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參數(shù)資料
| 型號： | LTC3406ES5-1.5 |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 1.5MHz, 600mA Synchronous Step-Down Regulator in ThinSOT |
| 中文描述： | 1.3 A SWITCHING REGULATOR, 1800 kHz SWITCHING FREQ-MAX, PDSO5 |
| 封裝： | PLASTIC, MO-193, TSOT-23, 5 PIN |
| 文件頁數(shù)： | 22/24頁 |
| 文件大小： | 516K |
| 代理商： | LTC3406ES5-1.5 |
LTC3455
22
3455f
Increasing 3.3V Output Current to 1.2A
With an internal current limit of 900mA, Switcher 2 typi-
cally provides a 3.3V, 600mA output. While this output
current is sufficient for many portable devices, some
applications need a 3.3V supply capable of providing more
than 1A. Figure 15 shows how to implement a higher
current 3.3V output using the LTC3455. By adding one tiny
SOT23 PMOS and using the AI/AO amplifier as an LDO, the
3.3V output now provides 1.2A of output current. Switcher
2 is programmed for an output voltage of 3.3V, and the
LDO is programmed for an output voltage of 3.2V (3%
lower). As long as the load current is low enough for
Switcher 2 to provide, the LDO is turned off completely.
This circuit is ideal for applications that need the higher
3.3V output current for only a brief time. Switcher 2 will
normally provide all of the output current, and the LDO will
turn on briefly to provide the higher load currents.
Figure 14. Standalone USB Power Supply with
Temporary Backup Power
11
10
13
14
C3
1
μ
F
C4
4700
μ
F
WALLFB
HSI
HSO
C1, C2, C3, C5, C6: X5R OR X7R CERAMIC
L1, L2: TOKO DB318C
ALL RESISTORS 1%
3.3V, HS
V
MAX
8
6
5
9
1
C6
4.7
μ
F
USB 5V
USB
SUSPEND
USBHP
4
2
3
18
12
SW2
FB2
249k
L2, 4.7
μ
H
80.6k
10pF
C2
10
μ
F
3.3V
0.4A
1
7
SW1
FB1
100k
L1, 4.7
μ
H
80.6k
10pF
C1
10
μ
F
1.8V
0.2A
TIMER
PROG
16
AI
17
AO
DROPOUT
V
MAX
24
23
20
21
15
19
22
V
BAT
20k
10k
1M
1.8V
V
MAX
82.5k
C5
10
μ
F
1M
2.49k
1M
1.8V
ON
25
GND
CHRG
PBSTAT
RST
MODE
HSON
LTC3455
ON2
PWRON
3455 TA02
μ
C
USB
CONTROLLER
ON/OFF
TYPICAL APPLICATIO S
and AO pins provides 150mV of hysteresis (the dropout
indicator stays low until the V
MAX
pin rises back above
4.15V). A 4700
μ
F backup capacitor connected to the V
BAT
pin briefly provides power to the system after the USB
supply has been removed, and also helps support tran-
sient loads that slightly exceed the USB current limit.
Connecting this large capacitance to the V
BAT
pin has
several advantages. It provides a large energy reservoir
that is isolated from both the USB pin (the USB specifica-
tion limits capacitance on the USB supply pin to 10
μ
F or
less) and the V
MAX
pin (using a very large capacitance on
this pin will delay the system turn-on), and it prevents
large inrush currents by using the battery charger to
slowly charge this capacitor (normally using such a large
capacitor would result in very large inrush currents). With
the TIMER pin tied to V
MAX
, the battery charger operates
in constant-current mode (the voltage-loop and timer
function are disabled), so the 4700
μ
F capacitor is always
fully charged to the available USB voltage.
11
10
13
14
1
C7
1
μ
F
C3
1
μ
F
C5
10
μ
F
D1
C4
4.7
μ
F
WALL 5V
C1 TO C8: X5R OR X7R CERAMIC
L1, L2: TOKO DB318C
D1: ON SEMI MBRM110E
ALL RESISTORS 1%
3.3V, HS
8
6
5
9
1
C6
4.7
μ
F
USB 5V
4
2
3
16
12
249k
L2, 4.7
μ
H
2.49k
80.6k
100pF
C2
2x10
μ
F
3.3V
1.2A
M1
FDN304P
OR
Si2305DS
1
7
100k
L1, 4.7
μ
H
80.6k
10pF
C1
10
μ
F
1.8V
0.4A
24
23
20
21
15
19
22
C8, 0.1
μ
F
1k
1k
V
MAX
1M
2.49k
1M
1.8V
25
3455 F15
μ
C
USB
CONTROLLER
1.24k
3.32k
ON/OFF
WALLFB
HSI
17
AO
HSO
V
MAX
USB
SUSPEND
USBHP
SW2
AI
18
FB2
SW1
FB1
TIMER
PROG
V
BAT
ON
GND
CHRG
PBSTAT
RST
MODE
HSON
LTC3455
ON2
PWRON
SINGLE
CELL Li-ION
3.3V TO 4.2V
+
Figure 15. LTC3455 Application with 3.3V Output Current
Increased to 1.2A
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