LT8602
42V Quad Monolithic
Synchronous Step-Down
Regulator
Description
Features
Flexible Power Supply System Providing Four
Outputs with a Wide Input Range
n Two High Voltage Synchronous Buck Regulators:
3V to 42V Input Voltage Range
Output Currents Up to 2.5A and 1.5A
High Efficiency Up to 93%
n Two Low Voltage Synchronous Buck Regulators:
2.6V to 5.5V Input Voltage Range
Output Currents Up to 1.8A and 94% Efficiency
n Resistor Programmable and Synchronizable
250kHz to 2.2MHz Switching Frequency
n Low Ripple Burst Mode® Operation:
30µA IQ at 12VIN
Output Ripple < 15mV
n Programmable Power-On Reset
n Power Good Indicators
n 2-Phase Clock Reduces Input Current Ripple
n Available in Thermally Enhanced 40-Lead QFN
(6mm × 6mm) or 48-Lead (7mm × 7mm) LQFP Packages
The LT®8602 is a quad channel, current mode, monolithic
buck switching regulator with a programmable power-on
reset. All regulators are synchronized to a single oscillator
with an adjustable frequency from 250kHz to 2.2MHz. The
LT8602 can be configured for micropower Burst Mode
operation or pulse-skipping operation at light load. Micropower operation results in quiescent current of 30µA
with all four regulators operating in the application below.
Applications
The LT8602 is available in either a 40-lead 6mm × 6mm
QFN or a 48-Lead 7mm × 7mm LQFP package.
n
The high voltage channels are synchronous buck regulators that operate from an input of 3V to 42V. The output
currents are up to 1.5A (OUT1) and 2.5A (OUT2). The
low voltage channels operate from an input of 2.6V to
5.5V. Internal synchronous power switches provide high
efficiency with output currents up to 1.8A. The LT8602
uses a 2-phase clock with channels 1 and 3 operating 180°
from channels 2 and 4 to reduce input ripple current on
both HV and LV inputs. All channels have cycle-by-cycle
current limit, providing protection against shorted outputs.
Thermal shutdown provides additional protection.
Automotive Systems
Distributed Supply Regulation
n Industrial Controls and Power Supplies
n
L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks
of Analog Devices, Inc. All other trademarks are the property of their respective owners.
n
VIN
BST1
PVIN2
SW1
FB1
PVIN1 LT8602
EN/UVLO
POREN
4
2
5V, 3.3V, 1.8V and 1.2V Step-Down Regulators
OUT1
5V, 1.5A
BST2
RST
SW2
FB2
PG1-4
RUN3-4
OUT2
3.3V*
SW3
FB3
PVIN4
OUT3
1.8V, 1.7A
INTVCC
CPOR
2
TRKSS1, 2
RT
SYNC
SW4
FB4
OUT4
1.2V, 1.8A
GND
*IOUT2 = 2.5A – IPVIN3 – IPVIN4
2.0
100
90
1.8
90
1.6
80
70
1.4
70
60
1.2
EFFICIENCY
80
FSW = 1MHz
FSW = 2MHz
50
40
1.0
0.8
0.4
20
0.2
10
0
0.3
0.6
0.9
LOAD CURRENT (A)
0
1.5
1.2
8602 TA01b
0.8
0.7
0.6
FSW = 1MHz
FSW = 2MHz
40
20
0
0.9
EFFICIENCY
50
0.6
POWER
LOSS
1.0
60
30
10
LV Channel Efficiency,
VOUT3 = 1.8V
0.5
0.4
0.3
30
0
0.2
POWER
LOSS
0
0.3
0.6
0.9
1.2
LOAD CURRENT (A)
POWER LOSS (W)
PVIN3
100
POWER LOSS (W)
BIAS
OUT2
HV Channel Efficiency,
VIN = 12V, VOUT1 = 5V
EFFICIENCY (%)
IN
6V TO 42V
EFFICIENCY (%)
Typical Application
0.1
1.5
0
1.8
8602 TA01c
8602 TA01a
8602fb
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1
LT8602
Absolute Maximum Ratings
(Note 1)
Supply Voltages
VIN, PVIN1,2............................................. –0.3V to 42V
PVIN3,4...................................................... –0.3V to 6V
PG1-4, SYNC, TRKSS1-2, RUN3-4, RST Voltages.........6V
RT, FB1-4, CPOR, POREN Voltages...........................3.6V
EN/UVLO Voltage.......................................................42V
BIAS Voltage............................................... –0.3V to 15V
Operating Junction Temperature (Notes 2, 3)
LT8602E............................................. –40°C to 125°C
