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TC18C43 TC28C43 TC38C43 BiCMOS CURRENT MODE PWM CONTROLLERS
FEATURES
s s s s s s s s s s s s s s Low Power BiCMOS Design Tough CMOSTM Construction Low Supply Current ............. 1.0mA Typ @ 100kHz Wide Supply Voltage Operation .............. 8V to 15V Latch-Up Immunity ................... 500mA on Outputs Input Will Withstand Negative Inputs to - 5 Volts High Output Drive .................................... 0.7A Peak (1.2A on 14-Pin and 16-Pin Versions) 2 kV ESD Protection Current Mode Control Fast Rise/Fall Time (Max) ........... 60nsec @ 1000pF High Frequency Operation ..........................500kHz Clock Ramp Reset Current ................. 2.5mA 10% Low Propagation Delay Current Amp to Output ............................................ 140nsec Typ. Pin Compatible with UC3843
1
GENERAL DESCRIPTION
The TC38C43 is a current mode BiCMOS PWM control IC. With a low 1.0 mA supply current along with high drive current (0.7A peak) it provides a low cost solution for a PWM that operates to 500 kHz and directly drives MOSFETs up to HEX 3 size. Performance of the oscillator and current sense amplifier have been greatly improved over previous bipolar versions. Voltage and temperature stability have been improved by a factor of 3. Noise immunity (PSRR) has also been improved. The TC38C43 is pin compatible with the earlier bipolar version so that designers can easily update older designs. Improvements have been added, though. For example, clock ramp reset current is specified at 2.5mA (10%) for accurate dead time control. A few component values must be changed (RT & CT) to use the TC38C43 in existing bipolar designs. The 14-pin DIP and 16-pin SOIC versions have separate and internally isolated grounds, and are rated for higher output current (1.2A). These separate grounds allow for `bootstrap' operation of the PWM to further improve efficiency. FUNCTIONAL BLOCK DIAGRAM
2 3 4 5 6 7
PIN NUMBERS FOR 14-PIN DIP
ORDERING INFORMATION
Part No. TC18C43MJA TC18C43MJD TC28C43EOE TC28C43EPA TC28C43EPD TC38C43COE TC38C43CPA TC38C43CPD Package 8-Pin CerDIP 14-Pin CerDIP Temperature - 55C to +125C - 55C to +125C
16-Pin SOIC (Wide) - 40C to +85C 8-Pin Plastic DIP - 40C to +85C 14-Pin Plastic DIP - 40C to +85C 16-Pin SOIC (Wide) 8-Pin Plastic DIP 14-Pin Plastic DIP 0C to +70C 0C to +70C 0C to +70C
VIN 12 VREF 2.5V 1.4V
VREF 14
RT/CT 7 OSC CLK 11 10 VDD OUTPUT POWER GROUND
PIN CONFIGURATIONS 8-Pin Plastic DIP
CMPTR VFB ISENSE RT / CT 1 2 3 4 8 VREF VIN OUTPUT GND 7 6 5
16-Pin SOIC (Wide)
NC NC CMPTR VFB ISENSE RT / CT 1 2 3 4 5 6 7 8 16 15 14 13 NC VREF VIN VDD OUTPUT GND POWER GND NC
UNDER VOLTAGE SECTION ANALOG GND 9
UV GOOD
8
TC18CMJA TC28CEPA TC38CCPA
0.4V SENSE 5- +
PWM COMPARATOR + SQ - CLK R
TC28CCOE TC38CEOE
12 11 10 9
14-Pin Plastic DIP
CMPTR NC VFB NC ISENSE NC RT / CT 1 2 3 4 5 6 7 14 VREF 13 NC 12 VIN
NC NC
ERROR AMP 2.5V VFB COMP 1 R 3 + - 2R
LIMIT BUFFER + - 1.4V
TC18CMJD TC28CEPD TC38CCPD
11 VDD 10 OUTPUT 9 8 GND POWER GND
8
TC38C43-7 10/21/96
TELCOM SEMICONDUCTOR, INC.
