Average Output Current.................................100mA
Operating Junction Temperature Range
(Note 2)..................................................–40°C to 125°C
Junction Temperature ........................................... 125°C
Storage Temperature Range...................–65°C to 150°C
24 23 22 21 20 19
UF PACKAGE
24-LEAD (4mm 4mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 40°C/W 1 LAYER BOARD,
θ
JA
= 30°C/W 4 LAYER BOARD
EXPOSED PAD (PIN 25) IS GND, MUST BE SOLDERED TO PCB
orDer inForMaTion
LEAD FREE FINISH
LTC3785EUF#PBF
LTC3785IUF#PBF
LEAD BASED FINISH
LTC3785EUF
LTC3785IUF
TAPE AND REEL
LTC3785EUF#TRPBF
LTC3785IUF#TRPBF
TAPE AND REEL
LTC3785EUF#TR
LTC3785IUF#TR
PART MARKING*
3785
3785
PART MARKING*
3785
3785
PACKAGE DESCRIPTION
24-Lead (4mm
×
4mm) Plastic QFN
24-Lead (4mm
×
4mm) Plastic QFN
PACKAGE DESCRIPTION
24-Lead (4mm
×
4mm) Plastic QFN
24-Lead (4mm
×
4mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 125°C
TEMPERATURE RANGE
–40°C to 85°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.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
This product is only offered in trays. For more information go to:
http://www.linear.com/packaging/
The
l
denotes the specifications which apply over the full operating junction
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= I
SVOUT
= V
DRV
= V
BST1
= V
BST2
= 3.6V, R
T
= 49.9k, R
ILSET
= 59k.
PARAMETER
V
IN
Supply
Input Operating Voltage
Quiescent Current—Burst Mode Operation
Quiescent Current—Shutdown
Quiescent Current—Active
Error Amp
Feedback Voltage
Feedback Input Current
(Note 5)
l
l
elecTrical characTerisTics
CONDITIONS
MIN
2.7
TYP
MAX
10
UNITS
V
µA
µA
mA
V
nA
3785fc
V
C
= 0V, MODE = 3.6V (Note 4)
RUN/SS = 0V, I
SVOUT
= 3.6V
MODE = 0V (Note 4)
1.200
86
15
0.8
1.225
1
200
25
1.5
1.25
500
LTC3785
elecTrical characTerisTics
PARAMETER
Error Amp Source Current
Error Amp Sink Current
Error Amp A
VOL
Overvoltage Threshold
V
SENSE
Pin % Above FB
LTC3785E
LTC3785I
V
SENSE
Pin % Below FB
LTC3785E
LTC3785I
V
SENSE
= Measured FB Voltage
V
IN
= 5V, I
VCC
= –20mA
V
IN
= 3.6V, I
VCC
= –20mA
I
SVOUT
= V
CC
= 5V
When IC is Enabled
When EA is at Maximum Boost Duty Cycle
RUN/SS = 0V
During Current Limit
I
SVIN
to I
SSW1
, R
ILSET
= 121k
I
SVIN
to I
SSW1
, R
ILSET
= 59k
I
SSW2
to I
SVOUT
, CCM > 2V
I
SSW2
to I
SVOUT
, CCM < 0.4V, LTC3785E
I
SSW2
to I
SVOUT
, CCM < 0.4V, LTC3785I
I
SVIN
I
SVOUT
I
SSW1
, I
SSW2
l
l
l
l
l
l
l
l
l
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
= I
SVOUT
= V
DRV
= V
BST1
= V
BST2
= 3.6V, R
T
= 49.9k, R
ILSET
= 59k.
CONDITIONS
MIN
TYP
–500
900
90
6
6
–3.5
–3.5
10
10
–6.5
–6.5
1
4.15
3.3
4.35
3.5
800
0.35
0.7
1.9
–1
20
20
55
–50
60
105
–110
–15
–15
80
10
0.1
2.2
0.4
0.01
l
MAX
UNITS
µA
µA
dB
14
15
–9.5
–10.5
500
4.55
3.6
%
%
%
%
nA
V
V
µA
Undervoltage Threshold
V
SENSE
Input Current
V
CC
Regulator
V
CC
Maximum Regulating Voltage
V
CC
Regulation Voltage
V
CC
Regulator Sink Current
Run/Soft-Start
RUN/SS Threshold
RUN/SS Input Current
RUN/SS Discharge Current
Current Limit
Current Limit Sense Threshold
Reverse Current Limit Sense Threshold
1.1
V
V
µA
µA
mV
mV
mV
mV
mV
µA
µA
µA
V
V
µA
V
µA
µs
30
100
155
–170
–35
–40
150
20
5
Input Current
CCM Input Threshold (High)
CCM Input Threshold (Low)
CCM Input Current
Burst Mode Operation
Mode Threshold
Mode Input Current
t
ON
Time
Oscillator
Frequency Accuracy
Switching Characteristics
Maximum Duty Cycle
TG1, TG2 Driver Impedance
BG1, BG2 Driver Impedance
TG1, TG2 Rise Time
C
LOAD
= 3300pF (Note 3)
Boost (% Switch BG2 On)
Buck (% Switch TG1 On)
CCM = 3.6V
1
2.2
1
0.8
1.5
0.01
1.4
l
370
80
509
90
99
2
2
20
650
kHz
%
%
Ω
Ω
ns
3785fc
l
LTC3785
elecTrical characTerisTics
PARAMETER
BG1, BG2 Rise Time
TG1, TG2 Fall Time
BG1, BG2 Fall Time
Buck Driver Nonoverlap Time
Boost Driver Nonoverlap Time
The
l
denotes the specifications which apply over the full operating junction
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= I
SVOUT
= V
DRV
= V
BST1
= V
BST2
= 3.6V, R
T
= 49.9k, R
ILSET
= 59k.
