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LT3688EFE#TRPBF

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P27P28-P28
LT3688
1
3688f
TYPICAL APPLICATION
FEATURES
APPLICATIONS
DESCRIPTION
Dual 800mA Step-Down
Switching Regulator with
Power-On Reset and
Watchdog Timer
The LT
®
3688 is an adjustable frequency (350kHz to
2.2MHz) dual monolithic step-down switching regulator
with two power-on reset timers and a watchdog timer.
The regulator operates off inputs up to 36V. Low ripple
Burst Mode
®
operation maintains high effi ciency at low
output current while keeping output ripple below 25mV in
a typical application, with input quiescent current of just
115A. Shutdown circuitry reduces input supply current
to less than 1A while EN/UVLO is pulled low.
The reset and watchdog timeout periods are both adjust-
able using external capacitors. Tight accuracy specifi ca-
tions and glitch immunity ensure reliable reset operation
without false triggering. The open collector RST pins will
pull down if the monitored output voltage drops 10%
below the programmed value. The LT3688 watchdog timer
monitors for watchdog falling edges grouped too close
together or too far apart.
The LT3688 is available in 24-Pin TSSOP and 4mm ×
4mm QFN packages, each with an exposed pad for low
thermal resistance.
5V and 3.3V Regulator with Power-On Reset and Watchdog Timers
n
Wide Input Range:
Operation from 3.8V to 36V
n
Low Ripple (<25mV
P-P
) Burst Mode Operation:
I
Q
= 115μA at 12V
IN
to 3.3V and 5V
n
Programmable, Defeatable Window Watchdog Timer
n
Two Independently Programmable Power-On-Reset
Timers
n
Synchronizable, Adjustable 350kHz-2.2MHz
Switching Frequency
n
Two 800mA Output Switching Regulators with Internal
Power Switches
n
Programmable Input Undervoltage Lockout with
Hysteresis
n
Thermally Enhanced 24-Pin TSSOP and 4mm × 4mm
QFN Packages
n
Automotive Electronic Control Units
n
Industrial Power Supplies
n
High-Reliability µProcessor Systems
EN/UVLO V
IN
LT3688
GND
BIAS
BST1
0.22µF
4.7µF
V
OUT1
5V
800mA
V
IN
6V TO 36V
22µF
22pF
18µH
12µH
523k
100k
316k
100k
1nF
1nF
µP
0.22µF
SW1
DA1
BST2
SW2
DA2
FB1
RUN/SS1
WDI
WDO
RST1
RST2
I/O
I/O
RESET
FB2
RUN/SS2
C
WDT
C
POR1
C
POR2
RT
SYNC
22µF
1nF
3688 TA01a
4.7nF
4.7nF
110k
f
SW
= 500kHz
V
OUT2
3.3V
800mA
22pF
Effi ciency
3688 TA01b
0.0001 10.001 0.01 0.1
LOAD CURRENT (A)
EFFICIENCY (%)
60
70
80
50
30
40
90
POWER LOSS (mW)
10.0
100.0
1000.0
1.0
0.01
0.1
10000.0
V
IN
= 12V
V
OUT
= 3.3V
L = 4.7µH
f = 800kHz
L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
LT3688
2
3688f
ABSOLUTE MAXIMUM RATINGS
V
IN
, EN/UVLO, CONFIG Voltage (Note 2) ...................36V
BST Voltage ..............................................................55V
BST above SW Voltage .............................................30V
BIAS Voltage .............................................................30V
WDE, WDI, RST, WDO Voltage ...................................6V
FB, RT
, SYNC, RUN/SS Voltage ..................................6V
C
WDT
, C
POR
Voltage ....................................................3V
1
2
3
4
5
6
7
8
9
10
11
12
TOP VIEW
FE PACKAGE
24-LEAD PLASTIC TSSOP
24
23
22
21
20
19
18
17
16
15
14
13
FB1
RUN/SS1
BST1
SW1
DA1
V
IN
CONFIG
DA2
SW2
BST2
RUN/SS2
FB2
EN/UVLO
SYNC
RT
C
WDT
C
POR1
BIAS
C
POR2
WDI
WDE
WDO
RST1
RST2
25
GND
θ
JA
= 38°C/W
EXPOSED PAD (PIN 25) IS GND, MUST BE ELECTRICALLY CONNECTED TO PCB
24 23 22 21 20 19
7 8 9
TOP VIEW
UF PACKAGE
24-LEAD (4mm × 4mm) PLASTIC QFN
10 11 12
6
5
4
3
2
1
13
14
15
16
17
18
RT
SYNC
EN/UVLO
FB1
RUN/SS1
BST1
WDO
RST1
RST2
FB2
RUN/SS2
BST2
C
WDT
C
POR1
BIAS
C
POR2
WDI
WDE
SW1
DA1
V
IN
CONFIG
DA2
SW2
25
GND
θ
JA
= 37°C/W
EXPOSED PAD (PIN 25) IS GND, MUST BE ELECTRICALLY CONNECTED TO PCB
PIN CONFIGURATION
ORDER INFORMATION
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LT3688EFE#PBF LT3688EFE#TRPBF LT3688FE 24-Lead Plastic TSSOP –40°C to 125°C
LT3688IFE#PBF LT3688IFE#TRPBF LT3688FE 24-Lead Plastic TSSOP –40°C to 125°C
LT3688HFE#PBF LT3688HFE#TRPBF LT3688FE 24-Lead Plastic TSSOP –40°C to 150°C
LT3688EUF#PBF LT3688EUF#TRPBF 3688
24-Lead (4mm × 4mm) Plastic QFN
–40°C to 125°C
LT3688IUF#PBF LT3688IUF#TRPBF 3688
24-Lead (4mm × 4mm) Plastic QFN
–40°C to 125°C
Consult LTC Marketing for parts specifi ed with wider operating temperature ranges. *The temperature grade is identifi ed by a label on the shipping container.
