LT3690 Datasheet, PDF (1/28 Pages) Linear Technology – 36V, 4A, 1.5MHz Synchronous Step-Down Switching Regulator

LT3690
FEATURES
36V, 4A, 1.5MHz Synchronous
Step-Down Switching Regulator
with 70µA Quiescent Current
DESCRIPTION
n _{Wide Input Range:}
– Operation from 3.9V to 36V
– Overvoltage Lockout Protects Circuits
Through 60V Transients
n _{4A Maximum Output Current}
n _{Integrated 30mΩ N-Channel Synchronous Switch}
n _{Low Ripple (<15mVP-P) Burst Mode}^® _Operation:
I_Q = 70µA at 12V_IN to 3.3V_OUT
n _{Programmable Input Undervoltage Lockout}
n _{0.8V Feedback Reference Voltage}
n _{Output Voltage: 0.8V to 20V}
n _{Programmable and Synchronizable Oscillator}
(170kHz to 1.5MHz)
n _{Soft-Startup and Output Voltage Tracking}
n _{Short-Circuit Robust}
n _{Power Good Flag}
n _{Small Thermally Enhanced 4mm × 6mm QFN Package}
APPLICATIONS
n _{Automotive Systems}
n _{Industrial Supplies}
n _{Distributed Supply Regulation}
The LT^®3690 is an adjustable frequency monolithic buck
switching regulator that accepts input voltages up to 36V.
A high efficiency 90mΩ switch is included on the device
along with the boost diode and the necessary oscillator,
control, and logic circuitry. The internal synchronous power
switch of 30mΩ increases efficiency and eliminates the
need for an external Schottky catch diode. Current mode
topology is used for fast transient response and good
loop stability. Shutdown reduces input supply current to
less than 1µA. The low ripple Burst Mode maintains high
efficiency at low output currents while keeping output
ripple below 15mV in typical applications.
The LT3690 features robust operation and is easily configu-
rable. Using a resistor divider on the UVLO pin provides a
programmable undervoltage lockout. A power good flag
signals when V_OUT reaches 90% of the programmed out-
put voltage. Protection circuitry senses the current in the
power switches to protect the LT3690 against short-circuit
conditions. Frequency foldback and thermal shutdown
provide additional protection. The LT3690 is available in
a 4mm × 6mm QFN package with exposed pads for low
thermal resistance.
L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks of
Linear Technology Corporation. All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
V_IN
4.5V TO 36V
10µF
3.3V Step-Down Converter
V_IN
0.68µF
EN
BST
UVLO
3.3µH
3.3V
SW
4A
LT3690
SS
BIAS
22k
680pF
V_C
V_CCINT
0.47µF
SYNC
PG
316k
FB
RT
GND
ƒ = 600kHz
32.4k 102k
100µF
3690 TA01a
Efficiency and Power Loss
100
2.5
V_OUT = 5V
90
2.0
V_OUT = 3.3V
80
1.5
V_OUT = 5V
70
1.0
V_OUT = 3.3V
60
V_IN = 12V ^0.5
L = 4.7µH
ƒ = 600kHz
50
0
0 0.5 1 1.5 2 2.5 3 3.5 4
LOAD CURRENT (A)
3690 TA01b
3690f
1