Datasheet
1
2
3
4
16
15
14
13
PVDD2
BOOT2
SW2
BP
PVDD1
BOOT1
SW1
GND
TPS55383
5
6
7
12
11
10
SEQ
ILIM2
FB2
EN1
EN2
FB1
Output
V
IN
UDG-08123
8 9COMP2COMP1
Bypass and FIltering
Overtemperature Protection and Junction Temperature Rise
( )
( )
2
2
OUTPUTx
RMS(outputx ) OUTPUTx
I
I D I
12
æ ö
æ ö
D
ç ÷
ç ÷
= ´ +
ç ÷
ç ÷
ç ÷
è ø
è ø
(16)
TPS55383 , , TPS55386
SLUS818 – SEPTEMBER 2008 .........................................................................................................................................................................................
www.ti.com
Figure 29. Multiphase Operation Schematic
As with any integrated circuit, supply bypassing is important for jitter-free operation. To improve the noise
immunity of the converter, ceramic bypass capacitors must be placed as close to the package as possible.
1. PVDD1 to GND: Use a 10- µ F ceramic capacitor
2. PVDD2 to GND: Use a 10- µ F ceramic capacitor
3. BP to GND: Use a 4.7- µ F to 10- µ F ceramic capacitor
The overtemperature thermal protection limits the maximum power to be dissipated at a given operating ambient
temperature. In other words, at a given device power dissipation, the maximum ambient operating temperature is
limited by the maximum allowable junction operating temperature. The device junction temperature is a function
of power dissipation, and the thermal impedance from the junction to the ambient. If the internal die temperature
should reach the thermal shutdown level, the TPS5538x shuts off both PWMs and remains in this state until the
die temperature drops below the hysteresis value, at which time the device restarts.
The first step to determine the device junction temperature is to calculate the power dissipation. The power
dissipation is dominated by the two switching MOSFETs and the BP internal regulator. The power dissipated by
each MOSFET is composed of conduction losses and output (switching) losses incurred while driving the
external rectifier diode. To find the conduction loss, first find the RMS current through the upper switch MOSFET.
where
• D is the duty cycle
• I
OUTPUTx
is the dc output current
• Δ I
OUTPUTx
is the peak ripple current in the inductor for Outputx
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Product Folder Link(s): TPS55383 TPS55386