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| EVALUATION KIT AVAILABLE 1 TC7662A CHARGE PUMP DC-TO-DC CONVERTER FEATURES s s s s s s s Wide Operating Range ............................. 3V to 18V Increased Output Current .............................. 40mA Pin Compatible with ICL7662/SI7661/TC7660/ LTC1044 No External Diodes Required Low Output Impedance @ IL = 20mA ....... 40 Typ. No Low-Voltage Terminal Required CMOS Construction GENERAL DESCRIPTION The TC7662A is a pin-compatible upgrade to the Industry standard TC7660 charge pump voltage converter. It converts a +3V to +18V input to a corresponding - 3V to -18V output using only two low-cost capacitors, eliminating inductors and their associated cost, size and EMI. In addition to a wider power supply input range (3V to 18V versus 1.5V to 10V for the TC7660), the TC7662A can source output currents as high as 40mA. The on-board oscillator operates at a nominal frequency of 12kHz. Operation below 10kHz (for lower supply current applications) is also possible by connecting an external capacitor from OSC to ground. The TC7662A directly is recommended for designs requiring greater output current and/or lower input/output voltage drop. It is available in 8-pin DIP packages in commercial and extended temperature ranges. PIN CONFIGURATION NC 1 C + 2 3 4 5 6 ORDERING INFORMATION Part No. TC7662ACPA TC7662AEPA TC7662AIJA TC7662AMJA TC7660EV Package Temperature Range 8-Pin Plastic DIP 0C to +70C 8-Pin Plastic DIP - 40C to +85C 8-Pin CerDIP - 25C to +85C 8-Pin CerDIP - 55C to +125C Evaluation Kit for Charge Pump Family 8 VDD 7 OSC 2 GND 3 C- 4 TC7662A 6 NC 5 VOUT NC = NO INTERNAL CONNECTION FUNCTIONAL BLOCK DIAGRAM 8 I COSC 7 LEVEL SHIFT P SW1 2 CAP+ VDD + - Q F/F C Q COMPARATOR WITH HYSTERESIS VREF LEVEL SHIFT N SW4 + CP EXT GND 3 + LEVEL SHIFT TC7662A OUT N SW2 4 CAP - CR EXT 7 RL LEVEL SHIFT N SW3 5 VOUT TC7662A-5 9/11/96 8 4-77 TELCOM SEMICONDUCTOR, INC. CHARGE PUMP DC-TO-DC CONVERTER TC7662A ABSOLUTE MAXIMUM RATINGS* Supply Voltage V DD to GND .................................... +18V Input Voltage (Any Pin) ........... (V DD + 0.3) to (V SS - 0.3) Current Into Any Pin ................................................. 10mA Operating Temperature Range C Suffix .................................................. 0C to +70C I Suffix .............................................. - 25C to +85C E Suffix ............................................. - 40C to +85C M Suffix .......................................... - 55C to +125C Power Dissipation (TA 70C) Plastic DIP ......................................................730mW CerDIP............................................................800mW Package Thermal Resistance CPA, EPA JA .............................................. 140C/W IJA, MJA JA .................................................. 90C/W Storage Temperature Range ................ - 65C to +150C Lead Temperature (Soldering, 10 sec) ................. +300C ESD Protection ..................................................... 2000V Output Short Circuit ................. Continuous (at 5.5V Input) *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 = +25C (See Test Circuit), unless otherwise specified. Symbol V DD IS Parameter Supply Voltage Supply Current V DD = +15V Test Conditions RL = 0C TA +70C - 55C TA +125C 0C TA +70C - 55C TA +125C IL = 20mA, V DD = +15V IL = 40mA, V DD = +15V IL = 3mA, V DD = +5V V DD = +15V RL = 2 k VDD = +15V RL = Over Operating Temperature Range Min 3 -- -- -- -- -- -- -- -- -- -- 93 99 96 Typ -- 510 560 650 190 210 210 40 50 100 12 97 99.9 -- Max 18 700 -- -- -- -- -- 50 60 125 -- -- -- -- Unit V A V DD = +5V RO Output Source Resistance Oscillator Frequency Power Efficiency Voltage Efficiency COSC PEFF VEFF kHz % % 4-78 TELCOM