Consult LTC Marketing for information on non-standard lead based fi nish parts.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifi
cations, go to: http://www
.linear.com/tapeandreel/
(Note 1)
Operating Junction Temperature Range (Note 3)
LT3688E, LT3688I ..............................–40°C to 125°C
LT3688H ............................................–40°C to 150°C
Maximum Junction Temperature
LT3688E, LT3688I ............................................. 125°C
LT3688H ........................................................... 150°C
Storage Temperature Range ...................–65°C to 150°C
Lead Temperature (Soldering, 10 sec)
FE Package ....................................................... 300°C
LT3688
3
3688f
The l denotes the specifi cations which apply over the full operating
junction temperature range, otherwise specifi cations are at T
A
= 25°C. V
IN
= 12V, unless otherwise noted. (Note 3)
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
V
IN
Undervoltage Lockout
l
3 3.5 3.8 V
Quiescent Current from V
IN
V
EN/UVLO
= 0.3V
V
BIAS
= 5V, Not Switching
V
BIAS
= 0V, Not Switching
l
0.01
65
235
1
105
310
µA
µA
µA
Quiescent Current from BIAS V
EN/UVLO
= 0.3V
V
BIAS
= 5V, Not Switching
V
BIAS
= 0V, Not Switching
l
0.01
155
–5
1
200
–20
µA
µA
µA
FB Voltage
l
0.790
0.784
0.800 0.810
0.814
V
V
FB Pin Bias Current V
FB
= 0.800V
l
–3 –50 nA
FB Voltage Line Regulation 5V < V
IN
< 36V 0.002 %/V
Switching Frequency R
T
= 20k, V
BST
= 12V
R
T
= 110k, V
BST
= 12V
l
l
1.85
460
2.1
500
2.35
540
MHz
kHz
Minimum Off-Time (Note 4) V
BST
= 12V
l
115 180 ns
Switch Current Limit (Note 5) DC = 15%
l
1.2 1.7 2.2 A
Switch V
CESAT
I
SW
= 0.8A 280 mV
Switch Leakage Current (Note 8) –0.01 –1 µA
DA Current Limit
l
0.9 1.2 1.6 A
Boost Schottky Reverse Leakage V
BIAS
= 0V 0.01 2 µA
Minimum BST Voltage above SW 2.15 2.5 V
BST Pin Current I
SW
= 0.8A 15 25 mA
EN/UVLO Threshold Voltage
l
1.15 1.25 1.35 V
EN/UVLO Input Current V
EN/UVLO
= 1.35V
V
EN/UVLO
= 1.15V 2.5
0.3
46
µA
µA
Threshold Current Hysteresis 2.5 3.7 5.5 µA
RUN/SS Pin Current V
RUN/SS
= 0V –1.4 –2.8 –4 µA
RUN/SS Switching Threshold 0.15 0.8 1 V
SYNC Threshold Voltage 0.4 0.8 1.3 V
V
UV
Reset Threshold % of FB Voltage, V
FB
Falling
l
88 90 92 %
t
RST
Reset Timeout Period C
POR
= 4700pF
l
21.2 23.5 25.8 ms
t
WDU
Watchdog Window Upper Boundary C
WDT
= 1000pF
l
18 20 22 ms
t
WDL
Watchdog Window Lower Boundary C
WDT
= 1000pF
l
0.8 1.25 1.6 ms
t
WDTO
Watchdog Timeout Period C
WDT
= 1000pF 2.5 ms
RST Output Voltage Low I
SINK
= 2.5mA, V
FB
= 0.6V
I
SINK
= 100µA, V
FB
= 0.6V
l
l
0.2
0.01
0.4
0.3
V
V
t
UV
UV Detect to RST Asserted V
FB
Set to 0.680V
l
41030 µs
WDI Input Threshold
l
0.4 0.95 1.3 V
WDI Input Pull-Up Current –2 µA
WDI Input Pulse Width
l
300 ns
WDE Threshold Voltage
l
0.4 0.65 1 V
WDE Input Pull-Down Current V
WDE
= 1.2V 3.5 µA
WDO Output Voltage Low I
SINK
= 2.5mA
I
SINK
= 100µA
l
l
0.2
0.01
0.4
0.3
V
V
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LT3688EFE#TRPBF

Mfr. #:
Buy LT3688EFE#TRPBF
Manufacturer:
Analog Devices / Linear Technology
Description:
Switching Voltage Regulators Dual 800mA Step-Down Switching Regulator with Power-On Reset and Watchdog Timer
Lifecycle:
New from this manufacturer.
Delivery:
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