TEA1202 データシートの表示（PDF） - Philips Electronics

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TEA1202

0.95 V starting power unit

Philips Electronics 

Philips Semiconductors

0.95 V starting power unit

Preliminary specification

TEA1202TS

8.9 External synchronization and PWM-only mode

If an external high-frequency clock or a HIGH level is

applied to pin SYNC/PWM, the TEA1202TS will use PWM

regulation independent of the load applied.

In the event a high-frequency clock is applied, the

switching frequency in the PWM mode will be exactly that

frequency divided by 22. In the PWM mode the quiescent

current of the device increases.

In the event that no external synchronization or PWM

mode selection is necessary, pin SYNC/PWM must be

connected to ground.

8.10 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:

• Upconversion: at an input voltage higher than the target

output voltage, but up to 5.5 V, the converter will stop

switching and the external Schottky diode will take over.

The output voltage will equal the input voltage minus the

diode voltage drop. Since all current flows through the

external diode in this situation, the current limiting

function is not active.

In the PWM mode, the P-type power MOSFET is always

on when the input voltage exceeds the target output

voltage. The internal synchronous rectifier ensures that

the inductor current does not fall below zero. As a result,

the achieved efficiency is higher in this situation than

standard PWM-controlled converters achieve.

• Downconversion: when the input voltage is lower than

the target output voltage, but higher than 2.2 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.

Both LDOs are protected from high temperature

(see Section 8.7).

Next to normal LDO functions, both regulators can be

switched off or can be used as switches. Each regulator

will act as a low-ohmic switch in the on-state when its

feedback input is connected to ground. When the

feedback input is higher than 2 V, the regulator will make

its power FET high-ohmic. So the feedback inputs of the

regulators can be used as digital inputs which make the

LDOs behave as switches.

8.12 Low battery detector

The low battery detector is an autonomous circuit which

can work at an input voltage down to 0.90 V. It is always

on, even when all other blocks are in the shut-down mode.

The detector has two inputs: the input on pin LBI1 is tuned

to accept a single-cell NiCd or NiMH battery voltage

directly, while the input on pin LBI2 can detect a two-cell

NiCd or NiMH battery voltage or higher voltage. The

detection level of the input on pin LBI2 can be set by using

a voltage divider between the battery voltage, pin LBI2 and

ground. Hysteresis is included for proper operating.

Furthermore, a capacitor of 10 nF (typical value) must be

connected between pin LBI1 and ground when the input

on pin LBI2 is used.

The output of the low battery detector on pin LBO is an

open-collector output. The output is high (i.e. no current is

sunk by the collector) when the input voltage of the

detector is below the lower detection level.

8.11 Low drop-out voltage regulators

The low drop-out voltage regulators are functionally equal

apart from the shut-down mechanism: LDO2 can be

controlled separately by pin SHDWN2, while LDO1 is

controlled by pin SHDWN0 like the DC-to-DC converter.

The input voltage of each LDO must be 250 mV (at

ILDO = 50 mA) higher than its output voltage to achieve full

specification on e.g. ripple rejection. However, the parts

will function like an LDO down to a margin of 45 mV (at

ILDO = 50 mA) between input and output: the so-called

drop-out voltage. At a lower margin between input and

output, the LDOs will behave like a resistor.

2002 Mar 14

10

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