Datasheet

C
BP(10 V)
+
Q
gHS
) Q
gSR
DV
+
2 Q
g
DV
+
36 nC
0.5 V
+ 72 nF
C
BOOST
+
Q
g
DV
+
18 nC
0.5 V
+ 36 nF
R
BIAS
+
0.7 V R1
V
O
* 0.7 V
+
0.7 V 100kW
3.3 V * 0.7 V
+ 26.9 kW, choose 26.7 kW
f
Z1
+
1
2p R2 C1
N C1 +
1
2p 97.6 kW 4.93 kHz
+ 331 pF, choose 330 pF
f
P1
+
1
2p R2 C2
N R2 +
1
2p 22 pF 73.3 kHz
+ 98.2 kW, choose 97.6 kW
f
C
+
1
2p R1 C2 G
N C2 +
1
2p 100 kW 3.29 20 kHz
+ 24.2 pF, choose 22 pF
f
P2
+
1
2p R3 C3
N R3 +
1
2p 330 pF 73.3 kHz
+ 6.55 kW, choose 6.49 kW
f
Z2
+
1
2p R1 C3
N C3 +
1
2p 100 kW 4.93 kHz
+ 323 pF, choose 330 pF
TPS40054
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SLUS593H DECEMBER 2003REVISED JULY 2012
Choose R1 = 100 k
The poles and zeros for a type III network are described in Equation 24 through Equation 28.
(75)
(76)
(77)
(78)
(79)
Calculate the value of R
BIAS
from Equation 22 with R1 = 100 k.
(80)
CALCULATING THE BOOST AND BP10V BYPASS CAPACITANCE
The size of the bypass capacitor depends on the total gate charge of the MOSFET being used and the amount
of droop allowed on the bypass capacitor. The BOOST capacitance for the Si7860DP, allowing for a 0.5 voltage
droop on the BOOST pin from Equation 31 is:
(81)
and the BP10V capacitance from Equation 32 is
(82)
For this application, a 0.1-µF capacitor is used for the BOOST bypass capacitor and a 1.0-µF capacitor is used
for the BP10V bypass.
DESIGN EXAMPLE SUMMARY
Figure 15 shows component selection for the 10-V to 24-V to 3.3-V at 8 A dc-to-dc converter specified in the
design example. For an 8-V input application, it may be necessary to add a Schottky diode from BP10 to BOOST
to get sufficient gate drive for the upper MOSFET. As seen in Figure 7, the BP10 output is about 6 V with the
input at 8 V so the upper MOSFET gate drive may be less than 5 V.
A schottky diode is shown connected across the synchronous rectifier MOSFET as an optional device that may
be required if the layout causes excessive negative SW node voltage, greater than or equal to 2 V.
TPS40054-Q1, TPS40055-Q1 and TPS40057-Q1 automotive qualified versions TPS40055-EP Enhanced product
4.5 to 18V controller with power good TPS40195 4.5 to 18V controller with synchronization power good
TPS40200 Wide input non-synchronous DC-DC controller
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