Switched-mode power supply control circuit

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Peregrine Ramsey
5 years ago
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1 DESCRIPTION The /SE6 is a control circuit for use in switched-mode power supplies. It contains an internal temperature- compensated supply, PWM, sawtooth oscillator, overcurrent sense latch, and output stage. The device is intended for low cost SMPS applications where extensive housekeeping functions are not required. PIN CONFIGURATION D, FE, N Packages 7 OUTPUT FEATURES Micro-miniature (D) package Pulse-width modulator Current limiting (cycle-by-cycle) Sawtooth generator Stabilized power supply Double pulse protection Internal temperature-compensated reference FEEDBACK GAIN 4 APPLICATIONS Switched-mode power supplies DC motor controller inverter DC/DC converter 6 CURRENT SENSE R T, C T Figure. Pin Configuration ORDERING INFORMATION DESCRIPTION TEMPERATURE RANGE ORDER CODE DWG # -Pin Plastic Dual In-Line Package (DIP) to +7 C N SOT97- -Pin Plastic Dual In-Line Package (DIP) - to + C SE6N SOT97- -Pin Ceramic Dual In-Line Package (CERDIP) - to + C SE6FE A -Pin Small Outline (SO) Package to +7 C D SOT96- BLOCK DIAGRAM R T, C T REF VOLTAGE SAWTOOTH GENERATOR + ERROR AMP S 7 OUTPUT FEEDBACK PWM R LATCH GAIN 4.V STABILIZED SUPPLY.V CURRENT SENSE 6 + SL Figure. Block Diagram 994 Aug -9 7

2 ABSOLUTE MAXIMUM RATINGS SYMBOL PARAMETER RATING UNIT Supply Voltage-forced mode + V Current-fed mode ma Output transistor (at -V max) I OUT Output current 4 ma V OUT Output voltage +.4V V Output duty cycle 9 % P D Maximum total power dissipation.7 W T A Operating temperature range SE6 - to + C to 7 C NOTES:. See Voltage-Current-fed supply characteristic curve. DC ELECTRICAL CHARACTERISTICS =V, T A = C, unless otherwise specified. SYMBOL PARAMETER TEST CONDITIONS Reference section SE6 Min Typ Max Min Typ Max V REF Internal ref voltage T A = C V Over temperature V Internal zener ref *I L =7mA V Oscillator section Current limiting UNIT Temp. coefficient of V REF ± ± ppm/ C Temp. coefficient of ± ± ppm/ C Frequency range Over temperature k k Hz Initial accuracy R T and C T constant % Duty cycle range f O =khz 9 9 % I IN Input current Pin 6=mV T A = C µa Error amplifier Single pulse inhibit delay Inhibit delay time for % overdrive at Over temp. - - µa I OUT =ma.... µs I OUT =4mA µs Current limit trip level V Open-loop gain 6 6 db Feedback resistor k k Ω BW Small-signal bandwidth MHz V OH Output voltage swing V V OL Output voltage swing.7.7 V Output stage I OUT Output current Over temperature ma V CE Sat I C =ma, Over temp..4.4 V 994 Aug

3 DC ELECTRICAL CHARACTERISTICS =V, T A = C, unless otherwise specified. SYMBOL PARAMETER TEST CONDITIONS Supply voltage/current I CC Supply current Supply voltage Low supply protection SE6 Min Typ Max Min Typ Max I Z=, T A = C.. voltage-forced Over temp... I CC =ma, current-fed I CC =ma current.... Pin threshold V UNIT ma V 994 Aug

4 TYPICAL PERFORMANCE CHARACTERISTICS 6 Error Amplifier Open-Loop Gain Error Amplifier Open-Loop Phase Transfer Curve of Pulse-Width Modulator Duty Cycle vs Input Voltage GAIN (db) 4 k k k M M PHASE ANGLE (DEG) 6 9 k k k M M (%) δ V4 FREQUENCY (Hz) FREQUENCY (Hz) Power Derating Curve Typical Frequency Plot vs R T and C T TOTAL PWR DISSIPATION (WATTS) P T = I CC + ( ) I Z + [V 7 I 7 x DUTY CYCLE] NE SE 7 AMBIENT TEMPERATURE ( C) f (khz) R=kΩ R=kΩ R=kΩ R=4kΩ C (nf) R T C T MAXIMUM DUTY CYCLE (%) Maximum Duty Cycle vs Base Voltage on Q Start-Up Circuit Slow-Start Voltage δ MAX (%) C V R R Q 4 V4 4 V max is a function of f R R R V BEQ Figure. Typical Performance Characteristics t = R C t SL6 994 Aug 4

5 R VCC ma Voltage-Current-Fed Supply Characteristics V Current-Fed Dropping Resistor V V S CC ( ma) NOTE: See DC Electrical Characteristics for Current Fed Range. VS R VCC SL7 Figure 4. Voltage-Current-Fed Supply Characteristics initially going to the extreme maximum (δ>9%). Either overcurrent limit or slow-start circuitry must be employed to limit duty cycle to a safe value during start-up. Both may be used, if desired. To implement slow-start, the start-up circuit can be used. The divider R and R sets a voltage, buffered by Q, such that the output of the error amplifier is clamped to a maximum output voltage, thereby limiting the maximum duty cycle. The addition of capacitor C will cause this voltage to ramp-up slowly when power is applied, causing the duty cycle to ramp-up simultaneously. Overcurrent limit may be used also. To limit duty cycle in this mode, the switch current is monitored at Pin 6 and the output of the 6 is disabled on a cycle-by-cycle basis when current reaches the programmed limit. With current limit control of slow-start, the duty cycle is limited to that value, just allowing maximum switch current to flow. (Approximately.V measured at Pin 6.) APPLICATIONS V,.A Buck Regulator Operates from V The converter design shows how simple it is to derive a TTL supply from a system supply of V (see Figure ). The drives a N49 PNP transistor directly to provide switching current to the inductor. Overall line regulation is excellent and covers a range of V to V with minimal change (<mv) in the output operating at full load. As with all circuits, the auxiliary slow start and δ MAX circuit is required, as evidenced by Q. The δ MAX limit may be calculated by using the relationship: R (.V) R R V MAX The maximum duty cycle is then determined from the pulse-width modulator transfer graph, with R and R being defined from the desired conditions. START-UP The start-up, or initial turn-on, of this device requires some degree of external protective duty cycle limiting to prevent the duty cycle from 994 Aug

Brushless DC motor controller

NE/SA7 DESCRIPTION The NE/SA/SE7 is a three-phase brushless DC motor controller with a microprocessor-compatible serial input data port; 8-bit monotonic digital-to-analog converter; PWM comparator; oscillator;