Datasheet

TPS61000, TPS61001, TPS61002, TPS61003, TPS61004, TPS61005, TPS61006, TPS61007
SINGLE- AND DUAL-CELL BOOST CONVERTER WITH START-UP INTO FULL LOAD
SLVS279C – MARCH 2000 – REVISED APRIL 2003
17
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
An additional ripple of 30 mV is the result of using a tantalum capacitor with a low ESR of 300 mΩ. The total ripple
is the sum of the ripple caused by the capacitance and the ripple caused by the ESR of the capacitor. In this
example, the total ripple is 45 mV. It is possible to improve the design by enlarging the capacitor or using smaller
capacitors in parallel to reduce the ESR or by using better capacitors with lower ESR, like ceramics. For exam-
ple, a 10-µF ceramic capacitor with an ESR of 50 mΩ is used on the evaluation module (EVM). Tradeoffs have to
be made between performance and costs of the converter circuit.
A 10-µF input capacitor is recommended to improve transient behavior of the regulator. A ceramic capacitor or a
tantalum capacitor with a 100-nF ceramic capacitor in parallel placed close to the IC is recommended.
rectifier selection
The rectifier diode has a major impact on the overall converter efficiency. Standard diodes are not suitable for
low-voltage switched mode power supplies. A Schottky diode with low forward voltage and fast reverse recovery
should be used as a rectifier to minimize overall losses of the dc-dc converter. The maximum current rating of the
diode must be high enough for the application. The maximum diode current is equal to the maximum current in
the inductor that was calculated in equation 3. The maximum reverse voltage is the output voltage. The chosen
diode should therefore have a reverse voltage rating higher than the output voltage.
Table 2. Recommended Diodes
VENDOR PART NUMBER
Motorola Surface Mount MBRM120LT3
MBR0520LT1
Motorola Axial Lead 1N1517
ROHM RB520S-30
RB160L–40
The typical forward voltage of those diodes is in the range of 0.35 to 0.45 V assuming a peak diode current of
600 mA.
compensation of the control loop
An R/C/C network must be connected to the COMP pin in order to stabilize the control loop of the converter. Both
the pole generated by the inductor L1 and the zero caused by the ESR and capacitance of the output capacitor
must be compensated. The network shown in Figure 19 satisfies these requirements.
C
C2
33 nF
C
C1
100 pF
R
C
10 kΩ
COMP
Figure 19. Compensation of the Control Loop