UC2845D8TR Texas Instruments 开关控制器 Current-Mode PWM Controller

1 Features

1

1

• Optimized for Off-Line and DC-to-DC Converters

• Low Start-Up Current (< 1 mA)

• Automatic Feedforward Compensation

• Pulse-by-Pulse Current Limiting

• Enhanced Load-Response Characteristics

• Undervoltage Lockout With Hysteresis

• Double-Pulse Suppression

• High-Current Totem-Pole Output

• Internally Trimmed Bandgap Reference

• Up to 500-kHz Operation

• Error Amplifier With Low Output Resistance

2 Applications

• Switching Regulators of Any Polarity

• Transformer-Coupled DC-DC Converters

3 Description

The UCx84x 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. The internally implemented circuits

include an undervoltage lockout (UVLO), featuring a

start-up current of less than 1 mA, and a precision

reference 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 that is designed to

source or sink high-peak current. The output stage,

suitable for driving N-channel MOSFETs, is low when

it is in the off state.

The UCx84x family offers a variety of package

options, temperature range options, choice of

maximum duty cycle, and choice of turnon and turnoff

thresholds and hysteresis ranges. Devices with

higher turnon or turnoff hysteresis are ideal choices

for off-line power supplies, while the devices with a

narrower hysteresis range are suited for DC-DC

applications. The UC184x devices are specified for

operation from –55°C to 125°C, the UC284x series is

specified for operation from –40°C to 85°C, and the

UC384x series is specified for operation from 0°C to

70°C.