Philips TEA1208T Technical data

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TEA1208T

High efficiency DC/DC converter

Product specification 2002 Nov 15

Philips Semiconductors Product specification

High efficiency DC/DC converter TEA1208T

FEATURES

• Fully integrated DC/DC converter circuit

• Up-or-down conversion

• Start-up from 1.85 V input voltage

• Adjustable output voltage

• High efficiency over a wide range of loads

• Power handling capability up to 0.42 A continuous

average current

• 275 kHz switching frequency

• Low quiescent power consumption

• External clock synchronization

• True current limit for Li-ion battery compatibility

• Up to 100% duty cycle in down conversion

• Undervoltage lockout

• Shut-down function

• 8-pin SO package.

APPLICATIONS

• Cellular and cordless phones, Personal Digital
Assistants (PDAs) and others

• Supply voltage source for low-voltage chip sets

• Portable computers

• Battery backup supplies

• Cameras.

GENERAL DESCRIPTION

The TEA1208T is a fully integrated DC/DC converter.
Efficient, compact and dynamic power conversion is
achieved using special digital control concepts - Pulse
Width Modulation (PWM) and Pulse Frequency
Modulation (PFM), integrated low R
switches with low parasitic capacitances, and fully
synchronous rectification.

The device operates at a switching frequency of 275 kHz
requiring only minimum sized external components.
Deadlock isprevented by an on-chip undervoltage lockout
circuit.

Efficient behaviour during short load peaks and
compatibility with Li-ion batteries is guaranteed by an
accurate current limiting function.

CMOS power

DSon

ORDERING INFORMATION

TYPE NUMBER

NAME DESCRIPTION VERSION

TEA1208T SO8 plastic small outline package; 8 leads; body width 3.9 mm SOT96-1

PACKAGE

2002 Nov 15 2

Philips Semiconductors Product specification

High efficiency DC/DC converter TEA1208T

QUICK REFERENCE DATA

SYMBOL PARAMETER CONDITIONS MIN. TYP. MAX. UNIT

Voltage levels

UP CONVERSION; pin U/D = LOW
V

I

V

O

V

I(start)

input voltage V
output voltage 2.80 − 5.50 V

start-up input voltage IL< 62 mA 1.40 1.60 1.85 V
DOWN CONVERSION; pin U/D = HIGH
V

I

V

O

ENERAL

G
V

fb

input voltage 2.80 − 5.50 V

output voltage 1.30 − 5.50 V

feedback voltage 1.19 1.24 1.29 V

Current levels

I

q

I

shdwn

I

LX

∆I

lim

quiescent current on pin 3 down conversion;

current in shut-down state − 210µA

maximum continuous current on pin 4 T

current limit deviation I

Power MOSFETs

R

DSon

drain-to-source on-state resistance

N-type 0.10 0.20 0.30 Ω
P-type 0.10 0.22 0.35 Ω

Efficiency

η

1

η

2

efficiency up conversion VI= 3.6 V; VO= 4.6 V;

efficiency down conversion VI= 3.6 V; VO= 2.0 V;

Timing

f

sw

f

sync

t

res

switching frequency PWM mode 220 275 330 kHz

synchronization clock input frequency 4 6.5 20 MHz

response time from standby to P

I(start)

52 65 72 µA

VI= 3.6 V

=80°C −−0.30 A

amb

= 0.5 to 2.5 A

lim

up conversion −17.5 − +17.5 %
down conversion −17.5 − +17.5 %

L1 = 10 µH

I

=1mA − 88 − %

L

I

= 200 mA − 95 − %

L

L1 = 10 µH

=1mA − 86 − %

I

L

I

= 200 mA − 93 − %

L

− 50 −µs

0(max)

− 5.50 V

2002 Nov 15 3

Philips Semiconductors Product specification

High efficiency DC/DC converter TEA1208T

BLOCK DIAGRAM

dbook, full pagewidth

UPOUT/DNIN

3

P-type POWER FET

SUPPLY

INTERNAL

sense FET

TEA1208T

CIRCUIT

START-UP

FB

7

AND

CONTROL LOGIC

MCE155

BAND GAP

REFERENCE

TIME

COUNTER

DIGITAL CONTROLLER

MODE GEARBOX

SHDWN

5681

GATE

SYNC

SYNC U/D

Fig.1 Block diagram.

