TEA1208T Просмотр технического описания (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
External component selection
INDUCTOR L1
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 µH 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.
INPUT CAPACITOR C1
The value of capacitor C1 strongly depends on the type of
input source. In general, a 100 µF tantalum capacitor will
do, or a 10 µF ceramic capacitor featuring very low series
resistance (ESR value).
OUTPUT CAPACITOR C2
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.
DIODE D1
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.
FEEDBACK RESISTORS R1 AND R2
The output voltage is determined by the resistors
R1 and R2. The following conditions apply:
• 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 kΩ when connected in parallel. A higher value will
result in inaccurate operation.
Under these conditions, the output voltage can be
calculated by the formula:
VO
=
1.24
×
1
+
RR-----12--
CURRENT LIMITING RESISTORS
The maximum instantaneous current is set by the external
resistor Rlim. The preferred type is SMD, 1% accurate.
The connection of resistor Rlim differs per mode:
• At up conversion: resistor Rlim must be connected
between pin 2 (ILIM) and pin 3 (UPOUT/DNIN).
The current limiting level is defined by: IIim = -R2---3-I-i-m8--
• At down conversion: resistor Rlim must be connected
between pin 2 (ILIM) and pin 6 (GND).
The current limiting level is defined by: IIim = -R2---7-I-i-m0--
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
Ilim < Isat (saturation current) of the inductor.
2002 Nov 15
12
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