High-Voltage Switchmode Controllers with MOSFET

Transcription

1 HV91 HV912 HV913 High-Voltage Switchmode Controllers with MOSFET Ordering Information V IN Feedback Max MOSFET Switch Package Options Min Max Voltage Duty Cycle BV DSS R DS (ON) 14 Pin Plastic DIP 2 Pin Plastic PLCC 1V 7V ± 1.% 49% 15V 5.Ω HV91P HV91PJ 1V 12V ± 1.% 49% 2V 7.Ω HV912P HV912PJ 1V 12V ±1.% 99% 2V 7.Ω HV913P HV913PJ Standard temperature range for all parts is industrial (-4 to 85 C). Features 1 to 12V input range 2V, 7.Ω output MOSFET Current-Mode Control High Efficiency Up to 1MHz Internal Oscillator Internal Start-up Circuit Applications DC/DC Converters Distributed Power Systems ISDN Equipment PBX Systems Modems Absolute Maximum Ratings V IN, Input Voltage 12V V DS 2V, Logic Voltage 15.V Input Voltage Logic, Linear, FB and Sense -.3V to.3v I D (Peak) 2.5A Storage Temperature -65 C to 15 C Power Dissipation, Plastic DIP 75mW Power Dissipation, PLCC 14mW General Description The Supertex HV91 through HV913 are a series of BiCMOS/ DMOS single-output, pulse width modulator ICs intended for use in high-speed high-efficiency switchmode power supplies. They provide all the functions necessary to implement a single-switch current-mode PWM, in any topology, with a minimum of external parts. Utilization of Supertex proprietary BiCMOS/DMOS technology results in a device with one tenth of the operating power of conventional bipolar PWM ICs, which can operate at more than twice their switching frequency. Dynamic range for regulation is also increased, to approximately 8 times that of similar bipolar parts. They start directly from any DC input voltage between 1 and 7VDC for the HV91 or 1 to 12VDC for the HV912 and HV913, requiring no external power resistor. The output stage for the HV91 is a 15V, 5. ohm MOSFET and for the HV912 and HV913 is a 2V, 7. ohm MOSFET. The clock frequency is set with a single external resistor. Accessory functions are included to permit fast remote shutdown (latching or nonlatching), and undervoltage shutdown. 11/12/1 1 For detailed circuit and application information, please refer to application notes AN-H13 and AN-H21 to AN-H24. Supertex Inc. does not recommend the use of its products in life support applications and will not knowingly sell its products for use in such applications unless it receives an adequate "products liability indemnification insurance agreement." Supertex does not assume responsibility for use of devices described and limits its liability to the replacement of devices determined to be defective due to workmanship. No responsibility is assumed for possible omissions or inaccuracies. Circuitry and specifications are subject to change without notice. For the latest product specifications, refer to the Supertex website: For complete liability information on all Supertex products, refer to the most current databook or to the Legal/Disclaimer page on the Supertex website.

2 HV91/HV912/HV913 Electrical Characteristics ( = 1V, V IN = 48V, Discharge = -V IN = V, R BIAS = 39KΩ, R OSC = 33KΩ,T A = 25 C, unless otherwise specified) Symbol Parameters Min Typ Max Unit Conditions V REF Output Voltage HV91/2/ V R L = 1MΩ HV912/ V IN = V IN, R L = 1MΩ T A = -55 C to 125 C Z OUT Output Impedance KΩ I SHORT Short Circuit Current 1 25 µa V REF = -V IN V REF Change in V REF with Temperature.25 mv/ C Oscillator f MAX Oscillator Frequency MHz R OSC = Ω f OSC Initial Accuracy KHz R OSC = 33KΩ R OSC = 15KΩ Voltage Stability 15 % 9.5V < < 13.5V Temperature Coefficient 17 ppm/ C PWM D MAX Maximum Duty Cycle HV91/ % HV Deadtime HV913 1 nsec D MIN Minimum Duty Cycle % Minimum Pulse Width nsec Before Pulse Drops Out 1 Error Amplifier V FB Feedback Voltage HV91/2/ V V FB Shorted to Comp I IN Input Bias Current 25 5 na V FB = 4.V V OS Input Offset Voltage nulled at trim mv Except 911 A VOL Open Loop Voltage Gain db gbw Unity Gain Bandwidth MHz Z OUT Output Impedance 1 See Fig. 2 Ω I SOURCE Output Current ma V FB = 3.4V I SINK Output Sink Current ma V FB = 4.5V PSRR Power Supply Rejection See Fig. 1 Current Limit V SOURCE Threshold Voltage V V FB = V, R L = 1Ω t d Delay to Output 1 15 ns V SOURCE = 1.5V, R L = 1Ω Notes: 1. Guaranteed by design. Not subject to production test. 2. Stray capacitance on OSC In pin 5pF. 2

