to-negative or negative-to-positive DC/DC conversion,
with rail-to-rail output current monitor and control. The
LT8709 is ideal for many local power supply designs. It
can be easily configured in buck, boost, buck-boost, and
inverting topologies with negative input voltages.
In addition, the LT8709’s rail-to-rail output current sense
allows the part to be configured in current limited applica-
tions such as battery or capacitor charging. The PG pin
is used for power good indication.
The LT8709’s switching frequency range can be set between
100kHz and 750kHz. The part may be clocked internally
at a frequency set by the resistor from the RT pin to the
–V
IN
pin, or it may be synchronized to an external clock.
The LT8709 also features innovative EN/FBIN pin circuitry
that allows for slowly varying input signals and an adjust-
able undervoltage lockout function. The pin is also used for
input voltage regulation to avoid collapsing a high imped-
ance input supply. Additional features such as frequency
foldback, thermal shutdown and soft-start are integrated.
The LT8709 is available in a 20-lead TSSOP package.
n
n
n
n
n
Wide Negative Input Range: –4.5V to –80V
Rail-to-Rail Output Current Monitor and Control
Input Voltage Regulation for High Impedance Inputs
Power Good Indication Pin
MODE Pin for Forced CCM (Continuous Conduction
Mode) or Pulse-Skipping/DCM (Discontinuous
Conduction Mode) Operation
Switching Frequency Up to 750kHz
Easily Configurable as a Buck, Boost, Buck-Boost, or
Inverting Converter with a Single Feedback Pin
Can be Synchronized to an External Clock
High Gain EN/FBIN Pin Accepts Slowly Varying Input
Signals
20-Lead TSSOP Package
High Power Negative Input, Negative Output Power
Supplies
High Power Negative Input, Positive Output Power
Supplies
Telecom Equipment Power Supplies
Cathodic Protection Power Supplies
APPLICATIONS
n
n
n
n
L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
250kHz, –16V to –30V Input to –12V/8.5A Output Buck
7.3µH
4m
V
OUT
–12V
8.5A
150µF
Efficiency and Power Loss
vs Load Current (–V
IN
= –24V)
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
1
2
5
7
3
4
6
LOAD CURRENT (A)
8
9
0
POWER LOSS (W)
10µF
×6
–V
IN
2.2µF
TG
GND
62.5k
EN/FBIN
10k
2.2µF
INTV
CC
100k
MODE
PG
RT
SYNC
143k
–V
IN
–16V TO –30V
–V
IN
68nF
IMON
CSP CSN
2m
BG
ISN
33k
22µF
×3
+
120µF
LT8709
ISP
FBY
4.99k
BIAS
2.2µF
INTV
EE
V
C
SS
470nF
100pF
5.9k
2.2nF
8709 TA01a
2.2µF
For more information
www.linear.com/LT8709
+
10
8709 TA01b
8709fa
1
LT8709
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
FBY
V
C
SS
PG
IMON
ISN
ISP
BIAS
INTV
EE
1
2
3
4
5
6
7
8
9
21
–V
IN
20 –V
IN
19 SYNC
18 RT
17 MODE
16 EN/FBIN
15 CSP
14 CSN
13 GND
12 INTV
CC
11 BG
GND Voltage with Reference to –V
IN
.......... –0.3V to 80V
BIAS Voltage with Reference to –V
IN
......... –0.3V to 80V
BG Voltage with Reference to –V
IN
.................... (Note 5)
