SLUU182 − March 2004
11
High-Performance Dual Synchronous Buck Conversion Using the TPS5124
Figure 4 shows the closed loop gain and phase. For Channel 1, the overall crossover frequency
is approximately 30 kHz and the phase margin is 58
°
. For Channel 2, the crossover frequency is
approximately 23 kHz and phase margin is 55
°
.
4.6
Current Limiting
The current limit in TPS5124 is set using an internal current source and an external resistor
(R13 and R14). The current limit protection circuit compares the drain to source voltage of the
high-side and low-side drivers with respect to the set-point voltage. If the voltage exceeds the
limit during high side conduction, the current limit circuit terminates the high side driver pulse. If
the set point voltage is exceeded during low side conduction, the low side pulse is extended
through the next cycle. Together this action has the effect of decreasing the output voltage until
the under voltage protection circuit is activated and the fault latch is set and both the high-side
and low-side MOSFET drivers are shut off. Equation (16) should be used for calculating the
external resistor value for current protection set point.
R
CL
+
1.3
R
DS(on)
ǒ
I
LIM
)
I
RIPPLE
2
Ǔ
I
TRIP
where
•
R
CL
is external current limit resistor (R13 and R14)
•
R
DS(on)
is the on−resistor of low side MOSFET (Q2 and Q4)
•
1.3 is the temperature coefficient of the R
DS(on)
•
I
LIM
is the required current limit
•
I
TRIP
is the internal current source with a typical value of 13
µ
A at 25
°
C
(16)
Содержание TPS5124EVM-001
Страница 1: ...User s Guide 1 User s Guide...