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IMP38HC43ESA Datasheet(PDF) 6 Page - IMP, Inc |
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IMP38HC43ESA Datasheet(HTML) 6 Page - IMP, Inc |
6 / 10 page IMP38C/HC/42/3/4/5 IMP38C/HC/42/3/4/5 6 408-432-9100/www.impweb.com © 2000 IMP, Inc. ! S Transient Protection Good high-frequency layout practices should be followed. Avoid long printed-circuit traces and component leads. Locate oscillator and compensation components near the IC. Avoid capacitive and inductive coupling of the switching waveform into the high-impedance inputs of the error amplifier, oscillator, and current-sense amplifier. VREF and VCC stability will be aided by using high-frequency decoupling capacitors. Undervoltage Lockout Several different thresholds are available. Under-voltage lockout (UVL) performance has been improved. When the power supply voltage is below the startup voltage, internal circuitry puts the output into a low impedance state and sets the output to zero. The output will sink up to 20mA in this controlled state and remain below 1.3V, well below the turn-on threshold voltage of the external MOSFET. With the IMP38C/HC4x output stage design, leakage current from the external power MOSFETs will not force the PWM output to rise and turn the external MOSFET on. Even when VDD drops to zero volts, the OUT pin will not rise above approximately 1.3V because the UVLO circuit is powered through the OUT pin. The IMP output stage performance in UVL mode, while sinking 20mA, is shown in Figure 2. Figure 2. Output Stage Performance in UVL Mode 0 VDD (V) 2.0 1.5 1.0 0.5 0 VOUT While Sinking 20mA 12345 7 69 8 38C/HC_05b.eps IMP38C/HC4x s d l o h s e r h T t u o k c o L e g a t l o v r e d n U V 4 . 8 t a p u -t r a t S V 6 . 7 = m u m i n i M g n i t a r e p O V 5 . 4 1 t a p u -t r a t S V 0 . 9 = m u m i n i M g n i t a r e p O 3 4 C H / 3 4 C 8 3 P M I2 4 C H / 2 4 C 8 3 P M I 5 4 C H / 5 4 C 8 3 P M I4 4 C H / 4 4 C 8 3 P M I s p e . 4 0 t _ C H / C 8 3 The IMP38C and IMP38HC devices are compatible with generic 384x PWM devices. The following discussion highlights the dif- ferences and advantages of the IMP ‘C’ and ‘HC’ designs. Start-up Current IMP’s BiCMOS process allows for substantial reduction in the start-up current. Typical start-up current is 95 µA, with a maxi- mum limit of 120 µA. Low start-up current allows high resistance, lower-wattage, start-up resistors to supply controller start-up power. Operating Current Operating current has been reduced to 1.5mA maximum. Compared to the 11mA needed for a typical bipolar controller and 6mA for competitive BiCMOS controllers, IMP's low operating current allows the controller to run cooler and with better effi- ciency. In addition, the VCC hold-up capacitance (used during start-up) can be reduced. Output Driver The IMP38HC4x/38C4x CMOS output stage drives external power MOSFETs to the full supply voltage. Low ON-resistance and high peak current drive combine to give greater than 1000pF gate capacitance drive capability. Rise and fall time requirements may dictate the appropriate value of output capacitance. Within the restrictions of output capacity and controller power dissipa- tion, switching frequencies can exceed 1MHz. The CMOS output stage “break-before-make” action is guaran- teed by design and insures that no cross-conduction current will flow. This minimizes heat dissipation, increases efficiency and enhances reliability. Oscillator Operation Two external components, RT and CT, set the switching frequency. With VCC = 14V, RT = 10k and CT = 3.3nF, nominal switching frequency is 50kHz. Figure 1. Oscillator Component Selection Application Information frequency Hz 1.73 RT CT F [] = []× [] Ω IMP38C4x IMP38HC4x VREF RT/CT GND 38C/HC_07.eps RT CT |
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