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TEA1206

High efficiency DC/DC converter

Philips Electronics 

Philips Semiconductors

High efficiency DC/DC converter

Preliminary specification

TEA1206T

Start-up

Start-up from low input voltage in boost mode is realised

by an independent start-up oscillator, which starts

switching the N-type powerfet as soon as the voltage at

pin 3 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 over the power MOSFETS.

Undervoltage lockout

As a result of too high load or disconnection of the input

power source, the output voltage can drop so low that

normal regulation cannot be guaranteed. In that case, the

device switches back to start-up mode. If the output

voltage would drop down even further, switching is

stopped completely.

Shut-down

When the shut-down pin is made HIGH, the converter

disables both switches and power consumption is reduced

to a few µA.

Power switches

The power switches in the IC are one N-type and one

P-type MOSFET, having a typical pin-to-pin resistance of

0.14 Ω and 0.16 Ω respectively. The maximum average

current in the switches is 1.0 A.

Temperature protection

When the device operates in PWM mode, and the device

temperature gets too high (typically 175 °C), the converter

stops operating. It resumes operation when the device

temperature falls below 175 °C again. As a result,

low-frequent cycling between on and off state will occur.

It should be noted that in the event of device temperatures

around the cut-off limit, the application differs strongly from

maximum specifications.

Current limiters

If the current in one of the power switches exceeds its limit

in PWM mode, current ramping is stopped immediately,

and the next switching phase is entered. Current limitation

is required to enable optimal use of energy in Lithium-Ion

batteries, and to keep power conversion efficient during

temporary high loads. Furthermore, current limitation

protects the IC against overload conditions, inductor

saturation, etc. The current limit level is set by an external

resistor which must be connected to pin 2.

External synchronisation

If a high-frequency clock is applied to the external

synchronisation pin, the switching frequency in PWM

mode will be exactly that frequency divided by 22. In PFM

mode, the switching frequency is always lower.

The quiescent current of the device increases when an

external clock is applied. In case no external

synchronisation is necessary, the sync pin must be tied to

ground level.

Behaviour at regulation limits

In two cases, the output voltage will not stay in normal

regulation because of excessive input voltage:

• Upconversion (see Fig.6): the output voltage will exceed

the high window limit if the input voltage is higher than

this limit plus the voltage drop over the diode. In that

case, the converter will stop switching and the external

schottky diode will take over all current. The output

voltage will be equal to Vi minus the diode voltage drop.

The input voltage must not exceed 5.5 V. The current

limit function is not active since all current flows through

the external diode in this situation.

• Downconversion (see Fig.7): the output voltage will get

lower than the lower window limit when the input voltage

is lower than this limit plus the voltage drop over the

P-type FET. In that case, the P-type FET will stay

conducting (100% duty cycle) resulting in Vo being equal

to Vi minus some resistive voltage drop. The input

voltage must not be lower than 2.8 V. The current limit

function remains active.

1999 Sep 16

6

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