30-V, 0.2A high Performance 500KHz current mode PWM with 8.4V/7.6V UVLO, 50% duty cycle, -40C to 85C

The TL284xB and TL384xB series of

control integrated circuits provide the features that are necessary to implement

off-line or dc-to-dc fixed-frequency current-mode control schemes, with a minimum

number of external components. Internally implemented circuits include an

undervoltage lockout (UVLO) and a precision reference that is trimmed for accuracy

at the error amplifier input. Other internal circuits include logic to ensure

latched operation, a pulse-width modulation (PWM) comparator that also provides

current-limit control, and a totem-pole output stage designed to source or sink

high-peak current. The output stage, suitable for driving N-channel MOSFETs, is low

when the output stage is in the off state.

The TL284xB and TL384xB series are pin

compatible with the standard TL284x and TL384x with the following improvements. The

start-up current is specified to be 0.5mA (max), while the oscillator discharge

current is trimmed to 8.3mA (typ). In addition, during undervoltage lockout

conditions, the output has a maximum saturation voltage of 1.2V while sinking 10mA

(VCC = 5V).

Major differences between members of

these series are the UVLO thresholds and maximum duty-cycle ranges. Typical UVLO

thresholds of 16V (on) and 10V (off) on the TLx842B and TLx844B devices make them

ideally suited to off-line applications. The corresponding typical thresholds for

the TLx843B and TLx845B devices are 8.4V (on) and 7.6V (off). The TLx842B and

TLx843B devices can operate to duty cycles approaching 100%. A duty-cycle range of

0% to 50% is obtained by the TLx844B and TLx845B by the addition of an internal

toggle flip-flop, which blanks the output off every other clock cycle. The

TL284xB-series devices are characterized for operation from –40°C to 85°C. The

TL384xB-series devices are characterized for operation from 0°C to 70°C.