tea1208t NXP Semiconductors, tea1208t Datasheet - Page 12

• Manufacturer Part Number: tea1208t
• Description: High Efficiency Dc/dc Converter
• Manufacturer: NXP Semiconductors

Philips Semiconductors
External component selection
I
The performance of the TEA1208T is not very sensitive to
the inductance value. Best efficiency performance over a
wide load current range is achieved by using e.g. Coilcraft
DO1608C, having an inductance of 10 H and a saturation
current level of 1.1 A. In case the maximum output current
is lower, other inductors are also suitable such as the small
sized Coilcraft DT1608 range or Murata LQH4N series.
I
The value of capacitor C1 strongly depends on the type of
input source. In general, a 100 F tantalum capacitor will
do, or a 10 F ceramic capacitor featuring very low series
resistance (ESR value).
O
The value and type of capacitor C2 depend on the
maximum output current and the ripple voltage which is
allowed in the application. Low-ESR tantalum as well as
ceramic capacitors show good results. The most important
specification of capacitor C2 is its ESR, which mainly
determines the output voltage ripple.
D
The Schottky diode is only used a short time during
takeover from N-type power MOSFET and P-type power
MOSFET and vice versa. Therefore, a medium-power
diode such as Philips PRLL5819 is sufficient.
2002 Nov 15
NDUCTOR
NPUT CAPACITOR
IODE
UTPUT CAPACITOR
High efficiency DC/DC converter
D1
L1
C1
C2
12
F
The output voltage is determined by the resistors
R1 and R2. The following conditions apply:
Under these conditions, the output voltage can be
calculated by the formula:
C
The maximum instantaneous current is set by the external
resistor R
The connection of resistor R
The average inductor current during limited current
operation also depends on the inductance value, input
voltage, output voltage and resistive losses in all
components in the power path. Ensure that
I
lim
EEDBACK RESISTORS
URRENT LIMITING RESISTORS
Use 1% accurate SMD type resistors only. In case larger
body resistors are used, the capacitance on pin 7
(feedback input) will be too large, causing inaccurate
operation.
Resistors R1 and R2 should have a maximum value of
50 k when connected in parallel. A higher value will
result in inaccurate operation.
At up conversion: resistor R
between pin 2 (ILIM) and pin 3 (UPOUT/DNIN).
The current limiting level is defined by:
At down conversion: resistor R
between pin 2 (ILIM) and pin 6 (GND).
The current limiting level is defined by:
< I
sat
(saturation current) of the inductor.
lim
. The preferred type is SMD, 1% accurate.
R1
AND
V
lim
O
R2
lim
differs per mode:
=
must be connected
lim
1.24
must be connected
Product specification
TEA1208T
1
I
I
Iim
Iim
+
R1
------- -
R2
=
=
--------- -
R
238
270
--------- -
R
Iim
Iim