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поискавой системы для электроныых деталей |
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поискавой системы для электроныых деталей |
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LT1769IGN датащи(PDF) 14 Page - Linear Integrated Systems |
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LT1769IGN датащи(HTML) 14 Page - Linear Integrated Systems |
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14 / 16 page  14 LT1769 1769fa APPLICATIONS INFORMATION Figure 11. Replacing the Input Diode CHARGE CURRENT (A) 0 40 50 2 1769 F09 30 20 0.5 1 1.5 70 60 NOTE: PEAK DIE TEMPERATURE WILL BE ABOUT 15 °C HIGHER AT 2A CHARGE CURRENT VIN = 19V VBAT = 12.3V VBOOST = 5V 2-LAYER BOARD ROOM TEMP = 24 °C 5 IN2 BOARD 25 IN2 BOARD BOARD AREA (IN 2) 0 45 40 35 30 25 20 15 10 15 25 1769 F08 510 20 30 35 MEASURED FROM AIR AMBIENT TO DIE USING COPPER LANDS AS SHOWN ON DATA SHEET 2-LAYER BOARD 4-LAYER BOARD Figure 8. LT1769 Thermal Resistance Figure 10. High Duty Cycle VIN SW BOOST SPIN SENSE BAT VCC VX 3V TO 6V CX 10 µF VBAT 1769 F11 C2 0.47 µF D2 D1 RX 50k Q2 Q1 LT1769 HIGH DUTY CYCLE CONNECTION Q1 = Si4435DY Q2 = TP0610L + + SW BOOST SPIN SENSE BAT VBAT C3 0.47 µF D2 LT1769 SW BOOST SPIN SENSE BAT VX 3V TO 6V CX 10 µF VBAT 1769 F10 C3 0.47 µF D2 LT1769 STANDARD CONNECTION HIGH DUTY CYCLE CONNECTION + + an 18V ±3% adapter is used to charge ten NiMH cells, the charger must put out approximaly 15V. A total of 1.6V is lost in the input diode, switch resistance, inductor resis- tance and parasitics, so the required duty cycle is 15/16.4 = 91.4%. The duty cycle can be extended to 93% by restricting boost voltage to 5V instead of using VBAT as is normally done. This lower boost voltage also reduces power dissipation in the LT1769, so it is a win-win decision. Connect an external source of 3V to 6V at VX node in Figure 10 with a 10 µF CX bypass capacitor. Lower Dropout Voltage For even lower dropout and/or reducing heat on the board, the input diode D3 can be replaced with a FET (see Figure 11). Connect a P-channel FET in place of the input diode with its gate connected to the battery causing the FET to turn off when the input voltage goes low. The problem is that the gate must be pumped low so that the FET is fully turned on even when the input is only a volt or two above the battery voltage. Also there is a turn-off speed issue. The FET should turn off instantly when the input is dead shorted to avoid large current surges from the battery back through the charger into the FET. Gate capacitance slows turn-off, so a small P-channel (Q2) is added to discharge the gate capacitance quickly in the event of an input short. The Q2 body diode creates the necessary pumping action to keep the gate of Q1 low during normal operation. Note that Q1 and Q2 have a VGS spec limit of 20V. This restricts VIN to a maximum of 20V. For low dropout operation with VIN > 20V consult factory. Figure 9. LT1769 Lead Temperature |
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