Texas Instruments TPS61150A-150 Evaluation Board TPS61150AEVM-150 TPS61150AEVM-150 TPS61150AEVM-150 Datenbogen
Produktcode
TPS61150AEVM-150
www.ti.com
LAYOUT CONSIDERATION
SLVS706 – OCTOBER 2006
For V
I
= 3.6V, V
iout
= 20V, and F
s
= 1.2MHz, 0.1% ripple (20mV) would require 1.0
µ
F capacitor. For this value,
ceramic capacitors are the best choice for its size, cost and availability.
The additional output ripple component caused by ESR is calculated using:
V
ripple_ESR
= I
out
×
R
ESR
Due to it's low ESR, V
ripple_ESR
can be neglected for ceramic capacitors, but must be considered if tantalum or
electrolytic capacitors are used.
During a load transient, the capacitor at the output of the boost converter has to supply or absorb additional
current before the inductor current ramps up the steady state value. Larger capacitors always help to reduce the
voltage over and under shoot during a load transient. A larger capacitor also helps loop stability.
current before the inductor current ramps up the steady state value. Larger capacitors always help to reduce the
voltage over and under shoot during a load transient. A larger capacitor also helps loop stability.
Care must be taken when evaluating a ceramic capacitor’s derating due to applied dc voltage, aging and
frequency response. For example, larger form factor capacitors (in 1206 size) have their self-resonant
frequencies in the range of TPS61150A’s switching frequency, so the effective capacitance is significantly lower.
Therefore, it may be necessary to use small capacitors in parallel instead of one large capacitor.
frequency response. For example, larger form factor capacitors (in 1206 size) have their self-resonant
frequencies in the range of TPS61150A’s switching frequency, so the effective capacitance is significantly lower.
Therefore, it may be necessary to use small capacitors in parallel instead of one large capacitor.
The popular vendors for high value ceramic capacitors are:
TDK (
Murata (
)
Table 4. Recommended Input and Output Capacitors
Capacitance (
µ
F)
Voltage (V)
Case
TDK
C3216X5R1E475K
4.7
25
1206
C2012X5R1E105K
1
25
805
C1005X5R0J105K
1
6.3
402
Murata
GRM319R61E475KA12D
4.7
25
1206
GRM216R61E105KA12D
1
25
805
GRM155R60J105KE19D
1
6.3
402
As for all switching power supplies, especially those providing high current and using high switching frequencies,
layout is an important design step. If layout is not carefully done, the regulator could show instability as well as
EMI problems, therefore, use wide and short traces for high current paths. The input capacitor needs not only to
be close to the VIN pin, but also to the GND pin in order to reduce the input ripple seen by the IC. The VIN and
SW pins are conveniently located on the edges of the IC, therefore the inductor can be placed close to the IC.
The output capacitor needs to be placed near the load to minimize ripple and maximize transient performance.
layout is an important design step. If layout is not carefully done, the regulator could show instability as well as
EMI problems, therefore, use wide and short traces for high current paths. The input capacitor needs not only to
be close to the VIN pin, but also to the GND pin in order to reduce the input ripple seen by the IC. The VIN and
SW pins are conveniently located on the edges of the IC, therefore the inductor can be placed close to the IC.
The output capacitor needs to be placed near the load to minimize ripple and maximize transient performance.
It is also beneficial to have the ground of the output capacitor close to the GND pin since there will be large
ground return current flowing between them. When laying out signal ground, it is recommended to use short
traces separated from power ground traces, and connect them together at a single point.
ground return current flowing between them. When laying out signal ground, it is recommended to use short
traces separated from power ground traces, and connect them together at a single point.
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