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PDF TEA1208T Data sheet ( Hoja de datos )
| Número de pieza | TEA1208T | |
| Descripción | High efficiency DC/DC converter | |
| Fabricantes | NXP Semiconductors | |
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INTEGRATED CIRCUITS
DATA SHEET
TEA1208T
High efficiency DC/DC converter
Product specification
2002 Nov 15
1 page  
Philips Semiconductors
High efficiency DC/DC converter
Product specification
TEA1208T
PINNING
SYMBOL
U/D
ILIM
UPOUT/DNIN
LX
SYNC
GND
FB
SHDWN
PIN DESCRIPTION
1 up-or-down conversion
selection input; active LOW for
up conversion
2 current limiting resistor
connection
3 output voltage in up conversion;
input voltage in down
conversion
4 inductor connection
5 synchronization clock input
6 ground
7 feedback input
8 shut-down input
handbook, halfpage
U/D 1
8 SHDWN
ILIM 2
7 FB
TEA1208T
UPOUT/DNIN 3
6 GND
LX 4
5 SYNC
MCE154
Fig.2 Pin configuration.
FUNCTIONAL DESCRIPTION
Control mechanism
The TEA1208T DC/DC converter is able to operate in
either PFM (discontinuous conduction) or PWM
(continuous conduction) mode. All switching actions are
completely determined by a digital control circuit which
uses the output voltage level as its control input. This
special design enables the use of a pulse width and
frequency modulation scheme, which ensures optimum
power efficiency over the complete operating range of the
converter.
When high output power is requested, the device operates
in PWM (continuous conduction) mode. This results in
minimum AC currents in the circuit components and hence
optimum efficiency, minimum costs and low EMC. In PWM
mode, the output voltage is allowed to vary between a
window represented by two predefined voltage levels.
As long as the output voltage stays within this window,
switching continues in a fixed pattern. When the output
voltage reaches a window border, the digital controller
immediately adjusts the pulse width and inserts a current
step so that the output voltage stays within the window with
higher or lower current capability. This approach enables
very fast reaction to load variations. Figure 3 shows the
converter’s response to a sudden load increase. The
upper trace shows the output voltage. The ripple on top of
the DC level is a result of the current in the output
capacitor, which changes sign twice per cycle, times the
capacitor’s internal Equivalent Series Resistance (ESR).
After each ramp-down of the inductor current, i.e. when the
ESR effect increases the output voltage, the converter
determines what to do in the next cycle.
As soon as more load current is taken from the output the
output voltage starts to decay.
When the output voltage becomes lower than the low limit
of the window, it is corrected by extending the period of the
inductor current ramp-up time. As a result, the DC current
level is increased and normal PWM control can continue.
The output voltage (including ESR effect) is again within
the predefined window. Figure 4 depicts the spread of the
output voltage window. The absolute value is most
dependent on spread, while the actual window size is not
affected. For a given device, the output voltage will not
vary more than 2% typically.
In low output power situations, the TEA1208T will switch
over to PFM (discontinuous conduction) operating mode.
In this mode, regulation information obtained in previous
PWM operating modes is used. This results in optimum
inductor peak current levels in the PFM mode, which are
slightly larger than the inductor ripple current in the PWM
mode. As a result, the transition between PFM and PWM
mode is optimum under all circumstances. In the PFM
mode the TEA1208T regulates the output voltage to the
high window limit as shown in Fig.3.
Synchronous rectification
For optimum efficiency over the whole load range,
synchronous rectifiers inside the TEA1208T ensure that
during the whole second switching phase, all inductor
current will flow through the low-ohmic power MOSFETs.
Special circuitry is included which detects that the inductor
current reaches zero. Following this detection, the digital
controller switches off the power MOSFET and starts
regulation.
2002 Nov 15
5
5 Page 
Philips Semiconductors
High efficiency DC/DC converter
APPLICATION INFORMATION
Product specification
TEA1208T
handbook, full pagewidth
VI
D1
L1
C1
UPOUT/DNIN
3
LX
4
TEA1208T
FB
7
165
8
2
U/D GND SYNC SHDWN ILIM
R1
R2
Rlim
C2
MCE156
VO
Fig.5 Complete application diagram for up conversion.
handbook, full pagewidth
VI
UPOUT/DNIN
3
LX
4
TEA1208T
FB
7
C1
1 25
68
U/D ILIM SYNC GND SHDWN
Rlim
L1
R1
D1 R2
VO
C2
MCE157
2002 Nov 15
Fig.6 Complete application diagram for down conversion.
11
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet TEA1208T.PDF ] | |
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