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參數(shù)資料
| 型號(hào)： | LTC3565EMSE#TRPBF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 2.5 A SWITCHING REGULATOR, 4000 kHz SWITCHING FREQ-MAX, PDSO10 |
| 封裝： | LEAD FREE, PLASTIC, MSOP-10 |
| 文件頁數(shù)： | 3/22頁 |
| 文件大?。?/td> | 587K |
| 代理商： | LTC3565EMSE#TRPBF |
LTC3565
3565fa
applications inForMation
A general LTC3565 application circuit is shown in
Figure 4.Externalcomponentselectionisdrivenbytheload
requirement, and begins with the selection of the inductor
L1. Once L1 is chosen, CIN and COUT can be selected.
Operating Frequency
Selection of the operating frequency is a trade-off between
efficiency and component size. High frequency operation
allows the use of smaller inductor and capacitor values.
Operation at lower frequencies improves efficiency by
reducing internal gate charge losses but requires larger
inductance values and/or capacitance to maintain low
output ripple voltage.
The operating frequency, fO, of the LTC3565 is determined
by an external resistor that is connected between the RT
pin and ground. The value of the resistor sets the ramp
current that is used to charge and discharge an internal
timingcapacitorwithintheoscillatorandcanbecalculated
by using the following equation:
RT = 1.21 × 106 (fO)–1.2674 (kΩ)
where RT is in kΩ and fO is in kHz or can be selected
using Figure 1.
The maximum usable operating frequency is limited by
the minimum on-time and the duty cycle. This can be
calculated as:
fO(MAX) ≈ 6.67
VOUT
VIN(MAX)
(MHz)
The minimum frequency is limited by leakage and noise
coupling due to the large resistance of RT.
Inductor Selection
The operating frequency, fO, has a direct effect on the
inductor value, which in turn influences the inductor ripple
current,
ΔIL:
ΔIL =
VOUT
fO L
1
VOUT
VIN
The inductor ripple current decreases with larger induc-
tance or frequency, and increases with higher VIN or VOUT.
Accepting larger values of
ΔIL allows the use of lower
inductances, but results in higher output ripple voltage,
greater core loss and lower output capability.
A reasonable starting point for setting ripple current is
ΔIL = 0.4IOUT(MAX),whereIOUT(MAX)is1.25A.Thelargest
ripple current
ΔILoccursatthemaximuminputvoltage.To
guarantee that the ripple current stays below a specified
maximum, the inductor value should be chosen according
to the following equation:
L =
VOUT
fO ΔIL
1
VOUT
VIN(MAX)
The inductor value will also have an effect on Burst Mode
operation. The transition from low current operation
begins when the peak inductor current falls below a level
set by the burst clamp. Lower inductor values result in
higher ripple current which causes this to occur at lower
load currents. This causes a dip in efficiency in the upper
range of low current operation. In Burst Mode operation,
lower inductance values will cause the burst frequency
to increase.
Figure 1. Frequency vs RT
Inductor Core Selection
Different core materials and shapes will change the
size/current and price/current relationship of an induc-
tor. Toroid or shielded pot cores in ferrite or permalloy
materials are small and don’t radiate much energy, but
generally cost more than powdered iron core inductors
with similar electrical characteristics. The choice of which
style inductor to use often depends more on the price vs
sizerequirementsandanyradiatedfield/EMIrequirements
than on what the LTC3565 requires to operate. Table 1
RT (k)
0
FREQUENCY
(kHz)
500
1500
2000
2500
5000
4500
3565 F01
1000
100
200
300
400
600
500
3000
3500
4000
TA = 25°C
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| LTC3565IMSE#PBF | 2.5 A SWITCHING REGULATOR, 4000 kHz SWITCHING FREQ-MAX, PDSO10 |
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| LTC3565IDD | 制造商:LINER 制造商全稱:Linear Technology 功能描述:1.25A, 4MHz, Synchronous Step-Down DC/DC Converter |
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