TC170COE

TC170 TELCOM | Alldatasheet

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Technical content

4-119TELCOM SEMICONDUCTOR, INC. TC170 CMOS CURRENT MODE PWM CONTROLLER

FEATURES

n Direct-Power MOSFET Drive n Differential Current-Sense Amplifier n Programmable Current Limit n Soft-Start Operation n Double-Pulse Suppression n Undervoltage Lockout n Available with Low OFF State Outputs n Low Power, Pin-Compatible Replacement for UC3846

ORDERING INFORMATION

Part No. Package Range TC170COE 16-Pin SOIC (Wide) 0 °C to +70°C TC170CPE 16-Pin Plastic DIP (Narrow) 0°C to +70°C GENERAL DESCRIPTION The TC170 brings low-power CMOS technology to the current-mode-switching power supply controller market. Maximum supply current is 3.8 mA. Bipolar current-mode control integrated circuits require five times more operating current. The dual totem-pole CMOS outputs drive power MOSFETs or bipolar transistors. The 50nsec typical output rise and fall times (1000pF capacitive loads) minimize MOSFET power dissipation. Output peak current is 300mA. The TC170 contains a full array of system-protection circuits (see features). Current-mode control lets users parallel power supply modules. Two or more TC170 controllers can be slaved together for parallel operation. Circuits can operate from a master TC170 internal oscillator or an external system oscillator. The TC170 operates from an 8V to 16V power supply. An internal 2%, 5.1V reference minimizes external compo- nent count. The TC170 is pin compatible with the Unitrode UC1846/2846/3846 bipolar controller. Other advantages inherent in current-mode control in- clude superior line and load regulation and automatic sym- metry correction in push-pull converters. 5.1-VOLT REFERENCE OSCILLATOR × 3.15 CURRENT AMPLIFIER PWM COMPARATOR POSITIVE FEEDBACK VIN SYNC (–) CURRENT SENSE INPUT (+) CURRENT SENSE INPUT COMP (+) ERROR AMP INPUT (–) ERROR AMP INPUT ERROR AMPLIFIER 100µA 0.75V LIMIT BUFFER AMPLIFIER 350mV LOCK-UP AMPLIFIER Q1 Q2 3.5kΩ SHUTDOWN COMPARATOR 350 mV 6k Ω SHUTDOWN CURRENT LIMIT/ SOFT-START ADJUST NOTE: Outputs low in OFF state. S S R Q C DQ Q GROUND VDD OUTPUT A ( ) PWM LATCH TC170 VREF – + R O C O VDD UNDERVOLTAGE LOCKOUT OUTPUT B ( ) TC170-5 10/1/96 FUNCTIONAL BLOCK DIAGRAM

4-120 TELCOM SEMICONDUCTOR, INC. ELECTRICAL CHARACTERISTICS: VIN = 16V, RO = 24kΩ , CO = 1 nF, TA = 25°C, unless otherwise indicated. Symbol Parameter Test Conditions Min Typ Max Unit Reference Voltage VREF Output Voltage I OUT = 1mA 5 5.1 5.3 V Line Regulation V IN = 8V to 16V 5 15 mV Load Regulation I OUT = 1mA to 10mA 13 20 mV VRTC Temperature Coefficient Over Operating Temperature Range 0.4 0.5 mV/ °C Oscillator Oscillator Frequency 35 42 46 kHz Voltage Stability V IN = 8V to 16V 1.1 1.5 %/V Temperature Stability Over Operating Temperature Range 5 10 % Error Amplifier VOS Input Offset Voltage 630 mV IB Input Bias Current 61n A VCMRR Common-Mode Input Voltage V IN = 8V to 16V 0 V DD – 2V V AVOL Open-Loop Voltage Gain V OUT = 1V to 6V 70 dB BW Unity Gain Bandwidth 1.2 MHz CMRR Common-Mode Rejection Ratio V CMV 0V to 14V 60 dB PSRR Power Supply Rejection Ratio V IN = 8V to 16V 60 dB Current Sense Amplifier Amplifier Gain Pin 3 = 0V to 1.1V 3 3.15 3.3 V/V Maximum Differential Input Signal VPIN4 – VPIN3 ≤1.1 V Common-Mode Input Voltage 0 V DD – 3V V Current Limit Adjust Current Limit Offset Voltage 0.5 1 V IB Input Bias Current 1n A Shutdown Terminal VTB Threshold Voltage 0.3 0.35 0.4 V VIN Input Voltage Range 0 V DD V Minimum Latching Current at Pin 1 125 µA Maximum Nonlatching Current at Pin 1 50 µA Output Stage VDD Output Voltage Pin 13 V IN – 0. 5 V IN VIN + 0.5 V VOL Output Low Level I SINK = 20mA 0.4 V VOL Output Low Level I SINK = 100mA 2 V ABSOLUTE MAXIMUM RATINGS* Plastic Package Thermal Resistance: CMOS CURRENT MODE PWM CONTROLLER TC170 Operating Temperature Range *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 perma- nent 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.

