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PDF LT3689-5 Data sheet ( Hoja de datos )
| Número de pieza | LT3689-5 | |
| Descripción | 700mA Step-Down Regulator | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LT3689/LT3689-5
FEATURES
700mA Step-Down
Regulator with Power-On Reset
and Watchdog Timer
DESCRIPTION
n Wide Input Range:
Operation from 3.6V to 36V
Overvoltage Lockout Protects Circuits through
60V Transients
n 85μA IQ at 12VIN to 3.3VOUT
n Low Ripple Burst Mode® Operation Allows Output
Ripple <15mVP-P
n Programmable, Defeatable Watchdog Timer with
Window or Timeout Control
n Programmable Power-On Reset Timer (POR)
n Synchronizable, Adjustable 350kHz to 2.2MHz
Switching Frequency
n 700mA Output Switching Regulator with Internal
Power Switch
n Fixed 5V or Adjustable Output Voltage
n 800mV Feedback Voltage
n Programmable Input Undervoltage Lockout with
Hysteresis
n 16-Pin 3mm × 3mm QFN and 16-Pin MSOP Packages
APPLICATIONS
n Automotive Electronic Control Units
n Industrial Power Supplies
The LT®3689 is an adjustable frequency (350kHz to 2.2MHz)
monolithic step-down switching regulator with a power-on
reset and watchdog timer. The regulator operates from
inputs up to 36V and withstands transients up to 60V. Low
ripple Burst Mode® operation maintains high efficiency at
low output current while keeping output ripple below 15mV
in a typical application, with input quiescent current of just
85μA. Shutdown circuitry reduces input supply current to
less than 1μA while EN/UVLO is pulled low. Using a resis-
tor divider on the EN/UVLO pin provides a programmable
undervoltage lockout. Current limit, frequency foldback
and thermal shutdown provide fault protection.
The reset and watchdog timeout periods are indepen-
dently adjustable using external capacitors. Tight accuracy
specifications and glitch immunity ensure reliable reset
operation of a system without false triggering. The open
collector RST will pull down if output voltage drops 10%
below the programmed value. The watchdog timer is
pin-selectable for window or timeout modes. In timeout
mode, WDO pulls low if too long of a period passes before
a watchdog transition is detected. In window mode, the
LT3689 monitors for WDI falling edges grouped too close
together or too far apart.
L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks of
Linear Technology Corporation. All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
3.3V Regulator with Power-On Reset Timer and Watchdog Timer
VIN
4.5V TO 36V
TRANSIENT TO 60V
2.2μF
μP
I/O
I/O
RESET
CWDT
10nF
tWDU = 182ms
tWDL = 5.9ms
CPOR
68nF
tRST = 157ms
VIN EN/UVLO OUT
BST
WDI
WDO LT3689
SW
RST
CWDT
CPOR
GND
DA
FB
RT
SYNC
fSW = 700kHz
0.1μF
12μH
10pF
3.3V
700mA
316k
20.5k 100k
22μF
3689 TA01
90
VIN = 12V
80 VOUT = 3.3V
f = 700kHz
70 L = 12μH
60 TA = 25°C
Efficiency
50
40
30
20
10
0
0.0001
0.001
0.01
0.1
LOAD CURRENT (A)
1000
100
10
1
1
3689 TA01b
3689fa
1
1 page  
TYPICAL PERFORMANCE CHARACTERISTICS
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LT3689/LT3689-5
No-Load Supply Current vs VIN
140
TA = 25°C
120
100
80
60
40
20
0
0 5 10 15 20 25 30 35 40
INPUT VOLTAGE (V)
3689 G04
No-Load Supply Current
800
CATCH DIODE: DIODES INC. B140HB
700 VIN = 12V
VOUT = 3.3V
600
500
INCREASED SUPPLY
400 CURRENT DUE TO
CATCH DIODE LEAKAGE
300 AT HIGH TEMPERATURE
200
100
0
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
3689 G05
Maximum Load Current, 5VOUT
1.4
TYPICAL
1.2
1.0
0.8 MINIMUM
0.6
0.4
0.2 TA = 25°C
L = 12μH
f = 1MHz
0
6 12
18 24
VIN (V)
30 36
3689 G06
Maximum VIN for Full Frequency
40
35 TA = 25°C
30 TA = 85°C
25
20
15
10
5
0
0
VO = 5V
L = 6.8μH
f = 2MHz
SYNC = 5V
0.1 0.2 0.3 0.4 0.5 0.6 0.7
LOAD CURRENT (A)
3689 G07
Switch Current Limit
vs Duty Cycle
2.0
TA = 25°C
SYNC = LOW
1.6
TYPICAL
1.2 MINIMUM
0.8
0.4
0
0 20 40 60 80 100
DUTY CYCLE (%)
3689 G10
Maximum VIN for Full Frequency
35
30 TA = 25°C
25 TA = 85°C
20
15
10
VO = 3.3V
5
L = 4.7μH
f = 2MHz
SYNC = 3.3V
0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
LOAD CURRENT (A)
3689 G08
Maximum Output Current, 3.3VOUT
1.2
TYPICAL
1.0
0.8
MINIMUM
0.6
0.4
0.2
0
4
TA = 25°C
L = 12μH
f = 700kHz
8 12 16 20 24 28 32 36
VIN (V)
3689 G09
Switch Current Limit
vs Temperature
2.0
SYNC = LOW
1.5
SYNC = HIGH
1.0
0.5
0
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
3689 G11
Switch Voltage Drop
600
500
400
TA = 25°C
300
TA = –50°C
200
TA = 125°C
100
0
0 200 400 600 800 1000
SWITCH CURRENT (mA)
3689 G12
3689fa
5
5 Page 
TIMING DIAGRAMS
VOUT
tUV
RST
VUV
tRST
POWER-ON RESET TIMING
WDI
WDO
tWDU
WATCHDOG TIMING (W/T = HIGH), TIMEOUT MODE
t < tWDL
WDI
WDO
tRST tWDU
WATCHDOG TIMING (W/T = LOW), WINDOW MODE
tUV = TIME REQUIRED TO ASSERT RST LOW ONCE VOUT GOES BELOW VUV
tRST = PROGRAMMED RESET PERIOD
tWDU = WATCHDOG UPPER BOUNDARY PERIOD
tWDL = WATCHDOG WINDOW MODE LOWER BOUNDARY PERIOD
VUV = OUTPUT VOLTAGE RESET THRESHOLD
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LT3689/LT3689-5
tRST
tRST
3689 TD
3689fa
11
11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet LT3689-5.PDF ] | |
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