LTC3446 Datasheet, PDF (1/20 Pages) Linear Technology – Monolithic Buck Regulator with Dual VLDO Regulators

FEATURES
n _{High Efficiency Triple Step-Down Outputs from a}
Single Input Supply
n _{1A Synchronous Buck Regulator Provides Main}
Step-Down Output and Powers Two 300mA
VLDO™ Linear Regulators
n _{Output Voltages as Low as 400mV (VLDO Outputs)}
n _{Power Good Output}
n _{Input Voltage Range: 2.7V to 5.5V}
n _{Independent Internal Soft-Start for Each Supply}
n _{Independent Enable Pin for Each Supply}
n _{Low (140μA Typ) No-Load Quiescent Current with}
all Outputs Enabled
n _{Constant Frequency Current Mode Operation}
n _{2.25MHz Switching Frequency Uses Small}
Inductors
n _{Defeatable Automatic Burst Mode}^® _{Operation for}
High Efficiency at Light Loads
n _{±1.5% Reference Accuracy}
n _{Overtemperature Protection}
n _{Thermally Enhanced 4mm × 3mm 14-Pin DFN}
Package
APPLICATIONS
n _{Low Power Handheld Devices}
n _{Low Voltage and Multivoltage Power for Digital}
Logic, I/O, FPGAs, CPLDs, ASICs and CPUs
LTC3446
Monolithic Buck Regulator
with Dual VLDO Regulators
DESCRIPTION
The LTC^®3446 combines a synchronous buck DC/DC con-
verter with two very low dropout (VLDO) linear regulators
to provide up to three stepped-down output voltages from
a single input voltage. The input voltage range is ideally
suited for Li-Ion battery-powered applications, as well
as powering low voltage logic from 5V or 3.3V rails. The
output voltage range extends down to 0.4V for the VLDO
regulators and 0.8V for the buck.
The 1A synchronous buck converter provides the main
output with high efficiency, typically 85%. The two 300mA
VLDO regulators can run off the main output to provide
two additional lower voltage outputs. A built-in supply
monitor provides a power good indication.
The buck converter switches at 2.25MHz, allowing the use
of small surface mount inductors and capacitors. Constant
frequency current mode operation produces controlled
output spectrum and fast transient response. A mode-
select pin allows automatic Burst Mode operation to be
enabled for higher efficiency at light load, or disabled for
lower noise operation down to very light loads. The two
VLDO regulators are stable with ceramic output capacitors
as small as 1μF.
L, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology Corporation.
VLDO is a trademark of Linear Technology Corporation. All other trademarks are the property
of their respective owners. Protected by U.S. Patents including 5481178, 6611131, 6304066,
6498466, 6580258.
TYPICAL APPLICATION
V_IN
2.9V TO 5.5V
22μF
X7R
DIGITAL
CONTROL
V_IN
SW
BUCKFB
LTC3446
LV_IN
PGOOD LV_OUT1
MODESEL
ENBUCK
ENLDO1 LVFB1
ENLDO2
1000pF
3.3k
I_TH
LV_OUT2
LV_FB2
GND
3446 TA01
L1
1.8μH
59k
47.5k
110k
40.2k
80.6k
40.2k
22μF
X7R
V_OUT
1.8V
400mA MAX
2.2μF
X7R
V_OUT
1.5V
300mA MAX
2.2μF
X7R
V_OUT
1.2V
300mA MAX
L1: TOKO A960AW-1R8M
Buck Efficiency vs Buck Load Current
100
Burst Mode
90
OPERATION
PWM
MODE
80
70
60
50
40
1
V_IN = 2.7V
V_IN = 3.6V
V_IN = 4.2V
10
100
LOAD CURRENT (mA)
1000
3446 TA01b
3446fd
1