LT3501
Monolithic Dual Tracking
3A Step-Down Switching
Regulator
Description
Features
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Wide Input Range: 3.1V to 25V
Two Switching Regulators with 3A Output Capability
Independent Supply to Each Regulator
Adjustable/Synchronizable Fixed Frequency
Operation from 250kHz to 1.5MHz
Antiphase Switching
Outputs Can be Paralleled
Independent, Sequential, Ratiometric or Absolute
Tracking Between Outputs
Independent Soft-Start and Power Good Pins
Enhanced Short-Circuit Protection
Low Dropout: 95% Maximum Duty Cycle
Low Shutdown Current: <10µA
20-Lead TSSOP Package with Exposed Leadframe
The LT®3501 is a dual-current mode PWM step-down
DC/DC converter with two internal 3.5A switches. Independent input voltage, feedback, soft-start and power
good pins for each channel simplify complex power
supply tracking/sequencing requirements.
Both converters are synchronized to either a common
external clock input or a resistor programmable fixed
250kHz to 1.5MHz internal oscillator. At all frequencies, a
180° phase relationship between channels is maintained,
reducing voltage ripple and component size. Programmable
frequency allows for optimization between efficiency and
external component size.
Minimum input-to-output voltage ratios are improved
by allowing the switch to stay on through multiple clock
cycles, only switching off when the boost capacitor needs
recharging, resulting in ~95% maximum duty cycle.
Applications
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DSP Power Supplies
Disc Drives
DSL/Cable Modems
Wall Transformer Regulation
Distributed Power Regulation
Each output can be independently disabled using its own
soft-start pin, or by using the SHDN pin the entire part can
be placed in a low quiescent current shutdown mode.
The LT3501 is available in a 20-lead TSSOP package with
exposed leadframe for low thermal resistance.
L, LT, LTC, LTM, Linear Technology, Burst Mode and the Linear logo are registered trademarks
and ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners.
Typical Application
3.3V and 1.8V Dual 3A Step-Down Converter with Output Tracking
Efficiency
VIN, 12V
100
4.7µH
PMEG4005
0.47µF
BST1
BST2
SW1
SW2
B360A
24.9k
47µF
470pF
8.06k
10pF
40.2k
3.3µH
B360A
0.1µF
VOUT2
1.8V, 3A
IND2
VOUT2
PG1
PG2
FB1
FB2
VC1
VC2
SS/TRACK1 SS/TRACK2
GND
100µF
10k
VOUT1 = 1.8V
70
VOUT1 = 2.5V
60
50
40
30
20
470pF
8.06k
VIN = 12V
IOUT2 = 0A
FREQUENCY = 500kHz
10
0
40.2k
VOUT1 = 3.3V
80
0.47µF
LT3501
IND1
VOUT1
VOUT1
3.3V, 3A
61.9k
EFFICIENCY (%)
VIN2
RT/SYNC
VIN1
SHDN
PMEG4005
VOUT1 = 5V
90
4.7µF
0
0.5
1.5
2
1
LOAD CURRENT (A)
2.5
3
3501 TA01b
47pF
3501 TA01a
3501fd
1