LT8602I.............................................. –40°C to 125°C
Storage Temperature Range................... –65°C to 150°C
Pin Configuration
TOP VIEW
PG3
POREN
GND
PVIN1
PVIN1
GND
SW3
GND
PVIN3
GND
SYNC
RSTB
48
47
46
45
44
43
42
41
40
39
38
37
CPOR
RST
SYNC
PVIN3
GND
SW3
PVIN1
GND
POREN
PG3
TOP VIEW
40 39 38 37 36 35 34 33 32 31
PG1 1
30 RUN3
GND 2
29 RT
SW1 3
28 INTVCC
BST1 4
27 FB3
BST2 5
26 FB1
41
GND
SW2 6
25 FB2
SW2 7
24 FB4
GND 8
23 VIN
GND 9
22 EN/UVLO
BIAS 10
PG1 1
GND 2
GND 3
SW1 4
SW1 5
BST1 6
BST2 7
SW2 8
SW2 9
GND 10
GND 11
BIAS 12
36
35
34
33
32
31
30
29
28
27
26
25
49
GND
CPOR
RUN3
RT
INTVCC
FB3
FB1
GND
FB2
FB4
VIN
EN/UVLO
TRKSS1
21 TRKSS1
UJ PACKAGE
40-LEAD (6mm × 6mm) PLASTIC QFN
θJC = 2°C/W, θJA = 33°C/W
EXPOSED PAD (PIN 41) IS GND, MUST BE SOLDERED TO PCB
Order Information
13
14
15
16
17
18
19
20
21
22
23
24
PG2
PG4
GND
PVIN2
PVIN2
GND
SW4
GND
PVIN4
GND
RUN4
TRKSS2
TRKSS2
NC
RUN4
PVIN4
GND
SW4
PVIN2
GND
PG4
PG2
11 12 13 14 15 16 17 18 19 20
LXE PACKAGE
48-LEAD (7mm × 7mm) PLASTIC LQFP
θJA = 20°C/W
EXPOSED PAD (PIN 49) IS GND, MUST BE SOLDERED TO PCB
http://www.linear.com/product/LT8602#orderinfo
LEAD FREE FINISH
TAPE AND REEL (QFN)/
TRAY (LXE)
PART MARKING*
PACKAGE DESCRIPTION
MSL
RATING
LT8602EUJ#PBF
LT8602EUJ#TRPBF
LT8602UJ
40-Lead (6mm × 6mm) Plastic QFN
1
–40°C to 125°C
LT8602IUJ#PBF
LT8602IUJ#TRPBF
LT8602UJ
40-Lead (6mm × 6mm) Plastic QFN
1
–40°C to 125°C
LT8602ELXE#PBF
LT8602ELXE#TRPBF
LT8602LXE
48-Lead (7mm × 7mm) Plastic eLQFP
3
–40°C to 125°C
LT8602ILXE#PBF
LT8602ILXE#TRPBF
LT8602LXE
48-Lead (7mm × 7mm) Plastic eLQFP
3
–40°C to 125°C
TEMPERATURE RANGE
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
8602fb
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LT8602
Electrical Characteristics
The l denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at TA = 25°C. VIN = PVIN1 = PVIN2 = 12V, EN/UVLO = 3V, PVIN3 = PVIN4 = 3.3V
unless otherwise noted. (Note 2)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Minimum Operating Voltage
l
2.7
3
V
Minimum Operating Voltage, to Start
l
3.1
3.5
V
1
VIN Quiescent Current, Shutdown
EN/UVLO = 0.4V
0.1
VIN Quiescent Current, Operating
No Load (Note 4)
100µA on VOUT2 (Note 4)
30
70
EN/UVLO Threshold
EN/UVLO Rising
1.15
EN/UVLO = 2V
–40
EN/UVLO Hysteresis
EN/UVLO Input Current
1.2
µA
µA
µA
1.25
50
V
mV
40
nA
Oscillator
l
1.8
0.225
SYNC Input Frequency Range
l
0.25
SYNC Input Voltage Low
l
SYNC Input Voltage High
l
Switching Frequency
RT = 28.9k
RT = 254k
SYNC Input Current
2
0.25
2.2
0.275
MHz
MHz
2.2
MHz
0.3
V
100
nA
1
1.012
V
0.002
0.01
%/V
100
nA
1.2
V
–100
Channel 1
Feedback Voltage
FB Voltage Line Regulation
0.988
l
–100
VIN = 3V to 42V
Input Current FB1
SW1 Peak Current Limit
l
VIN = PVIN1 = 6V
2.3
SW1 Leakage Current
2.7
3.0
A
0.1
1
µA
SW1 Top On Resistance
ISW1 = 1A
240
mΩ
SW1 Bottom On Resistance
ISW1 = 1A
170
mΩ
Lower FB1 Power Good Threshold
Percentage of VFB1
l
89
92
95
%
Upper FB1 Power Good Threshold
Percentage of VFB1
l
105
108
111
%
PG1 Output Voltage Low
IPG1 = –100μA
l
0.1
0.2
V
l
30
µA
2.4
3.1
μA
PG1 Leakage Current
PG1 = 5V, FB1 = 1V
TRKSS1 Pull-Up Current
SS1 = 0.2V
Minimum Switch-On Time
ISW1 = 1A
60
ns
Minimum Switch-Off Time
ISW1 = 1A
70
ns
1.5
8602fb
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3
LT8602
Electrical Characteristics
The l denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at TA = 25°C. VIN = PVIN1 = PVIN2 = 12V, EN/UVLO = 3V, PVIN3 = PVIN4 = 3.3V
unless otherwise noted. (Note 2)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
l
0.988
1
1.012
V
0.002
0.01
%/V
l
–100
100
nA
Channel 2
Feedback Voltage
FB Voltage Line Regulation