4-121TELCOM SEMICONDUCTOR, INC. ELECTRICAL CHARACTERISTICS (Cont.): VIN = 16V, RO = 24kΩ , CO = 1nF, TA = 25°C, unless otherwise indicated. Symbol Parameter Test Conditions Min Typ Max Unit Output Stage (Cont.) VOH Output High Level I SOURCE = 20mA V DD – 1V V VOL Output High Level I SOURCE = 100mA V DD – 4V V tR Output Rise Time C L = 1000pF 50 150 nsec tF Output Fall Time C L = 1000pF 50 150 nsec Undervoltage Lockout Start-Up Threshold 7.15 7.7 8.25 V Threshold Hysteresis 0.5 0.75 1 V Supply IS Standby Supply Current 2.7 3.8 mA Pin No. (16-Pin PDIP) Symbol Description 1 SOFT START/I LIM Soft Start Adjust / Current Limit. For setting the peak current threshold of sense inputs (pins 3 and 4). Second function of this pin is Soft-Start Adjust. 2V REF OUT Reference supply output of 5.1 volts. It can supply a minimum of 10mA. 3– I SENSE IN – Current Sense Input. Inverting input for sensing peak current of the pass transistor through series sense current monitor resistor. 4+ I SENSE IN + Current Sense Input. Non-inverting input used in conjunction with pin 3. This senses the positive end of current monitor resistor. 5 + ERROR AMP IN + Error Amp In. Non-inverting input for output voltage regulation. 6 – ERROR AMP IN – Error Amp In. Inverting input of the amplifier for the reference voltage. 7 CMPTR For compensation of the feedback loop response. O Timing capacitor (CO) input to set oscillator frequency in conjunction with pin 9, RO , resistor input. Second function is for setting crossover dead time of pin 11and 14 outputs. 9R O Timing resistor (RO) input to set oscillator frequency by setting constant current charge rate to charge capacitor CO . 10 SYNC For PWM controller oscillator synchronization of two or more controllers. or as a clock input to sync oscillator from external signal. 11 OUTPUT A A output drive of phase A from push pull transistors. 12 GND Ground return for all input and output pins. 13 V DD Supplies power to operate the output drivers only. 14 OUTPUT B Output of phase B from push pull transistors. 15 V IN Voltage bias supply for all TC170 circuits except the output transistors. 16 SHUTDOWN Input pin to disable both output drives to 0V OFF. PIN CONFIGURATIONS (DIP and SOIC) TC170 CPE SHDN VDD SOFT START/ ILIM OUTPUT B VREF – I SENSE IN + I SENSE IN + ERROR AMP IN CMPTR GND OUTPUT A SYNC R O OUT – ERROR AMP IN NOTE: Outputs LOW in "OFF" state. VIN C O ACOM TC170COE BUF VSS C INT –VREF C REF C REF C AZ CMPTR OUT A DIGITAL GND B VDD VIN VIN VREF CMOS CURRENT MODE PWM CONTROLLER TC170 PIN DESCRIPTION

