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EVALUATION KIT AVAILABLE
1
TC962
HIGH CURRENT CHARGE PUMP DC-TO-DC CONVERTER
FEATURES
s s s s s s s s Pin Compatible With TC7662/ICL7662/SI7661 High Output Current ....................................... 80mA No External Diodes Required Wide Operating Range ............................. 3V to 18V Low Output Impedance ............................. 28 Typ. No Low Voltage Terminal Required Application Zener On Chip OSC Frequency Doubling Pin Option for Smaller Output Capacitors
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 28 (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.
2 3 4 5 6 7
PIN CONFIGURATIONS (DIP and SOIC)
8-Pin DIP 8-Pin CerDIP
ZENER CATHODE + C GND - C 1 2 3 4
*
TC962CPA TC962EPA TC962IJA TC962MJA
8 7 6 5
VDD COSC
FREQ x 2
V OUT
16-Pin SOIC Wide
ZENER CATHODE NC C+
NC GND NC
1 2 3 4 5 6 7 8
16 15 14 13
VDD
NC COSC NC FREQ x 2 NC
V OUT NC
TC962COE
12 11 10 9
ORDERING INFORMATION
Part No.
TC962COE TC962CPA TC962EPA TC962IJA TC962MJA TC7660EV
C-
NC
Package
Temp. Range
16-Pin SOIC Wide 0C to +70C 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
VDD TC962
FUNCTIONAL BLOCK DIAGRAM
8 FREQ X 2 - OSC/C TIMING 6 7 LEVEL SHIFT P SW1 2 CAP + I I
Q + - F/F C Q
COMPARATOR WITH HYSTERESIS
LEVEL SHIFT
N SW4
+ CP EXTERNAL 3 GND
ZENER CATHODE
1 6.4V VREF + LEVEL SHIFT OUT N SW2 4 - CR EXT
CAP
RL
LEVEL SHIFT
N SW3 5 VOUT
8
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 12 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. Package Power Dissipation (TA 70C) SOIC ............................................................... 760mW PDIP ............................................................... 730mW CerDIP ............................................................800mW Package Thermal Resistance CerDIP, RJ-A ................................................ 90C/W PDIP, RJ-A ................................................. 140C/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.
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 ................ - 65C to +150C Lead Temperature (Soldering, 10 sec) ................. +300C Operating Temperature Range CPA, COE ............................................. 0C to +70C IJA .................................................... - 25C to +85C EPA .................................................. - 40C to +85C MJA ................................................ - 55C to +125C
ELECTRICAL CHARACTERISTICS: VDD = 15V, TA = +25C (See Test Circuit), unless otherwise indicated.
Symbol
V DD IS
Parameter
Supply Voltage Supply Current V DD = 15V
Test Conditions
RL = TA = +25C 0 TA +70C -55 TA +125C TA = +25C 0 TA < +70C -55 TA +125C 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 k V DD = 15V RL = Over Temperature Range IZ = 5mA IL = 2.5mA to 7.5mA
Min
3
--
Typ
--
Max
18
--
Unit
V A A A A A A kHz kHz % % % V
--
V DD = 5V
RO
Output Source Resistance Oscillator Frequency Power Efficiency Voltage Efficiency
--
COSC PEFF VDEF
-- 93 99 96 6.0 --
510 560 650 190 210 210 32 35 -- 12 24 97 99.9 -- 6.2 12
700
37 40 50 -- -- --
VZ ZZT
Zener Voltage Zener Impedance
6.4
4-38
TELCOM SEMICONDUCTOR, INC.
HIGH CURRENT CHARGE PUMP DC -TO-DC CONVERTER 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) 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 2f C where DS (duty cycle) = 50%. Thus, ZC 2.6 at f = 12kHz, where C = 10F. For the TC962, f = 12,000 Hz, and a typical value of C would be 10F. This is a reactive impedance of 2.6. If the ESR is as great as 5, the reactive value is not as critical as it would first appear, as the ESR would predominate. The 5 value is typical of a general-purpose electrolytic capacitor.
1
2 3 4 5 6
ESL
ESR
C
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.) 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 36 to 28, an improvement of 23%! TELCOM SEMICONDUCTOR, INC.
1 2 + 10F CP 3 4
690 IS IL C OSC 5 RL VOUT (-5V) CR + 10F V+ (+5V)
NC
8 7 TC962
7
8
4-39
HIGH CURRENT CHARGE PUMP DC -TO-DC CONVERTER TC962
TYPICAL APPLICATIONS
Combined Negative Converter and Positive Multiplier
V+ 1 2 + 10F 3 CP2 4 CP1 + TC962 8 7 6 5 VOUT = -V + C R1 + 10F CR + 10F VD1 VD2 + VOUT = 2V +-2VD 10F CP + 10F 1 2 3 4 TC962 8 7 6 5 + VOUT = V 2
Split V + In Half
V+
Lowering Output Resistance by Paralleling Devices
V+
Positive Voltage Multiplier
V+
1 2 CP1 + 10F 3 4 TC962
8 7 6 5 CP2 + 10F
1 2 3 4 TC962
8 7 6 5 CR VOUT 10F
1 2 3 4 TC962
8 7 6 5 CP + 10F VD1 VD2 CP + VOUT = + 2V -2 VD 10F
+
4-40
TELCOM SEMICONDUCTOR, INC.
HIGH CURRENT CHARGE PUMP DC -TO-DC CONVERTER TC962
TYPICAL CHARACTERISTICS
Supply Current vs. Temperature
700 600 SUPPLY CURRENT (A) 500 400 300 200 100 0 -60 -40 -20 10 0 20 40 60 80 100 120 140 TEMPERATURE (C) 1 10 100 1000 10,000 CAPACITANCE (pF) V + = 15V 10k TA = +25C 18 FREQUENCY (kHz) 16 14 12 10 8 6 -60 -40 -20 0 20 40 60 80 100 120 140 TEMPERATURE (C)
1
Oscillator Frequency vs. C EXT
20
Frequency vs. Temperature
2 3 4
SUPPLY CURRENT (mA)
FREQUENCY (Hz)
1k
100
V + = 15V
Output Resistance vs. Temperature
80 OUTPUT RESISTANCE ( ) 70 60 50 40 30 20 10 -60 -40 -20 V+ = 15V IL = 20mA 10 0 4.5 + V = 5V IL = 3mA 50
Current vs. Zener Voltage
POWER CONVERSION EFFICIENCY (%) TA = +25C
Power Conversion Efficiency vs. I LOAD
100 90 80 70 60 50 40 30 20 10 0 8 16 24 32 40 48 56 64 72 80 SUPPLY CURRENT EFFICIENCY TA = +25C 150 135 120 105 90 75 60 45 30 15 0 LOAD CURRENT (mA)
CURRENT (mA)
40
30
20
5 6 7
0 20 40 60 80 100 120 140 TEMPERATURE (C)
4.0
5.5
6.0
6.5
7.0
ZENER VOLTAGE (V)
Output Resistance vs. Input Voltage
110 100 OUTPUT RESISTANCE () 90 80 70 60 50 40 30 20 10 0 2 4 6 8 10 12 14 16 18 INPUT VOLTAGE (V) 20 3mA 20mA TA = +25C
8
TELCOM SEMICONDUCTOR, INC.
4-41

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