VIN = 3V to 42V
Input Current FB2
SW2 Peak Current Limit
VIN = PVIN2 = 6V
3.5
SW2 Leakage Current
4.0
4.5
A
0.1
1
µA
SW2 Top On Resistance
ISW2 = 1A
150
mΩ
SW2 Bottom On Resistance
ISW2 = 1A
100
mΩ
Lower FB2 Power Good Threshold
Percentage of VFB2
l
89
92
95
%
Upper FB2 Power Good Threshold
Percentage of VFB2
l
105
108
111
%
PG2 Output Voltage Low
IPG2 = –100μA
l
0.1
0.2
V
l
30
µA
2.4
3.1
µA
PG2 Leakage Current
PG2 = 5V, FB2 = 1V
TRKSS2 Pull-Up Current
SS2 = 0.2V
Minimum Switch-On Time
ISW2 = 2A
60
ns
Minimum Switch-Off Time
ISW2 = 2A
70
ns
1.5
Channel 3
Operating Voltage
Feedback Voltage
FB Voltage Line Regulation
l
2.6
l
790
VIN = 3V to 42V
5.5
V
800
810
mV
0.002
0.01
%/V
100
nA
3.1
3.5
A
PVIN3 = 5.5V
0.1
1
µA
SW3 PMOS On Resistance
ISW3 = 1A
150
mΩ
SW3 NMOS On Resistance
ISW3 = 1A
120
mΩ
Input Current FB3
l
SW3 Average Current Limit
SW3 Leakage
–100
1.8
Lower FB3 Power Good Threshold
Percentage of VFB3
l
89
92
95
%
Upper FB3 Power Good Threshold
Percentage of VFB3
l
105
108
111
%
PG3 Output Voltage Low
IPG3 = –100μA
l
0.1
0.2
V
PG3 Leakage Current
PG3 = 5V, FB3 = 0.8V
l
30
µA
RUN3 Threshold Voltage
RUN3 Input Current
RUN3 = 3.3V
Soft-Start Time
l
0.695
l
–100
l
0.7
0.72
1
0.75
V
100
nA
1.3
ms
Minimum Switch-On Time
ISW3 = 1A
70
ns
Minimum Switch-Off Time
ISW3 = 1A
70
ns
PVIN3 UVLO
4
2.35
2.6
V
8602fb
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LT8602
Electrical Characteristics
The l denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at TA = 25°C. VIN = PVIN1 = PVIN2 = 12V, EN/UVLO = 3V, PVIN3 = PVIN4 = 3.3V
unless otherwise noted. (Note 2)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Channel 4
Operating Voltage
Feedback Voltage
FB Voltage Line Regulation
l
2.6
l
790
VIN = 3V to 42V
Input Current FB4
l
SW4 Average Current Limit
5.5
800
810
mV
0.002
0.01
%/V
–100
1.8
V
100
nA
3.1
3.5
A
1
SW4 Leakage
PVIN4 = 5.5V
0.1
SW4 PMOS On Resistance
ISW4 = 1A
150
SW4 NMOS On Resistance
ISW4 = 1A
Lower FB4 Power Good Threshold
Percentage of VFB4
l
89
92
95
%
Upper FB4 Power Good Threshold
Percentage of VFB4
l
105
108
111
%
PG4 Output Voltage Low
IPG4 = –100μA
l
0.1
0.2
V
PG4 Leakage Current
PG4 = 5V, FB4 = 0.8V
l
30
µA
120
RUN4 Threshold Voltage
RUN4 Input Current
RUN4 = 3.3V
Soft-Start Time
Minimum Switch-On Time
ISW4 = 1A
Minimum Switch-Off Time
ISW1 = 1A
l
0.695
l
–100
l
0.7
0.72
1
mΩ
0.75
V
100
nA
1.3
ms
70
ns
70
PVIN4 UVLO
2.35
µA
mΩ
ns
2.6
V
Power-On Reset
CPOR Pull-Up Current
CPOR = 0V
POR Delay Time
CPOR = 1000pF
2
31
RST Output Voltage Low
IRST = –100μA
RST Pull-Up Current
POR Timed Out, RST = 0V
RST Leakage Current
RST = 6V, EN/UVLO = 0V
l
POREN Threshold
POREN Pull-Up Current
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 LT8602E 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
LT8602I is guaranteed to meet performance specifications from –40°C to
125°C junction temperature.
35.2
39.4
0.1
0.2
20
–40
l
POREN = 0V
μA
ms
V
μA
40
nA
1.15
1.2
1.25
V
0.8
1.2
1.6
μA
Note 3: This IC includes overtemperature protection that is intended to
protect the device during overload conditions. Junction temperature will
exceed 150°C when overtemperature protection is active. Continuous
operation above the specified maximum operating junction temperature
will reduce lifetime.
Note 4: All four channels enabled as shown in the application circuit
details of front page application (using the 1MHz component values) found
in the Typical Application section.
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5
LT8602
T
Typical
Performance Characteristics A = 25°C, VIN = PVIN1 = PVIN2 = 12V, EN/UVLO = 3V
and PVIN3 = PVIN4 = 3.3V, unless otherwise noted.
