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Current Sense Resistor, R
SENSE
1 25
SOC(min)
SENSE
L _ PEAK (max)
V
R
. I
£
2
RSENSE IN _ RMS (max) SENSE
P ( I ) R=
PCL
PCL
SENSE
V
I
R
=
Gate Driver
VCC
VCC
GATE
C
OUT
L
BST
D
BST
V
OUT
Rectified
AC
GND
R
GATE
UVLO
IBOP
OLP
From
PWM
Latch
10k
S Q
QR
PCL
OVP
Clock
Pre-Drive and
Clamp Circuit
Q
BST
Fault
Logic
UCC28019
SLUS755B – APRIL 2007 – REVISED DECEMBER 2007
The current sense resistor, R
SENSE
, is sized using the minimum threshold value of Soft Over Current (SOC),
V
SOC(min)
= 0.66 V. To avoid triggering this threshold during normal operation, taking into account the gain of the
internal non-linear power limit, resulting in a decreased duty cycle, the resistor is typically sized for an overload
current of 25% more than the peak inductor peak current.
Since R
SENSE
sees the average input current, worst-case power dissipation occurs at input low line when input
line current is at its maximum. Power dissipated by the sense resistor is:
Peak Current Limit (PCL) protection turns off the output driver when the voltage across the sense resistor
reaches the PCL threshold, V
PCL
. The absolute maximum peak current, I
PCL
, is given as:
The GATE output is designed with a current-optimized structure to directly drive large values of total MOSFET
gate capacitance at high turn-on and turn-off speeds. An internal clamp limits voltage on the MOSFET gate to
12.5 V. An external gate drive resistor, R
GATE
, limits the rise time and dampens ringing caused by parasitic
inductances and capacitances of the gate drive circuit thus reducing EMI. The final value of the resistor depends
upon the parasitic elements associated with the layout and other considerations. A 10-k Ω resistor close to the
gate of the MOSFET, between the gate and ground, discharges stray gate capacitance and protects against
inadvertent dv/dt-triggered turn-on.
Figure 26. Gate Driver
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