Datasheet

´
> ´
OUT OUT
IN
V I
0.8 100 mA
V
³ ´
2
L
C
2
TPS61097
www.ti.com SLVS872C –JUNE 2009– REVISED DECEMBER 2011
Equation 3 provides an easy way to estimate whether the device is operating in continuous or discontinuous
operation. As long as the equation is true, continuous operation is typically established. If the equation becomes
false, discontinuous operation is typically established.
(3)
Due to the use of current hysteretic control in the TPS61097, the series resistance of the inductor can impact the
operation of the main switch. There is a simple calculation that can ensure proper operation of the TPS61097
boost converter. The relationship between the series resistance (R
IN
), the input voltage (V
IN
) and the switch
current limit (I
SW
) is shown in Equation 4.
R
IN
< V
IN
/ I
SW
(4) (4)
Examples:
I
SW
= 400 mA, V
IN
= 2.5 V (5) (5)
In Equation 5, R
IN
< 2.5 V / 400 mA; therefore, R
IN
must be less than 6.25 Ω.
I
SW
= 400 mA, V
IN
= 1.8 V (6) (6)
In Equation 6, R
IN
< 1.8 V / 400 mA; therefore, R
IN
must be less than 4.5 Ω.
The following inductor series from different suppliers have been used with TPS61097 converters:
Table 3. List of Inductors
VENDOR INDUCTOR SERIES
Coilcraft DO3314
TDK NLC565050T
Taiyo Yuden CBC2012T
Capacitor Selection
Input Capacitor
The input capacitor should be at least 10-μF to improve transient behavior of the regulator and EMI behavior of
the total power supply circuit. The input capacitor should be a ceramic capacitor and be placed as close as
possible to the VIN and GND pins of the IC.
Output Capacitor
For the output capacitor C
2
, it is recommended to use small ceramic capacitors placed as close as
possible to the VOUT and GND pins of the IC. If, for any reason, the application requires the use of large
capacitors which can not be placed close to the IC, the use of a small ceramic capacitor with an capacitance
value of around 2.2μF in parallel to the large one is recommended. This small capacitor should be placed as
close as possible to the VOUT and GND pins of the IC.
A minimum capacitance value of 4.7 μF should be used, 10 μF are recommended. If the inductor value exceeds
4.7 μH, the value of the output capacitance value needs to be half the inductance value or higher for stability
reasons, see Equation 7.
(7)
The TPS61097 is not sensitive to the ESR in terms of stability. Using low ESR capacitors, such as ceramic
capacitors, is recommended to minimize output voltage ripple. If heavy load changes are expected, the output
capacitor value should be increased to avoid output voltage drops during fast load transients.
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