LT3742 Datasheet, PDF (1/24 Pages) Linear Technology – Dual, 2-Phase Step-Down Switching Controller

FEATURES
■ _{Wide Input Voltage Range: 4V to 30V}
■ _{Wide Output Voltage Range: 0.8V to VIN}
■ _{Low Shutdown IQ: 20μA}
■ _{Out-of-Phase Controllers Reduce Required Input}
Capacitance and Power Supply Induced Noise
■ _{0.8V ±1.5% Voltage Reference}
■ _{500kHz Current Mode Fixed Frequency Operation}
■ _{Internal Boost Converter Provides Bias Rail for}
N-Channel MOSFET Gate Drive
■ _{Power Good Voltage Monitor for Each Output}
■ _{Programmable Soft-Start}
■ _{24-Lead 4mm × 4mm × 0.75mm Package}
APPLICATIONS
■ _{Satellite and Cable TV Set-Top Boxes}
■ _{Distributed Power Regulation}
■ _{Automotive Systems}
■ _{Super Capacitor Charger}
LT3742
Dual, 2-Phase Step-Down
Switching Controller
DESCRIPTION
The LT^®3742 is a dual step-down DC/DC switching regulator
controller that drives high side N-channel power MOSFETs.
A 500kHz fixed frequency current mode architecture pro-
vides fast transient response with simple loop compensa-
tion components and cycle-by-cycle current limiting. The
output stages of the two controllers operate 180° out of
phase to reduce the input ripple current, minimizing the
noise induced on the input supply, and allowing less input
capacitance.
An internal boost regulator generates a bias rail of V_IN + 7V
to provide gate drive for the N-channel MOSFETs allowing
low dropout and 100% duty cycle operation. The LT3742
can be used for applications where both controllers need
to operate independently, or where both controllers are
used to provide a single higher current output.
The device is available in a thermally enhanced 4mm ×
4mm QFN package.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
8V and 5V Dual Step-Down Converter
V_IN
V_OUT1
8V
4A
47μF
RUN1
10μH
V_IN
4.7μF
14V
45.3k _VIN
1μF
UVLO
SWB BIAS
20.0k
10μF
0.010Ω ^6.5μH
1.8k
200Ω
LT3742
G1
G2
SW1
SENSE1⁺
SENSE1^–
FB1
SW2
SENSE2⁺
SENSE2^–
FB2
6.5μH 0.010Ω
1.05k
200Ω
V_IN
10μF
V_OUT2
5V
4A
47μF
PG1 PG1
PG2
PG2
RUN/SS1 RUN/SS2
V_C1
V_C2
30k
1nF 1000pF
GND
20k
1000pF
1nF
RUN2
3742 TA03a
Efficiency vs Load Current
100
8V_OUT
90
5V_OUT
80
70
60
50
40
0 0.5 1 1.5 2 2.5 3 3.5 4
LOAD CURRENT (A)
3742 TA03b
3742f
1