SLVS141A Datasheet, PDF (11/18 Pages) Texas Instruments – FIXED NEGATIVE 5-V 200-mA INVERTING DC/DC CONVERTER

TPS6735
FIXED NEGATIVE 5ĆV 200ĆmA INVERTING DC/DC CONVERTER
SLVS141A − JULY 1996 − REVISED JANUARY 1997
APPLICATION INFORMATION
system typical characteristics (continued)
SOFT-START DELAY
vs
CAPACITANCE
70
C6 varied
(see Figure 7)
60
VI = 4 V
50
40
VI = 6 V
30
VI = 5 V
20
10
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4
C − Capacitance − µF
Figure 13
DRAIN-SOURCE ON-STATE RESISTANCE
vs
TEMPERATURE
0.7
0.6
VI = 6 V
0.5
0.4
VI = 4 V
VI = 5 V
0.3
0.2
0.1
0
− 40 − 20
0 20 40 60 80 100 120 140
T − Temperature − °C
Figure 14
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-MΩ 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).
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