Storage Temperature Range...................–65°C to 150°C
Lead Temperature (Soldering, 10 sec)
FE Package ....................................................... 300°C
PIN CONFIGURATION
TOP VIEW
C
WDT
FB1
RUN/SS1
BST1
SW1
DA1
V
IN
CONFIG
DA2
SW2
1
2
3
4
5
6
7
8
9
25
GND
24 EN/UVLO
23 SYNC
22 RT
21 C
WDT
20 C
POR1
19 BIAS
18 C
POR2
17 WDI
16
WDE
15
WDO
14
RST1
13
RST2
RT 1
SYNC 2
EN/UVLO 3
FB1 4
RUN/SS1 5
BST1 6
7
SW1
8
DA1
9 10 11 12
CONFIG
DA2
SW2
V
IN
25
GND
TOP VIEW
C
POR1
C
POR2
BIAS
WDE
18
WDO
17
RST1
16
RST2
15 FB2
14 RUN/SS2
13 BST2
WDI
24 23 22 21 20 19
BST2 10
RUN/SS2 11
FB2 12
FE PACKAGE
24-LEAD PLASTIC TSSOP
θ
JA
= 38°C/W
EXPOSED PAD (PIN 25) IS GND, MUST BE ELECTRICALLY CONNECTED TO PCB
UF PACKAGE
24-LEAD (4mm
×
4mm) PLASTIC QFN
θ
JA
= 37°C/W
EXPOSED PAD (PIN 25) IS GND, MUST BE ELECTRICALLY CONNECTED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LT3688EFE#PBF
LT3688IFE#PBF
LT3688HFE#PBF
LT3688EUF#PBF
LT3688IUF#PBF
TAPE AND REEL
LT3688EFE#TRPBF
LT3688IFE#TRPBF
LT3688HFE#TRPBF
LT3688EUF#TRPBF
LT3688IUF#TRPBF
PART MARKING*
LT3688FE
LT3688FE
LT3688FE
3688
3688
PACKAGE DESCRIPTION
24-Lead Plastic TSSOP
24-Lead Plastic TSSOP
24-Lead Plastic TSSOP
24-Lead (4mm
×
4mm) Plastic QFN
24-Lead (4mm
×
4mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
–40°C to 150°C
–40°C to 125°C
–40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/
3688f
2
LT3688
ELECTRICAL CHARACTERISTICS
SYMBOL
PARAMETER
V
IN
Undervoltage Lockout
Quiescent Current from V
IN
V
EN/UVLO
= 0.3V
V
BIAS
= 5V, Not Switching
V
BIAS
= 0V, Not Switching
V
EN/UVLO
= 0.3V
V
BIAS
= 5V, Not Switching
V
BIAS
= 0V, Not Switching
The
l
denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 12V, unless otherwise noted. (Note 3)
CONDITIONS
l
l
MIN
3
TYP
3.5
0.01
65
235
0.01
155
–5
MAX
3.8
1
105
310
1
200
–20
0.810
0.814
–50
2.35
540
180
2.2
–1
1.6
2
2.5
25
1.35
6
5.5
–4
1
1.3
92
25.8
22
1.6
0.4
0.3
30
1.3
UNITS
V
μA
μA
μA
μA
μA
μA
V
V
nA
%/V
MHz
kHz
ns
A
mV
μA
A
μA
V
mA
V
μA
μA
μA
μA
V
V
%
ms
ms
ms
ms
V
V
μs
V
μA
ns
Quiescent Current from BIAS
l
FB Voltage
FB Pin Bias Current
FB Voltage Line Regulation
Switching Frequency
Minimum Off-Time (Note 4)
Switch Current Limit (Note 5)
Switch V
CESAT
Switch Leakage Current (Note 8)
DA Current Limit
Boost Schottky Reverse Leakage
Minimum BST Voltage above SW
BST Pin Current
EN/UVLO Threshold Voltage
EN/UVLO Input Current
Threshold Current Hysteresis
RUN/SS Pin Current
RUN/SS Switching Threshold
SYNC Threshold Voltage
V
UV
t
RST
t
WDU
t
WDL
t
WDTO
Reset Threshold
Reset Timeout Period
Watchdog Window Upper Boundary
Watchdog Window Lower Boundary
Watchdog Timeout Period
RST
Output Voltage Low
t
UV
UV Detect to
RST
Asserted
WDI Input Threshold
WDI Input Pull-Up Current
WDI Input Pulse Width
WDE
Threshold Voltage
WDE
Input Pull-Down Current
WDO
Output Voltage Low
V
WDE
= 1.2V
I
SINK
= 2.5mA
I
SINK
= 100μA
% of FB Voltage, V
FB
Falling
C
POR
= 4700pF
C
WDT
= 1000pF
C
WDT
= 1000pF
C
WDT
= 1000pF
I
SINK
= 2.5mA, V
FB
= 0.6V
I
SINK
= 100μA, V
FB
= 0.6V
V
FB
Set to 0.680V
V
RUN/SS
