EVALUATION KIT AVAILABLE 1 TC962 HIGH CURRENT CHARGE PUMP DC-TO-DC CONVERTER 2 FEATURES GENERAL DESCRIPTION ■ ■ ■ ■ ■ ■ ■ ■ The TC962 is an advanced version of the industrystandard 7662 high-voltage DC-to-DC converter. Using improved design techniques and CMOS construction, the TC962 can source as much as 8mA versus the 7662’s 20mA capability. As an inverter, the TC962 can put out voltages as high as 18V and as low as 3V without the need for external diodes. The output impedance of the device is a low 28Ω (with the proper capacitors), voltage conversion efficiency is 99.9%, and power conversion efficiency is 97%. The low voltage terminal (pin 6) required in some 7662 applications has been eliminated. Grounding this terminal will double the oscillator frequency from 12kHz to 24kHz. This will allow the use of smaller capacitors for the same output current and ripple, in most applications. Only two external capacitors are required for inverter applications. In the event an external clock is needed to drive the TC962 (such as paralleling), driving this pin directly will cause the internal oscillator to sync to the external clock. Pin Compatible With TC7662/ICL7662/SI7661 High Output Current ....................................... 80mA No External Diodes Required Wide Operating Range ............................. 3V to 18V Low Output Impedance ............................. 28Ω Typ. No Low Voltage Terminal Required Application Zener On Chip OSC Frequency Doubling Pin Option for Smaller Output Capacitors PIN CONFIGURATIONS (DIP and SOIC) 8-Pin DIP 8-Pin CerDIP ZENER CATHODE + C GND – C 1 • 8 2 3 4 TC962CPA TC962EPA TC962IJA TC962MJA 7 VDD COSC 6 FREQ x 2 5 VOUT 16-Pin SOIC Wide ZENER CATHODE 1 16 VDD NC C+ 2 15 NC 3 14 NC 4 13 NC GND 5 12 FREQ x 2 NC 6 11 NC 7 10 VOUT 8 9 C– NC TC962COE COSC NC Part No. Package TC962COE TC962CPA TC962EPA TC962IJA TC962MJA TC7660EV 16-Pin SOIC Wide 0°C to +70°C 8-Pin Plastic DIP 0°C to +70°C 8-Pin Plastic DIP – 40°C to +85°C 8-Pin CerDIP – 25°C to +85°C 8-Pin CerDIP – 55°C to +125°C Evaluation Kit for Charge Pump Family 8 Temp. Range FREQ X 2 – OSC/C TIMING 5 6 TC962 7 LEVEL SHIFT Q + – F/F C Q COMPARATOR WITH HYSTERESIS ZENER CATHODE VDD I I 4 ORDERING INFORMATION FUNCTIONAL BLOCK DIAGRAM 6 3 P SW1 2 LEVEL SHIFT N SW4 CAP + + CP EXTERNAL 3 GND 7 1 6.4V VREF + LEVEL SHIFT OUT 4 LEVEL SHIFT CR EXT N SW2 CAP – RL N SW3 8 5 VOUT TC962-8 9/16/96 TELCOM SEMICONDUCTOR, INC. 4-37 HIGH CURRENT CHARGE PUMP DC -TO-DC CONVERTER TC962 Pin 1, which is used as a test pin on the 7662, is a voltage reference zener on the TC962. This zener (6.4V at 5 mA) has a dynamic impedance of 12Ω and is intended for use where the TC962 is supplying current to external regulator circuitry and a reference is needed for the regulator circuit. (See applications section.) The TC962 is compatible with the LTC1044, SI7661, and ICL7662. It should be used in designs that require greater power and/or less input to output voltage drop. It offers superior performance over the ICL7660S. ABSOLUTE MAXIMUM RATINGS* Supply Voltage (VDD to GND) .................................. +18V Input Voltage Any Pin ............... (V DD + 0.3) to (V SS – 0.3) Current Into Any Pin ................................................. 10mA ESD Protection ..................................................... ±2000V Output Short Circuit ................. Continuous (at 5.5V Input) Storage Temperature Range ................ – 65°C to +150°C Lead Temperature (Soldering, 10 sec) ................. +300°C Operating Temperature Range CPA, COE ............................................. 