TG Voltage with Reference to BIAS .................... (Note 5)
RT Voltage with Reference to –V
IN
............... –0.3V to 5V
SS Voltage with Reference to –V
IN
............... –0.3V to 3V
FBY Voltage with Reference to GND............. –3V to 0.3V
V
C
Voltage with Reference to –V
IN
............... –0.3V to 2V
EN/FBIN Voltage with Reference to –V
IN
.... –0.3V to 80V
SYNC Voltage with Reference to –V
IN
....... –0.3V to 5.5V
PG Voltage with Reference to –V
IN
.............. –0.3V to 7V
PG Current ............................................................. ±1mA
MODE Voltage with Reference to –V
IN
....... –0.3V to 40V
INTV
CC
Voltage with Reference to –V
IN
....... –0.3V to 7V
INTV
EE
Voltage with Reference to BIAS ............. (Note 5)
CSP Voltage with Reference to –V
IN
............ –0.3V to 2V
CSN Voltage with Reference to –V
IN
............ –0.3V to 2V
ISP Voltage ................................. ISN – 0.4V to ISN + 2V
ISN Voltage with Reference to –V
IN
........... –0.3V to 80V
IMON Voltage with Reference to –V
IN
....... –0.3V to 2.5V
Operating Junction Temperature Range
LT8709E............................................. –40°C to 125°C
LT8709I ............................................. –40°C to 125°C
Storage Temperature Range .................. –65°C to 150°C
TG 10
FE PACKAGE
20-LEAD PLASTIC TSSOP
T
JMAX
= 125°C,
θ
JA
= 38°C/W,
θ
JC
= 10°C/W
EXPOSED PAD (PIN 21) IS –V
IN
, MUST BE SOLDERED TO PCB
ORDER INFORMATION
(http://www.linear.com/product/LT8709#orderinfo)
LEAD FREE FINISH
LT8709EFE#PBF
LT8709IFE#PBF
TAPE AND REEL
LT8709EFE#TRPBF
LT8709IFE#TRPBF
PART MARKING*
LT8709FE
LT8709FE
PACKAGE DESCRIPTION
20-Lead Plastic TSSOP
20-Lead Plastic TSSOP
TEMPERATURE RANGE
–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.
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/.
Some packages are available in 500 unit reels through
designated sales channels with #TRMPBF suffix.
2
8709fa
For more information
www.linear.com/LT8709
LT8709
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications for each channel are at T
A
= 25°C. V
GND
– V
–VIN
= 12V, V
EN/FBIN
– V
–VIN
= 12V,
V
BIAS
– V
–VIN
= 12V, unless otherwise noted. Pin voltages have the following relations: FBY is relative to the GND pin, TG and INTV
EE
to the BIAS pin, and all other pins to the –V
IN
pin, unless otherwise stated. Pin currents have the following relations: positive current is
denoted as current flowing into the pin; negative current is denoted as current flowing out of the pin, unless otherwise stated. (Note 2)
PARAMETER
Minimum Operating Input Voltage
Quiescent Current, I
GND
,
Not Switching
Quiescent Current in Shutdown, I
GND
EN/FBIN Minimum Input Voltage High,
Releases SS
EN/FBIN Minimum Input Voltage High,
Chip-On but SS Held Low
EN/FBIN Minimum Input Voltage High
Hysteresis
EN/FBIN Input Voltage Low
EN/FBIN Pin Bias Current
Shutdown Mode
V
EN/FBIN
= 3V
V
EN/FBIN
= 1.7V
V
EN/FBIN
= 1.6V