4-122 TELCOM SEMICONDUCTOR, INC. CMOS CURRENT MODE PWM CONTROLLER TC170 Peak Current Limit Setup Resistors R1 and R2 at the current limit input (pin 1) set the TC170 peak current limit (Figure 1). The potential at pin 1 is easily calculated: V1 = V REF R1 + R2 R1 should be selected first. The shutdown circuit fea- ture is not latched for (VREF – 0.35)/R1 < 50µA and is latched for currents greater than 125µA. The error amplifier output voltage is clamped from going above V1 through the limit buffer amplifier. Peak current is sensed by RS and amplified by the current amplifier which has a fixed gain of 3.15. I PCL , the peak current limit, is the current that causes the PWM comparator noninverting input to exceed V1, the potential at the inverting input. Once the comparator trip point is exceeded, both outputs are disabled. I PCL is easily calculated: IPCL = V1 – 0.75V 3.15 (RS) where: V1 = VREF VREF = Internal voltage reference = 5.1V 3.15 = Gain of current-sense amplifier 0.75V = Current limit offset Both driver outputs (pins 11 and 14) are OFF (LOW) when the peak current limit is exceeded. When the sensed current goes below I PCL , the circuit operates normally. Output Shutdown The TC170 outputs can be turned OFF quickly through the shutdown input (pin 16). A signal greater than 350 mV at pin 16 forces the shutdown comparator output HIGH. The PWM latch is held set, disabling the outputs. Q2 is also turned ON. If V REF /R1 is greater than 125µA, positive feedback through the lock-up amplifier and Q1 keeps the inverting PWM comparator inverting input below 0.75V. Q3 remains ON even after the shutdown input signal is removed, because of the positive feedback. The state can be cleared only through a power-up cycle. Out- puts will be disabled whenever the potential at pin 1 is below 0.75V. The shutdown terminal gives a fast, direct way to dis- able the TC170 output transistors. System protection and remote shutdown applications are possible. R1 + R2 The input pulse to pin 16 should be at least 500 nsec wide and have an amplitude of at least 1V in order to get the minimum propagation delay from input to output. If these parameters are met, the delay should be less than 600nsec at 25°C; however, the delay time will increase as the device temperature rises. Soft Restart From Shutdown A soft restart can be programmed if nonlatched shut- down operation is used. A capacitor at pin 1 will cause a gradual increase in potential toward V1. When the voltage at pin 1 reaches 0.75V, the PWM latch set input is removed and the circuit establishes a regulated output voltage. The soft-start opera- tion forces the PWM output drivers to initially operate with minimum duty cycle and low peak currents. Even if a soft start is not required, it is necessary to insert a capacitor between pin 1 and ground if the current I L is greater than 125µA. This capacitor will prevent "noise triggering" of the latch, yet minimize the soft-start effect. Soft-Start Power-Up During power-up, a capacitor at R1, R2 initiates a soft- start cycle. As the input voltage (pin 15) exceeds the undervoltage lockout potential (7.7V), Q4 is turned OFF, ending undervoltage lockout. Whenever the PWM com- parator inverting input is below 0.5V, both outputs are disabled. When the undervoltage lockout level is passed, the capacitor begins to charge. The PWM duty cycle increases until the operating output voltage is reached. Soft-start operation forces the PWM output drivers to initially operate with minimum duty cycle and low peak current. Current-Sense Amplifier The current-sense amplifier operates at a fixed gain of 3.15. Maximum differential input voltage (VPIN4 – VPIN3) is 1.1V. Common-mode input voltage range is 0V to VIN – 3V. Resistive-sensing methods are shown in Figure 2. In Figure 2(A), a simple RC filter limits transient voltage spikes at pin 4, caused by external output transistor-collector capacitance. Transformer coupling (Figure 3) offers isola- tion and better power efficiency, but cost and complexity increase. In order to minimize the propagation delay from the input to the current amplifier to the output terminals, the current ramp should be in the order of 1µs in width (min). Typical time delay values are in the 300 to 400nsec region at 25°C. The delay time increases with device temperature so that at 50°C, the delay times may be increased by as much as 100nsec.

4-123TELCOM SEMICONDUCTOR, INC.

3.15 CURRENT-

Figure 1. R1 and R2 Set Maximum Peak Output Current Figure 2. Resistive Sensing

3.15 CURRENT-SENSE×

4-124 TELCOM SEMICONDUCTOR, INC.

3.15 CURRENT–

Figure 5. External Clock Synchronization Figure 4. Master/Slave Parallel Operation to make it an effective driver, a buffer is required (Figure 4). collector TTL driver should be used.

4-126 TELCOM SEMICONDUCTOR, INC. CMOS CURRENT MODE PWM CONTROLLER TC170 TYPICAL CHARACTERISTICS TA = +25°C C LOAD = 500pF VS = 16V Output Rise and Fall Times Output Rise and Fall Times Output Rise and Fall Times DIV 50nsec DIV DIV 5 nsec DIV TA = +25°C C LOAD = 1800pF VS = 16V TA = +25°C C LOAD = 1000pF VS = 16V DIV 50nsec DIV