
TPS61000, TPS61001, TPS61002, TPS61003, TPS61004, TPS61005, TPS61006, TPS61007
SINGLE-AND DUAL-CELL BOOST CONVERTER WITH START-UP INTO FULL LOAD
SLVS279B – MARCH 2000 – REVISED AUGUST 2000
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 m
. 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 will be 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
example, a 10-
μ
F ceramic capacitor with an ESR of 50 m
is used on the evaluation module (EVM). Tradeoffs
have to be made between performance and costs of the converter circuit.
A 10-
μ
F 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
MBRM120LT3
Motorola Surface Mount
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 will satisfy these requirements.
CC2
33 nF
CC1
100 pF
RC
10 k
COMP
Figure 19. Compensation of the Control Loop