V
EN/FBIN
= 0V
V
SS
= 50mV, Current Flowing Out of SS Pin
Part Exiting Undervoltage Lockout
SS Rising
SS Falling
l
l
l
ELECTRICAL CHARACTERISTICS
CONDITIONS
V
GND
– V
–VIN
OR V
BIAS
– V
–VIN
V
GND
– V
–VIN
, if V
BIAS
– V
–VIN
≥ 4.5V
V
BIAS
– V
–VIN
= 8V, V
ISN
– V
–VIN
= 8V
V
BIAS
– V
–VIN
= 6.3V, V
BIAS
– V
INTVEE
= 6.3V
V
EN/FBIN
= 0V
EN/FBIN Rising
EN/FBIN Rising
EN/FBIN Falling
l
l
l
l
MIN
0
TYP
4.25
4
5.5
0
MAX
4.5
5.5
7.5
1
1.76
1.38
1.34
UNITS
V
V
mA
mA
µA
V
V
V
mV
1.64
1.22
1.18
1.7
1.3
1.26
44
0.3
14
13
7
18
1.5
1.3
44
19.5
17.5
0
10.1
50
1.8
1.7
100
60
25
22.5
0.1
13.8
82
2.1
2.05
V
µA
µA
µA
µA
µA
mV
V
V
mV
SS Charge Current
SS Low Detection Voltage
SS Hi Detection Voltage
SS Hi Detection Hysteresis
Low Dropout Regulators, INTV
CC
and INTV
EE
INTV
CC
Voltage
INTV
CC
Undervoltage Lockout
INTV
CC
Undervoltage Lockout Hysteresis
INTV
CC
Dropout Voltage,
V
GND
– INTV
CC
INTV
CC
Load Regulation
INTV
CC
Line Regulation
INTV
CC
Maximum External Load Current
INTV
EE
Voltage, V
BIAS
– V
INTVEE
INTV
EE
Undervoltage Lockout,
V
BIAS
– V
INTVEE
INTV
EE
Undervoltage Lockout
Hysteresis, V
BIAS
– V
INTVEE
INTV
EE
Dropout Voltage, V
INTVEE
– V
–VIN
V
BIAS
– V
–VIN
= 6V, I
INTVEE
= 10mA
I
INTVEE
= 10mA
V
BIAS
– V
INTVEE
Rising
V
BIAS
– V
INTVEE
Falling
l
l
l
I
INTVCC
= 10mA
INTV
CC
Rising
INTV
CC
Falling
V
GND
– V
–VIN
= 6V, V
BIAS
– V
–VIN
= 0V, I
INTVCC
= 10mA
V
GND
– V
–VIN
= 0V, V
BIAS
– V
–VIN
= 6V, I
INTVCC
= 10mA
V
GND
– V
–VIN
= 0V, I
INTVCC
= 0mA to 80mA
V
BIAS
– V
–VIN
= 0V, I
INTVCC
= 0mA to 40mA
10V ≤ V
GND
– V
–VIN
≤ 80V, V
BIAS
– V
–VIN
= 0V, I
INTVCC
= 10mA
10V ≤ V
BIAS
– V
–VIN
≤ 80V, V
GND
– V
–VIN
= 0V, I
INTVCC
= 10mA
l
l
l
6.2
3.88
3.5
6.3
4
3.73
270
255
280
–0.44
–0.34
–0.003
–0.006
6.4
4.12
3.95
V
V
V
mV
mV
mV
–2
–2
–0.03
–0.03
5
6.33
3.6
3.48
%
%
%/V
%/V
mA
V
V
V
mV
V
6.03
3.24
2.94
6.18
3.42
3.22
200
0.75
8709fa
For more information
www.linear.com/LT8709
3
LT8709
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications for each channel are at T
A
= 25°C. V
GND
– V
–VIN
= 12V, V
EN/FBIN
– V
–VIN
= 12V,
V
BIAS
– V
–VIN
= 12V, unless otherwise noted. Pin voltages have the following relations: FBY is relative to the GND pin, TG and INTV
EE
to the BIAS pin, and all other pins to the –V
IN
pin, unless otherwise stated. Pin currents have the following relations: positive current is
denoted as current flowing into the pin; negative current is denoted as current flowing out of the pin, unless otherwise stated. (Note 2)
PARAMETER
Current Limit Voltage, V
CSP
– V
CSN
CONDITIONS
I
FBY
= –67.9µA, Minimum Duty Cycle
I
FBY
= –67.9µA, Maximum Duty Cycle
I
FBY
= –108µA, MODE = 0V, Minimum Duty Cycle
I
FBY
= –108µA, MODE = 0V, Maximum Duty Cycle
FBY Voltage for Negative Output Voltage Q1 Conducting Current, Current Flowing Out of FBY Pin
Regulation
FBY Voltage for Positive Output Voltage
Regulation
Negative FBY Pin Bias Current
Positive FBY Pin Bias Current
