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TPS61040 Datasheet

  • TPS61040

  • 采用 SOT-23 封裝用于 LCD 和白光 LED 的 28V 400mA 開關(guān)升壓轉(zhuǎn)...

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  • TI

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TPS61040
TPS61041
SLVS413B 鈥?OCTOBER 2002 鈥?REVISED MAY 2004
Terminal Functions
TERMINAL
NAME
SW
GND
FB
EN
VIN
NO.
1
2
3
4
5
I
I
I
I/O
I
DESCRIPTION
Connect the inductor and the Schottky diode to this pin. This is the switch pin and is connected to the drain of the
internal power MOSFET.
Ground
This is the feedback pin of the device. Connect this pin to the external voltage divider to program the desired output
voltage.
This is the enable pin of the device. Pulling this pin to ground forces the device into shutdown mode reducing the
supply current to less than 1 碌A(chǔ). This pin should not be left floating and needs to be terminated.
Supply voltage pin
DETAILED DESCRIPTION
OPERATION
The TPS61040/41 operates with an input voltage range of 1.8 V to 6 V and can generate 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
up to 1 MHz, the device enables the use of very small external components.
The converter monitors the output voltage, and as soon as the feedback voltage falls below the reference voltage
of typically 1.233 V, the internal switch turns on and the current ramps up. The switch turns off as soon as the
inductor current reaches the internally set peak current of typically 400 mA (TPS61040) or 250 mA (TPS61041).
Refer to the section
peak current control
for more information. The second criteria that turns off the switch is the
maximum on-time of 6 碌s (typical). This is just to limit the maximum on-time of the converter to cover for extreme
conditions. As the switch is turned off the external Schottky diode is forward biased delivering the current to the
output. The switch remains off for a minimum of 400 ns (typical), or until the feedback voltage drops 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 output current, which results in very high
efficiency over the entire load current range. This regulation scheme is inherently stable, allowing a wider
selection range for the inductor and output capacitor.
PEAK CURRENT CONTROL
The internal switch turns on until the inductor current reaches the typical dc current limit (I
LIM
) of 400 mA
(TPS61040) or 250 mA (TPS61042). Due to the internal propagation delay of typical 100 ns, theactualcurrent
exceeds the dc current limit threshold by a small amount. The typical peak current limit can be calculated:
I
+
I
)
Vin
100 ns
peak(typ)
LIM
L
I
+
400 mA
)
Vin
100 ns for the TPS61040
peak(typ)
L
100 ns for the TPS61041
I
+
250 mA
)
Vin
peak(typ)
L
(1)
The higher the input voltage and the lower the inductor value, the greater the peak.
By selecting the TPS61040 or TPS61041, it is possible to tailor the design to the specific application current limit
requirements. A lower current limit supports applications requiring lower output power and allows the use of an
inductor with a lower current rating and a smaller form factor. A lower current limit usually has a lower output
voltage ripple as well.
SOFTSTART
All inductive step-up converters exhibit high inrush current during start-up if no special precaution is made. This
can cause voltage drops at the input rail during start up and may result in an unwanted or early system shut
down.
3

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