TCM680 TELCOM | Alldatasheet

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Technical content

4-13TELCOM SEMICONDUCTOR, INC.

FEATURES

n 99% Voltage Conversion Efficiency n 85% Power Conversion Efficiency n Only 4 External Capacitors Required n Space Saving 8-Pin SOIC Design

APPLICATIONS

n ±10V From +5V Logic Supply n ±6V From a 3V Lithium Cell n Handheld Instruments n Portable Cellular Phones n LCD Display Bias Generator n Panel Meters n Operational Amplifier Power Supplies GENERAL DESCRIPTION The TCM680 is a dual charge pump voltage converter that develops output voltages of +2VIN and – 2VIN from a single input voltage of +2.0V to +5.5V. Common applica- tions include ±10V from a single +5V logic supply, and ±6V from a +3V lithium battery. The TCM680 is packaged in a space-saving 8-pin SOIC package and requires only four inexpensive external capacitors. The charge pumps are clocked by an on-board 8kHz oscillator. Low output source impedances (typically 150Ω ) provides maximum output currents of 10mA for each output. Typical power conversion efficiency is 85%. High efficiency, small installed size and low cost make the TCM680 suitable for a wide variety of applications that need both positive and negative power supplies derived from a single input voltage. TYPICAL OPERATING CIRCUIT PIN CONFIGURATIONS (DIP AND SOIC) C 1 C 1 VIN VOUT VOUT = (– 2 x VIN)VOUT VOUT = (2xV IN) GND GND GND TCM680 4.7µF 4.7µFC 4 4.7µF 2.0V<VIN < +5.5V 4.7µF +5V C 2 C 2 + + C 1 VOUT VOUT VOUT VOUT VIN GND C 1– VIN GND TCM680CPA TCM680EPA 2 7 3 6 4 5 TCM680COA TCM680EOA C 1 +C 2 C 1 C 2 C 2 C 2

ORDERING INFORMATION

Part No. Package Temperature TCM680COA 8-Pin SOIC 0 °C to +70°C TCM680CPA 8-Pin Plastic DIP 0 °C to +70°C TCM680EOA 8-Pin SOIC – 40 °C to +85°C TCM680EPA 8-Pin Plastic DIP – 40 °C to +85°C TC7660EV Charge Pump Family Evaluation Kit +5V TO ±10V VOLTAGE CONVERTER TCM680 EVALUATION KIT AVAILABLE TC660-2 9/4/96

4-14 TELCOM SEMICONDUCTOR, INC. Figure 1. Test Circuit ELECTRICAL CHARACTERISTICS: VIN = +5V, TA = +25°C, test circuit Figure 1, unless otherwise indicated. any circuits described herein and makes no representations that they are free from patent infringement. – Input. Capacitor C1 negative terminal. + Input. Capacitor C2 positive terminal. 3C 2– Input. Capacitor C2 negative terminal. OUT Output. Negative output voltage (–2VIN). 6V IN Input. Power supply voltage. + Input. Capacitor C1 positive terminal. indicated in the operation section of the specification is not implied. periods of time may affect device reliability.

4-16 TELCOM SEMICONDUCTOR, INC. TCM680 +5V TO ±10V VOLTAGE CONVERTER EFFICIENCY CONSIDERATIONS Theoretically a charge pump can approach 100% effi- ciency under the following conditions:

  • The charge Pump switches have virtually no offset and extremely low on resistance
  • Minimal power is consumed by the drive circuitry
  • The impedances of the reservoir and pump capaci- tors are negligible For the TCM680, efficiency is as shown below: Efficiency V + = VDD /(2VIN) VDD = 2VIN – V+DROP V+DROP = (I+OUT )(R+OUT ) Efficiency V– = VSS /(– 2VIN) VSS = 2VIN – V–DROP V–DROP = (I–OUT )(R–OUT ) Power Loss =( V+DROP )(I+OUT ) + (V–DROP )(I–OUT ) There will be a substantial voltage difference between (V+OUT – VIN) and VIN for the positive pump and between V+OUT and V –OUT if the impedances of the pump capacitors C1 and C2 are high with respect to the output loads. Larger values of reservoir capacitors C3 and C4 will reduce output ripple. Larger values of both pump and reservoir capacitors improve the efficiency. See "Capacitor Selection" in Applications Section.

Positive and negative Converter The most common application of the TCM680 is as a dual charge pump voltage converter which provides positive and negative outputs of two times a positive input voltage. The simple circuit of Figure 6 performs this same function using the TCM680 and external capacitors, C1, C2, C3 and C4. Figure 6. Positive and Negative Converter greater while C2 and C3 must be rated at 12VDC or greater. for different values of C3 and C4 (assume 1Ω ESR).

4-18 TELCOM SEMICONDUCTOR, INC. Figure 8. Split Supply Derived from 3V Battery

4-19TELCOM SEMICONDUCTOR, INC. TYPICAL CHARACTERISTICS 1 2 3 45 6 VIN (V) R OUT R OUT 300 250 200 150

100 OUTPUT RESISTANCE ( Ω )

OUT or V– OUT Output Resistance vs. VIN C 1 – C4 = 10µF -50 0 50 100 TEMPERATURE ( °C) 180 160 140 120 100OUTPUT SOURCE RESISTANCE ( Ω ) Output Source Resistance vs. Temperature 1 2 3 45 6 VIN (V) 1.4 1.2 1.0 0.8 0.6 0.4 0.2 SUPPLY CURRENT (mA) Supply Current vs. VIN NO LOAD 0 5 10 15 LOAD CURRENT (mA) 10.0 9.0 8.0 7.0 10.0 9.0 8.0 7.0 VOUT (V)VOUT (V) VOUT or VOUT vs. Load Current VIN = 5V VIN = 5V + – 0 2 4 68 1 0 OUTPUT CURRENT (mA) From V OUT TO VOUT Output Voltage vs. Output Current From VOUT to VOUT + – VIN = 5V IOUT = 10mA TCM680 +5V TO ±10V VOLTAGE CONVERTER