TEA1208T Ver la hoja de datos (PDF) - Philips Electronics
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TEA1208T Datasheet PDF : 20 Pages
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Philips Semiconductors
High efficiency DC/DC converter
Product specification
TEA1208T
Start-up
Start-up from low input voltage in up conversion is realized
by an independent start-up oscillator, which starts
switching the N-type power MOSFET as soon as the
voltage at pin UPOUT/DNIN is measured to be sufficiently
high. 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 over the control of 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 case, the
device switches back to start-up mode. If the output
voltage drops even further, switching stops completely.
Shut-down
When the shut-down input is made HIGH, the converter
disables both power switches reducing the power
consumption to a few microamperes.
Power switches
The device has two power switches - one N-type and one
P-type power MOSFET, having a typical drain-to-source
resistance of 0.20 Ω and 0.22 Ω respectively.
The maximum average current in the power switches is
0.30 A at Tamb = 80 °C.
Temperature protection
In PWM mode, the device will stop operating if the die
temperature is too high (typically 175 °C). Operation
resumes when the die temperature falls below 175 °C.
As a result, low-frequency cycling between the on and off
state will occur. Note that if the temperature of the device
approaches Tmax, the actual maximum parameter limits
may be very different from those specified.
Current limiters
If the current in one of the power switches exceeds its limit
in the PWM mode, the current ramp is stopped
immediately, and the next switching phase is entered.
Current limiting is required to enable optimal use of energy
in Li-ion batteries, and 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.
External synchronization
If an external high-frequency clock is applied to the
synchronization clock input, the switching frequency in
PWM mode will be exactly that frequency divided by 22.
In the PFM mode, the switching frequency is always lower.
The quiescent current of the device increases when
external clock pulses are applied. When no external
synchronization is necessary, the synchronization clock
input must be connected to ground level.
Behaviour at input voltage exceeding the specified
range
In general, an input voltage exceeding the specified range
is not recommended since instability may occur. There are
two exceptions:
• Up conversion: at an input voltage higher than the target
output voltage, but up to 6 V, the converter will stop
switching and the internal P-type power MOSFET will be
conducting. The output voltage will equal the input
voltage minus some resistive voltage drop. The current
limiting function is not active.
• Down conversion: when the input voltage is lower than
the target output voltage, but higher than 2.8 V, the
P-type power MOSFET will stay conducting resulting in
an output voltage being equal to the input voltage minus
some resistive voltage drop. The current limiting
function remains active.
2002 Nov 15
6
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