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1
TC170 CMOS CURRENT MODE PWM CONTROLLER
FEATURES
s s s s s s s s s s s s s s s 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
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.
2 3 4 5 6 7
ORDERING INFORMATION
Part No. TC170COE TC170CPE Package Temperature Range
16-Pin SOIC (Wide) 0C to +70C 16-Pin Plastic DIP (Narrow) 0C to +70C
FUNCTIONAL BLOCK DIAGRAM
VREF 2 VIN RO CO SYNC (-) CURRENT SENSE INPUT (+) CURRENT SENSE INPUT COMP (+) ERROR AMP INPUT (-) ERROR AMP INPUT 15 5.1-VOLT REFERENCE TC170 9 8 10 3 4 7 VDD 5 6 + - ERROR AMPLIFIER 350mV LOCK-UP AMPLIFIER - Q1 + POSITIVE FEEDBACK 3.5k Q2 - 100A - + x 3.15 CURRENT AMPLIFIER + - 0.75V PWM COMPARATOR S - S LIMIT BUFFER AMPLIFIER + - Q4 SHUTDOWN COMPARATOR 16 + 350 mV 6k Q3 SHUTDOWN PWM LATCH 1 R Q OSCILLATOR UNDERVOLTAGE LOCKOUT DQ C Q 14 12 OUTPUT B( ) GROUND 11
13
VDD OUTPUT A( )
+
CURRENT LIMIT/ SOFT-START ADJUST
NOTE: Outputs low in OFF state.
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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 ................ - 65C to +150C Lead Temperature (Soldering, 10 sec) ................. +300C Maximum Chip Temperature ................................... 150C Plastic Package Thermal Resistance: JA (Junction to Ambient) ............................. 140C/W JC (Junction to Case) ................................... 70C/W Operating Temperature Range Commercial ........................................... 0C to +70C
*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 = 24k, CO = 1 nF, TA = 25C, unless otherwise indicated.
Symbol
VREF
Parameter
Output Voltage Line Regulation Load Regulation Temperature Coefficient Oscillator Frequency Voltage Stability Temperature Stability
Test Conditions
IOUT = 1mA VIN = 8V to 16V IOUT = 1mA to 10mA Over Operating Temperature Range
Min
5
Typ
5.1 5 13 0.4 42 1.1 5
Max
5.3 15 20 0.5 46 1.5 10 30 1 VDD - 2V
Unit
V mV mV mV/C kHz %/V % mV nA V dB MHz dB dB V/V V V V nA V V A A V V V
Reference Voltage
VRTC
Oscillator
35 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 Amplifier Gain Maximum Differential Input Signal Common-Mode Input Voltage
VIN = 8V to 16V VOUT = 1V to 6V VCMV 0V to 14V VIN = 8V to 16V Pin 3 = 0V to 1.1V VPIN4 - VPIN3
0 70 1.2 60 60 3 0 0.5 3.15
Current Sense Amplifier
3.3 1.1 VDD - 3V 1 1 0.35 0.4 VDD 50 VIN - 0. 5 VIN VIN + 0.5 0.4 2
Current Limit Adjust
IB VTB VIN Current Limit Offset Voltage Input Bias Current Threshold Voltage Input Voltage Range Minimum Latching Current at Pin 1 Maximum Nonlatching Current at Pin 1 Output Voltage Output Low Level Output Low Level Pin 13 ISINK = 20mA ISINK = 100mA
Shutdown Terminal
0.3 0 125
Output Stage
VDD VOL VOL
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CMOS CURRENT MODE PWM CONTROLLER TC170
ELECTRICAL CHARACTERISTICS (Cont.): VIN = 16V, RO = 24k, CO = 1nF, TA = 25C, unless otherwise indicated.
Symbol
VOH VOL tR tF
1
Parameter
Output High Level Output High Level Output Rise Time Output Fall Time Start-Up Threshold Hysteresis
Test Conditions
ISOURCE = 20mA ISOURCE = 100mA CL = 1000pF CL = 1000pF Threshold
Min
VDD - 1V VDD - 4V
Typ
Max
Unit
V V nsec nsec V V mA
Output Stage (Cont.)
2 3 4 5 6 7
50 50 7.15 0.5 7.7 0.75 2.7
150 150 8.25 1 3.8
Undervoltage Lockout
Supply
IS Standby Supply Current
PIN DESCRIPTION
Pin No. (16-Pin PDIP)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Symbol
SOFT START/ILIM VREF OUT - ISENSE IN + ISENSE IN + ERROR AMP IN - ERROR AMP IN CMPTR CO RO SYNC 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.
