UCC2808A-1Q1
UCC2808A-2Q1
SGLS183B –AUGUST 2003–REVISED JULY 2012
www.ti.com
ELECTRICAL CHARACTERISTICS (continued)
T
A
= –40°C to 125°C for the UCC2808A-xQ1, V
DD
= 10 V
(1)
, 1-μF capacitor from V
DD
to GND, R = 22 kΩ, C = 330 pF T
A
= T
J
,
(unless otherwise noted)
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
OUT high level I = −50 mA, V
DD
– OUT 0.5 1 V
Rise time C
L
= 1 nF 25 60 ns
Fall time C
L
= 1 nF 25 60 ns
Undervoltage Lockout Section
UCCx808A−1
(1)
11.5 12.5 13.5 V
Start threshold
UCCx808A−2 4.1 4.3 4.5 V
UCCx808A−1 7.6 8.3 9 V
Minimum operating voltage after start
UCCx808A−2 3.9 4.1 4.3 V
UCCx808A−1 3.5 4.2 5.1 V
Hysteresis
UCCx808A−2 0.1 0.2 0.3 V
Soft Start Section
COMP rise time FB = 1.8 V, rise from 0.5 V to 4 V 3.5 20 ms
Overall Section
Startup current V
DD
< start threshold 130 260 µA
Operating supply current FB = 0 V, CS = 0 V
(6)(1)
1 2 mA
V
DD
zener shunt voltage I
DD
= 10 mA
(7)
13 14 15 V
(6) Does not include current in the external oscillator network.
(7) Start threshold and zener shunt threshold track one another.
PIN ASSIGNMENTS
COMP: COMP is the output of the error amplifier and the input of the PWM comparator. The error amplifier in the
UCC2808A-xQ1 is a true low-output impedance, 2-MHz operational amplifier. As such, the COMP pin can both
source and sink current. However, the error amplifier is internally current limited, so that zero duty cycle can be
externally forced by pulling COMP to GND.
The UCC2808A-xQ1 family features built-in full-cycle soft start. Soft start is implemented as a clamp on the
maximum COMP voltage.
CS: The input to the PWM, peak current, and overcurrent comparators. The overcurrent comparator is only
intended for fault sensing. Exceeding the overcurrent threshold will cause a soft start cycle. An internal MOSFET
discharges the current sense filter capacitor to improve dynamic performance of the power converter.
FB: The inverting input to the error amplifier. For best stability, keep FB lead length as short as possible and FB
stray capacitance as small as possible.
GND: Reference ground and power ground for all functions. Due to high currents, and high frequency operation
of the UCC2808A-xQ1, a low impedance circuit board ground plane is highly recommended.
OUTA and OUTB: Alternating high current output stages. Both stages are capable of driving the gate of a power
MOSFET. Each stage is capable of 500-mA peak-source current, and 1-A peak-sink current.
The output stages switch at half the oscillator frequency, in a push-pull configuration. When the voltage on the
RC pin is rising, one of the two outputs is high, but during fall time, both outputs are off. This dead time between
the two outputs, along with a slower output rise time than fall time, insures that the two outputs can not be on at
the same time. This dead time is typically 60 ns to 200 ns and depends upon the values of the timing capacitor
and resistor.
The high-current output drivers consist of MOSFET output devices, which switch from V
DD
to GND. Each output
stage also provides a very low impedance to overshoot and undershoot. This means that in many cases, external
schottky-clamp diodes are not required.
RC: The oscillator programming pin. The oscillator of the UCC2808Ax-Q1 tracks V
DD
and GND internally, so that
variations in power supply rails minimally affect frequency stability. shows the oscillator block diagram.
4 Copyright © 2003–2012, Texas Instruments Incorporated
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