Channel 2 Efficiency vs Load
VOUT2 = 3.3V, FSW = 2MHz
100
100
3.6
90
80
80
3.2
80
70
70
2.8
70
50
40
30
PV IN = 12V
PV IN = 28V
PV IN = 42V
10
0
0.0001
0.001
0.01
0.1
LOAD CURRENT (A)
2.4
60
50
40
30
1.6
1.2
20
0.4
10
1.0
1.5
LOAD CURRENT (A)
80
80
70
70
EFFICIENCY (%)
90
40
30
20
10
0
0.0001
0
0.0001
PV IN2 = 5.5V
PV IN2 = 12V
PV IN2 = 28V
0.001
0.01
0.1
LOAD CURRENT (A)
1
40
30
0
0.0001
1 2
8602 G03
2.8
50
10
8602 G04
PVIN4 = 2.6V
PVIN4 = 3.3V
PVIN4 = 5.5V
0.001
0.01
0.1
LOAD CURRENT (A)
2.6
2.4
2.2
2.0
1.8
1.6
1 2
0
10 20 30 40 50 60 70 80 90 100
DUTY CYCLE (%)
8602 G06
8602 G05
Channel 2 Peak Current Limit vs
Duty Cycle
Channel 3/Channel 4 Maximum
Output Current vs Duty Cycle
Channel 3/4 Peak Current Limit
vs Duty Cycle
5.0
3
Channel 1 Peak Current Limit vs
Duty Cycle
60
20
PVIN3 = 2.6V
PVIN3 = 3.3V
PVIN3 = 5.5V
0.001
0.01
0.1
LOAD CURRENT (A)
0
2.5
2.0
LV Channel Efficiency vs Load
VOUT4 = 1.2V, FSW = 2MHz
100
90
50
30
8602 G02
LV Channel Efficiency vs Load
VOUT3 = 1.8V, FSW = 1MHz
60
40
10
8602 G01
100
50
0.8
0.5
Channel 2 Efficiency vs Load
VOUT2 = 3.3V, FSW = 1MHz
60
20
0
0.0
1 2
2.0
PVIN2 = 5.5V
PVIN2 = 12V
PVIN2 = 24V
TOP FET CURRENT LIMIT (A)
60
EFFICIENCY (%)
90
EFFICIENCY (%)
90
20
EFFICIENCY (%)
4.0
POWER LOSS (W)
EFFICIENCY (%)
100
Channel 1 Efficiency vs Load
VOUT1 = 8V, FSW = 2MHz
2.0
4.0
4.0
3.5
3.0
3.5
MAX OUTPUT CURRENT (A)
4.5
TOP FET CURRENT LIMIT (A)
TOP FET CURRENT LIMIT (A)
1.8
3.0
2.5
2.0
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
2.5
0
10 20 30 40 50 60 70 80 90 100
DUTY CYCLE (%)
8602 G07
6
1.5
0
10 20 30 40 50 60 70 80 90 100
DUTY CYCLE (%)
8602 G08
0
0
20
40
60
DUTY CYCLE (%)
80
100
8602 G09
8602fb
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LT8602
T
Typical
Performance Characteristics A = 25°C, VIN = PVIN1 = PVIN2 = 12V, EN/UVLO = 3V
and PVIN3 = PVIN4 = 3.3V, unless otherwise noted.
Switching Frequency vs
Temperature
RT = 30k
RT = 60k
RT = 250k
8
6
TRKSS CURRENT (µA)
FREQUENCY CHANGE (%)
TRKSS Pull-Up Current vs Voltage
4
2
0
–2
–4
–6
RST Pull-Up Current vs Voltage
1
10
0
0
RST CURRENT (µA)
10
–1
–2
–10
–20
–8
10
–50 –30 –10 10 30 50 70 90 110 130 150
TEMPERATURE (°C)
–3
0
0.5
1
1.5
2
2.5
TRKSS VOLTAGE (V)
8602 G10
350
2.00
300
1.75
200
150
0.50
10000
0.25
8602 G13
60
50
CHANNEL 1
0
0.5
1
1.5
SWITCH CURRENT (A)
2
2.5
8602 G16
5
10
15
25 30
VIN (V)
35
40
45
8602 G15
90
ISW = 1A
80
80
CHANNEL 1
CHANNEL 2
70
CHANNEL 2
70
60
CHANNEL 1
50
60
50
20
Minimum On-Time vs
Temperature
Minimum Off-Time vs ISW
90
MINIMUM OFF-TIME (ns)
MINIMUM ON-TIME (ns)
90
70
30
10
25 50 75 100 125 150 175 200 225 250 275
RT (kΩ)
100
CHANNEL 2
3.5
Quiescent Current vs VIN
8602 G14
Minimum On-Time vs ISW
80
3
20
MINIMUM ON-TIME (ns)
100
1.5
2
2.5
RST VOLTAGE (V)
1.00
50
8000
1
40
1.25
0.75
4000
6000
CPOR (pF)
0.5
1.50
100
2000
50
IQ (µA)
FREQUENCY (MHz)
POR DELAY TIME (ms)
2.25
250
0
8602 G12
Switching Frequency vs RT
Power-On Reset Time vs CPOR
0
–30
3.5
8602 G11
400
0
3
0
0.5
1
1.5
2
SWITCH CURRENT (A)
2.5
8602 G17
40
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
8602 G18
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LT8602
T
Typical
Performance Characteristics A = 25°C, VIN = PVIN1 = PVIN2 = 12V, EN/UVLO = 3V
and PVIN3 = PVIN4 = 3.3V, unless otherwise noted.
