1 TC170 CMOS CURRENT MODE PWM CONTROLLER 2 FEATURES 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 component count. The TC170 is pin compatible with the Unitrode UC1846/2846/3846 bipolar controller. Other advantages inherent in current-mode control include superior line and load regulation and automatic symmetry correction in push-pull converters. ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Low Supply Current With CMOS Technology ................................. 3.8mA Max Internal Reference ............................................. 5.1V Fast Rise/Fall Times (CL = 1000pF) ............. 50nsec Dual Push-Pull Outputs Direct-Power MOSFET Drive High Totem-Pole Output Drive .................... 300mA Differential Current-Sense Amplifier Programmable Current Limit Soft-Start Operation Double-Pulse Suppression Undervoltage Lockout Wide Supply Voltage Operation ............... 8V to16V High Frequency Operation .......................... 200kHz Available with Low OFF State Outputs Low Power, Pin-Compatible Replacement for UC3846 ORDERING INFORMATION Temperature Range Part No. Package TC170COE TC170CPE 16-Pin SOIC (Wide) 0°C to +70°C 16-Pin Plastic DIP (Narrow) 0°C to +70°C 3 4 5 FUNCTIONAL BLOCK DIAGRAM VREF 2 VIN 15 RO 9 5.1-VOLT REFERENCE 13 TC170 CO SYNC (–) CURRENT SENSE INPUT (+) CURRENT SENSE INPUT COMP (+) ERROR AMP INPUT (–) ERROR AMP INPUT 8 11 UNDERVOLTAGE LOCKOUT OSCILLATOR D Q C Q 10 3 – 4 × 3.15 CURRENT AMPLIFIER + – + 0.75V 7 6 R Q – S + 14 S LIMIT BUFFER AMPLIFIER VDD 5 + PWM COMPARATOR 100µA 12 PWM LATCH 1 + – – 6 VDD OUTPUT A( ) OUTPUT B( ) GROUND 7 CURRENT LIMIT/ SOFT-START ADJUST Q4 ERROR AMPLIFIER SHUTDOWN COMPARATOR 350mV LOCK-UP AMPLIFIER 16 – + Q1 + Q2 – POSITIVE FEEDBACK SHUTDOWN 350 mV 6k Ω Q3 3.5k Ω 8 NOTE: Outputs low in OFF state. TC170-5 10/1/96 TELCOM SEMICONDUCTOR, INC. 4-119 CMOS CURRENT MODE PWM CONTROLLER TC170 ABSOLUTE MAXIMUM RATINGS* Supply Voltage ............................................................18V Output Voltage ................................................ VDD or 18V Analog Inputs ..................................... – 0.3V to VS + 0.3V Storage Temperature Range ................ – 65°C to +150°C Lead Temperature (Soldering, 10 sec) ................. +300°C Maximum Chip Temperature ................................... 150°C Plastic Package Thermal Resistance: θJA (Junction to Ambient) ............................. 140°C/W θJC (Junction to Case) ................................... 70°C/W Operating Temperature Range Commercial ........................................... 0°C to +70°C *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: VIN = 16V, RO = 24kΩ, CO = 1 nF, TA = 25°C, unless otherwise indicated. Symbol Parameter Test Conditions Min Typ Max Unit 5 5.1 5 13 0.4 5.3 15 20 0.5 V mV mV mV/°C 35 42 1.1 5 46 1.5 10 kHz %/V % 630 61 VDD – 2V mV nA V dB MHz dB dB 3.3 ≤1.1 VDD – 3V V/V V V 1 1 V nA 0.4 VDD 50 V V µA µA VIN + 0.5 0.4 2 V V V Reference Voltage VREF VRTC Output Voltage Line Regulation Load Regulation Temperature Coefficient IOUT = 1mA VIN = 8V to 16V IOUT = 1mA to 10mA Over Operating Temperature Range Oscillator Oscillator Frequency Voltage Stability Temperature Stability VIN = 8V to 16V Over Operating Temperature Range Error Amplifier VOS IB VCMRR AVOL BW CMRR PSRR Input Offset Voltage Input Bias Current Common-Mode Input Voltage Open-Loop Voltage Gain Unity Gain Bandwidth Common-Mode Rejection Ratio Power Supply Rejection Ratio VIN = 8V to 16V VOUT = 1V to 6V 0 70 VCMV 0V to 14V VIN = 8V to 16V 60 60 Pin 3 = 0V to 1.1V VPIN4 – VPIN3 3 1.2 Current Sense Amplifier Amplifier Gain Maximum Differential Input Signal Common-Mode Input Voltage 3.15 0 Current Limit Adjust IB Current Limit Offset Voltage Input Bias Current 0.5 Shutdown Terminal VTB VIN Threshold Voltage Input Voltage Range Minimum Latching Current at Pin 1 Maximum Nonlatching Current at Pin 1 0.3 0 125 0.35 Output Stage VDD VOL VOL 4-120 Output Voltage Output Low Level Output Low Level Pin 13 ISINK = 20mA ISINK = 100mA VIN – 0. 