4-93
TC18C43 TC28C43 TC38C43
ABSOLUTE MAXIMUM RATINGS*
Supply Voltage ............................................................18V Maximum Chip Temperature ................................... 150C Storage Temperature ............................ - 65C to +150C Lead Temperature (Soldering, 10 sec) ................. +300C Package Thermal Resistance CerDip RJ-A ................................................ 150C/W CerDip RJ-C .................................................. 55C/W
BiCMOS CURRENT MODE PWM CONTROLLERS
PDIP RJ-A ................................................... 125C/W PDIP RJ-C ..................................................... 45C/W SOIC RJ-A ................................................... 250C/W SOIC RJ-C ..................................................... 75C/W Operating Temperature 18C4x ...................................... - 55C TA +125C 28C4x ........................................ - 40C TA +85C 38C4x ............................................. 0C TA +70C
ELECTRICAL CHARACTERISTICS unless otherwise stated, these specifications apply over specific temperature range. VIN = VDD = 15V; RT = 71 k; CT = 150 pF. TC18C43 TC28C43 TC38C43
Parameter Reference Section
Output Voltage Line Regulation Load Regulation Temp Stability Output Noise Voltage Long Term Stability Output Short Circuit TA = 25C, IO = 1mA 9.5V VIN 15V, IO = 1mA 1mA lO 11mA (Note 1) 10Hz f 10 kHz,TA = 25C (Note 1) TA = 125C, 1000 Hrs. (Note 1) 4.9 -- -- -- -- -- -20 90 -- -- 2.25 2.45 1 -- -- 70 650 80 1.2 3 5.65 0.1 -- -- 2.8 0.85 70 -- -- 5 3 5 0.25 100 0.5 -50 100 0.2 0.01 2.5 2.65 -- 15 0.3 90 750 100 1.5 3.4 6 0.7 5 3 2.9 0.95 80 0.3 140 5.1 10 15 0.5 -- -- -100 110 0.3 0.05 2.75 2.85 -- 50 2 -- -- -- -- -- 6.5 1.1 7 5 3.1 1.05 -- 2 160 4.90 -- -- -- -- -- -30 93.8 -- -- 2.25 2.45 1 -- -- 70 650 80 1.5 3.9 5.65 0.1 -- -- 2.8 0.85 70 -- -- 5 3 3 0.25 100 0.5 -50 100 0.2 0.01 2.5 2.65 -- 15 0.3 90 750 100 1.7 4.2 6 0.7 5 3 2.9 0.95 80 0.3 140 5.10 10 10 0.5 -- -- -100 106.5 0.3 0.03 2.75 2.85 -- 50 2 -- -- -- -- -- 6.5 1.1 7 5 3.1 1.05 -- 2 150 V mV mV mV/C V(rms) % mA kHz % %/C mA V MHz mV nA dB kHz dB mA mA V V sec sec V/V V dB nA nsec
Test Conditions
Min
Typ
Max
Min
Typ
Max
Units
Oscillator Section
Initial Accuracy Voltage Stability Temp Stability Clock Ramp Reset Amplitude Maximum Freq TA = 25C (Note 4) 9.5V VIN 15V TMIN TA TMAX (Note 1); Figure 2 RT/CT Pin at 4V RT/CT Pin Peak to Peak Note 1 V(CMPTR) = 2.5V (Note 1) 2V VO 4V (Note 1) 9.5V VIN 15V VFB = 2.7V, V(CMPTR) = 1.1V (Note 1) VFB = 2.3V, V(CMPTR) = 5V (Note 1) VFB = 2.3V, RL = 10k to Ground VFB = 2.7V, RL = 10k to VREF Note 1 Note 1 Notes 2 & 3 V(CMPTR) = 5V (Note 2) 9.5V VIN 15V (Notes 1, 2 & 5) Note 1 V(ISENSE) = 1V (Note 1); Figure 3
Error Amp Section
Input Offset Voltage Input Bias Current AVOL Gain Bandwidth Product PSRR Output Sink Current Output Source Current VOUT High VOUT Low Rise Response Fall Response
Current Sense Section
Gain Ratio Maximum Input Signal PSRR Input Bias Current Delay to Output
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TELCOM SEMICONDUCTOR, INC.
BiCMOS CURRENT MODE PWM CONTROLLERS
TC18C43 TC28C43 TC38C43
1
ELECTRICAL CHARACTERISTICS (Cont): unless otherwise stated, these specifications apply over specified
temperature range. VIN = VDD = 15V; RT = 71 k; CT = 150 pF. TC18C4X TC28C4X Parameter Output Section
RDS RDS
2
TC38C4X Max
15 20 60 60 -- 18 8.8 7.9 100 0 300 2
Test Conditions
ISINK = 20mA ISOURCE = 20mA CL = 1nF (Note 1) CL = 1nF (Note 1) In Coulombs (Note 1) Note 1 x8C43 x8C43 x8C43 (Note 1)
Min
-- -- -- -- -- -- 7.9 7.2 95
Typ
7 11 40 30 6.5 -- 8.4 7.6 97
Min
-- -- -- -- -- -- 7.9 7.2 95
Typ
7 11 35 30 6.5 -- 8.4 7.6 97
Max
15 15 60 40 -- 18 8.8 7.9 100 0 300 1.5
Units
nsec nsec nC V V V % % A mA
(ON) (ON) Rise Time Fall Time Cross Conduction VDD Ma Start Threshold Undervoltage Threshold
3 4 5 6 7
Undervoltage Lockout Section
PWM Section
Maximum Duty Cycle Minimum Duty Cycle
Supply Current
Start Up Operating TA = 25C, VIN < VUV; Figure 1 VFB = V(ISENSE) = 0V; Figure 4 50 170 1 50 170 1
NOTES: 1. These parameters, although guaranteed over the recommended operating conditions, are not tested in production. 2. Parameter measured at trip point of latch. 3. Gain ratio is defined as: VCOMP V(ISENSE)
where 0 V(ISENSE) 0.8V 4. Output frequency equals oscillator frequency for the x8C43. 5. PSRR of VREF, Error Amp and PWM Comparator combination.
