TEA1207T Philips Semiconductors, TEA1207T Datasheet - Page 5

• Manufacturer Part Number: TEA1207T
• Description: High efficiency DC/DC converter
• Manufacturer: Philips Semiconductors

Philips Semiconductors
PINNING
FUNCTIONAL DESCRIPTION
Control mechanism
The TEA1207T DC/DC converter is able to operate in PFM
(discontinuous conduction) or PWM (continuous
conduction) operating mode. All switching actions are
completely determined by a digital control circuit which
uses the output voltage level as its control input. This novel
digital approach enables the use of a new 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 will
operate in PWM (continuous conduction) operating mode.
This results in minimum AC currents in the circuit
components and hence optimum efficiency, minimum
costs and low EMC. In this operating mode, the output
voltage is allowed to vary between two predefined voltage
levels. As long as the output voltage stays within this
so-called window, switching continues in a fixed pattern.
When the output voltage reaches one of the window
borders, the digital controller immediately reacts by
adjusting the pulse width and inserting a current step in
such a way 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 in 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
1999 Oct 21
U/D
ILIM
UPOUT/DNIN
LX
SYNC
GND
FB
SHDWN
High efficiency DC/DC converter
SYMBOL
PIN
1
2
3
4
5
6
7
8
up-or-down mode selection
input; active LOW for up mode
current limiting resistor
connection
output voltage in up mode;
input voltage in down mode
inductor connection
synchronization clock input
ground
feedback input
shut-down input
DESCRIPTION
5
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, a corrective action is taken by a ramp-up of
the inductor current during a much longer 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 one specific device, the output voltage
will not vary more than 2% typically.
In low output power situations, the TEA1207T will switch
over to PFM (discontinuous conduction) operating mode.
In this mode, regulation information from earlier 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
TEA1207T 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 TEA1207T 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 proceeds
regulation.
handbook, halfpage
UPOUT/DNIN
ILIM
U/D
Fig.2 Pin configuration.
LX
1
2
3
4
TEA1207T
MGR666
Preliminary specification
8
7
6
5
SHDWN
FB
GND
SYNC
TEA1207T