CONDITIONS
C
LOAD
= 3300pF (Note 3)
C
LOAD
= 3300pF (Note 3)
C
LOAD
= 3300pF (Note 3)
TG1 to BG1
TG2 to BG2
MIN
TYP
20
20
20
100
100
MAX
UNITS
ns
ns
ns
ns
ns
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:
The LTC3785E is guaranteed to meet performance specifications
from 0°C to 85°C. Specifications over the –40°C to 85°C operating
junction temperature range are assured by design, characterization and
correlation with statistical process controls. The LTC3785I is guaranteed
to meet performance specifications over the full –40°C to 125°C operating
junction temperature range.
Note 3:
Specification is guaranteed by design and not 100% tested in
production.
Note 4:
Current measurements are performed when the outputs are not
switching.
Note 5:
The IC is tested in a feedback loop to make the measurement.
Typical perForMance characTerisTics
Li-Ion to 3.3V Efficiency
vs Load Current
100
90
80
EFFICIENCY (%)
FIXED
FREQUENCY
V
IN
= 4.2V
V
IN
= 3.6V
V
IN
= 3V
MOSFET Si7940
L = 4.7µH WURTH WE-PD
f
OSC
= 500kHz
0.001
0.1
0.01
LOAD CURRENT (A)
1
10
3785 G01
T
A
= 25°C, unless otherwise noted.
Li-Ion/9V to 5V V
OUT
Efficiency
vs Load Current
100
90
80
Burst Mode
OPERATION
Two Li-Ion to 7V Efficiency
vs Load Current
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.0001
0.001
V
IN
= 8.4V
V
IN
= 7.2V
V
IN
= 5.4V
MOSFET Si7940
L = 5.6µH MSS1260
f
OSC
= 430kHz
0.01
0.1
LOAD CURRENT (A)
1
10
3785 G02
Burst Mode
OPERATION
Burst Mode
OPERATION
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.0001
70
60
50
40
30
20
10
0
0.0001
0.001
FIXED
FREQUENCY
V
IN
= 9V
V
IN
= 4.2V
V
IN
= 3.6V
V
IN
= 2.7V
MOSFET Si7940
L = 5.6µH MSS1260
f
OSC
= 430kHz
0.01
0.1
LOAD CURRENT (A)
1
10
3785 G03
FIXED
FREQUENCY
Burst Mode Ripple
V
OUT
500mV/
DIV
V
IN
3V TO
8.5V
V
OUT
= 3.3V
C
OUT
= 100µF
5µs/DIV
3785 G04
Line Transient Response
V
OUT
200mV/
DIV
V
OUT
Load Transient
V
OUT
50mV/DIV
AC
COUPLED
INDUCTOR
CURRENT
1A/DIV
I
LOAD
10mA TO 2A
I
LOAD
= 300mA
V
OUT
= 5V
C
OUT
= 100µF
500µs/DIV
3785 G05
V
IN
= 3.6V
V
OUT
= 3.3V
C
OUT
= 100µF
100µs/DIV
3785 G06
3785fc
LTC3785
Typical perForMance characTerisTics
1.2255
1.2250
CHANGE FROM 25°C (%)
1.2245
1.2240
V
FB
(V)
1.2235
1.2230
1.2225
1.2220
1.2215
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3785 G07
T
A
= 25°C, unless otherwise noted.
V
FB
vs Temperature
1.0
0.8
0.6
0.4
0.2
0
–0.2
–0.4
–0.6
–0.8
Normalized Oscillator Frequency
vs Temperature
1200
OSCILLATOR FREQUENCY (kHz)
1000
800
600
400
200
0
Oscillator Frequency vs RT
–1.0
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3785 G08
20
40
60
RT (k )
80
100
3785 G09
V
IN
Start-Up Voltage
vs Temperature
2.490
100
V
IN
Burst Quiescent Current
vs Temperature
12
10
8
THRESHOLD (%)
6
4
2
0
–2
–4
–6
OV and UV Thresholds
vs Temperature
OV THRESHOLD
V
IN
START-UP VOLTAGE (V)
2.485
V
IN
CURRENT (µA)
95
2.480
90
2.475
2.470
2.465
–50 –25
85
UV THRESHOLD
25 50 75 100 125 150
TEMPERATURE (°C)
3785 G12
0
25 50 75 100 125 150
TEMPERATURE (°C)
3785 G10
80
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3785 G11
–8
–50 –25
0
pin FuncTions
RUN/SS (Pin 1):
Run Control and Soft-Start Input. An
internal 1µA charges the soft-start capacitor and will
charge to approximately 2.5V. During a current limit fault,
the soft-start capacitor will incrementally discharge. Once
the pin drops below 1.225V the IC will enter fault mode,
turning off the outputs for 32 times the soft-start time. If
>5µA (at RUN/SS = 1.225V) is applied externally, the part
will latch off after a fault is detected. If >40µA (at RUN/SS
= 1.225V) is applied externally, current limit faults will not
discharge the SS capacitor.
V
C
(Pin 2):
Error Amp Output. A frequency compensa-
tion network is connected from this pin to the FB pin to
compensate the loop. See Closing the Feedback Loop in
the Applications Information section for guidelines.
FB (Pin 3):
Feedback Pin. Connect resistor divider tap
here. The feedback reference voltage is typically 1.225V
The output voltage can be adjusted from 2.7V to 10V ac-
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