PIN CONFIGURATIONS (DIP and SOIC)
SOFT START/ ILIM 1 VREFOUT 2 - I SENSE IN 3 + I SENSE IN 4 + ERROR AMP IN 5 - ERROR AMP IN 6 CMPTR 7 CO 8 16 SHDN 15 VIN 14 OUTPUT B 13 VDD 12 GND 11 OUTPUT A 10 SYNC 9 RO CINT VSS CAZ BUF ACOM CREF CREF VREF
- + -
1 2 3 4 5 6 7 8
16 15 14
VDD DIGITAL GND CMPTR OUT B A
+ VIN - VIN +
TC170 CPE
TC170COE
13 12 11 10 9
VREF
NOTE: Outputs LOW in "OFF" state.
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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 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 25C; 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 125A. This capacitor will prevent "noise triggering" of the latch, yet minimize the soft-start effect.
R1 should be selected first. The shutdown circuit feature is not latched for (VREF - 0.35)/R1 < 50A and is latched for currents greater than 125A. 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 = where: V1 = VREF R2 R1 + R2 V1 - 0.75V 3.15 (RS)
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.
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.
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 VREF/R1 is greater than 125A, 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.
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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 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 s in width (min). Typical time delay values are in the 300 to 400nsec region at 25C. The delay time increases with device temperature so that at 50C, the delay times may be increased by as much as 100nsec. TELCOM SEMICONDUCTOR, INC.
CMOS CURRENT MODE PWM CONTROLLER TC170
SWITCH CURRENT x 3.15 CURRENT-SENSE AMPLIFIER 4 3 RS 7 VDD 100 A ERROR AMPLIFIER 5 6 + - V1 + - LIMIT BUFFER AMPLIFIER Q4 + - PWM COMPARATOR - + + S - FROM UNDERVOLTAGE LOCKOUT S PWM LATCH 5.1V VREF 2 R1 1 V1 Q R
1
10
2
"A" = 1 OUTPUT OFF (LOW)
0.75V
3 4 5 6
R2
Q3 350mV -
LOCK-UP AMPLIFIER Q1 + POSITIVE FEEDBACK Q2
SHUTDOWN COMPARATOR + - 6k 16
350mV TC170 IL 3.5k
Figure 1.
R1 and R2 Set Maximum Peak Output Current
I x 3.15 CURRENTSENSE AMPLIFIER
RS VOUT
x 3.15 CURRENTSENSE AMPLIFIER + - TC170
I 4 C 3 *OPTIONAL RC FILTER R* RS
+ - TC170
4
3
7
(A) Ground Reference
(B) Above-Ground Resistive Sensing
Figure 2.
Resistive Sensing
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x 3.15 CURRENT- SENSE AMPLIFIER + - TC170 4 + VS - I * RS VS = S N
9
N 1 IS
RO TC170
3
8C O MASTER
SYNC 10
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).
2 VREF 10 SYNC 7 CMPTR
9R O 8 CO
TC170
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.
SLAVE
Figure 4.
Master/Slave Parallel Operation
VDD
EXTERNAL* OSCILLATOR
1/2 TC4427
15 VIN 10 CO SYNC TC170 VREF RO 2 + VS 15 VIN 10 SYNC TC170 VREF RO 2 9 CO 9 8
*PULSE WIDTH OF OSCILLATOR IS = TD
Figure 5.
External Clock Synchronization
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CMOS CURRENT MODE PWM CONTROLLER TC170
1
VDD PIN 8
1 FO
2 3
2.3V 4.3V
ICHARGE
2.3V RO
+ -
2.3V PIN 10
ON-TIME
10 SYNC DISCHARGE CURRENT 1 mA
8
9 RO
OUTPUT DEAD TIME (TD)
CO
4
Figure 6 . Oscillator Circuit
Oscillator Frequency and Output Dead Time
The oscillator frequency for R O = 24k and CO = 1000pF is:
OSCILLATOR RESISTANCE (k)
50 45 40 35 30 25 20 15 10 5 0 500pF 1000pF 750pF 20 40 60 80 100 120 140 160 180 200 OSCILLATOR FREQUENCY (kHz) 250pF TA = +25C
FO =
[
1.27 2800 - ROCO RO2CO
]
CO CO + 150 x 10-12
5 6 7
where: RO = Oscillator Resistor () CO = Oscillator Capacitor (F) FO = Oscillator Frequency (Hz) The oscillator resistor can range from 5 k to 50 k. 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-
Figure 7.
Oscillator Frequency vs Oscillator Resistance
()
2.3 RO
where: RO = Oscillator Resistor (k) CO = Oscillator Capacitor (pF) TD = Output Dead Time (sec) Maximum possible duty cycle is set by the dead time.
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TYPICAL CHARACTERISTICS
Output Rise and Fall Times
TA = +25C CLOAD = 500pF VS = 16V
Output Rise and Fall Times
TA = +25C CLOAD = 1800pF VS = 16V
Output Rise and Fall Times
TA = +25C CLOAD = 1000pF VS = 16V
5V DIV 50nsec DIV
5V DIV 5 nsec DIV 5V DIV 50nsec DIV
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