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SLUS488E − SEPTEMBER 2002 − REVISED JULY 2009
1
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FEATURES
D Programmable Slope Compensation
D Internal Soft-Start on the UCC38083/4
D Cycle-by-Cycle Current Limiting
D Low Start-Up Current of 120 µA and 1.5 mA
Typical Run Current
D Single External Component Oscillator
Programmable from 50 kHz to 1 MHz
D High-Current Totem-Pole Dual Output Stage
Drives Push-Pull Configuration with 1-A Sink
and 0.5-A Source Capability
D Current Sense Discharge Transistor to
Improve Dynamic Response
D Internally Trimmed Bandgap Reference
D Undervoltage Lockout with Hysteresis
APPLICATIONS
D High-Efficiency Switch-Mode Power Supplies
D Telecom dc-to-dc Converters
D Point-of-Load or Point-of-Use Power Modules
D Low-Cost Push-Pull and Half-Bridge
Applications
DESCRIPTION
The UCC38083/4/5/6 is a family of BiCMOS pulse width
modulation (PWM) controllers for dc-to-dc or off-line
fixed-frequency current-mode switching power
supplies. The dual output stages are configured for the
push-pull topology. Both outputs switch at half the
oscillator frequency using a toggle flip-flop. The dead
time between the two outputs is typically 110 ns, limiting
each output’s duty cycle to less than 50%.
The new UCC3808x family is based on the UCC3808A
architecture. The major differences include the addition
of a programmable slope compensation ramp to the CS
signal and the removal of the error amplifier. The current
flowing out of the ISET pin through an external resistor
is monitored internally to set the magnitude of the slope
compensation function. This device also includes an
internal discharge transistor from the CS pin to ground,
which is activated at each clock cycle after the pulse is
terminated. This discharges any filter capacitance on
the CS pin during each cycle and helps minimize filter
capacitor values and current sense delay.
The UCC38083 and the UCC38084 devices have a
typical soft-start interval time of 3.5 ms while the
UCC38085 and the UCC38086 has less than 100 µs for
applications where internal soft-start is not desired.
The UCC38083 and the UCC38085 devices have the
turn-on/off thresholds of 12.5 V / 8.3 V, while the
UCC38084 and the UCC38086 has the turn-on/off
thresholds of 4.3 V / 4.1 V. Each device is offered in 8-pin
TSSOP (PW), 8-pin SOIC (D) and 8-pin PDIP (P)
packages.
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Copyright 2002−2009, Texas Instruments Incorporated
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.
UDG−01080
BASIC APPLICATION
OUTA
OUTB
CS
CTRL
RT
ISET
GND
VDD
R
SET
R
T
POWER
TRANSFORMER
C
F
R
F
R
S
V
IN
UCC3808x
FEEDBACK
V
OUT
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