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参数资料
| 型号： | LTC3809IDD-1 |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 1 A SWITCHING CONTROLLER, 600 kHz SWITCHING FREQ-MAX, PQCC10 |
| 封装： | 3 X 3 MM, PLASTIC, DFN-10 |
| 文件页数： | 13/24页 |
| 文件大小： | 256K |
| 代理商： | LTC3809IDD-1 |
LTC3809-1
20
38091fc
pulse of 20% to 100% of full load current having a rise
time of 1μs to 10μs will produce output voltage and ITH
pin waveforms that will give a sense of the overall loop
stability. The gain of the loop will be increased by increas-
ing RC and the bandwidth of the loop will be increased
by decreasing CC. The output voltage settling behavior is
related to the stability of the closed-loop system and will
demonstrate the actual overall supply performance. For
a detailed explanation of optimizing the compensation
components, including a review of control loop theory,
refer to Application Note 76.
A second, more severe transient is caused by switching
in loads with large (>1μF) supply bypass capacitors. The
discharged bypass capacitors are effectively put in parallel
with COUT, causing a rapid drop in VOUT. No regulator can
deliver enough current to prevent this problem if the load
switch resistance is low and it is driven quickly. The only
solution is to limit the rise time of the switch drive so that
the load rise time is limited to approximately (25) (CLOAD).
Thus a 10μF capacitor would be require a 250μs rise time,
limiting the charging current to about 200mA.
Design Example
As a design example, assume VIN will be operating from a
maximum of 4.2V down to a minimum of 2.75V (powered
by a single lithium-ion battery). Load current requirement
is a maximum of 2A, but most of the time it will be in a
standby mode requiring only 2mA. Efciency at both low
and high load currents is important. Burst Mode operation
at light loads is desired. Output voltage is 1.8V. The IPRG
pin will be left oating, so the maximum current sense
threshold
ΔVSENSE(MAX) is approximately 125mV.
Maximum Duty Cycle
V
OUT
IN MIN
=
()
.%
= 65 5
From Figure 1, SF = 82%.
RSF
V
I
DS ON MAX
SENSE MAX
OUT MAX
()
.
=
Δ
5
6
09
ρρT
=Ω
0 032
.
APPLICATIONS INFORMATION
A 0.032Ω P-channel MOSFET in Si7540DP is close to
this value.
The N-channel MOSFET in Si7540DP has 0.017Ω RDS(ON).
The short-circuit current is:
I
mV
A
SC =
Ω
=
90
0 017
53
.
So the inductor current rating should be higher than 5.3A.
The LTC3809-1 operates at a frequency of 550kHz. For
continuous Burst Mode operation with 600mA IRIPPLE,
the required minimum inductor value is:
L
V
kHz
mA
V
H
MIN =
=μ
18
550
600
1
18
275
188
.
.
A 6A 2.2μH inductor works well for this application.
CIN will require an RMS current rating of at least 1A
at temperature. A COUT with 0.1Ω ESR will cause
approximately 60mV output ripple.
PC Board Layout Checklist
When laying out the printed circuit board, use the following
checklist to ensure proper operation of the LTC3809-1.
The power loop (input capacitor, MOSFET, inductor,
output capacitor) should be as small as possible and
isolated as much as possible from LTC3809-1.
Put the feedback resistors close to the VFB pins. The ITH
compensation components should also be very close
to the LTC3809-1.
The current sense traces should be Kelvin connections
right at the P-channel MOSFET source and drain.
Keeping the switch node (SW) and the gate driver nodes
(TG, BG) away from the small-signal components,
especially the feedback resistors, and ITH compensation
components.
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