Datenblatt-Suchmaschine für elektronische Bauteile |
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AAT3171 Datenblatt(PDF) 12 Page - Advanced Analogic Technologies |
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AAT3171 Datenblatt(HTML) 12 Page - Advanced Analogic Technologies |
12 / 19 page AAT3171 High Current, High Efficiency Charge Pump with Auto-Timer 12 3171.2007.03.1.1 For examples of standard 1% values where the LED flash current level is targeted for 700mA, see Table 3. Table 3: Open-Drain I/O Example Resistor Values. If the I/O port must be configured as an open-drain PMOS type output, the appropriate equations can be generated from these same concepts. As done in the previous example, the necessary values can then be calculated. As a reference, the equations applicable to the PMOS case are: The value to use for VIO must come from the I/O supply voltage used in the system. 0.7V is the typ- ical value of the VRSET parameter found in the Electrical Characteristics. For a push-pull I/O port output configuration, first calculate the overall RSET value needed for the desired flash level LED current: Next, choose a reasonable value for R1. A value that is slightly larger than RSET, calculated from above, is appropriate. Calculate R2 and then calcu- late the torch mode current level that results: Once again, the current and resistance values used in the equations come from the conditions placed on the IDX parameter of the Electrical Characteristics table. 0.7V is the typical value for the VRSET param- eter. The value to use for VIO must come from the I/O supply voltage used in the system. Example standard 1% values are provided in Table 4. Table 4: Push-Pull I/O Example Resistor Values. In all of the approaches mentioned, the open-drain NMOS or PMOS type configurations offer the most flexibility for current level selection. When configured as an output, if the I/O port is only push-pull type, then the equivalent open-drain NMOS can also be realized. To realize this, acti- vate the port as output only when driving the line low. Otherwise, to release the line, set the port to be tri-stated. Device Power Efficiency The AAT3171 power conversion efficiency depends on the charge pump mode. By definition, device efficiency is expressed as the output power delivered to the LED divided by the total input power consumed. η = POUT PIN R1 R2 ILED ILED (k Ω Ω)(kΩ Ω) Torch (mA) Flash (mA) 169 1000 95 776 165 1000 111 792 162 1000 124 805 160 1000 132 813 ILED (torch) = 600mA · 187kΩ · - R2 - R1 R1 · R2 VIO 0.7V · R2 ⎛ ⎝ ⎞ ⎠ RSET · R1 R1 - RSET R2 = 600mA · 187kΩ ILED (flash) RSET = VIO 0.7 1 R1 ILED (torch) 600mA · 187kΩ R2 = - 1 - 600mA · 187kΩ ILED (flash) R1 = R1 R2 ILED ILED (k Ω Ω)(kΩ Ω) Torch (mA) Flash (mA) 920 193 122 703 732 205 153 701 649 210 173 707 562 223 200 703 |
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