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2002 Nov 15 4

CURRENT LIMIT

I/V

CONVERTER

4

LX

2

ILIM

COMPARATORS

TEMPERATURE

I/V

CONVERTER

N-type

POWER

PROTECTION

FET

sense

FET

13 MHz

OSCILLATOR

GND

Philips Semiconductors Product specification

High efficiency DC/DC converter TEA1208T

PINNING

SYMBOL PIN DESCRIPTION

U/D 1 up-or-down conversion

selection input; active LOW for
up conversion

ILIM 2 current limiting resistor

connection

UPOUT/DNIN 3 output voltage in up conversion;

input voltage in down

conversion
LX 4 inductor connection
SYNC 5 synchronization clock input
GND 6 ground
FB 7 feedback input
SHDWN 8 shut-down input

handbook, halfpage

UPOUT/DNIN GND

1

U/D SHDWN

2

ILIM FB

TEA1208T

3
4

LX SYNC

8
7
6
5

MCE154

Fig.2 Pin configuration.

FUNCTIONAL DESCRIPTION
Control mechanism

The TEA1208T DC/DC converter is able to operate in
either PFM (discontinuous conduction) or PWM
(continuous conduction) mode. All switching actions are
completely determined by a digital control circuit which
uses the output voltage level as its control input. This
special design enables the use of a pulse width and
frequency modulation scheme, which ensures optimum
power efficiency over the complete operating range of the
converter.

Whenhigh outputpower is requested,the deviceoperates
in PWM (continuous conduction) mode. This results in
minimumAC currentsinthe circuitcomponentsand hence
optimumefficiency, minimumcosts and lowEMC. InPWM
mode, the output voltage is allowed to vary between a
window represented by two predefined voltage levels.
As long as the output voltage stays within this window,
switching continues in a fixed pattern. When the output
voltage reaches a window border, the digital controller
immediately adjusts the pulse width and inserts a current
stepso that theoutputvoltagestays within thewindowwith
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 sign twice per cycle, times the
capacitor’s internal Equivalent Series Resistance (ESR).
Aftereach ramp-down oftheinductor current, i.e.whenthe
ESR effect increases the output voltage, the converter
determines what to do in the next cycle.

As soon as more load current is taken from the output the
output voltage starts to decay.

When theoutput voltage becomes lower than the low limit
ofthe window,it is correctedby extendingthe period ofthe
inductor current ramp-up 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 a given device, the output voltage will not
vary more than 2% typically.

In low output power situations, the TEA1208T will switch
over to PFM (discontinuous conduction) operating mode.
In this mode, regulation information obtained in previous
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 TEA1208T 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 TEA1208T ensure that
during the whole second switching phase, all inductor
current will flow through the low-ohmic power MOSFETs.
Special circuitry isincluded whichdetects thatthe inductor
current reaches zero. Following this detection, the digital
controller switches off the power MOSFET and starts
regulation.

2002 Nov 15 5

Philips Semiconductors Product specification

High efficiency DC/DC converter TEA1208T

Start-up

Start-upfrom lowinput voltage in up conversionis realized
by an independent start-up oscillator, which starts
switching the N-type power MOSFET as soon as the
voltage at pin UPOUT/DNIN ismeasured tobe sufficiently
high. The switch actions of the start-up oscillator will
increase the output voltage.As soonas theoutput 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 T

amb

=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 T

, the actual maximum parameter limits

max

may be very different from those specified.

Current limiters

If the current inone ofthe powerswitches exceeds its limit
in the PWM mode, the current ramp is stopped
immediately, and the next switching phase is entered.
Currentlimiting isrequired to enable optimal useof energy
in Li-ion batteries, and to keep power conversion efficient
during temporaryhigh 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 thePFM mode, theswitching frequency isalwayslower.
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 thespecified range
isnot recommendedsince instability mayoccur. Thereare
two exceptions:

• Upconversion: atan input voltage higher thanthe target
output voltage, but up to 6 V, the converter will stop
switchingand the internalP-type power MOSFETwillbe
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