Datasheet

I
RMSCout
+ Vout
1 *
Vout
Vin
L ƒ
1
2 3
Ǹ
DVout + Vout
1 *
Vout
Vin
L ƒ
ǒ
1
8 Cout ƒ
) ESR
Ǔ
TPS62400, TPS62401
TPS62402, TPS62403, TPS62404
SLVS681E –JUNE 2006–REVISED APRIL 2010 www.ti.com
Table 7. List of Inductors
DIMENSIONS [mm
3
] INDUCTOR TYPE SUPPLIER
3.2×2.6×1.0 MIPW3226 FDK
3×3×0.9 LPS3010 Coilcraft
2.8×2.6×1.0 VLF3010 TDK
2.8x2.6×1.4 VLF3014 TDK
3×3×1.4 LPS3015 Coilcraft
3.9×3.9×1.7 LPS4018 Coilcraft
Output Capacitor Selection
The advanced fast response voltage mode control scheme of the converters allows the use of tiny ceramic
capacitors with a typical value of 10mF to 22mF, without having large output voltage under and overshoots during
heavy load transients. Ceramic capacitors with low ESR values results in lowest output voltage ripple, and are
therefore recommended. The output capacitor requires either X7R or X5R dielectric. Y5V and Z5U dielectric
capacitors are not recommended due to their wide variation in capacitance.
If ceramic output capacitors are used, the capacitor RMS ripple current rating always meets the application
requirements. The RMS ripple current is calculated as:
(8)
At nominal load current the inductive converters operate in PWM mode and the overall output voltage ripple is
the sum of the voltage spike caused by the output capacitor ESR, plus the voltage ripple caused by charging and
discharging the output capacitor:
(9)
Where the highest output voltage ripple occurs at the highest input voltage Vin.
At light load currents the converters operate in Power Save Mode and the output voltage ripple is dependent on
the output capacitor value. The output voltage ripple is set by the internal comparator delay and the external
capacitor. Higher output capacitors like 22mF values minimize the voltage ripple in PFM Mode and tighten DC
output accuracy in PFM Mode.
Input Capacitor Selection
Because of the nature of the buck converter having a pulsating input current, a low ESR input capacitor is
required to prevent large voltage transients that can cause misbehavior of the device or interference with other
circuits in the system. An input capacitor of 10mF is sufficient.
LAYOUT CONSIDERATIONS
As for all switching power supplies, the layout is an important step in the design. Proper function of the device
demands careful attention to PCB layout. Care must be taken in board layout to get the specified performance. If
the layout is not carefully done, the regulator could show poor line and/or load regulation, stability issues as well
as EMI problems. It is critical to provide a low-inductance, impedance ground path. Therefore, use wide and
short traces for the main current paths as indicated in bold in Figure 48.
The input capacitor should be placed as close as possible to the IC pins VIN and GND, the inductor and output
capacitor as close as possible to the pins SW1 and GND.
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