TPS6735

FIXED NEGATIVE 5V 200mA INVERTING DC/DC CONVERTER

SLVS141A − JULY 1996 − REVISED JANUARY 1997

11

POST OFFICE BOX 655303

POST OFFICE BOX 1443

APPLICATION INFORMATION

system typical characteristics (continued)

The TPS6735 operates in the voltage-inverting circuit, shown in Figure 15, which can generate a −5-V output.

The circuit is ideal for applications that require a negative polarity voltage on the output with respect to the input

ground, and for energy management systems. The TPS6735 can be placed in a shutdown mode (1-

µA

quiescent current) by forcing EN low.

soft start

The soft-start capacitor provides an orderly start-up of the converter by slowly increasing the switch current limit

during power-up. The soft-start timing is controlled by the SS capacitance (see Figure 13 for the capacitance

value corresponding to the desired delay time). The switch current limit is proportional to the voltage applied

to SS, which is internally pulled to REF by a 1.2-M

Ω resistor. SS can be externally pulled lower than REF to limit

the switch current. A UVLO condition or an overcurrent condition initiates an SS cycle by discharging the SS

capacitor to ground through an internal transistor. A minimum of a 10-nF capacitor must be connected to SS

to current limit correctly.

inductor selection

The standard 10-

µH inductor required by the TPS6735 must have a saturation current greater than the peak

switch current at the desired maximum load. Operation over the full voltage range and current range is assured

by the 10-

µH inductor. To determine the required inductor staturation level, refer to the typical operating

characteristics graph for peak inductor current versus load current (see Figure 8).

Figure 13

40

20

10

0

0.1 0.2 0.3

0.5 0.6 0.7

0.9

50

60

SOFT-START DELAY

vs

CAPACITANCE

70

1 1.1 1.2

1.4

0.4

0.8

1.3

30

C − Capacitance −

µF

C6 varied

(see Figure 7)

VI = 4 V

VI = 5 V

VI = 6 V

Figure 14

0.3

0.1

0

0.6

DRAIN-SOURCE ON-STATE RESISTANCE

vs

TEMPERATURE

0.7

0.5

0.4

0.2

− 40 − 20

0

20

40

T − Temperature −

°C

60

80

100

120

140

VI = 4 V

VI = 6 V

VI = 5 V