SLUS495H − SEPTEMBER 2001 − REVISED AUGUST 2007
UCC29002
UCC29002/1
UCC39002
FUNCTIONAL DESCRIPTION
The UCC39002 does not have an undervoltage lockout circuit. The bias OK comparator works as an enable
function with a 4.375-V threshold. While V
DD
< 4.375 V the load share control functions are disabled. While this
might be inconvenient for some low voltage applications it is necessary to ensure high accuracy. The load share
accuracy is dependent on working with relatively large signal amplitudes on the load share bus. If the internal
offsets, current sense error and ground potential difference between the UCC39002 controllers are comparable
in amplitude to the load share bus voltage, they can cause significant current distribution error in the system.
The maximum voltage on the load share bus is limited approximately 1.7-V below the bias voltage level (V
DD
)
which would result in an unacceptably low load share bus amplitude therefore poor accuracy at low V
DD
levels.
To circumvent this potential design problem, the UCC39002 won’t operate below the above mentioned 4.375-V
bias voltage threshold. If the system does not have a suitable bias voltage available to power the UCC39002,
it is recommended to use an inexpensive charge pump which can generate the bias voltage for all the
UCC39002s in the load share system.
The maximum V
DD
of the UCC39002 is 15 V. For higher-voltage applications, use the application solution as
recommended in Figure 4. A Zener clamp on the VDD pin is provided internally so the device can be powered
from higher voltage rails using a minimum number of external components.
The CSA inputs must be adjusted so as to not exceed their absolute maximum voltage ratings.
LOAD CURRENT DIRECTION
VOUT+
R ADJ
SNS+
RBIAS1
LOAD
POWER SUPPLY
OUTPUT
1
2
3
R BIAS2
C BIAS
4
UCC39002
CS−
CS+
VDD
CSO
LS
EAO
8
7
6
CCOMP
GND
ADJ
5
RCOMP
SYSTEM
GROUND
LS BUS
TO OTHER
UCC39002
DEVICES
POWER SUPPLY
OUTPUT
SNS−
RSHUNT
VOUT−
Figure 4. High Voltage Application
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