SEMICONDUCTOR, INC. CHARGE PUMP DC-TO-DC CONVERTER TC7662A TEST CIRCUIT EPR 1 NC + 10 F CP 1 2 3 4 TC7662A 8 7 6 5 NC C OSC IS IL RL V (+5V) ESL ESR C + 2 3 4 5 6 7 VOUT (-5V) CR + 10 F Figure 1. Capacitor Equivalent Circuit APPLICATIONS INFORMATION Theory of Operation The TC7662A is a capacitive charge 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 C1 to the supply voltage, VDD. This assumes that the ON resistance of the MOSFETs in series with the capacitor produce a charging time (3 time constants) less than the ON time provided by the oscillator frequency, as shown: 3 (RDS(ON) C1) Note one of its characteristics is ESR (equivalent series resistance). This parasitic resistance winds up in series with the load. Thus, both voltage and power conversion efficiency are compromised if a low ESR capacitor is not used. For example, in the "Test Circuit", changing CP and CR capacitors from typical ESR to low ESR types, the effective converter output impedance changed from 45 to 40, an improvement of 12%. This applies to all types of capacitors, including film types (polyester, polycarbonate etc.). Some applications information suggests that the capacitor is not critical and attributes the limiting factor to the capacitor's reactance value. Let's examine this: XC = X 1 and ZC = C , DS 2f C where DS (duty cycle) = 50%. Thus, ZC 1.33 at f = 12kHz, where C = 10 F. For the TC7662A, f = 12,000Hz, and a typical value of C would be 10 F. This is a reactive impedance of 1.33. If the ESR is as great as 5, the reactive value is not as critical as it would first appear, since the ESR would dominate. The 5 value is typical of a general-purpose electrolytic capacitor. Synchronizing The TC7662A may be synchronized by connecting pin 7 of the TC7662A through a 100k resistor in series with a diode to a negative-going pulse source. The negative pulse voltage can be +5V with a 5 microsecond duration going negative to 0V. Q TTL 100 k Q TO PIN 7 TC7662A Capacitors In early charge pump converters, 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). TELCOM SEMICONDUCTOR, INC. Figure 2. Synchronization 4-79 8 CHARGE PUMP DC-TO-DC CONVERTER TC7662A TYPICAL APPLICATIONS Combined Negative Converter and Positive Multiplier V+ 1 2 CP2 + 10 F 3 4 CP1 + TC7662A 8 7 6 V 5 OUT + VD1 = -V+ VD2 + C R2 10 F VOUT = 2V+ -2VD C R1 10 F Lowering Output Resistance by Paralleling Devices V+ 1 2 CP1 + 10 F 3 4 TC7662A 8 7 6 5 CP2 + 10 F 1 2 3 4 TC7662A 8 7 6 5 CR 10 F + VOUT Positive Voltage Multiplier V+ 1 2 3 4 TC7662A 8 7 6 5 + VD1 VD2 CP 10 F + VOUT = 2V+-2 VD CR 10 F Split V+ In Half V+ 1 2 CP + 10 F 3 4 TC7662A 8 7 6 5 V+ VOUT = 2 CR + 100 F 4-80 TELCOM SEMICONDUCTOR, INC. CHARGE PUMP DC-TO-DC CONVERTER TC7662A TYPICAL CHARACTERISTICS Supply Current vs. Temperature 700 TA = +25C 1 Oscillator Frequency vs. CEXT 10k 2 3 SUPPLY CURRENT (A) 600 500 400 300 200 100 0 -60 -40 -20 0 20 40 60 80 TEMPERATURE (C) 100 120 140 V + = 5V + V = 15V FREQUENCY (Hz) 1k 100 10 1 10 100 1000 CAPACITANCE (pF) 10,000 Frequency vs. Temperature 20 160 Output Resistance vs. Temperature 4 5 16 14 12 10 8 6 -60 -40 -20 0 20 40 60 80 TEMPERATURE (C) 100 120 140 OUTPUT RESISTANCE ( ) 18 140 120 100 80 60 40 20 -60 -40 -20 V+ = 15V, IL = 20 mA V + = 5V, IL = 3 mA FREQUENCY (kHz) 0 20 40 60 80 TEMPERATURE (C) 100 120 140 6 7 Power Conversion Efficiency vs. I LOAD POWER CONVERSION EFFICIENCY (%) 110 100 90 80 70 60 50 40 30 20 10 0 8 16 48 24 32 40 56 LOAD CURRENT (mA) TA = +25C 64 72 80 SUPPLY CURRENT EFFICIENCY 165 150 110 100 Output Resistance vs. Input Voltage TA = +25C OUTPUT RESISTANCE () SUPPLY CURRENT (mA) 135 120 105 90 75 60 45 30 15 0 90 80 70 60 50 40 30 20 10 0 2 4 8 12 14 6 10 INPUT VOLTAGE (V) 16 18 20 4-81 20 mA 8 TELCOM SEMICONDUCTOR, INC. |
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