TelCom Semiconductor reserves the right to make changes in the circuitry or specifications detailed in this manual at any time without notice. Minimums and maximums are guaranteed. All other specifications are intended as guidelines only. TelCom Semiconductor assumes no responsibility for the use of any circuits described herein and makes no representations that they are free from patent infringement. *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.
PIN DESCRIPTION
Pin No. 8-Pin Pin No 14-Pin
2 4 1 3 5 7
Pin No 16-Pin
1 2 3 4 5 6
Symbol
NC NC CMPTR VFB ISENSE RT/CT
Description
No Connection No Connection Compensation of the feedback loop response. Feedback of voltage to error amplifier to regulate voltage. For sensing pass transistor current and terminate drive when current limit threshold is reached at this pin. Capacitor and resistor input to set oscillator frequency of this PWM controller. The resistor is connected from VREF output to RT/CT. The capacitor is connected from RT/CT to ANALOG GND.
4-95
1 2 3 4
8
TELCOM SEMICONDUCTOR, INC.
TC18C43 TC28C43 TC38C43
PIN DESCRIPTION (Cont.)
Pin No. 8-Pin Pin No 14-Pin
6 13 8 9 10 11 12 14
BiCMOS CURRENT MODE PWM CONTROLLERS
Pin No 16-Pin
7 8 9 10 11 12 13 14 15 16
Symbol
NC NC NC POWER GROUND ANALOG GND OUTPUT VDD VIN VREF NC
Description
No Connection No Connection No Connection Ground return of output driver. For all the low level analog signal returns. Output to drive switching transistor gate input. Supply power input terminal for the output drivers. Voltage bias supply of all PWM Controller circuit functions. Reference: 5.0 volt output. No Connection.
5 6 7 8
REFERENCE SECTION
The reference is a zener-based design with a buffer amplifier to drive the output. It is unstable with capacitances between 0.01F and 3.3F. In a normal application a 4.7F is used. In some lower noise layouts the capacitor can be eliminated entirely. The reference is active as soon as the 38C4x has power supplied. This is different than its bipolar counterparts, in that the bipolar reference comes on only after the IC has come out of its under voltage mode. Thus, on the 38C4x, the reference pin can not be used as a reset function such as on a soft start circuit. fO
1 (RT in Ohms and CT in Farads) RT CT
The value of RT affects the discharge current and the upper and lower comparators each have delays. As RT gets smaller and as the frequency of operation gets higher, the above equation is no longer valid.
14
VREF (5V)
OSCILLATOR SECTION
The oscillator frequency is set by the combination of a resistor from the reference to the RT/CT pin and by a capacitor from this pin to ground. The oscillator is designed to have ramp amplitude from 0.15 to 2.5 volts. This is approximate, as over shoot on the oscillator comparator causes the ramp amplitude to increase with frequency due to comparator delay. Minimum values for CT and RT are 33pF and 1k respectively. Maximum values are dependent on leakage currents in the capacitor, not on the input currents to the RT/CT pin.
RT 7 RT/CT CT 9 GND
PIN NUMBERS FOR 14-PIN DIP
FREQUENCY OF OPERATION
The frequency of oscillation for the TC38C43 is controlled by a resistor to VREF (RT) and a capacitor to ground (CT). VREF supplies current through the resistor and charges the capacitor until its voltage reaches the threshold of the upper comparator (2.5V). A 2.5mA current is then applied to the capacitor to discharge it to near ground (0.15V). The discharge current is then shut off and the cycle repeats. An approximate equation for the frequency of operation is:
4-96
TELCOM SEMICONDUCTOR, INC.