Minimum Off-Time vs
Temperature
180
ISW = 1A
100
160
80
CHANNEL 1
70
CHANNEL 2
60
PVIN = 2.6V
120
100 PVIN = 3.3V
80
60
PVIN = 5.5V
40
0
0
25 50 75 100 125 150
TEMPERATURE (°C)
0
0.3
0.6
0.9
ISW (A)
8602 G19
Channel 1 RDSON vs Temperature
500
80
70
60
50
20
50
–50 –25
1.2
40
1.5
400
0
0.3
8602 G20
0.6
0.9
ISW (A)
1.2
1.5
8602 G21
Channel 3/Channel 4 RDSON vs
Temperature
Channel 2 RDSON vs Temperature
ISW1 = 1A
Channel 3/Channel 4 Minimum
Off-Time vs ISW
90
140
MINIMUM OFF-TIME (ns)
90
MINIMUM ON-TIME (ns)
MINIMUM OFF-TIME (ns)
100
Channel 3/Channel 4 Minimum
On-Time vs ISW
300
ISW2 = 1A
ISW = 1A
250
300
TOP FET
300
200
TOP FET
200
100
0
0
–50 –25
25 50 75 100 125 150
TEMPERATURE (°C)
0
100
0
–50 –25
25 50 75 100 125 150
TEMPERATURE (°C)
3.0
45
2.5
CHANNELS 3, 4
2.0
1.5
1.0
0
0.790
25 50 75 100 125 150
TEMPERATURE (°C)
0.0
20
VOUT = 3.3V
VOUT = 5V
10
5
0
5
10
15
20
25
30
VEN/UVLO (V)
35
8602 G25
8
25
15
0.5
0.990
–50 –25
FULL FREQUENCY
REGION (2MHz)
30
0.795
0.995
RT = 28.9k
35
VIN (V)
IEN/UVLO (µA)
CHANNELS 1, 2 VFB (V)
CHANNELS 3, 4 VFB (V)
0.800
25 50 75 100 125 150
TEMPERATURE (°C)
Channel 1 Full Frequency
VIN vs Load Current
40
0.805
CHANNELS 1, 2
0
8602 G24
EN/UVLO Current vs Voltage
0.810
1.000
BOTTOM FET
8602 G23
Feedback Voltage vs Temperature
1.005
TOP FET
150
50
8602 G22
1.010
200
BOTTOM FET
BOTTOM FET
100
–50 –25
RDSON (mΩ)
RDSON (mΩ)
RDSON (mΩ)
400
40
45
8602 G26
0
0
0.2
0.4
0.6
0.8 1
IOUT (A)
1.2
1.4
1.6
8602 G27
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LT8602
T
Typical
Performance Characteristics A = 25°C, VIN = PVIN1 = PVIN2 = 12V, EN/UVLO = 3V
and PVIN3 = PVIN4 = 3.3V, unless otherwise noted.
45
Channel 2 Full Frequency
VIN vs Load Current
6.0
RT = 28.9k
40
VIN (V)
FULL FREQUENCY
REGION (2MHz)
15
FULL FREQUENCY
REGION (2MHz)
4.5
25
20
VIN
5.0
VOUT = 3.3V
VOUT = 5V
30
VIN (V)
RT = 28.9k
5.5
35
VOUT1
2V/DIV
4.0
3.5
VOUT = 1.8V
VOUT = 1.2V
3.0
10
100ms/DIV
2.5
5
0
Channel 1 Start-Up and Dropout,
RL = 20Ω
Channel 3, 4 Full Frequency
VIN vs Load Current
0
0.3
0.7
1
1.3 1.6
IOUT (A)
1.9
2.3
2.0
2.6
0
0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8
IOUT (A)
2
8602 G29
8602 G28
Channel 1 Start-Up and Dropout,
RL = 3.3Ω
Channel 2 Start-Up and Dropout,
RL = 20Ω
VIN
Channel 2 Start-Up and
Dropout, RL = 2Ω
VIN
VIN
VOUT1
2V/DIV
100ms/DIV
8602 G29
2V/DIV
8602 G30
VOUT2
100ms/DIV
2V/DIV
8602 G32
Full Frequency Waveforms
VOUT2
100ms/DIV
8602 G33
Light Load Waveforms
VOUT
20mV/DIV
VSW1
10V/DIV
VSW2
10V/DIV
VSW
5V/DIV
VSW3
2V/DIV
IL
0.5A/DIV
VSW4
2V/DIV
200ns/DIV
8602 G34
VOUT1 = 5V
VOUT2 = 3.3V
VOUT3 = 1.8V
VOUT4 = 1.2V
5µs/DIV
CHANNEL 1
12VIN TO 5VOUT AT 10mA
VSYNC = 0V
8602 G35
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9
LT8602
T
Typical
Performance Characteristics A = 25°C
Radiated EMI Performance, (CISPR25 Radiated Emission Tests with Class 5 Peak Limit)
Vertical Polarization
Horizontal Polarization
DC1949A Demo Board with EMI Filter Installed 14VIN, 1A at All Outputs, FSW = 2MHz
10
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LT8602
Pin Functions
(QFN/LXE)
BIAS (Pin 10/Pin 12): Power to the internal INTVCC regulator. Connect to an output ≥3.1V when such a supply
is available. Leaving BIAS unconnected will result in a
decrease in efficiency at light load. Decouple to ground
with a low ESR capacitor.
INTVCC (Pin 28/Pin 33): Internal Regulator Bypass. Do not
load the INTVCC pin with external circuitry. INTVCC is 3.1V
when BIAS < 3.1V; 3.4V when BIAS > 3.4V; and equal to
BIAS when BIAS is between 3.1V and 3.4V. Decouple to
ground with a low ESR 4.7μF capacitor.
