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REG71055DDCTG4 Datasheet(PDF) 7 Page - Burr-Brown (TI) |
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REG71055DDCTG4 Datasheet(HTML) 7 Page - Burr-Brown (TI) |
7 / 18 page REG710 SBAS221E − DECEMBER 2001 − REVISED SEPTEMBER 2003 www.ti.com 7 THEORY OF OPERATION The REG710 regulated charge pump provides a regulated output voltage for input voltages ranging from less than the output to greater than the output. This is accomplished by au- tomatic mode switching within the device. When the input voltage is greater than the required output, the unit functions as a variable frequency switch-mode regulator. This opera- tion is shown in Figure 1. Transistors Q1 and Q3 are held off, Q4 is on, and Q2 is switched as needed to maintain a regu- lated output voltage. OFF SWITCHED Step−Down (Buck) Mode OFF ON C PUMP Q 1 Q 3 Q 2 Q 4 C IN C OUT V OUT V IN Figure 1. Simplified Schematic of the REG710 Operating in the Step-Down Mode When the input voltage is less than the required output voltage, the device switches to a step-up or boost mode of operation, as shown in Figure 2. A conversion clock of 50% duty cycle is generated. During the first half cycle the FET switches are configured as shown in Figure 2A, and CPUMP charges to VIN. During the second half cycle the FET switched are config- ured as shown in Figure 2B, and the voltage on CPUMP is added to VIN. The output voltage is regulated by skipping clock cycles as necessary. PEAK CURRENT REDUCTION In normal operation, the charging of the pump and output capacitors usually leads to relatively high peak input cur- rents which can be much higher than that of the average load current. The regulator incorporates circuitry to limit the input peak current, lowering the total EMI production of the device and lowering output voltage ripple and input cur- rent ripple. Input capacitor (CIN) supplies most of the charge required by input current peaks. PROTECTION The regulator has thermal shutdown circuitry that protects it from damage caused by overload conditions. The ther- mal protection circuitry disables the output when the junc- tion temperature reached approximately 160 °C, allowing the device to cool. When the junction temperature cools to approximately 140 °C, the output circuitry is automatically reenabled. Continuously running the regulator into thermal shutdown can degrade reliability. The regulator also pro- vides current limit to protect itself and the load. SHUTDOWN MODE A control pin on the regulator can be used to place the de- vice into an energy-saving shutdown mode. In this mode, the output is disconnected from the input as long as VIN is greater than or equal to minimum VIN and the input quies- cent current is reduced to 1 µA maximum. Step−Up (Boost) Mode (A) (B) OFF ON ON OFF CPUMP Q2 Q4 COUT VOUT CPUMP Q2 Q4 COUT V OUT OFF ON Q1 Q3 ON OFF Q1 Q3 CIN VIN CIN VIN Figure 2. Simplified Schematic of the REG710 Operating in the Step-Up or Boost Mode |
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