3 Electrical Characteristics HV91/HV912/HV913 (Continued) ( = 1V, V IN = 48V, Discharge = -V IN = V, R BIAS = 39KΩ, R OSC = 33KΩ,T A = 25 C, unless otherwise specified) Symbol Parameters Min Typ Max Unit Conditions Pre-Regulator/Startup V IN Allowable Input Voltage HV91 7 V I IN = 1µA HV912/3 12 Input Leakage Current 1 µa > 9.4V V TH Pre-regulator Turn-off V I PREREG = 1µA Threshold Voltage V LOCK Undervoltage Lockout V R L = 1Ω from to Supply I DD Supply Current.6 1. ma.55 ma = -V IN I BIAS Bias Current 2 µa Operating Range V Logic t SD Delay Time ns V SOURCE = -V IN t SW Pulse Width 1 5 ns t RW RESET Pulse Width 1 5 ns t LW Latching Pulse Width 1 25 ns V IL Input Low Voltage 2. V V IH Input High Voltage 7. V I IH Input High Current µa V IN = 1V I IL Input Low Current µa V IN = V MOSFET Switch BV DSS Breakdown Voltage HV91 15 V V SOURCE = = V, HV912/3 2 I D = 1µA, T A = -55 C to 125 C R DS(ON) -to- HV Ω V SOURCE = V, I D = 1mA On-resistance HV912/3 7. Ω I DSS OFF State Leakage Current 1 µa V SOURCE = = V, V DRAIN = 1V C DS Capacitance 35 pf V DS = 25V, = V Note: 1. Guaranteed by design. Not subject to production test. Truth Table Output H H Normal Operation H H L Normal Operation, No Change L H Off, Not Latched L L Off, Latched L H L Off, Latched, No Change 3

4 Switching Waveforms HV91/HV912/HV V t F 1ns 5% t R 1ns 5% t d t SD 9% 9% t SW 5% 5% t R, t F 1ns t LW 5% 5% 5% t RW Functional Block Diagram FB COMP Discharge OSC In OSC Out V REF BIAS V IN 1 (14) 1 (2) 6 (9) 2 (3) 14 (2) REF GEN Current s Error Amplifier 4V To Internal Circuits 13 (18) 8.1V 2V 1.2V 9 (12) Current-mode Comparator C/L Comparator Undervoltage Comparator 8 (11) 7 (1) OSC R S Q T 913 S Q R Q (5) 3 (8) 5 -V IN (7) 4 (16) 11 (17) V Pre-regulator/Startup Pin numbers in parentheses are for PLCC pacage. 4

5 Typical Performance Curves HV91/HV912/HV913 Fig. 1 PSRR Error Amplifier and Fig. 3 8 Error Amplifier Open Loop Gain/Phase (db) Gain (db) Phase Hz 1Hz 1KHz 1KHz 1KHz 1MHz -1 1Hz 1KHz 1KHz 1KHz Frequency 1MHz Fig. 2 Error Amplifier Output Impedance (Z ) Fig M Output Switching Frequency vs. Oscillator Resistance (Ω) f OUT (Hz) 1k HV91, 911, 912 HV Hz 1KHz 1KHz 1KHz 1MHz 1MHz 1k 1k 1 k R OSC (Ω) 1M Test Circuits 1V ( ) Error Amp Z OUT 1.V swept 1Hz 2.2MHz.1V swept 1Hz 1MHz PSRR (FB) GND (V IN ).1µF 6.4K Tektronix P621 V (1 turn 1 V 2 secondary) 4.2K 1.V 1K1% 4.V.1µF 1K1% V 2 V 1 NOTE: Set Feedback Voltage so that V COMP = V DIVIDE ± 1mV before connecting transformer 5

