TEA1202TS_00 View Datasheet(PDF) - Philips Electronics
Part Name
Description
Manufacturer
TEA1202TS_00 Datasheet PDF : 24 Pages
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Philips Semiconductors
Battery power unit
Objective specification
TEA1202TS
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 shows the spread of the output voltage window.
The absolute value is mostly dependent on spread, while
the actual window size (Vh − Vl) is not affected. For one
specific device, the output voltage will not vary more
than 2% (typical value).
In low output power situations, the TEA1202TS will switch
over to PFM (discontinuous conduction) operating mode.
In this mode, regulation information from an earlier PWM
operating mode 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
TEA1202TS 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 TEA1202TS 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 when the
inductor current reaches zero. Following this detection, the
digital controller switches off the power MOSFET and
proceeds with regulation.
Start-up
Start-up from low input voltage in the boost mode is
realized by an independent start-up oscillator, which starts
switching the N-type power MOSFET as soon as the
low-battery detector detects a sufficiently high voltage.
The inductor current is limited internally to ensure
soft-starting. The switch actions of the start-up oscillator
will increase the output voltage. As soon as the output
voltage is high enough for normal regulation, the digital
control system takes control over the power MOSFETs.
Undervoltage lockout
As a result of too high a load or disconnection of the input
power source, the output voltage can drop so low that
normal regulation cannot be guaranteed. In this event, the
device switches back to start-up mode. If the output
voltage drops even further, switching is stopped
completely.
Shut-down
When the shut-down input is set HIGH, the DC/DC
converter disables both switches and power consumption
is reduced to a few microamperes.
Power switches
The power switches in the IC are one N-type and one
P-type power MOSFET, both having a typical
drain-to-source resistance of 100 mΩ. The maximum
average current in the power switches is 1.0 A at
Tamb = 80 °C.
Temperature protection
When the DC/DC converter operates in the PWM mode,
and the die temperature gets too high (typical value is
160 °C), the converter and both LDOs stop operating.
They resume operation when the die temperature falls
below 90 °C again. As a result, low frequent cycling
between the on and off state will occur. It should be noted
that in the event of device temperatures at the cut-off limit,
the application differs strongly from maximum
specifications.
Current limiters
If the current in one of the power switches exceeds the
programmed limit in the PWM mode, the current ramp is
stopped immediately and the next switching phase is
entered. Current limiting is required to keep power
conversion efficient during temporary high loads.
Furthermore, current limiting protects the IC against
overload conditions, inductor saturation, etc.
The current limiting level is set by an external resistor
which must be connected between pin ILIM and ground for
downconversion, or between pins ILIM and UPOUT/DNIN
for upconversion.
2000 Jun 08
7
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