TC18C43 TELCOM | Alldatasheet
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4-93TELCOM SEMICONDUCTOR, INC. BiCMOS CURRENT MODE PWM CONTROLLERS UNDER VOLTAGE SECTION VREF OSC ERROR AMP LIMIT BUFFER R CLK PWM COMPARATOR 2.5V 1.4V UV GOOD VREF R/T C T VDD OUTPUT10 PIN NUMBERS FOR 14-PIN DIP COMP VFB 2.5V SENSE ANALOG GND VIN CLK 0.4V – ++ S R POWER GROUND Q 1.4V+ TC38C43-7 10/21/96
FEATURES
n Tough CMOS TM Construction n Input Will Withstand Negative Inputs to – 5 Volts (1.2A on 14-Pin and 16-Pin Versions) n 2 kV ESD Protection n Current Mode Control n Low Propagation Delay Current Amp n Pin Compatible with UC3843
ORDERING INFORMATION
Part No. Package Temperature TC18C43MJA 8-Pin CerDIP – 55 °C to +125°C TC18C43MJD 14-Pin CerDIP – 55 °C to +125°C TC28C43EOE 16-Pin SOIC (Wide) – 40 °C to +85°C TC28C43EPA 8-Pin Plastic DIP – 40 °C to +85°C TC28C43EPD 14-Pin Plastic DIP – 40 °C to +85°C TC38C43COE 16-Pin SOIC (Wide) 0 °C to +70°C TC38C43CPA 8-Pin Plastic DIP 0 °C to +70°C TC38C43CPD 14-Pin Plastic DIP 0 °C to +70°C 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 ampli- fier have been greatly improved over previous bipolar ver- sions. Voltage and temperature stability have been im- proved 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 (R T & CT) to use the TC38C43 in existing bipolar designs. The 14-pin DIP and 16-pin SOIC versions have sepa- rate 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 effi- ciency. FUNCTIONAL BLOCK DIAGRAM VREFCMPTR OUTPUTISENSE VIN GNDR T /CT VFB TC18CMJA TC28CEPA TC38CCPA NCNC NC OUTPUT POWER GND GNDNC VREF VIN R T /CT ISENSE CMPTR VDD VFB 11 4 21 3 31 2 41 1 51 0 NCNC NC NC OUTPUT POWER GND GND NC VREF VINCMPTR VDDVFB TC18CMJD TC28CEPD TC38CCPD NC R T /CT ISENSE TC28CCOE TC38CEOE 14-Pin Plastic DIP 16-Pin SOIC (Wide)8-Pin Plastic DIP PIN CONFIGURATIONS TC18C43 TC28C43 TC38C43
4-94 TELCOM SEMICONDUCTOR, INC. ABSOLUTE MAXIMUM RATINGS* Package Thermal Resistance Operating Temperature ELECTRICAL CHARACTERISTICS unless otherwise stated, these specifications apply over specific temperature range. VIN = VDD = 15V; RT = 71 kΩ ; CT = 150 pF. TC18C43 TC28C43 TC38C43 Parameter Test Conditions Min Typ Max Min Typ Max Units Reference Section Output Voltage T A = 25°C, IO = 1mA 4.9 5 5.1 4.90 5 5.10 V Line Regulation 9.5V ≤ VIN ≤ 15V, IO = 1mA — ±3 ±10 — ±3 ±10 mV Load Regulation 1mA ≤ lO ≤ 11mA — ±5 ±15 — ±3 ±10 mV Temp Stability (Note 1) — ±0.25 ±0.5 — ±0.25 ±0.5 mV/ °C Output Noise Voltage 10Hz ≤ f ≤ 10 kHz,TA = 25°C (Note 1) — 100 — — 100 — µV(rms) Long Term Stability T A = 125°C, 1000 Hrs. (Note 1) — ±0.5 — — ±0.5 — % Output Short Circuit -20 -50 -100 -30 -50 -100 mA Oscillator Section Initial Accuracy T A = 25°C (Note 4) 90 100 110 93.8 100 106.5 kHz Temp Stability T MIN ≤ TA ≤ TMAX (Note 1); Figure 2 — ±0.01 ±0.05 — ±0.01 ±0.03 %/ °C Maximum Freq Note 1 1 — — 1 — — MHz Error Amp Section Input Offset Voltage V (CMPTR) = 2.5V — ±15 ±50 — ±15 ±50 mV Input Bias Current (Note 1) — ±0.3 ±2— ±0.3 ±2n A AVOL 2V ≤ VO ≤ 4V 70 90 — 70 90 — dB Gain Bandwidth Product (Note 1) 650 750 — 650 750 — kHz PSRR 9.5V ≤ VIN ≤ 15V 80 100 — 80 100 — dB Output Source Current VFB = 2.3V, V(CMPTR) = 5V (Note 1) 3 3.4 — 3.9 4.2 — mA Rise Response Note 1 — 5 7 — 5 7 µsec Fall Response Note 1 — 3 5 — 3 5 µsec Current Sense Section PSRR 9.5V ≤ VIN ≤ 15V (Notes 1, 2 & 5) 70 80 — 70 80 — dB Input Bias Current Note 1 — ±0.3 ±2— ±0.3 ±2n A Delay to Output V (ISENSE ) = 1V (Note 1); Figure 3 — 140 160 — 140 150 nsec TC18C43 TC28C43 TC38C43 BiCMOS CURRENT MODE PWM CONTROLLERS
