IMP has announced eight pulse width modulation (PWM) controller integrated circuits for switch mode power supply (SMPS) and DC-to-DC converter manufacturers. Notable among the improvements of the BiCMOS IMP38C4x and IMP38HC4x devices are zero cross-conduction/shoot-through current, reduced start-up and operating current, improved undervoltage lockout and lower current-sense delay times. All improvements increase efficiency or improve system reliability.
The IMP38C4x and IMP38HC4x output driver stage has zero cross-conduction current. A proprietary output state-machine monitors each output MOSFET and guarantees by design that the output driver devices will not be on at the same time, thus eliminating transient shorting of the supply voltage to ground. This feature increases overall efficiency and reliability.
Under-voltage lockout (UVLO) 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 20 mA and remain below 1,3 V, well below the turn-on threshold voltage of external MOSFETs. Even when the supply voltage drops to zero volts, the output will not rise above approximately 1,3 V because the UVLO circuit is powered through the device output pin. Leakage current from the external power MOSFETs will not force the PWM output to rise and turn the external MOSFETs on.
Start-up current has been reduced to 120 µA maximum and operating current has been reduced to 1,5 mA.
Complete family serves DC-DC and off-line applications
The IMP38C4x and IMP38HC4x are fixed frequency, high performance, current-mode PWM controllers that are pin compatible with bipolar and BiCMOS 384x devices but feature improvements resulting from IMP's BiCMOS processing and circuit design. The IMP38C42, IMP38HC42, IMP38C44 and IMP38HC44 have 14,5 V start-up levels and the IMP38C43, IMP38HC43, IMP38C45 and IMP38HC45 have 8,4 V start-up levels. Output stage drive is 0,5 A for IMP38C4x devices. Designed to give full rail-to-rail gate drive to large power MOSFETs, the high-drive IMP38HC4x family is rated at 1,0 A peak current drive.
The IMP38C43/45, IMP38HC43/45 devices are often used in DC-DC converter applications. The C/HC43 and C/HC45 devices have lower start-up voltages, 8,4 V, with less hysteresis since the controller receives its input voltage from a usually more constant source. The IMP38C42/44, IMP38HC42/44 devices have a 14,5 V start-up voltage and a 9 V minimum operating voltage, giving a wider hysteresis range that is usually desirable in off-line applications.
Current-sense propagation delay time is typically 50 ns, 65 ns maximum, representing a 75% reduction over other BiCMOS 38xx implementations. Like conventional 384x controllers, the IMP38C4x and IMP38HC4x controllers use the current-mode architecture for superior load regulation, pulse-by-pulse current limiting and output MOSFET protection.
Package options include 8-pin SO, MicroSO and DIP packages and 14-pin SO and DIP packages.
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