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UC1524 UC2524 UC3524
Advanced Regulating Pulse Width Modulators
FEATURES
* Complete PWM Power Control Circuitry * Uncommitted Outputs for Single-ended or Push-pull Applications * Low Standby Current...8mA Typical * Interchangeable with SG1524, SG2524 and SG3524, Respectively
DESCRIPTION
The UC1524, UC2524 and UC3524 incorporate on a single monolithic chip all the functions required for the construction of regulating power supplies, inverters or switching regulators. They can also be used as the control element for high-power-output applications. The UC1524 family was designed for switching regulators of either polarity, transformer-coupled dc-to-dc converters, transformerless voltage doublers and polarity converter applications employing fixed-frequency, pulse-width modulation techniques. The dual alternating outputs allow either single-ended or push-pull applications. Each device includes an on-chip reference, error amplifier, programmable oscillator, pulse-steering flip-flop, two uncommitted output transistors, a high-gain comparator, and current-limiting and shut-down circuitry. The UC1524 is characterized for operation over the full military temperature range of -55C to +125C. The UC2524 and UC3524 are designed for operation from -25C to +85C and 0 to +70C, respectively.
BLOCK DIAGRAM
VREF 16 OSC OUT 3
VIN
15
REFERENCE REGULATOR +5V Q
+5V TO ALL INTERNAL CIRCUITRY
12
CA
RT CT (RAMP)
6 OSC 7 R Q 11 13 EA CB
INV INPUT NI INPUT GROUND (SUBSTRATE)
1 2
+5V EA
+5V COMPARATOR
14 10k 5 4 10 SHUTDOWN 9 COMPENSATION
EB -SENSE +SENSE
8
1k
CL
SLUS180B - NOVEMBER 1999 - REVISED JUNE 2000
UC1524 UC2524 UC3524 ABSOLUTE MAXIMUM RATINGS (Note 1)
Supply Voltage, VCC (Notes 2 and 3) . . . . . . . . . . . . . . . . . 40V Collector Output Current. . . . . . . . . . . . . . . . . . . . . . . . . 100mA Reference Output Current . . . . . . . . . . . . . . . . . . . . . . . . 50mA Current Through CT Terminal . . . . . . . . . . . . . . . . . . . . . . -5mA Power Dissipation at TA = +25C (Note 4). . . . . . . . . . 1000mW Power Dissipation at TC = +25C (Note 4). . . . . . . . . . 2000mW Operating Junction Temperature Range . . . . -55C to +150C Storage Temperature Range . . . . . . . . . . . . . -65C to +150C
CONNECTION DIAGRAM
INV INPUT NON INV INPUT OSC OUT CLSENSE(+) 1 EA 2 3 4 CL CLSENSE (--) RT CT GND 5 6 OSC 7 8 16 15 14 13 12 11 S/D 10 9 VREF VIN EB CB CA EA S/D COMP
REF REG
Note 1: Over operating free-air temperature range unless otherwise noted. Note 2: All voltage values are with respect to the ground terminal, pin 8. Note 3: The reference regulator may be bypassed for operation from a fixed 5V supply by connecting the VCC and reference output pins both to the supply voltage. In this configuration the maximum supply voltage is 6V. Note 4: Consult packaging section of databook for thermal limitations and considerations of package.
RECOMMENDED OPERATING CONDITIONS
Supply Voltage, VCC. . . . . . . . . . . . . . . . . . . . . . . . . . 8V to 40V Reference Output Current . . . . . . . . . . . . . . . . . . . . . 0 to 20mA Current through CT Terminal . . . . . . . . . . . . . -0.03mA to -2mA Timing Resistor, RT . . . . . . . . . . . . . . . . . . . . . 1.8k to 100k Timing Capacitor, CT . . . . . . . . . . . . . . . . . . . 0.001F to 0.1F Operating Ambient Temperature Range UC1524 . . . . . . . . . . . . . . . . . . . . . . . . . . . . -55C to +125C UC2524 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -25C to +85C UC3524 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0C to +70C
ELECTRICAL CHARACTERISTICS: Unless otherwise stated, these specifications apply for T A = -55C to +125C for the UC1524, -25C to +85C for the UC2524, and 0C to +70C for the UC3524, V IN = 20V, and f = 20kHz, T A = T J. UC1524/UC2524 UC3524 UNITS PARAMETER TEST CONDITIONS MIN TYP MAX MIN TYP MAX Reference Section Output Voltage 4.8 5.0 5.2 4.6 5.0 5.4 V 10 20 10 30 mV Line Regulation VIN = 8 to 40V 20 50 20 50 mV Load Regulation IL = 0 to 20mA 66 66 dB Ripple Rejection f = 120Hz, TJ = 25C 100 100 mA Short Circuit Current Limit VREF = 0, TJ = 25C Temperature Stability Over Operating Temperature Range 0.3 1 0.3 1 % 20 20 mV Long Term Stability TJ = 125C, t = 1000 Hrs. Oscillator Section 300 300 kHz Maximum Frequency CT = .001mfd, RT = 2k 5 5 % Initial Accuracy RT and CT Constant 1 1 % Voltage Stability VIN = 8 to 40V, TJ = 25C Temperature Stability Over Operating Temperature Range 5 5 % 3.5 3.5 V Output Amplitude Pin 3, TJ = 25C 0.5 0.5 Output Pulse Width CT = .01mfd, TJ = 25C s Error Amplifier Section 0.5 5 2 10 mV Input Offset Voltage VCM = 2.5V 2 10 2 10 Input Bias Current VCM = 2.5V A Open Loop Voltage Gain 72 80 60 80 dB 1.8 3.4 1.8 3.4 V Common Mode Voltage TJ = 25C 2
UC1524 UC2524 UC3524