FBY Voltage-to-Current Amp
Transconductance, ΔI
FBY
/ΔV
FBY
FBY Error Amp Transresistance
ΔV
VC
/ΔI
FBY
FBY Error Amp Current Gain
ΔI
VC
/ΔI
FBY
FBY Line Regulation
Output Current Sense Regulation
Voltage, V
ISP
– V
ISN
IMON Regulation Voltage, EA2
Output Current Sense Amp
Transconductance, A7
Output Current Sense Amp Voltage
Gain, A7
Output Current Sense Amp Input
Dynamic Range, A7
IMON Amp Transconductance, EA2
IMON Amp Voltage Gain, EA2
EN/FBIN Input Regulation Voltage, EA3
EN/FBIN Amp Transconductance, EA3
EN/FBIN Amp Voltage Gain, EA3
MODE Forced CCM Threshold
MODE Forced CCM Threshold
Hysteresis
DCM Comparator Threshold in
Pulse-Skipping Mode, MODE = 2V
DCM Comparator Threshold in
Forced CCM, MODE = 0V
V
ISN
= 80V, To Enter DCM Mode, V
ISP
– V
ISN
Falling
V
ISN
= 12V, To Enter DCM Mode, V
ISP
– V
ISN
Falling
V
ISN
= 0V, To Enter DCM Mode, V
ISP
– V
ISN
Falling
V
ISN
= 80V, To Enter DCM Mode, V
ISP
– V
ISN
Falling
V
ISN
= 12V, To Enter DCM Mode, V
ISP
– V
ISN
Falling
V
ISN
= 0V, To Enter DCM Mode, V
ISP
– V
ISN
Falling
l
l
l
l
l
l
l
l
l
l
l
l
l
l
ELECTRICAL CHARACTERISTICS
MIN
46
23
–41
–65
–1.28
–60
81.4
80.1
TYP
50
31
–32
–51
–1.234
–15.8
83.5
83.9
1.8
1.05
508
516
1.5
MAX
54
38
–23
–38
–1.18
25
85.7
87.5
UNITS
mV
mV
mV
mV
V
mV
µA
µA
mS
mS
kΩ
kΩ
A/A
Control Loops (Refer to Block Diagram to Locate Amplifiers)
M1 Conducting Current, Current Flowing into FBY Pin
Current Flowing Out of FBY Pin
Current Flowing Into FBY Pin
Current Flowing Out of FBY Pin, ΔI
FBY
= 10µA
Current Flowing into FBY Pin, ΔI
FBY
= 10µA
Current Flowing Out of FBY Pin, ΔV
VC
= 200mV
Current Flowing into FBY Pin, ΔV
VC
= 200mV
ΔI
VC
= 2µA
4.5V ≤ V
GND
– V
–VIN
≤ 80V, V
BIAS
– V
–VIN
= 0V
V
ISN
= 80V, I
FBY
= –53µA
V
ISN
= 12V, I
FBY
= –53µA
V
ISN
= 0V, I
FBY
= –53µA
V
ISN
= 12V, I
FBY
= –53µA, INTV
EE
in UVLO and SS > 1.8V
I
FBY
= –53µA
I
FBY
= –53µA, INTV
EE
in UVLO and SS > 1.8V
ΔI
IMON
= 10μA
–0.02
l
l
l
l
l
l
0.003
50
50
50
25
1.213
0.916
1000
11.9
0.02
57
57
60
34
1.24
0.947
%/V
mV
mV
mV
mV
V
V
µS
V/V
mV
mV
µS
V/V
43
43
40
17
1.184
0.885
Negative Input Range
Positive Input Range
ΔI
VC
= 2μA, I
FBY
= –53µA
V
ISN
= 12V, I
FBY
= –53µA
I
FBY
= –53µA
ΔI
VC
= 2µA, I
FBY
= –53µA
I
FBY
= –53µA
To Exit Forced CCM Mode, MODE Rising
To Enter Forced CCM Mode, MODE Falling
l
l
l
500
–51.8
165
65
1.55
1.607
140
55
1.662
V
µS
V/V
1.19
1.125
1.224
1.175
49
1.258
1.23
V
V
mV
–4.5
–4.5
–7.5
–380
–380
–380
2.8
2.8
2.8
–300
–300
–300
10
10
13
–220
–220
–220
mV
mV
mV
mV
mV
mV
8709fa
4
For more information
www.linear.com/LT8709
LT8709
ELECTRICAL CHARACTERISTICS
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications for each channel are at T
A
= 25°C. V
GND
– V
–VIN
= 12V, V
EN/FBIN
– V
–VIN
= 12V,
V
BIAS
– V
–VIN
= 12V, unless otherwise noted. Pin voltages have the following relations: FBY is relative to the GND pin, TG and INTV
EE
to the BIAS pin, and all other pins to the –V