6 Technical Description Preregulator The preregulator/startup circuit for the HV91x consists of a highvoltage N-channel depletion-mode DMOS transistor driven by an error amplifier to form a controlled current path between the V IN terminal and the terminal. Maximum current (about 2 ma) occurs when =, with current reducing as rises. This path shuts off altogether when rises to somewhere between 7.8 and 9.4V, so that if is held at 1 or 12V by an external source (generally the supply the chip is controlling) no current other than leakage is drawn through the high voltage transistor. This minimizes dissipation. An external capacitor between and V SS is generally required to store energy used by the chip during the time between shutoff of the high voltage path and the supply s output rising enough to take over the powering of the chip. This capacitor generally also serves as the output filter capacitor for that output from the supply. 1µF is generally sufficient to assure against double-starting. Capacitors as small as.1µf can work when faster response from the line is required. Whatever capacitor is chosen should have very good high frequency characteristics. Stacked polyester or ceramic capacitors work well. Electrolytic capacitors are generally not suitable. A common resistor divider string is used to monitor for both the undervoltage lockout circuit and the shutoff circuit of the high voltage FET. Setting the undervoltage sense point about.6v lower on the string than the FET shutoff point guarantees that the undervoltage lockout always releases before the FET shuts off. Bias Circuit An external bias resistor, connected between the bias pin and V SS is required to set currents in a series of current mirrors used by the analog sections of the chip. Nominal external bias current requirement is 15 to 2µA, which can be set by a 39KΩ to 51KΩ resistor if a 1V is used, or a 51KΩ to 68KΩ resistor if a 12V is used. A precision resistor is NOT required; ± 5% is fine. For extremely low power operation, the value of bias current can be reduced to as low as 5µA by further increases in the value of the bias resistor. This will reduce quiescent current by about a third, reduce bandwidth of the error amp by about half, and slow the current sense comparator by about 3%. Clock Oscillator The clock oscillator of the HV91x consists of a ring of CMOS inverters, timing capacitors, a capacitor discharge FET, and, in the 5% maximum duty cycle versions, a frequency dividing flipflop. A single external resistor between the OSC In and OSC Out pins is required to set oscillator frequency (see Fig. 4). For the 5% maximum duty cycle versions the Discharge pin is internally connected to GND. For the 99% duty cycle version, Discharge can either be connected to V SS directly or connected to V SS through a resistor used to set a deadtime. One difference exists between the Supertex HV91x and competitive parts. The oscillator of the HV91x is shut off when a shutoff command is received. This saves about 15µA of quiescent current, which aids in situations where an absolute minimum of quiescent power dissipation is required. HV91/HV912/HV913 The reference consists of a stable bandgap reference followed by a buffer amplifier which scales the voltage up to approximately 4.V. The scaling resistors of the reference buffer amplifier are trimmed during manufacture so that the output of the error amplifier when connected in a gain of -1 configuration is as close to 4.V as possible. This nulls out any input offset of the error amplifier. As a consequence, even though the observed reference voltage of a specific part may not be exactly 4V, the feedback voltage required for proper regulation will be 4V. A resistor of approximately 5KΩ is placed internally between the output of the reference buffer amplifier and the circuitry it feeds (reference output pin and NON-INVERTING input to the error amplifier). This allows overriding the internal reference with a lowimpedance voltage source 6V. Using an external reference reinstates the input offset voltage of the error amplifier, and its effect of the exact value of feedback voltage required. In general, because the reference voltage of the Supertex HV91x is not noisy, as some previous devices have been, overriding the reference should seldom be necessary. Because the reference is a high impedance node, and usually there will be significant electrical noise near it, a bypass capacitor between the reference pin and V SS is strongly recommended. The reference buffer amplifier is intentionally compensated to be stable with a capacitive load of.1 to.1µf. Error Amplifier The error amplifier is a true low-power differential input operational amplifier intended for around-the-amplifier compensation. It is of mixed CMOS-bipolar construction: a PMOS input stage is used so the common-mode range includes ground and the input impedance is very high. This is followed by bipolar gain stages which provide high gain without the electrical noise of all-mos amplifiers. The amplifier is unity-gain stable. Current Sense Comparators The HV91x uses a true dual comparator system with independent comparators for modulation and current limiting. This allows the designer greater latitude in compensation design, as there are no clamps (except ESD protection) on the compensation pin. Like the error amplifier, the comparators are of low-noise BiCMOS construction. Remote The shutdown and reset pins can be used to perform either latching or non-latching shutdown of a converter as required. These pins have internal current source pull-ups so they can be driven from open-drain logic. When not used, they should be left open, or connected to. Main Switch The main switch is a normal N-channel power MOSFET. Unlike the situation with competitive devices, the body diode can be used if desired without destroying the chip. 6

7 Pinout HV91/HV912/HV913 COMP V REF BIAS 1 14 Feedback V IN 2 13 COMP V IN V REF Feedback Discharge OSC In 6 9 Discharge BIAS 2 1 OSC Out OSC Out 7 8 OSC In V IN 3 9 top view 14-pin DIP V IN top view 2-pin PJ Package 21 Supertex Inc. All rights reserved. Unauthorized use or reproduction prohibited. 7 11/12/ Bordeaux Drive, Sunnyvale, CA 9489 TEL: (48) FAX: (48)