Datasheet

TPS61097-33
V
0.9 V to 3.3V
IN
VOUT
EN
L
GND
VIN
L1
R2
R1
C1
C2
V
+3.3V
OUT
´
´
´
IN OUT IN
OUT
V (V - V )
1
L =
f 200 mA V
´
ì
ï
´
í
ï
î
OUT OUT
IN
L,MAX
V I
+ 100 mA; continous current operation
0.8 V
I =
200 mA; discontinuous current operation
TPS61097
SLVS872C –JUNE 2009– REVISED DECEMBER 2011 www.ti.com
APPLICATION INFORMATION
Design Procedure
The TPS61097 DC/DC converters are intended for systems powered by a single up to triple cell Alkaline, NiCd,
NiMH battery with a typical terminal voltage between 0.9 V and 5.5 V. They can also be used in systems
powered by one-cell Li-Ion or Li-Polymer with a typical voltage between 2.5 V and 4.2 V. Additionally, any other
voltage source like solar cells or fuel cells with a typical output voltage between 0.9 V and 5.5 V can power
systems where the TPS61097 is used. The TPS61097 does not down-regulate VIN; therefore, if VIN is greater
than VOUT, VOUT tracks VIN.
Adjustable Bypass Switching
The EN pin can be set up as a low voltage control for the bypass switch. By setting the desired ratio of R1 and
R2, the TPS61097 can be set to switch on the bypass at a defined voltage level on VIN. For example, setting R1
and R2 to 200K Ω would set V
EN
to half of VIN. The voltage level of VIN engaging the bypass switch is based on
the V
IL
level of EN (0.65 V). If VIN is less than 1.30 V then the bypass switch will be enabled. For VIN values
above 1.50 V (50% of V
IH
) the bypass switch is disabled.
Figure 18. Adjustable Bypass Switching
Inductor Selection
To make sure that the TPS61097 devices can operate, a suitable inductor must be connected between pin VIN
and pin L. Inductor values of 4.7 μH show good performance over the whole input and output voltage range .
Choosing other inductance values affects the switching frequency f proportional to 1/L as shown in Equation 1.
(1)
Choosing inductor values higher than 4.7 μH can improve efficiency due to reduced switching frequency and
therefore with reduced switching losses. Using inductor values below 2.2 μH is not recommended.
Having selected an inductance value, the peak current for the inductor in steady state operation can be
calculated. Equation 2 gives the peak current estimate.
(2)
I
L,MAX
is the inductor's required minimum current rating. Note that load transient or over current conditions may
require an even higher current rating.
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