參數(shù)資料
型號(hào)： TPS40042DRCTG4
廠商： TEXAS INSTRUMENTS INC
元件分類： 穩(wěn)壓器
英文描述： SWITCHING CONTROLLER, 700 kHz SWITCHING FREQ-MAX, PDSO10
封裝： 3 X 3 MM, GREEN, PLASTIC, SON-10
文件頁(yè)數(shù)： 7/35頁(yè)
文件大?。?/td> 746K
代理商： TPS40042DRCTG4
www.ti.com
VDD Bypass and Filtering
VDD Filter Resistor
Thermal Shutdown
Package Power Dissipation
(
)
(
)
f
T
DD
SW
SR
P
V
Iq
Q
=
+
+
(3)
SLUS777 – NOVEMBER 2007
hard enough to rapidly replenish the charge required to turn on an (high gate charge) external high-side
MOSFET. For this situation, an external Schottky diode between the VDD and BOOT pins may be added. While
the diode carries very small average current (QG x FSW) it may be required to carry several hundred mA of peak
surge current. The diode should be rated for at least 500 mA of surge current. For higher input voltage
applications, if a resistor is used in series with the boost capacitor, connect the diode to the junction of the
resistor and capacitor to remove the added resistance from the capacitor’s charge path.
For low input voltages, and a high gate charge upper switch MOSFET, a small
DESIGN
Schottky diode should be placed from VDD to BOOT. Do not use a resistor in
HINT:
series with the boost capacitor.
To prevent switching noise from being injected into the TPS40042 control circuitry, a ceramic capacitor (1
F
minimum) must be placed as close to the VDD pin and GND pad as possible.
To further limit the noise on VDD, a small 1-
to 2- resistor may be placed between the input voltage and the
VDD pin to create a small filter to VDD. The resistor should connect near the drain of the upper switch MOSFET
to prevent trace IR drops from increasing the sensed voltage drop. The resistor itself should be placed close to
Pin 5.
The current through the resistor includes the device's no-load switching current of 2 mA plus gate switching
current. The voltage drop induced across this resistor reduces the VDD-to-SW voltage sensed by the over
current protection circuitry within the device. This results with the apparent voltage drop across the upper switch
MOSFET being increased, thereby decreasing the current at which protection will occur. To minimize this effect,
the resistor value should be selected to yield less than a 25-mV drop.
If the junction temperature of the device reaches the thermal shutdown level, the PWM and the oscillator are
turned off and HDRV and LDRV are driven off. When the junction cools to the required level, the PWM soft starts
as during a normal power-up cycle.
The power dissipation in a controller is largely dependent on the MOSFET driver currents and the input voltage.
The driver current is proportional to the total gate charge, Qg, of the external MOSFETs, and the operating
frequency of the converter. The total power dissipation is:
where
I
Q is the quiescent operating current (neglecting drivers)
Qg
SWis the total gate charges of the upper switch MOSFET
Qg
SR is the total gate charges of the synchronous rectifier MOSFET
The maximum power capability of the PowerPad package is dependent on the layout as well as air flow. The
thermal impedance from junction-to-air assuming 2-oz. copper trace and thermal pad with solder and no air flow
is detailed in Reference [5].
Copyright 2007, Texas Instruments Incorporated
15
Product Folder Link(s): TPS40042
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