BiCMOS CURRENT MODE PWM CONTROLLERS
TC18C43 TC28C43 TC38C43
Current is sensed through voltage drop across resistor RS. A small RC filter may be required to suppress switching transient. This voltage enters PWM Controller at ISENSE, pin 5. A voltage of 0.4 V is added before this is fed into PWM Comparator (+) input. The PWM Comparator (-) input senses the voltage feedback error amp output with a limit buffer that limits this voltage to 1.4V maximum. This limit buffer limits the peak current across RS to a maximum of 0.95V. In normal operation, the error amplifier controls the current limit threshold. SHUTDOWN METHODS
1
Dead Time
The value of RT has an effect on the discharge rate but the primary consideration is the value of CT. The time required to discharge the capacitor is approximately 1000 CT. UNDERVOLTAGE LOCKOUT RANGE
VIN
2 3 4
IS TCx8C43 VON = 8.4V VOFF = 7.6V 1mA TCx8C43
14
TCx38C43
TCx38C43
1 VREF CMPTR
170A 8.4 V 7.6V
VDD
5k
SHUTDOWN 9 5.1k 5 ISENSE
ANALOG GND
Undervoltage Lockout Range
The TCx8C43 PWM Controller is used where wide ranges of input voltage is not required. The range from starting Vin voltage threshold to under voltage threshold is approximately 9.5% of the starting voltage. The typical startup voltage is 8.4V and dropout voltage is 7.6V. This range is used most in DC-to-DC converter applications.
SHUTDOWN TO CURRENT SENSE RESISTOR
5 6 7
Duty Cycle Limit
The TCx8C43 PWM Controller has a duty cycle limit maximum of 99%. The oscillator is running at the same frequency as the output.
CURRENT SENSE CIRCUIT
ISENSE R 5 0.4V PWM COMPARATOR
Shutdown can be accomplished by either pulling ISENSE above 1 volt or pulling CMPTR, pin 1 to GND. This will set the PWM latch so that the output will remain low until the next clock pulse after the shutdown condition is removed.
BENCH TEST OPERATIONAL SIMULATION
The timing ramp (RT/CT) is buffered by the emitter fullpower and fed back to the ISENSE input. This ramp simulates the dI/dT current ramp which would flow through the primary of the transformer. The output voltage of the power supply is simulated by feeding some of the reference voltage into VFB. The combination of the two levels determined the operating characteristics of the current mode controller.
LIMIT BUFFER 2R
-
RS C GND 9
+
+ -
+ -
1.4V
ERROR AMP
R
PEAK CURRENT (IS) FORMULA: IS = 0.95V RS
8
4-97
TELCOM SEMICONDUCTOR, INC.
TC18C43 TC28C43 TC38C43
BiCMOS CURRENT MODE PWM CONTROLLERS
BENCH TEST OPERATIONAL SIMULATION
10k Q1
RT 100k
1
CMPTR
VREF
8 4.7F
5k 5k 10k
2N2222 OR EQUIV IRAMP
2 3 4
VFB ISENSE RT/CT
VIN OUTPUT GND
7 6 5 1F RL = 1k, 1W
VDD (15V)
GND
CT
TYPICAL CHARACTERISTICS
Start Current vs. Temperature
150 145 140 135
ISTART (A)
Oscillator Frequency Changes vs. Temperature
101 150 VIN = 15V 100
FREQUENCY (kHz) DELAY (nse c)
ISENSE to Out Delay
140 130 120 110 100 90 -55
VIN = VSTART
MAX TYP
130 125 120 115 110 105 MIN TYP 100 -60 -40 -20 0 20 40 60 80 100 120 140 TEMPERATURE (C)
99
98
97
96 -60 -40 -20 0 20 40 60 80 100120 140 TEMPERATURE (C)
0
25 50 70 TEMPERATURE (C)
125
4-98
TELCOM SEMICONDUCTOR, INC.
BiCMOS CURRENT MODE PWM CONTROLLERS
TC18C43 TC28C43 TC38C43
1
TYPICAL CHARACTERISTICS (Cont.)
IDD vs. Temperature
2.0 VIN = 15V f = 100kHz RT = 10 k RT = 22 k RT = 47 k RT = 100 k 10 nF
Frequency of Operation
10nF
Dead Time vs. CT
2 3
1.8
IDD (mA)
1.6
CT
1nF
CT
1nF
1.4
1.2
100pF 1.0 -60 -40-20 0 20 40 60 80 100 120 140 10 kHz TEMPERATURE (C)
100kHz FREQUENCY
1 MHz
100pF 100nsec
1 sec DISCHARGE TIME
10sec
1000 PDIP SLOPE = - 8mW/C CerDIP SLOPE = - 6.4mW/C
4 5
SOIC SLOPE = - 4mW/C 50 75 100 125 150 AMBIENT TEMPERATURE (C)
800
P D (mW)
600
400
200
0 25
6 7
8
TELCOM SEMICONDUCTOR, INC.
4-99

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