Datasheet

IN
POS
V η
D = 1
V
´
-
TPS65137
SLVS929A –MAY 2010–REVISED OCTOBER 2012 www.ti.com
Table 1. Programming Table for OUTN
BIT/RISING EDGES OUTN (Vss) DAC VALUE BIT/RISING EDGES OUTN(Vss) DAC VALUE
Default –4.93 V 00000 16 –3.7 V 10000
1 –5.23 V 00001 17 –3.62 V 10001
2 –5.13 V 00010 18 –3.52 V 10010
3 –5.03 V 00011 19 –3.42 V 10011
4 –4.93 V 00100 20 –3.32 V 10100
5 –4.83 V 00101 21 –3.22 V 10101
6 –4.73 V 00110 22 –3.12 V 10110
7 –4.63 V 00111 23 –3.02 V 10111
8 –4.53 V 01000 24 –2.92 V 11000
9 –4.43 V 01001 25 –2.82 V 11001
10 –4.33 V 01010 26 –2.72 V 11010
11 –4.23 V 01011 27 –2.62 V 11011
12 –4.13 V 01100 28 –2.52 V 11100
13 –4.03 V 01101 29 –2.42 V 11101
14 –3.93 V 01110 30 –2.31 V 11110
15 –3.82 V 01111 31 –2.21 V 11111
V
neg
Programming Transition Time t
set
for OUTN (C
T
)
The TPS65137 allows setting the transition time t
set
using an external capacitor connected to pin CT. The
transition time is the time period required to move OUTN from one voltage level to the next programmed voltage
level. When the CT pin is left open then the shortest possible transition time is programmed. When connecting a
capacitor to the CT pin then the transition time is given by the R-C time constant. This is given by the output
impedance of the CT pin of typically 250kΩ and the external capacitance. Within one τ the output voltage OUTN
has reached 70% of its programmed value. An example is given when using 100nF for C
T
.
τ ≈ t
set70%
= 250 kΩ × C
T
= 250 kΩ × 100 nF = 25 mS
INPUT CAPACITOR SELECTION
The device typically requires a 4.7μF ceramic input capacitor. Larger values can be used to lower the input
voltage ripple.
Table 2. Input Capacitor Selection
CAPACITOR COMPONENT SUPPLIER SIZE
4.7 μF/10 V Taiyo Yuden LMK107BJ475 0603
10 μF/10 V Taiyo Yuden LMK212BJ106 0805
10 μF/6.3 V Taiyo Yuden JMK107BJ106 0603
BOOST CONVERTER DESIGN CONSIDERATION, V
pos
The positive output consists of a boost converter using a LDO as post regulator. The maximum output current is
limited by the minimum current limit of the LDO, of 200mA. The component values and output current are
calculated at maximum load current in continuous conduction operation. The typical switching frequency during
this operation mode is 1.4MHz.
The boost converter duty cycle is:
(1)
To calculate the duty cycle, a good estimation for the efficiency, η, is 75% or it can be taken out of the typical
curve in Figure 1. In order to calculate the maximum output current of the boost converter for a certain input
voltage, the following formula is used:
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