting Panel Mode Operation 4.69 V HIGH Uses dedicated PM switch 4.06 V HIGH Uses dedicated PM switch 3.44 V LOW Uses H-bridge for PM operation 2.81 V MED. Uses H-bridge for PM operation 2.19 V HIGH Uses H-bridge for PM operation 1.56 V LOW Uses dedicated PM switch 0.94 V MED. Uses dedicated PM switch 0.31 V HIGH Uses dedicated PM switch The user can also select the output voltage slew rate, minimum current threshold and duration of Panel Mode after the soft-start period has finished, by changing the voltage level on pin A6 which is the input of ADC channel 6. The slew rate limiter takes control of the duty cycle if the output voltage rises faster than the programmed limit while the unit is running in Boost mode (output voltage higher than input voltage). The device will control the duty cycle so that the output voltage stays within the allowed slew rate. The slew rate is never limited in Buck mode (output voltage lower than input voltage). Table 2. Programmable Settings on Pin A6 A6 Output Voltage Starting Panel Mode MPPT Exit MPPT Start Starting boost ratio Slew Rate Limit Time Threshold (on Threshold (on AIOUT or AIIN) AIOUT) 4.69 V 10V/1.2s Not applicable 0 V 0 V N/A 4.06 V 10V/1.2s 60s 0.006xVDDA 0.010xVDDA 1:1 3.44 V 10V/1.2s 0s 0.023xVDDA 0.039xVDDA 1:1 2.81 V 10V/1.2s 120s 0.023xVDDA 0.039xVDDA 1:1 2.19 V 10V/1.2s Not applicable 0.006xVDDA 0.010xVDDA 1:1.2 1.56 V 10V/1.2s 60s 0.023xVDDA 0.039xVDDA 1:1 0.94 V 10V/0.6s 60s 0.023xVDDA 0.039xVDDA 1:1 0.31 V No slew rate limit 60s 0.023xVDDA 0.039xVDDA 1:1 PARAMETER DEFINITIONS Output Voltage Slew Rate Limit Settling Time: Time constant of the internal filter used to limit output voltage change. At the fast slew rate, the output voltage will be held for 60 ms for every 1V increase, whereas in the slow slew rate, the output voltage will be held for 120ms for every 1V increase. (See Figure 10). Starting PM Time: After initial power-up or reset, the output soft-starts and then enters Panel Mode for this amount of time. Copyright © 2012, Texas Instruments Incorporated Submit Documentation Feedback 9 Product Folder Links: SM72445 |
Numéro de pièce similaire - SM72445_15 |
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Description similaire - SM72445_15 |
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