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PDF TLF50251EL Data sheet ( Hoja de datos )
| Número de pieza | TLF50251EL | |
| Descripción | 2.2 MHz Step-Down Regulator | |
| Fabricantes | Infineon Technologies | |
| Logotipo |  |
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TLF50251EL
2.2 MHz Step-Down Regulator 500 mA, 5 V, low quiescent current
Data Sheet
Rev. 1.0, 2013-06-19
Automotive Power
1 page  
TLF50251EL
3 Pin Configuration
3.1 Pin Assignment
Pin Configuration
RO 1
TLF50251EL
14 EN
N.C.
2
13 VS
N.C.
3
12 N.C.
SYNC
FREQ
RTADJ
FB
4
5
6
7
Figure 2 Pin Configuration
11 SWO
10 GND
9 GND
P G -S S O P 1 4
8 N.C.
3.2 Pin Definitions and Functions
Pin Symbol Function
1 RO
Reset Output
Provides the reset output signal. Open collector output, connect a pull up resistor to VCC or
another voltage source, if feature is used, if not, leave open.
2 N.C.
Not Connected.
Internally not connected. Leave open or connect to GND.
3 N.C.
Not Connected.
Internally not connected. Leave open or connect to GND.
4 SYNC Synchronization Input
Connect to an external clock signal in order to synchronize/adjust the switching frequency. This
feature is not functionally in PFM mode.
5 FREQ Frequency Adjustment Pin
Connect an external resistor to GND to adjust the switching frequency, do not leave open. In
case the synchronization option is used, the resistor must be dimensioned close to the desired
synchronization frequency.
6 RTADJ Reset Threshold Adjust Pin
Connect an external resistor divider to adjust the Reset threshold. If function is not used, connect
to VCC .
7 FB
Feedback Input
Connect this pin directly to the output capacitor. Also input for internal power supply. The internal
power supply is taken from the output voltage.
8 N.C.
Not Connected.
Internally not connected. Leave open or connect to GND.
9 GND Ground
Connect this pin directly with low inductive and broad trace to ground, do not leave open.
Data Sheet
5 Rev. 1.0, 2013-06-19
5 Page 
TLF50251EL
Buck Regulator
5.1.2
PWM (Pulse Width Modulation) Mode
Under normal conditions the TLF50251EL will operate with a constant switching frequency fOSC in PWM mode.
The ratio between switch-on-time TON and switch-off-time TOFF is mainly determined by the ratio between the input
voltage VS and the output voltage VCC and is influenced by the output current ICC.
In PWM mode the device may operate with 100% duty cycle, in this case the internal PMOS is constantly
conducting current. The current limitation feature is operating under this condition.
If the switch-on-time TON should theoretically be below the minimum threshold TON,min (due to low load or due to
the ratio between input voltage VS and output voltage VCC depending on the switching frequency), it will be reduced
to the minimum value switch-on-time TON,min and stay there. As a consequence the output voltage VCC will
increase. The PFM comparator detects the PFM threshold and will then switch the device into PFM mode. There
is no possibility to disable the PFM function.
5.1.3
PFM (Pulse Frequency Modulation) Mode
To optimize the efficiency and to reduce the current consumption, the TLF50251EL automatically switches to PFM
mode under low load conditions. In PFM mode the internal power stage including the driver stage is switched off
and will only be switched on for applying pulses to charge the output capacitor. The pulses will be created by
monitoring the voltage of the output filter capacitor COUT. Thus in PFM mode the repetition time of pulses depend
on the output current and/or the ratio between input voltage VS and output voltage VCC.
Transition from PWM to PFM:
Figure 4 is showing the transition from Pulse Width Modulation to Pulse Frequency Modulation under the
assumption, that the input voltage VS will be constant and only the output current ICC will vary. The diagram shows
the principle, in reality the signals might look slightly different. The diagram is without scale in respect of time,
voltage and current values.
Starting from left of the figure a certain output current, here named i1, is applied to the regulator output. This results
in a duty cycle D1 with the on-time TON1 of the internal power stage. The switching frequency fOSC is constant as
set by the frequency setting resistor RFREQ. The regulator is in PWM mode, the output voltage is VREF_PWM which
is equal to VFB in PWM mode.
At point t1 the output current decreases from i1 to a lower i2. This results in a duty cycle D2 with the on-time TON2
of the internal power stage. Due to the reduced output load the on-time TON2 is shorter (the regulator is in
Discontinuous Conduction Mode DCM) than TON1. The switching frequency fOSC is constant as set by the
frequency setting resistor RFREQ. The regulator is still in PWM mode, the output voltage is VREF_PWM which is equal
to VFB in PWM mode. In Continuous Conduction Mode CCM the variation from TON1 to TON2 will be very small due
to smaller conduction losses.
At point t2 the output current decreases again from i2 to a lower i3. As a consequence the on-time TON will be
reduced also. The output current i3 is so low, that the on-time TON3 would be smaller than the TON,min. The regulator
does not allow a on-time smaller than TON,min. Therefore we can say that the output current i3 is under the
imaginary current threshold for transition from PWM to PFM iPWM/PFM. With the pulse staying at on-time TON,min the
output voltage VCC will rise. The regulator is still in PWM mode, but the output voltage rises.
Data Sheet
11 Rev. 1.0, 2013-06-19
11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet TLF50251EL.PDF ] | |
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