5 VIN TELCOM SEMICONDUCTOR, INC. CMOS CURRENT MODE PWM CONTROLLER 1 TC170 ELECTRICAL CHARACTERISTICS (Cont.): VIN = 16V, RO = 24kΩ, CO = 1nF, TA = 25°C, unless otherwise indicated. Symbol Parameter Test Conditions Min ISOURCE = 20mA ISOURCE = 100mA CL = 1000pF CL = 1000pF VDD – 1V VDD – 4V Typ Max Unit 50 50 150 150 V V nsec nsec 7.7 0.75 8.25 1 V V 2.7 3.8 mA Output Stage (Cont.) VOH VOL tR tF Output High Level Output High Level Output Rise Time Output Fall Time Undervoltage Lockout Start-Up Threshold Hysteresis Threshold 7.15 0.5 2 3 Supply IS Standby Supply Current PIN DESCRIPTION Pin No. (16-Pin PDIP) Symbol 1 SOFT START/ILIM 2 3 VREF OUT – ISENSE IN 4 + ISENSE IN 5 6 7 8 + ERROR AMP IN – ERROR AMP IN CMPTR CO 9 RO 10 SYNC 11 12 13 14 15 16 OUTPUT A GND VDD OUTPUT B VIN SHUTDOWN Description 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. Reference supply output of 5.1 volts. It can supply a minimum of 10mA. – Current Sense Input. Inverting input for sensing peak current of the pass transistor through series sense current monitor resistor. + Current Sense Input. Non-inverting input used in conjunction with pin 3. This senses the positive end of current monitor resistor. + Error Amp In. Non-inverting input for output voltage regulation. – Error Amp In. Inverting input of the amplifier for the reference voltage. For compensation of the feedback loop response. 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. Timing resistor (RO) input to set oscillator frequency by setting constant current charge rate to charge capacitor CO. For PWM controller oscillator synchronization of two or more controllers. or as a clock input to sync oscillator from external signal. A output drive of phase A from push pull transistors. Ground return for all input and output pins. Supplies power to operate the output drivers only. Output of phase B from push pull transistors. Voltage bias supply for all TC170 circuits except the output transistors. Input pin to disable both output drives to 0V OFF. CINT 1 16 VDD 15 VIN VSS 2 15 DIGITAL GND – I SENSE IN 3 14 OUTPUT B CAZ 3 14 CMPTR OUT + I SENSE IN 4 13 VDD BUF 4 13 B 12 GND ACOM 5 + ERROR AMP IN 5 – ERROR AMP IN 6 CMPTR 7 CO 8 16 SHDN TC170 CPE CREF 10 SYNC CREF 9 RO TELCOM SEMICONDUCTOR, INC. + – VREF TC170COE 12 A 6 11 + VIN 7 10 – VIN 8 9 VREF – 11 OUTPUT A 5 6 7 PIN CONFIGURATIONS (DIP and SOIC) SOFT START/ ILIM 1 VREFOUT 2 4 8 + NOTE: Outputs LOW in "OFF" state. 4-121 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 = VREF R2 R1 + R2 R1 should be selected first. The shutdown circuit feature 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. IPCL, 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. IPCL is easily calculated: IPCL = V1 – 0.75V 3.15 (RS) where: V1 = VREF R2 R1 + R2 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 IPCL, the circuit operates normally. 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 shutdown 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 operation 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 IL 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 softstart cycle. As the input voltage (pin 15) exceeds the undervoltage lockout potential (7.7V), Q4 is turned OFF, ending undervoltage lockout. Whenever the PWM comparator 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. Output Shutdown Current-Sense Amplifier 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 VREF/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. Outputs will be disabled whenever the potential at pin 1 is below 0.75V. The shutdown terminal gives a fast, direct way to disable the TC170 output transistors. System protection and remote shutdown applications are possible. 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 isolation 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 1 µs 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. 4-122 TELCOM SEMICONDUCTOR, INC. CMOS CURRENT MODE PWM CONTROLLER 1 TC170 SWITCH CURRENT 2 10 × 3.15 CURRENT-SENSE AMPLIFIER 4 3 RS PWM COMPARATOR + + – – "A" = 1 OUTPUT OFF (LOW) R + S 0.75V Q – 7 S FROM UNDERVOLTAGE LOCKOUT VDD 100 µA 5.1V VREF Q4 2 ERROR AMPLIFIER 5 + 6 – 3 PWM LATCH R1 1 + V1 – LIMIT BUFFER AMPLIFIER Q3 R2 – 16 + Q1 + 4 SHUTDOWN COMPARATOR LOCK-UP AMPLIFIER 350mV V1 Q2 – POSITIVE FEEDBACK 6k 5 350mV TC170 IL Figure 1. 