ELECTRICAL CHARACTERISTICS: Unless otherwise stated, these specifications apply for T A = -55C to +125C for the UC1524, -25C to +85C for the UC2524, and 0C to +70C for the UC3524, V IN = 20V, and f = 20kHz, T A = T J. UC1524/UC2524 UC3524 UNITS PARAMETER TEST CONDITIONS MIN TYP MAX MIN TYP MAX Error Amplifier Section (cont.) 70 70 dB Common Mode Rejection Ratio TJ = 25C 3 3 MHz Small Signal Bandwidth AV = 0dB, TJ = 25C 0.5 3.8 0.5 3.8 V Output Voltage TJ = 25C Comparator Section Duty-Cycle % Each Output On 0 45 0 45 % Input Threshold Zero Duty-Cycle 1 1 V Maximum Duty-Cycle 3.5 3.5 V Input Bias Current 1 1 A Current Limiting Section 190 200 210 180 200 220 mV Sense Voltage Pin 9 = 2V with Error Amplifier Set for Maximum Out, TJ = 25C Sense Voltage T.C. 0.2 0.2 mV/C Common Mode Voltage -1 +1 -1 +1 V Output Section (Each Output) Collector-Emitter Voltage 40 40 V 0.1 50 0.1 50 Collector Leakage Current VCE = 40V A Saturation Voltage IC = 50mA 1 2 1 2 V 17 18 17 18 V Emitter Output Voltage VIN = 20V 0.2 0.2 Rise Time RC = 2k, TJ = 25C s 0.1 0.1 Fall Time RC = 2k, TJ = 25C s VIN = 40V 8 10 8 10 mA Total Standby Current (Note)
Note: Excluding oscillator charging current, error and current limit dividers, and with outputs open.
PRINCIPLES OF OPERATION
The UC1524 is a fixed-frequency pulse-width-modulation voltage regulator control circuit. The regulator operates at a frequency that is programmed by one timing resistor (RT), and one timing capacitor (CT), RT establishes a constant charging current for CT. This results in a linear voltage ramp at CT, which is fed to the comparator providing linear control of the output pulse width by the error amplifier. The UC1524 contains an on-board 5V regulator that serves as a reference as well as powering the UC1524's internal control circuitry and is also useful in supplying external support functions. This reference voltage is lowered externally by a resistor divider to provide a reference within the common-mode range of the error amplifier or an external reference may be used. The power supply output is sensed by a second resistor divider network to generate a feedback signal to the error amplifier. The amplifier output voltage is then compared to the linear voltage ramp at CT. The resulting modulated pulse out of the high-gain comparator is then steered to 3 the appropriate output pass transistor (Q1 or Q2) by the pulse-steering flip-flop, which is synchronously toggled by the oscillator output. The oscillator output pulse also serves as a blanking pulse to assure both outputs are never on simultaneously during the transition times. The width of the blanking pulse is controlled by the valve of CT. The outputs may be applied in a push-pull configuration in which their frequency is half that of the base oscillator, or paralleled for single-ended applications in which the frequency is equal to that of the oscillator. The output of the error amplifier shares a common input to the comparator with the current limiting and shutdown circuitry and can be overridden by signals from either of these inputs. This common point is also available externally and may be employed to control the gain of, or to compensate, the error amplifier or to provide additional control to the regulator.
UC1524 UC2524 UC3524 TYPICAL CHARACTERISTICS
Open-loop voltage amplification of error amplifier vs frequency.
Oscillator frequency vs timing components.
Output dead time vs timing capacitance value.
Output saturation voltage vs load current.
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UC1524 UC2524 UC3524 APPLICATION INFORMATION
Oscillator The oscillator controls the frequency of the UC1524 and is programmed by RT and CT according to the approximate formula: 1.18 f RT CT where where where RT is in k CT is in mF f is in kHz Synchronous Operation When an external clock is desired, a clock pulse of approximately 3V can be applied directly to the oscillator output terminal. The impedance to ground at this point is approximately 2k. In this configuration RT CT must be selected for a clock period slightly greater than that of the external clock. If two or more UC1524 regulators are to operated synchronously, all oscillator output terminals should be tied together, all CT terminals connected to single timing capacitor, and the timing resistor connected to a single RT, terminal. The other RT terminals can be left open or shorted to VREF. Minimum lead lengths should be used between the CT terminals.
VREF COMP 16 1N916 9 5k
Practical values of CT fall between 0.001mF and 0.1mF. Practical values of RT fall between 1.8k and 100k. This results in a frequency range typically from 120Hz to 500kHz. Blanking The output pulse of the oscillator is used as a blanking pulse at the output. This pulse width is controlled by the value of CT. If small values of CT are required for frequency control, the oscillator output pulse width may still be increased by applying a shunt capacitance of up to 100pF from pin 3 to ground. If still greater dead-time is required, it should be accomplished by limiting the maximum duty cycle by clamping the output of the error amplifier. This can easily be done with the circuit in Figure 1:
GND
8
Figure 1. Error amplifier clamp.
Figure 2. Single-ended LC switching regulator circuit.
5
UC1524 UC2524 UC3524
Figure 3. Push-pull transformer coupled circuit.
Figure 4. Open loop test circuit.
UNITRODE CORPORATION 7 CONTINENTAL BLVD. * MERRIMACK, NH 03054 TEL. (603) 424-2410 FAX (603) 424-3460
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Copyright (c) 2000, Texas Instruments Incorporated

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