Datasheet

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UDG-01069
8
4
V
REF
R
T
/ C
T
UCC28C42
PWM
R
T
C
T
24
SYNCHRONIZATION
CIRCUIT INPUT
ON .
LOW LOWHIGH
ON . OFF .
CLOCK
INPUT
PWM
OUT
UPPER THRESHOLD
LOWER THRESHOLD
OUTPUT A
COMBINED
UPPER THRESHOLD
LOWER THRESHOLD
V
CT
V
CT
(ANALOG)
V
SYNC
(DIGITAL)
UDG−01070
Precautions
Circuit Applications
UCC28C4x-EP
BiCMOS LOW-POWER CURRENT-MODE PWM CONTROLLERS
SGLS352B – DECEMBER 2006 – REVISED MAY 2007
APPLICATION INFORMATION (continued)
Figure 2. Oscillator Synchronization Circuit
Figure 3. Synchronization to an External Clock
The absolute maximum supply voltage is 20 V, including any transients that may be present. If this voltage is
exceeded, device damage is likely. This is in contrast to the predecessor bipolar devices that could survive up to
30 V. Thus, the supply pin should be decoupled as close to the ground pin as possible. Also, since no clamp is
included in the device, the supply pin should be protected from external sources that could exceed the 20 V
level.
Careful layout of the printed board has always been a necessity for high-frequency power supplies. As the
device switching speeds and operating frequencies increase, the layout of the converter becomes increasingly
important.
This 8-pin device has only a single ground for the logic and power connections. This forces the gate drive
current pulses to flow through the same ground that the control circuit uses for reference. Thus, the interconnect
inductance should be minimized as much as possible. One implication is to place the device (gate driver)
circuitry close to the MOSFET it is driving. Note that this can conflict with the need for the error amplifier and the
feedback path to be away from the noise generating components.
Figure 4 shows a typical off-line application.
9
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