0°C to +70°C IJA .................................................... – 25°C to +85°C EPA .................................................. – 40°C to +85°C MJA ................................................ – 55°C to +125°C Package Power Dissipation (TA ≤ 70°C) SOIC ............................................................... 760mW PDIP ............................................................... 730mW CerDIP ............................................................800mW Package Thermal Resistance CerDIP, RθJ-A ................................................ 90°C/W PDIP, RθJ-A ................................................. 140°C/W *Static-sensitive device. Unused devices must be stored in conductive material. Protect devices from static discharge and static fields. Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only and functional operation of the device at these or any other conditions above those indicated in the operational sections of the specifications is not implied. Exposure to Absolute Maximum Rating Conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS: VDD = 15V, TA = +25°C (See Test Circuit), unless otherwise indicated. Symbol Parameter V DD IS Supply Voltage Supply Current V DD = 15V V DD = 5V RO Output Source Resistance COSC Oscillator Frequency PEFF Power Efficiency VDEF Voltage Efficiency VZ ZZT 4-38 Zener Voltage Zener Impedance Test Conditions Min Typ 3 RL = ∞ TA = +25°C 0 ≤ TA ≤ +70°C –55 ≤ TA ≤ +125°C TA = +25°C 0 ≤ TA < +70°C –55 ≤ TA ≤ +125°C IL = 20mA, V DD = 15V IL = 80mA, V DD = 15V IL = 3mA, V DD = 5V Pin 6 Open Pin 6 GND V DD = 15V RL = 2 kΩ V DD = 15V RL = ∞ Over Temperature Range IZ = 5mA IL = 2.5mA to 7.5mA Max Unit 18 V — — — 700 93 510 560 650 190 210 210 32 35 — 12 24 97 — µA µA µA µA µA µA Ω Ω Ω kHz kHz % 99 99.9 — % 96 6.0 — — 6.2 12 6.4 % V Ω — — — 37 40 50 — TELCOM SEMICONDUCTOR, INC. HIGH CURRENT CHARGE PUMP DC -TO-DC CONVERTER 1 TC962 APPLICATIONS INFORMATION Theory of Operation The TC962 is a capacitive pump (sometimes called a switched capacitor circuit), where four MOSFET switches control the charge and discharge of a capacitor. The functional diagram (page 1) shows how the switching action works. SW1 and SW2 are turned on simultaneously, charging CP to the supply voltage, VIN. This assumes that the on resistance of the MOSFETs in series with the capacitor results in a charging time (3 time constants) that is less than the on time provided by the oscillator frequency as shown: 3 (RDS(ON) CP) <CP/(0.5 fOSC) In the next cycle, SW1 and SW2 are turned off and after a very short interval of all switches being off (this prevents large currents from occurring due to cross conduction), SW3 and SW4 are turned on. The charge in CP is then transferred to CR, BUT WITH THE POLARITY INVERTED. In this way, a negative voltage is now derived. Page 1 shows a functional diagram of the TC962. An oscillator supplies pulses to a flip-flop that is then fed to a set of level shifters. These level shifters then drive each set of switches at one-half the oscillator frequency. The oscillator has two pins that control the frequency of oscillation. Pin 7 can have a capacitor added that is returned to ground. This will lower the frequency of the oscillator by adding capacitance to the timing capacitor internal to the TC962. Grounding pin 6 will turn on a current source and double the frequency. This will double the charge current going into the internal capacitor, as well as any capacitor added to pin 7. A zener diode has been added to the TC962 for use as a reference in building external regulators. This zener runs from pin 1 to ground. This applies to all types of capacitors, including