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参数资料
| 型号： | TPS61045DRBT |
| 厂商： | TEXAS INSTRUMENTS INC |
| 元件分类： | 稳压器 |
| 英文描述： | 0.45 A SWITCHING REGULATOR, 1000 kHz SWITCHING FREQ-MAX, PDSO8 |
| 封装： | 3 X 3 MM, GREEN, PLASTIC, SON-8 |
| 文件页数： | 20/21页 |
| 文件大小： | 582K |
| 代理商： | TPS61045DRBT |
IN
P(typ)
(LIM)
V
I
= I
+
x 100 ns
L
IN
P(typ)
V
I
= 375 m A +
x 100 ns
L
SLVS440B – JANUARY 2003 – REVISED MARCH 2009
www.ti.com
DETAILED DESCRIPTION
OPERATION
The TPS61045 operates with an input voltage range of 1.8 V to 6 V and generates output voltages up to 28 V.
The device operates in a pulse frequency modulation (PFM) scheme with constant peak current control. This
control scheme maintains high efficiency over the entire load current range and, with a switching frequency of up
to 1 MHz, the device enables the use of small external components.
The converter monitors the output voltage and when the feedback voltage falls below the reference voltage of
1.233 V (typ) the main switch turns on and the current ramps up. The main switch turns off when the inductor
current reaches the internally set peak current of 375 mA (typ). See the peak current control section for more
information. The second criteria that turns off the main switch is the maximum on-time of 6 ms (typ). This limits
the maximum on-time of the converter in extreme conditions. As the switch is turned off, the external Schottky
diode is forward biased delivering the current to the output. The main switch remains off until the minimum off
time of 400 ns (typ) has passed and the feedback voltage is below the reference voltage again. Using this PFM
peak current control scheme, the converter operates in discontinuous conduction mode (DCM) where the
switching frequency depends on the input voltage, output voltage and output current. This gives a high efficiency
over the entire load current range. This regulation scheme is inherently stable which allows a wider range for the
selection of the inductor and output capacitor.
PEAK CURRENT CONTROL
The internal switch is turned on until the inductor current reaches the typical dc current limit (ILIM) of 375 mA. Due
to the internal current limit delay of 100 ns (typ) the actual current exceeds the dc current limit threshold by a
small amount. The typical peak current limit can be calculated:
The higher the input voltage and the lower the inductor value, the greater the current limit overshoot.
SOFTSTART
All inductive step-up converters exhibit high inrush current during start up if no special precautions are taken.
This can cause voltage drops at the input rail during start-up, which may result in an unwanted or premature
system shut down.
When the device is enabled, the internal input switch (Q1) is slowly turned on to reduce the in-rush current
charging the capacitor (C2) connected to pin L. Furthermore, the TPS61045 limits this in-rush current during
start-up by increasing the current limit in two steps starting from ILIM/4 for 256 switch cycles to ILIM/2 for the next
256 switch cycles.
ENABLE (CTRL PIN)
The CTRL pin serves two functions. One is the enable and disable of the device. The other is the output voltage
programming of the device. If the digital interface is not required, the CTRL pin is used as a standard enable pin
for the device.
Pulling the CTRL pin high enables the device beginning with the softstart cycle.
Pulling the CTRL pin to ground for a period of
≥ 560 ms shuts down the device, reducing the shutdown current to
0.1 mA (typ). During shutdown the internal input switch (Q1) remains open and disconnects the load from the
input supply of the device.
This pin must be terminated. For more details on how to use the interface function, see the DIGITAL
INTERFACE (CTRL) section.
8
Copyright 2003–2009, Texas Instruments Incorporated
Product Folder Link(s): TPS61045
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