4-95TELCOM SEMICONDUCTOR, INC. Output Section R DS (ON) I SINK = 20mA — 7 15 — 7 15 Ω R DS (ON) I SOURCE = 20mA — 11 20 — 11 15 Ω Rise Time C L = 1nF (Note 1) — 40 60 — 35 60 nsec Fall Time C L = 1nF (Note 1) — 30 60 — 30 40 nsec Cross Conduction In Coulombs (Note 1) — 6.5 — — 6.5 — nC VDD Ma Note 1 — — 18 — — 18 V Undervoltage Lockout Section PWM Section Maximum Duty Cycle x8C43 (Note 1) 95 97 100 95 97 100 % Minimum Duty Cycle 0 0 % Supply Current Start Up T A = 25°C, VIN < VUV ; Figure 1 50 170 300 50 170 300 µA Operating V FB = V(ISENSE ) = 0V; Figure 4 1 2 1 1.5 mA ELECTRICAL CHARACTERISTICS (Cont): unless otherwise stated, these specifications apply over specified temperature range. VIN = VDD = 15V; RT = 71 kΩ ; CT = 150 pF. TC18C4X TC28C4X TC38C4X Parameter Test Conditions Min Typ Max Min Typ Max Units 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. 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: DVCOMP DV(ISENSE ) 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. Pin No Pin No 8-Pin 14-Pin 16-Pin Symbol Description 2 1 NC No Connection 4 2 NC No Connection 1 1 3 CMPTR Compensation of the feedback loop response. 234 V FB Feedback of voltage to error amplifier to regulate voltage.
355 I SENSE For sensing pass transistor current and terminate drive when current
limit threshold is reached at this pin. 4 7 6 R T/CT 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. TC18C43 TC28C43 TC38C43 BiCMOS CURRENT MODE PWM CONTROLLERS
4-96 TELCOM SEMICONDUCTOR, INC. TC18C43 TC28C43 TC38C43 BiCMOS CURRENT MODE PWM CONTROLLERS Pin No. Pin No Pin No 8-Pin 14-Pin 16-Pin Symbol Description PIN DESCRIPTION (Cont.) 6 7 NC No Connection 13 8 NC No Connection
9 NC No Connection
8 10 POWER GROUND Ground return of output driver. 5 9 11 ANALOG GND For all the low level analog signal returns. 6 10 12 OUTPUT Output to drive switching transistor gate input. 11 13 V DD Supply power input terminal for the output drivers. 71 2 1 4 V IN Voltage bias supply of all PWM Controller circuit functions. 81 4 1 5 V REF Reference: 5.0 volt output. 16 NC No Connection. FREQUENCY OF OPERATION The frequency of oscillation for the TC38C43 is con- trolled 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: VREF PIN NUMBERS FOR 14-PIN DIP R T/CT GND (5V) R T C T REFERENCE SECTION The reference is a zener-based design with a buffer amplifier to drive the output. It is unstable with capacitances between 0.01µF and 3.3µF. In a normal application a 4.7µF 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 counter- parts, 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. 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 C T and RT are 33pF and 1kΩ respectively. Maximum values are depen- dent on leakage currents in the capacitor, not on the input currents to the R T/CT pin. 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.
