TD1501 Techcode, TD1501 Datasheet - Page 12

• Manufacturer Part Number: TD1501
• Description: PWM Buck DC/DC Converter
• Manufacturer: Techcode

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Function Description(Cont.)
this is the output (switch) pin, which should not have
large areas of copper.) Large areas of copper provide the
best transfer of heat (lower thermal resistance) to the
surrounding air, and moving air lowers the thermal
resistance even further.
Setting the Output Voltage
The output voltage is set using a resistive voltage divider
from the output voltage to FB(TD1501-ADJ) The voltage
divider divides the output voltage down by the ratio:
VFB = VOUT * R1 / (R1 + R2)
Thus the output voltage is:
VOUT = 1.235 * (R1 + R2) / R1
R1 can be as high as 100KΩ, but a typical value is 10KΩ.
Using that value, R2 is determined by:
R2 ~= 8.18 * (VOUT – 1.235) (KΩ)
For example, for a 3.3V output voltage, R1 is 10KΩ, and
R2is 17KΩ.
Inductor
The inductor is required to supply constant current to the
output load while being driven by the switched input
voltage. A larger value inductor results in less ripple
current that in turn results in lower output ripple voltage.
However, the larger value inductor has a larger physical
size, higher series resistance, and/or lower saturation
current. Choose an inductor that does not saturate under
the worst-case load conditions. A good rule for
determining the inductance is to allow the peak-to-peak
ripple current in the inductor to be approximately 30% of
the maximum load current. Also, make sure that the peak
inductor current (the load current plus half the peak to
peak inductor ripple current) is below the TBDA minimum
current limit. The inductance value can be calculated by
the equation:
December, 20, 2005. Techcode Semiconductor Limited www.techcodesemi.com
T
3A 150KHz PWM Buck DC/DC Converter
echcode
®
12
L = (VOUT) * (VIN-VOUT) / VIN * f * ∆I
Where VOUT is the output voltage, VIN is the input
voltage, f is the switching frequency, and ∆I is the
peak-to-peak inductor ripple current.
Input Capacitor
The input current to the step-down converter is
discontinuous, and so a capacitor is required to supply
the AC current to the step-down converter while
maintaining the DC input voltage. A low ESR capacitor is
required to keep the noise at the IC to a minimum.
Ceramic capacitors are preferred, but tantalum or
low-ESR electrolytic capacitors may also suffice.
The input capacitor value should be greater than 10μF.
The capacitor can be electrolytic, tantalum or ceramic.
However since it absorbs the input switching current it
requires an adequate ripple current rating. Its RMS
current rating should be greater than approximately
1/2 of the DC load current.
For insuring stable operation should be placed as close
to the IC as possible. Alternately a smaller high quality
ceramic 0.1μF capacitor may be placed closer to the IC
and a larger capacitor placed further away. If using this
technique, it is recommended that the larger capacitor be
a tantalum or electrolytic type. All ceramic capacitors
should be places close to the TD1501.
Output Capacitor
The output capacitor is required to maintain the DC
output voltage. Low ESR capacitors are preferred to
keep the output voltage ripple low. The characteristics of
the output capacitor also affect the stability of the
regulation control system. Ceramic, tantalum, or low
ESR electrolytic capacitors are recommended. In the
case of ceramic capacitors, the impedance at the
switching frequency is dominated by the capacitance,
DATASHEET
TD1501
Datasheet pdf - http://www.DataSheet4U.net/