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

APPLICATION INFORMATION

An additional ripple of 30 mV is the result of using a tantalum capacitor with a low ESR of 300 m

Ω. 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.

CC2

33 nF

CC1

100 pF

RC

10 k

Ω

COMP

Figure 19. Compensation of the Control Loop