4-97TELCOM SEMICONDUCTOR, INC. TC18C43 TC28C43 TC38C43 BiCMOS CURRENT MODE PWM CONTROLLERS 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 C Undervoltage Lockout Range The TCx8C43 PWM Controller is used where wide ranges of input voltage is not required. The range from starting V in voltage threshold to under voltage threshold is approximately 9.5% of the starting voltage. The typical start- up voltage is 8.4V and dropout voltage is 7.6V. This range is used most in DC-to-DC converter applications. 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 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 I SENSE , 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 can be accomplished by either pulling I SENSE 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. SHUTDOWN METHODS TCx8C43 VON = 8.4V VOFF = 7.6V IS 7.6V 8.4 V 1mA 170µA VDD VIN TCx8C43 ERROR AMP LIMIT BUFFER 1.4V2R R GND C R ISENSE 5 0.4V PWM COMPARATOR R S PEAK CURRENT (I S) FORMULA: IS = 0.95V R S CURRENT SENSE CIRCUIT ISENSE5 TCx38C43 VREF SHUTDOWN TO CURRENT SENSE RESISTOR 5.1k TCx38C43 SHUTDOWN ANALOG GND CMPTR 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 V FB . The combination of the two levels deter- mined the operating characteristics of the current mode controller. UNDERVOLTAGE LOCKOUT RANGE
4-98 TELCOM SEMICONDUCTOR, INC. TC18C43 TC28C43 TC38C43 BiCMOS CURRENT MODE PWM CONTROLLERS TYPICAL CHARACTERISTICS 150 145 140 135 130 125 120 115 110 105 100 –40 –20 0 20 40 60 80 100 120 140–60 MAX TYP MIN TYP TEMPERATURE ( °C) ISTART (µA) VIN = VSTART Start Current vs. Temperature 101 100
96 FREQUENCY (kHz)
–60 –40–20 0 20 40 60 80 100120 140 TEMPERATURE ( °C) VIN = 15V Oscillator Frequency Changes vs. Temperature 150 140 130 120 110 100 –55 0 2 55 07 0 1 2 5 TEMPERATURE ( °C) DELAY (nse c) ISENSE to Out Delay IRAMP 10k 10k C T 100k R T CMPTR VFB ISENSE R T/CT VREF VIN OUTPUT GND 1µF R L = 1k, 1W 4.7µF VDD (15V) GND 2N2222 OR EQUIV BENCH TEST OPERATIONAL SIMULATION
4-99TELCOM SEMICONDUCTOR, INC. TC18C43 TC28C43 TC38C43 BiCMOS CURRENT MODE PWM CONTROLLERS 1000 25 50 75 100 125 150 AMBIENT TEMPERATURE ( °C) P (mW)D 800 600 400 200 SOIC SLOPE = – 4mW/ °C CerDIP SLOPE = – 6.4mW/°C PDIP SLOPE = – 8mW/ °C TYPICAL CHARACTERISTICS (Cont.) DISCHARGE TIME C T 100nsec 100pF 1 µsec 10 µsec 1nF 10nF Dead Time vs. CT 2.0 1.8 1.6 1.4 1.2 1.0 –60 –40–20 0 20 40 60 80 100120 140 TEMPERATURE ( °C) IDD (mA) VIN = 15V f = 100kHz IDD vs. Temperature Frequency of Operation FREQUENCY C T 10 kHz 100pF 100kHz 1 MHz 1nF 10 nF R T = 10 k R T = 22 k R T = 47 k R T = 100 k