FEATURES
Programmable Output Turn On Delay; Zero Delay Available
Compatible with Voltage Mode or Current Mode Topologies
10-MHz Error Amplifier Pin Programmable Undervoltage Lockout Low Startup Current 150 µA Soft Start Control Outputs Active Low During UVLO
DESCRIPTION
The UC3879 controls a bridge power stage by phase shifting the switching of one half-bridge with respect to the other. This allows constant frequency pulse width modulation in combination with resonant, zero-voltage switching for high efficiency performance. The UC3879 can be configured to provide control in either voltage mode or current mode operation, with overcurrent shutdown for fast fault protection.
Independently programmable time delays provide dead-time at the turn-on of each output stage, allowing time for each resonant switching interval.
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of the Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters.
With the oscillator capable of operating in excess of 600 kHz, overall output switching frequencies to 300 kHz are practical. In addition to the standard free running mode, with the CLKSYNC pin, the user may configure the UC3879 to accept an external clock synchronization signal. Alternatively, up to three units can be locked together with the operational frequency determined by the fastest device.
Protective features include an undervoltage lockout and overcurrent protection. Additional features include a 10-MHz error amplifier, a 5-V precision reference, and soft start. The UC3879 is available in 20 pin N, J, DW, and Q and 28 pin L packages.
PARAMETER Supply voltage (VC, VIN) Output current, source or sink, dc Output current, source, sink peak for µs at max frequency of 300 kHz Analog inputs
(1) Pin references are to 20-pin DIL and SOIC packages. All voltages are with respect to ground unless otherwise stated. Currents are positive into, negative out of the specified terminal.
over operating free-air temperature range (unless otherwise noted)
(1) JC data values stated were derived from MIL-STD-1835B. MIL-STD-1835B states "The baseline values shown are worst case (mean +2s) for x 60 mil microcircuit device silicon die and aplicable for devices with die sizes to 14400 square mils. For devices die sizes greater than 14400 square mils use the following values; dual-in-line, 11°C/W; flat pacl 10°C/W; pin grid array, 10°C/W".
(2) Specified JA (junction-to-ambient) is for devices mounted FR4 PC board with one ounce copper wire where noted. When resistance range is given, lower values are for 5-in2 aluminum PC board. Test PWB was 0.062 in thick and typically used 0.635-mm
trace widths for power packages and 1.3-mm trace widths for non-power packages with x 100 mil probe land area at the end of
each trace. (3) JC estimated for backside of device, through the metalized thermal conduction pads.
20 GND 19 RAMP RT 17 CLKSYNC 16 UVSEL 15 DELSETA-B CT 13 OUTA 12 OUTB 11 PWRGND
Required
