switching regulator that accepts input voltages up to 36V.
A high efficiency 90mΩ switch is included on the device
along with the boost diode and the necessary oscillator,
control, and logic circuitry. The internal synchronous power
switch of 30mΩ increases efficiency and eliminates the
need for an external Schottky catch diode. Current mode
topology is used for fast transient response and good
loop stability. Shutdown reduces input supply current to
less than 1µA. The low ripple Burst Mode maintains high
efficiency at low output currents while keeping output
ripple below 15mV in typical applications.
The LT3690 features robust operation and is easily con-
figurable. Using a resistor divider on the UVLO pin provides
a programmable undervoltage lockout. A power good flag
signals when V
OUT
reaches 90% of the programmed out-
put voltage. Protection circuitry senses the current in the
power switches to protect the LT3690 against short-circuit
conditions. Frequency foldback and thermal shutdown
provide additional protection. The LT3690 is available in
a 4mm
×
6mm QFN package with exposed pads for low
thermal resistance.
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.
n
n
n
n
n
n
n
n
n
n
n
Wide Input Range:
– Operation from 3.9V to 36V
– Overvoltage Lockout Protects Circuits
Through 60V Transients
4A Maximum Output Current
Integrated 30mΩ N-Channel Synchronous Switch
Low Ripple (<15mV
P-P
) Burst Mode
®
Operation:
I
Q
= 70µA at 12V
IN
to 3.3V
OUT
Programmable Input Undervoltage Lockout
0.8V Feedback Reference Voltage
Output Voltage: 0.8V to 20V
Programmable and Synchronizable Oscillator
(170kHz to 1.5MHz)
Soft-Startup and Output Voltage Tracking
Short-Circuit Robust
Power Good Flag
Small Thermally Enhanced 4mm
×
6mm QFN Package
applicaTions
n
n
n
Automotive Systems
Industrial Supplies
Distributed Supply Regulation
Typical applicaTion
3.3V Step-Down Converter
V
IN
4.5V TO 36V
10µF
EN
UVLO
SS
V
C
22k
V
CCINT
0.47µF
SYNC
GND
ƒ = 600kHz
LT3690
V
IN
BST
3.3µH
SW
BIAS
PG
FB
RT
32.4k
102k
3690 TA01a
Efficiency and Power Loss
100
V
OUT
= 5V
3.3V
4A
EFFICIENCY (%)
90
V
OUT
= 3.3V
2.0
POWER LOSS (W)
2.5
0.68µF
80
V
OUT
= 5V
70
V
OUT
= 3.3V
V
IN
= 12V
L = 4.7µH
ƒ = 600kHz
0
0.5
1
1.5 2 2.5 3
LOAD CURRENT (A)
3.5
4
1.5
316k
1.0
60
100µF
50
0.5
680pF
0
3690 TA01b
3690fa
1
LT3690
absoluTe MaxiMuM raTings
(Note 1)
pin conFiguraTion
TOP VIEW
EN, UVLO, V
IN
Voltage (Note 2) ................................60V
BST Voltage .............................................................55V
BST Voltage Above SW Voltage ...............................30V
BIAS, PG Voltage . ....................................................30V
FB, RT, SS, SYNC, V
C
, V
CCINT
Voltage . .......................6V
Operating Junction Temperature Range (Notes 3 and 4)
LT3690E ........................................... –40°C to 125°C
LT3690I ............................................ –40°C to 125°C
LT3690H ........................................... –40°C to 150°C
LT3690MP ........................................ –55°C to 150°C
Storage Temperature Range ................. –65°C to 150°C
SW
SW
SW
SW
SYNC
GND
RT
V
C
FB
1
2
3
4
5
6
7
8
9
28
GND
27
SW
26 SW
25 SW
24 SW
23 SW
22 BST
21 GND
20 V
CCINT
19 BIAS
18 PG
17 EN
SS 11
UVLO 12
V
IN
13
V
IN
14
V
IN
15
GND 16
GND 10
UFE PACKAGE
26-LEAD (4mm
×
6mm) PLASTIC QFN
θ
JA
= 40°C/W,
θ
JC
= 2.7°C/W
EXPOSED PAD (PIN 27) IS SW, MUST BE SOLDERED TO PCB
EXPOSED PAD (PIN 28) IS GND, MUST BE SOLDERED TO PCB
orDer inForMaTion
LEAD FREE FINISH
LT3690EUFE#PBF
LT3690IUFE#PBF
LT3690HUFE#PBF
LT3690MPUFE#PBF
TAPE AND REEL
LT3690EUFE#TRPBF
LT3690IUFE#TRPBF
LT3690HUFE#TRPBF
LT3690MPUFE#TRPBF
PART MARKING*
3690
3690
3690
3690
PACKAGE DESCRIPTION
26-Lead (4mm
×
6mm) Plastic QFN
26-Lead (4mm
×
6mm) Plastic QFN
26-Lead (4mm
×
6mm) Plastic QFN
26-Lead (4mm
×
6mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
–40°C to 150°C
–55°C to 150°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/
3690fa
2
LT3690
elecTrical characTerisTics
PARAMETER
V
IN
Fixed Undervoltage Lockout
V
IN
Overvoltage Lockout OVLO
Quiescent Current from V
IN
V
IN
Rising
V
EN
= 0.2V
V
BIAS
= 3V, V
FB
= 0.85V Not Switching
V
BIAS
= 0V, V
FB
= 0.85V Not Switching
Quiescent Current from BIAS Pin
V
EN
= 0.2V
V
BIAS
= 3V, V
FB
= 0.85V Not Switching
V
BIAS
= 0V, V
FB
= 0.85V Not Switching
Boost Schottky Diode Drop (V
BIAS
– V
BST
)
BST Voltage (Note 5) (V
BST
– V
SW
)
BST Pin Current
BST Pin Leakage
HS Switch Drop (V
IN
– V
SW
)
HS Switch Current Limit (Note 6)
HS Switch Leakage Current
HS Minimum Switch Off-Time
LS Switch Off Voltage Drop
LS Switch On-Resistance
LS Switch On-Resistance
LS Switch Current Threshold
LS Switch Leakage Current
V
CCINT
Pin Output Voltage
V
CCINT
Pin Output Voltage
EN Input Current
EN Input Voltage, Enable
EN Input Voltage, Disable
UVLO Threshold Voltage
UVLO Pin Current
UVLO Pin Current
UVLO Pin Current Hysteresis
Pull-Up Current at SS Pin
Tracking Offset (V
SS
– V
FB
)
SYNC Input Voltage High
SYNC Input Voltage Low
SYNC Input Resistance to GND
SYNC Input Frequency
Feedback Reference Voltage
l
l
l
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C, V
IN
= 12V unless otherwise noted (Notes 3, 7).