3.5k R1 and R2 Set Maximum Peak Output Current 6 I × 3.15 CURRENTSENSE AMPLIFIER + I TC170 + RS – 3 4 7 3 TC170 *OPTIONAL RC FILTER (A) Ground Reference (B) Above-Ground Resistive Sensing Figure 2. TELCOM SEMICONDUCTOR, INC. VOUT × 3.15 CURRENTSENSE AMPLIFIER R* 4 C – RS Resistive Sensing 8 4-123 CMOS CURRENT MODE PWM CONTROLLER TC170 × 3.15 CURRENT– SENSE AMPLIFIER + – TC170 9 4 + VS – 3 N RO 1 TC170 IS 8 C O SYNC 10 MASTER I • RS VS = S N CMPTR 7 1/2 TC4427 Figure 3 Transformer Isolated Current Sense VDD Undervoltage Lockout The undervoltage lockout circuit forces the TC170 outputs OFF (low) if the supply voltage is below 7.7V. Threshold hysteresis is 0.75V and guarantees clean, jitter-free turn-on and turn-off points. The hysteresis also reduces capacitive filtering requirements at the PWM controller supply input (pin 15). 9 R O 8 4-124 10 7 SYNC CMPTR TC170 CO SLAVE Circuit Synchronization Current-mode-controlled power supplies can be operated in parallel with a common load. Paralleled converters will equally share the load current. Voltage-mode controllers unequally share the load current, decreasing system reliability. Two or more TC170 controllers can be slaved together for parallel operation. Circuits can operate from a master TC170 internal oscillator with an external driver (Figure 4). Devices can also be slaved to an external oscillator (Figure 5). Disable internal slave device oscillators by grounding pin 8. Slave controllers derive an oscillator from the bidirectional synchronization output signal at pin 10. Pin 10 is bidirectional in that it is intended to be both a sync output and input. This is accomplished by making the output driver "weak." This is advantageous in that it eliminates an additional pin from the package but does not enable the device to directly drive another device. In order to make it an effective driver, a buffer is required (Figure 4). In order to use pin 10 as a sync input, it is necessary to overcome the internal driver. This requires a pulse with an amplitude equal to VIN. Since VIN must be above 8.25V for the undervoltage lockout to be disabled, a CMOS or opencollector TTL driver should be used. 2 VREF Figure 4. Master/Slave Parallel Operation VDD 1/2 TC4427 EXTERNAL* OSCILLATOR 15 VIN 10 8 CO SYNC TC170 VREF RO 2 9 + VS *PULSE WIDTH OF OSCILLATOR IS = TD 15 VIN 10 SYNC TC170 VREF RO 2 Figure 5. CO 9 External Clock Synchronization TELCOM SEMICONDUCTOR, INC. CMOS CURRENT MODE PWM CONTROLLER 1 TC170 VDD 2 1 FO PIN 8 2.3V 4.3V ICHARGE 2.3V RO 8 10 + – ON-TIME 2.3V 3 PIN 10 9 OUTPUT DEAD TIME (TD) RO SYNC DISCHARGE CURRENT 1 mA CO 4 Figure 6 . Oscillator Circuit Oscillator Frequency and Output Dead Time 50 FO = [ 1.27 2800 – ROCO RO2CO ] CO CO + 150 × 10–12 where: RO = Oscillator Resistor (Ω) CO = Oscillator Capacitor (F) FO = Oscillator Frequency (Hz) The oscillator resistor can range from 5 kΩ to 50 kΩ. Oscillator capacitor can range from 250 pF to 1000 pF. Figure 7 shows typical operation for various resistance and capacitance values. During transitions between the two outputs, simultaneous conduction is prevented. Oscillator fall time controls the output off, or dead time (Figure 6). Dead time is approximately: TD = 2000 [CO] 1– ( ) 2.3 RO OSCILLATOR RESISTANCE (kΩ) The oscillator frequency for R O = 24kΩ and CO = 1000pF is: 45 5 TA = +25°C 40 35 30 25 20 250pF 15 10 6 500pF 5 1000pF 750pF 0 Figure 7. 20 40 60 80 100 120 140 160 180 200 OSCILLATOR FREQUENCY (kHz) Oscillator Frequency vs Oscillator Resistance 7 where: RO = Oscillator Resistor (kΩ) CO = Oscillator Capacitor (pF) TD = Output Dead Time (sec) Maximum possible duty cycle is set by the dead time. 8 TELCOM SEMICONDUCTOR, INC. 4-125 CMOS CURRENT MODE PWM CONTROLLER TC170 TYPICAL CHARACTERISTICS Output Rise and Fall Times Output Rise and Fall Times TA = +25°C CLOAD = 1800pF VS = 16V TA = +25°C CLOAD = 500pF VS = 16V Output Rise and Fall Times TA = +25°C CLOAD = 1000pF VS = 16V 5V DIV 5V DIV 50nsec DIV 5 nsec DIV 5V DIV 50nsec DIV 4-126 TELCOM SEMICONDUCTOR, INC.