Features: · Ideal for Multiple Output and/or High Voltage Output Voltage Converters
· Up to 500 kHz Operation
· High Voltage, High Current Floating Driver for Buck Converter Stage
· UC3827-1 Current Fed Controller has Push-Pull Drivers with Overlapping Conduction Periods
· UC3827-2 Voltage Fed Controller has Push-Pull Drivers with Nonoverlapping Conduction Periods
· Average Current Mode, Peak Current Mode or Voltage Mode with Input Voltage Feedforward Control for Buck Power Stage
· Wide Bandwidth, Low Offset,Differential Current Sense Amplifier
· Precise Short Circuit Current Control
Pinout
Specifications
| |
UC2827-1
UC2827-2
UC3827-1
UC3827-2 |
UNITS |
| Supply voltage, VCC |
20 |
V |
| Input voltage range |
CEAO, CEA+, CEA-, CSAO, CSA+, CSA-, CT, DELAY, PUSH, PULL, RAMP, RT, SS, SYNC, VEA+, VEAO, |
0.3 to 5 |
| V+ and BUCK |
90 |
| SRC |
90-VCC |
| BUCK driver |
I/O continuous |
±250 |
mA |
| I/O peak |
±1 |
A |
| PUSH/PULL driver |
I/O continuous |
±200 |
mA |
| I/O peak |
±0.8 |
A |
| Storage temperature |
65 to 150 |
|
| Junction temperature |
55 to 150 |
| Lead temperature (soldering, 10 sec) |
300 |
(1) Voltages are referenced to ground. Currents are positive into, negative out of the specified terminal. Consult Packaging section of atabook for thermal limitations and considerations of packages.DescriptionThe UC3827 family of controller devices provides an integrated control solution for cascaded buck and push-pull converters. These converters are known as current fed or voltage fed push-pull converters and are ideally suited for multiple output and/or high voltage output applications. In both current fed and voltage fed modes, the push-pull switches are dri at 50% nominal duty cycles and at one half the switching frequency of the buck stage. In the curre fed mode, the two switches are driven with a speciPush fied over-lap period to prevent ringing and voltage stress on the devices. In the voltage fed mode, the two switches are driven with a specified gap time between the switches to prevent shorting the trans- former across the energy storage capacitor and to prohibit excessive currents flowing through the devices.
The converter's output voltage is regulated by p width modulation of the buck switch. The UC3827 contains complete protection and PWM control functions for the buck converter. Easy control of the floating switch is accomplished by the floating drive circuitry. The gate drive waveform is level shifted to support an input voltage up to 72 VDC.
The UC3827 can be set up in traditional voltage mode control using input voltage feedforward technique or in urrent mode control. Using current mode control prevents potential core saturation of the push-pull transformer ue to mismatches in timing and in component tolerances. With average current mode control, precise control of he inductor current feeding the push-pull stage is possible without the noise sensitivity associated with peak urrent mode control. The UC3827 average current mode loop can also be connected in parallel with the voltage egulation loop to assist only in fault conditions.
Other valuable features of the UC3827 include bidirectional synchronization capability, user programmable verlap time (UC3827-1), user programmable gap time (UC3827-2), a high bandwidth differential current sense mplifier, and soft start circuitry.
UC3827-2 Data Sheet