CONDITIONS
l
l
MIN
36
TYP
3.0
38.2
0.1
35
110
0.1
70
–3
820
MAX
3.9
40
1
60
150
1
110
–10
950
2.3
140
6
600
8
2
210
850
60
90
6.5
10
95
5.3
5.3
15
6
0.4
UNITS
V
V
µA
µA
µA
µA
µA
µA
mV
V
mA
µA
mV
A
µA
ns
mV
mΩ
mΩ
A
µA
µA
V
V
µA
µA
V
V
V
µA
µA
µA
µA
mV
V
V
kΩ
MHz
mV
mV
nA
%/V
3690fa
I
BIAS
= 200mA
Minimum BOOST Voltage Above SW, I
SW
= 4A
I
SW
= 4A
V
SW
= 12V, V
BIAS
= 0V
I
SW
= 4A
5.5
V
SW
= 0V
l
l
1.6
70
0.1
370
6.6
0.1
700
30
30
4
5
0.1
4.3
4.2
4.9
4.8
8
2.5
1.5
1.1
I
SW
= 4A
I
SW
= 4A, V
CCINT
= 5V
I
SW
= 4A, V
CCINT
= 4V
V
EN
= 0V, V
SW
= 12V, V
BST
=12V
V
EN
= 0V, V
SW
= 12V, V
BST
= 12V, T
J
= 125°C
I
VCCINT
= 0µA
I
VCCINT
= –10mA
V
EN
= 12V
V
EN
= 2.5V
1.33
–2.0
0.1
–3.8
1
2.8
–2.8
15
0.4
V
UVLO
= 1.33V
V
UVLO
= 1.1V
I
UVH
– I
UVL
V
SS
= 0.8V
V
SS
= 0.4V
1.2
–1.2
–4
0.8
150
0.17
792
786
2
–2
7
300
800
800
–8
0.001
600
1.5
808
814
–40
0.01
FB Pin Bias Current Flows Out of Pin
FB Voltage Line Regulation
V
FB
= 800mV
3.6V < V
IN
< 36V
l
3
LT3690
elecTrical characTerisTics
PARAMETER
PG Threshold as Percentage of V
FB
PG Hysteresis
PG Sink Current
PG Leakage
Error Amplifier Transconductance
Error Amp Voltage Gain
V
C
Source Current
V
C
Sink Current
V
C
Pin to Switch Current Gain
Transconductance
V
C
Switching Threshold
V
C
Clamp Voltage
Programmable Switching Frequency
R
T
= 10kΩ
R
T
= 24.9kΩ
R
T
= 180kΩ
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 EN, UVLO and V
IN
pins is 36V
for continuous operation. For non-repetitive 1 second transients while
T
J
< 125°C, the absolute maximum voltage is 60V.
Note 3:
The LT3690E 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
LT3690I is guaranteed over the full –40°C to 125°C operating junction
temperature range. The LT3690H is guaranteed over the full –40°C to
150°C operating junction temperature range. The LT3690MP is guaranteed
over the full –55°C to 150°C operating junction temperature range. High
junction temperatures degrade operating lifetime. Operating lifetime is
derated at junction temperatures greater than 125°C.
1.32
660
122
V
PG
= 0.3V
V
PG
= 5V
l
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C, V
IN
= 12V unless otherwise noted (Notes 3, 7).
CONDITIONS
V
FB
Rising
MIN
88
100
TYP
90
12
500
0.1
400
60
–50
50
4.6
0.7
2.0
1.5
750
138
1.68
840
154
1
MAX
92
UNITS
%
mV
µA
µA
µA/V
dB
µA
µA
A/V
V
V
MHz
kHz
kHz
Note 4:
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 overtemperature protection is active. Continuous operation above
the specified maximum operating junction temperature may impair device
reliability.
Note 5:
This is the minimum voltage across the boost capacitor needed to
guarantee full saturation of the switch.
Note 6:
Current limit guaranteed by design and/or correlation to static test.
Slope compensation reduces current limit at higher duty cycles. Current
limit reduced when feedback voltage is below the reference voltage.
Note 7:
The voltages are referred to GND and currents are assumed
positive, when the current flows into the pin. Negative magnitudes are
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