BST1, BST2 (Pins 4, 5/Pins 6, 7): Boost Voltage for HV
Channels. The Boost Voltage provides a drive voltage higher
than PVIN to the gate of the NMOS top switch.
PG1, PG2 (Pins 1, 11/Pins 1, 13): Power Good Indicators for Channels 1 and 2. Open drain logic output pulls
down until the corresponding FB pin rises above 0.92V
but remains below 1.08V.
CPOR (Pin 31/Pin 36): Power-On Reset Timer. Connect a
capacitor from this pin to ground to program the power-on
reset timer. CPOR has a 2μA pull-up current.
EN/UVLO (Pin 22/Pin 26): Enable/Undervoltage Lockout
Input. The LT8602 is in low power shutdown when this pin
is below 0.4V. Between 0.4V and 1.1V, the part will turn
on the internal reference. A precision threshold at 1.2V
(rising) enables the switching regulators. This allows the
EN/UVLO pin to be used as an input undervoltage lockout
by connecting to a resistor divider between VIN and GND.
When the EN/UVLO voltage is between 0.4V and 1.2V, the
LT8602 input current will depend on the mode selected,
the VIN voltage and the EN/UVLO voltage. Connect to VIN
if the UVLO function is not needed.
FB1, FB2 (Pins 26, 25/Pins 31, 29): Feedback Input Pins
for the High Voltage Converters. The converters regulate
the corresponding feedback pin to the lesser of 1V or the
voltage on the associated TRKSS pin.
FB3, FB4 (Pins 27, 24/Pins 32, 28): Feedback Input Pins
for the Low Voltage Converters. The converters regulate
the corresponding feedback pin to 800mV.
GND (Pins 2, 8, 9, 13, 16, 35, 38, 41/Pins 2, 3, 10, 11,
15, 18, 20, 22, 30, 39, 41, 43, 46): Ground. These pins
must be soldered to PCB ground. The exposed pad (pin
41) must also be soldered to PCB ground.
PG3, PG4 (Pins 40, 12/Pins 48, 14): Power Good Indicators for Channels 3 and 4. Open drain logic output pulls
down until the corresponding FB pin rises above 0.736V
but remains below 0.864V.
POREN (Pin 39/Pin 47): Power On Reset Enable. This
is a logic input that starts the ramp on the POR timing
capacitor. This input has a weak pull-up.
PVIN1, PVIN2 (Pins 37, 14/Pins 44, 45, 16, 17): Input
Supply Voltage to HV Channels 1 and 2, respectively. These
pins are independent and can be powered from different
sources if necessary. Bypass each input with a low ESR
capacitor to the adjacent GND pin.
PVIN3, PVIN4 (Pins 34, 17/Pins 40, 21): Input Supply
Voltage to low voltage Channels 3 and 4. These pins are
typically connected to one of the high voltage converter
outputs and should be locally bypassed with a low ESR
capacitor. PVIN3 and PVIN4 are independent and do not
need to be connected to the same supply voltage.
RST (Pin 32/Pin 37): Power-On Reset Output. CMOS
output with weak pull-up, this pin is held low until the
POR times out.
RT (Pin 29/Pin 34): Frequency Programming Resistor.
Connect a resistor from this pin to ground to set the
internal oscillator frequency.
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11
LT8602
Pin Functions
(QFN/LXE)
RUN3, RUN4 (Pins 30, 18/Pin 35, 23): Run Inputs for
the low voltage converters.
SW1 (Pin 3/Pins 4, 5): Channel 1 Switch Node. This is
the output of the internal power switches for Channel 1.
SW2 (Pins 6, 7/Pins 8, 9): Channel 2 Switch Node. This
is the output of the internal power switches for Channel
2. These pins must be connected together.
SW3, SW4 (Pins 36, 15/Pins 42, 19): Switch Nodes
for low voltage converters. These are the outputs of the
internal power switches for Channels 3 and 4.
SYNC (Pin 33/Pin 38): Clock Synchronization Input. A digital input to allow the LT8602 to synchronize its switching
12
frequency to an external clock. If clock synchronization is
not used, connect this pin to ground to enable low ripple
burst mode or connect high to enable pulse skip operation
of the synchronous converters. Do not allow SYNC to float.
TRKSS1, TRKSS2 (Pins 21, 20/Pins 25, 24): Track/SoftStart Inputs for the High Voltage Converters. When this
pin is below 1V, the converter regulates the FB pin to the
TRKSS voltage instead of the internal reference. The TRKSS
pin has a 2.4μA pull-up current. TRKSS may be left floating
VIN (Pin 23/Pin 27): Input Supply Voltage to Internal Functions. This pin is independent from any PVIN pin and can
be powered from different sources if necessary. VIN must
be above 3V for the part to operate.