= 0V
V
EN/UVLO
= 1.35V
V
EN/UVLO
= 1.15V
I
SW
= 0.8A
V
BIAS
= 0V
V
FB
= 0.800V
5V < V
IN
< 36V
R
T
= 20k, V
BST
= 12V
R
T
= 110k, V
BST
= 12V
V
BST
= 12V
DC = 15%
I
SW
= 0.8A
l
l
l
l
l
l
0.790
0.784
0.800
–3
0.002
1.85
460
1.2
2.1
500
115
1.7
280
–0.01
l
0.9
1.2
0.01
2.15
15
l
1.15
2.5
2.5
–1.4
0.15
0.4
1.25
0.3
4
3.7
–2.8
0.8
0.8
90
23.5
20
1.25
2.5
0.2
0.01
l
l
l
l
l
l
l
l
l
l
l
l
88
21.2
18
0.8
4
0.4
300
0.4
10
0.95
–2
0.65
3.5
0.2
0.01
1
0.4
0.3
V
μA
V
V
3688f
3
LT3688
ELECTRICAL CHARACTERISTICS
SYMBOL
PARAMETER
RST
Pull-Up Current (Note 6)
WDO
Pull-Up Current (Note 6)
CONFIG Low Level Input Voltage
CONFIG High Level Input Voltage
CONFIG Pin Voltage When Open
Maximum CONFIG Input Current in Open
State
CONFIG Pin Bias Current
V
CONFIG
= 0V, V
IN
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
Absolute Maximum Voltage at the V
IN
, CONFIG and EN/UVLO pins
is 36V for continuous operation.
Note 3:
The LT3688 is tested under pulsed load conditions such that
T
J
= T
A
. The LT3688E is guaranteed to meet performance specifications
from 0°C to 125°C junction temperature. Specifications over the –40°C
to 125°C operating junction temperature range are assured by design,
characterization and correlation with statistical process controls. The
LT3688I is guaranteed over the full –40°C to 125°C operating junction
temperature range. The LT3688H is guaranteed over the full –40°C to
150°C operating junction temperature range. High junction temperatures
degrade operating lifetimes. Operating lifetime is derated at junction
temperatures greater than 125°C. The junction temperature (T
J
, in °C) is
calculated from the ambient temperature (T
A
, in °C) and power dissipation
(PD, in Watts) according to the formula:
T
J
= T
A
+ (PD
θ
JA
), where
θ
JA
(in °C/W) is the package thermal
impedance.
l
l
l
l
The
l
denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 12V, unless otherwise noted. (Note 3)
CONDITIONS
MIN
–1.5
–1.5
1.4
0.64
±1
±20
TYP
–2.5
–2.5
0.2
MAX
UNITS
μA
μA
V
V
V
μA
μA
Note 4:
The LT3688 contains circuitry that extends the maximum duty
cycle if the BST voltage is 2V greater than the SW voltage. See the
Applications Information section for more details.
Note 5:
Current limit is guaranteed by design and/or correlation to static
test. Slope compensation reduces current limit at higher duty cycles.
Note 6:
The outputs of
RST
and
WDO
have a weak pull-up to V
BIAS
of
typically 2.5μA. However, external pull-up resistors may be used when
faster rise times are required or for V
OH
higher than V
BIAS
.
Note 7:
This IC includes overtemperature protection that is intended
to protect the device during momentary overload conditions. Junction
temperature will exceed the maximum operating junction temperature
when over-temperature protection is active. Continuous operation above
the specified maximum operating junction temperature may impair device
reliability.
Note 8:
All currents into pins are positive; all voltages are referenced to
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