IN
pin, unless otherwise stated. Pin currents have the following relations: positive current is
denoted as current flowing into the pin; negative current is denoted as current flowing out of the pin, unless otherwise stated. (Note 2)
CONDITIONS
R
T
= 46.4k
R
T
= 357k
Compared to Normal f
OSC
Free-Running or Synchronizing
l
l
l
l
l
PARAMETER
Oscillator
Switching Frequency, f
OSC
Switching Frequency in Foldback
Switching Frequency Range
SYNC High Level for Sync
SYNC Low Level for Sync
SYNC Clock Pulse Duty Cycle
Recommended Min SYNC Ratio
Gate Drivers, BG and TG
BG Rise Time
BG Fall Time
TG Rise Time
TG Fall Time
BG and TG Non-Overlap Time
BG Minimum On-Time
BG Minimum Off-Time
TG Minimum On-Time
TG Minimum Off-Time
Power Good Indicators, PG
PG Power Good Threshold for Negative
FBY Voltage
PG Power Good Threshold for Positive
FBY Voltage
PG Power Good Hysteresis for Negative
FBY Voltage
PG Power Good Hysteresis for Positive
FBY Voltage
PG Anti-Glitch Delay
PG Output Voltage Low
PG Leakage Current
MIN
640
85
100
1.5
TYP
750
100
1/5
MAX
860
115
750
0.4
UNITS
kHz
kHz
ratio
kHz
V
V
%
V
SYNC
= 0V to 3V
f
SYNC
/f
OSC
C
BG
= 3300pF (Note 3)
C
BG
= 3300pF (Note 3)
C
TG
= 3300pF (Note 3)
C
TG
= 3300pF (Note 3)
TG Rising to BG Rising, C
BG
= C
TG
= 3300pF (Note 3)
BG Falling to TG Falling, C
BG
= C
TG
= 3300pF (Note 3)
C
BG
= C
TG
= 3300pF
C
BG
= C
TG
= 3300pF
C
BG
= C
TG
= 3300pF
C
BG
= C
TG
= 3300pF
Current Out of FBY Pin Rising
Current Out of FBY Pin Falling
Current into FBY Pin Rising
Current into FBY Pin Falling
l
l
l
l
20
3/4
24
21
15
16
80
45
150
100
0
290
71
63.5
71.5
63.5
74.9
67.5
75.4
67.5
7.4
7.9
140
90
80
ns
ns
ns
ns
220
150
420
480
150
770
79
71.5
79.5
71.5
ns
ns
ns
ns
ns
ns
µA
µA
µA
µA
µA
µA
µs
50
1
mV
µA
Delay from PG Threshold Trip to PG Toggle
100µA into PG Pin, |I
FBY
| < PG Threshold
V
PG
= 7V, |I
FBY
| > PG Threshold
l
100
9
0.01
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 LT8709E is guaranteed to meet performance specifications
from 0°C to 125°C junction temperature. Specifications over the
–40°C to 125°C operating temperature range are assured by design,
characterization and correlation with statistical process controls. The
LT8709I is guaranteed over the full –40°C to 125°C operating junction
temperature range.
Note 3:
Rise and fall times are measured using 10% and 90% levels. Delay
times are measured using 50% levels.
Note 4:
This IC includes overtemperature protection that is intended
to protect the device during momentary overload conditions. Junction
temperature will exceed 125°C when overtemperature protection is active.
Continuous operation over the specified maximum operating junction
temperature may impair device reliability.
Note 5:
Do not apply a positive or negative voltage or current source to the
BG, TG, and INTV
EE
pins, otherwise permanent damage may occur, except
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