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LT8602
Block Diagram
POREN
RST
VIN
INTVCC
RT
SYNC
INTVCC
CPOR
POWER-ON
RESET
EN/UVLO
REGULATOR
OSCILLATOR
1V
REFERENCE
0.8V
SS3
ENABLE
SS4 CLK1 CLK2
BIAS
BST1
BST2
ILIM1
PVIN1
–
+
CLK1
CLK2
CURRENT
SENSE
COMPARATOR
LOGIC
SW2
LOGIC
DRIVER
–
+
DRIVER
–
+
+
2.4µA
–
+
REVERSE
CURRENT
COMPARATOR
REVERSE
CURRENT
COMPARATOR
LOOP
COMPENSATION
ILIM1
ILIM2
FB2
–
+
+
LOOP
COMPENSATION
2.4µA
1V
TRKSS1
1V
0.92V
1.08V
PG1
–
+
–
+
ILIM3
PVIN3
–
+
CLK1
0.86V
–
+
REVERSE
CURRENT
COMPARATOR
GND
ERROR
AMPLIFIER
LOOP
COMPENSATION
ILIM4
ILIM3
FB4
–
+
+
LOOP
COMPENSATION
0.8V
0.74V
PVIN4
–
+
DRIVER
REVERSE
CURRENT
COMPARATOR
–
+
+
SS3
PG2
SW4
ERROR
AMPLIFIER
FB3
1.08V
LOGIC
DRIVER
–
+
0.92V
CURRENT
SENSE
COMPARATOR
LOGIC
TRKSS2
ILIM4
CLK2
CURRENT
SENSE
COMPARATOR
SW3
GND
GND
ERROR
AMPLIFIER
ERROR
AMPLIFIER
FB1
PVIN2
–
+
CURRENT
SENSE
COMPARATOR
SW1
GND
ILIM2
SS4
0.8V
–
+
PG3
GND
RUN3
RUN4
PG4
–
+
0.74V
0.86V
8602 BD
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13
LT8602
Operation
The LT8602 is a quad channel, constant frequency, current
mode, monolithic buck switching regulator with power-on
reset. All channels are synchronized to a single oscillator.
Two of the channels are high voltage (up to 42V input)
while the other two are low voltage (up to 5.5V input) and
are typically powered from the high voltage buck outputs.
Start-Up
When enabled by setting the EN/UVLO voltage above its
threshold, the LT8602 starts charging the INTVCC capacitor
from VIN. If BIAS is higher than 3.1V, BIAS supplies current
to the INTVCC regulator to reduce VIN quiescent current.
High Voltage Buck Regulators
Each high voltage channel is a synchronous buck regulator
that operates from an independent PVIN pin. The internal
top power MOSFET is turned on at the beginning of each
oscillator cycle, and turned off when the current flowing
through the top MOSFET reaches a level determined by
the error amplifier. The error amplifier measures the output
voltage through an external resistor divider tied to the FB
pin to control the peak current in the top switch. The reference of the error amplifier is determined by the lower of
the internal 1V reference and the voltage at its TRKSS pin.
While the top MOSFET is off, the bottom MOSFET is
turned on for the remainder of the oscillator cycle or
until the inductor current starts to reverse. If overload
conditions result in more than 2A (Ch 1) or 3.3A (Ch 2)
flowing through the bottom switch, the next clock cycle
will be delayed until switch current returns to a safe level.
Low Voltage Buck Regulators
Each low voltage channel is a synchronous buck regulator
that operates from an independent PVIN pin. The PVIN pins
have an undervoltage lockout set at 2.35V. Each internal
top power MOSFET is turned on at the beginning of each
oscillator cycle, and turned off when the current flowing
14
through the top MOSFET reaches a level determined
by the error amplifier. The error amplifier measures the
output voltage through an external resistor divider tied to
the FB pin to control the peak current in the top switch.
The reference of the error amplifier is an internal 800mV
reference. Each LV channel has a RUN pin to allow power
sequencing and an internal soft-start circuit ramps the
output voltage up in 1ms.
While the top MOSFET is off, the bottom MOSFET is turned
on for the remainder of the oscillator cycle or until the
inductor current starts to reverse. If overload conditions
result in more than 2.4A flowing through the bottom switch,
the next clock cycle will be delayed until switch current
returns to a safe level.
Multiphase Switching
The oscillator generates two clock signals 180° out of
phase. Channels 1 and 3 operate on CLK1, while channels 2
and 4 operate on CLK2. Since a buck regulator only draws
input current during the top switch on cycle, multiphase
operation reduces peak input current and doubles the input
current frequency. These effects reduce input current ripple
and reduce the input capacitance required.
Light Load Operation
At light load, the regulators operate in low ripple burst
mode. Low ripple burst mode shuts down most internal
circuitry between switch on cycles to conserve power
while still retaining low ripple at the output.
Undervoltage Lockout
The EN/UVLO pin is used to put the LT8602 in shutdown,
reducing the input current to less than 1μA. The accurate
1.2V threshold of the EN/UVLO pin allows a programmable
VIN undervoltage lockout through an external resistor
divider tied to the EN/UVLO pin. A 50mV (typ) hysteresis
voltage on the EN/UVLO pin prevents switching noise from
inadvertently shutting down the LT8602.
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LT8602
Operation
Power Good Comparators
Power-On Reset Timer
Each channel has a power good comparator that trips
when the feedback pin is above or below its reference
voltage by more than 8%. The PG output pins are open
drain. The PG pin for each channel is pulled low when the
corresponding output is out of regulation. The PG outputs
are not valid until INTVCC rises to 2.7V
The LT8602 includes a power-on reset timer. The poweron reset time is adjustable using an external capacitor on
the CPOR pin. The timer is enabled by the POREN pin.
The RST pin is the output of the POR timer and is an
open-drain output with a weak internal pull-up. The RST
pin is valid when the LT8602 is enabled and INTVCC is
above 2.7V.