film types (polyester, polycarbonate, etc.). Some applications information suggest that the capacitor is not critical and attribute the limiting factor of the capacitor to its reactive value. Let's examine this: XC 1 XC = and ZC = , DS 2πf C where DS (duty cycle) = 50%. Thus, ZC ≈ 2.6Ω at f = 12kHz, where C = 10µF. For the TC962, f = 12,000 Hz, and a typical value of C would be 10µF. This is a reactive impedance of ' 2.6Ω. If the ESR is as great as 5Ω, the reactive value is not as critical as it would first appear, as the ESR would predominate. The 5Ω value is typical of a general-purpose electrolytic capacitor. ESL Figure 1. Typical Electrolytic Capacitor Latch Up All CMOS structures contain a parasitic SCR. Care must be taken to prevent any input from going above or below the supply rail, or latch up will occur. The result of latch up is an effective short between VDD and VSS. Unless the power supply input has a current limit, this latch-up phenomena will result in damage to the device. (See Application Note 31 for additional information.) TELCOM SEMICONDUCTOR, INC. 5 6 TEST CIRCUIT Capacitors In early charge pump converters, the capacitors were not considered critical due to the high RDS(ON) of the MOSFET switches. In order to understand this, let’s look at a model of a typical electrolytic capacitor (Figure 1). Note that one of its characteristics is ESR (equivalent series resistance). This parasitic resistance winds up in series with the load. Thus, both voltage conversion efficiency and power conversion efficiency are compromised if a low ESR capacitor is not used. In the test circuit, for example, just changing two capacitors, CP and CR, from capacitors with unspecified ESR to low ESR-type output, impedance changes from 36Ω to 28Ω, an improvement of 23%! 3 4 C ESR 2 690Ω NC + 10µF CP 1 8 2 7 3 4 IS IL C OSC TC962 V+ (+5V) RL 7 VOUT (–5V) 5 CR + 10µF 8 4-39 HIGH CURRENT CHARGE PUMP DC -TO-DC CONVERTER TC962 TYPICAL APPLICATIONS Split V + In Half Combined Negative Converter and Positive Multiplier V+ 1 8 2 7 + 10µF 3 CP2 TC962 6 5 4 VD1 VD2 VOUT = –V + C R1 + CP1 + V+ + VOUT = 2V +–2VD 10µF CP + 10µF 1 8 2 7 3 TC962 4 6 5 + VOUT = V 2 10µF CR Lowering Output Resistance by Paralleling Devices + 10µF Positive Voltage Multiplier V+ V+ CP1 + 10µF 1 8 1 8 1 8 2 7 2 7 2 7 6 3 3 4 TC962 6 5 CP2 + 10µF 3 4 TC962 4 5 CR 4-40 + VOUT 10µF TC962 VD1 VD2 6 5 CP + 10µF CP + VOUT = + 2V –2 VD 10µF TELCOM SEMICONDUCTOR, INC. HIGH CURRENT CHARGE PUMP DC -TO-DC CONVERTER 1 TC962 TYPICAL CHARACTERISTICS 20 700 V + = 15V 400 300 200 V + = 15V 18 FREQUENCY (kHz) 500 FREQUENCY (Hz) 1k 100 16 14 3 12 10 8 100 0 –60 –40 –20 10 0 20 40 60 80 100 120 140 6 1 10 100 1000 CAPACITANCE (pF) TEMPERATURE (°C) Output Resistance vs. Temperature Current vs. Zener Voltage CURRENT (mA) 60 + V = 5V IL = 3mA 40 TA = +25°C 40 30 20 V+ = 15V IL = 20mA 30 10 20 10 –60 –40 –20 0 20 40 60 80 100 120 140 TEMPERATURE (°C) 0 4.5 TA = +25°C 100 150 135 90 80 EFFICIENCY 120 105 70 SUPPLY CURRENT 60 90 75 50 40 60 30 45 20 30 10 15 5.5 6.0 ZENER VOLTAGE (V) 6.5 7.0 5 0 0 4.0 4 Power Conversion Efficiency vs. I LOAD POWER CONVERSION EFFICIENCY (%) 50 70 0 20 40 60 80 100 120 140 TEMPERATURE (°C) 80 50 –60 –40 –20 10,000 SUPPLY CURRENT (mA) SUPPLY CURRENT (µA) TA = +25°C 10k 600 OUTPUT RESISTANCE ( Ω) 2 Frequency vs. Temperature Oscillator Frequency vs. C EXT Supply Current vs. Temperature 8 16 24 32 40 48 56 64 72 80 LOAD CURRENT (mA) 6 Output Resistance vs. Input Voltage 110 TA = +25°C OUTPUT RESISTANCE (Ω) 100 90 80 70 3mA 60 20mA 7 50 40 30 20 10 0 2 4 6 8 10 12 14 16 18 INPUT VOLTAGE (V) 20 8 TELCOM SEMICONDUCTOR, INC. 4-41