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15
LT8602
Applications Information
Setting the Output Voltages
The output voltages are set by the resistor dividers on the
outputs as shown in Figure 1. The formula used is:
COUT
LT8602
R1
Cff
OPTIONAL
FBx
R2
⎛V
⎞
R1= R2 • ⎜ OUTx – 1⎟
⎝ FBREF ⎠
8602 F01
Figure 1. Feedback Resistor Divider
where VOUTx is the output voltage of regulator x and FBREF
is the feedback reference voltage. FBREF is 1V for the high
voltage regulators (1 and 2) and 800mV for the low voltage
channels (3 and 4). Use 1% resistors in the dividers. R2
should be 200k or less to avoid noise problems.
To improve the frequency response, a feedforward capacitor
Cff may be used. Typical values are 10pf to 100pf. Great
care should be taken to route the VFB node away from
noise sources, such as the inductor or a SW line.
Switching Frequency
The LT8602 uses a constant frequency architecture that
can be programmed from 250kHz to 2.2MHz by tying a
resistor from the RT pin to ground. Table 1 shows the
value of RT for common switching frequencies.
Table 1. Switching Frequency vs RT Value
SWITCHING FREQUENCY (MHz)
RT (kΩ)
0.25
254
0.35
179
16
VOUTx
SWx
The following equation approximates the values shown
in Table 1:
RT =
61.9
– 1.9
fS – 0.009
where RT is in kΩ and fS is in MHz.
Selection of the operating frequency is mainly a trade-off
between efficiency and component size. The advantage
of high frequency operation is that smaller inductor and
capacitor values may be used. The advantage of low frequency operation is higher efficiency.
The high switching frequency also decreases the duty
cycle range because of finite minimum on- and off-times
which are independent of the switching frequency. The
top switch in the high voltage channel has a minimum
on-time of 60ns and minimum off-time of of 70ns. The top
switch in the low voltage channel has a minimum on-time
of 70ns and minimum off-time of 70ns. The minimum and
maximum duty cycles are:
0.5
124
0.75
81.2
DCMIN = fS • tON(MIN)
1.0
60.4
1.25
47.6
DCMAX = 1 – fS • tOFF(MIN)
1.5
39.4
1.75
33.3
2.0
28.9
2.2
26.3
where fS is the switching frequency, tON(MIN) is the minimum switch on-time, and tOFF(MIN) is the minimum switch
off-time. These equations illustrate how duty cycle range
increases when the switching frequency decreases.
The internal oscillator of the LT8602 can be synchronized to
an external 250kHz to 2.2MHz clock signal on the SYNC pin.
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LT8602
Applications Information
VIN Voltage Range
The LT8602’s minimum operating voltage is 3V. To program a higher minimum operating voltage, use a resistor
divider between the VIN pin and the EN/UVLO pin. The EN/
UVLO threshold is 1.2V. The EN/UVLO pin has 50mV of
hysteresis to prevent glitches from falsely disabling the
LT8602.
The UVLO circuit is shown in Figure 3, Reverse Protection
Diodes. The calculation for the lockout voltage is:
VIN(UVLO) =
RUV1 +RUV2
•1.2V
RUV2
calculated maximum voltage, the channel starts to skip
switch on cycles (pulse-skipping). In this case, the channel
switching frequency will no longer be the programmed
frequency. The output will continue to regulate, but the
peak inductor current and output ripple will increase
significantly.
Inductor Selection
Inductor selection involves inductance, saturation current,
series resistance (DCR) and magnetic loss.
A good starting point for the inductance values are:
Lx = Kx •
VOUTx PVINx – VOUTx
•
PVINx
fS
PVIN Voltage Range
Each switching regulator channel operates from its own
PVIN pin (PVIN1 to PVIN4). The PVIN pin can be connected
to either an independent voltage supply or a high voltage
channel output. The PVIN1 and PVIN2 voltage range is 3.0V
to 42V. The PVIN3 and PVIN4 voltage range is 2.6V to 5.5V.
Once the inductance is selected, the inductor current ripple
and peak current can be calculated:
where fS is the switching frequency in MHz, Lx is in µH,
VOUTx is the channel output voltage and K1 = 1.6, K2 =
1.0 and K3 and K4 = 1.3.
The minimum PVIN voltage to regulate output voltage at
full frequency is:
PVINx(MIN) =
VOUTx
DCMAX
Where DCMAX is the maximum duty cycle (refer to Switching Frequency section) for that channel. If PVIN is below
the calculated minimum voltage, the channel starts to skip
switch off cycles. At low input voltages the part will turn
on the top switch for longer than a full switch cycle in
order to extend the effective duty cycle. When the part is
extending the effective duty cycle the switching frequency
will drop to one half (or less) of the programmed frequency.
The maximum PVIN voltage to regulate output voltage at
full frequency is:
PVINx(MAX) =
VOUTx
DCMIN
Where DCMIN is the minimum duty cycle (refer to Switching
Frequency section) for that channel. If PVIN is above the
ΔILx =
VOUTx
Lx • fS
⎛
VOUTx ⎞
• ⎜ 1–
⎟
⎝ PVINx(MAX) ⎠
ILx(PEAK) =IOUTx(MAX) +
ΔILx
2
To guarantee sufficient output current, peak inductor current must be lower than the switch current limit (ILIM).
To keep the efficiency high, the inductor series resistance
(DCR) should be as small as possible (must be
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