LTC3836_15 Datasheet, PDF (1/30 Pages) Linear Technology – Dual 2-Phase, No RSENSETM Low VIN Synchronous Controller

LTC3836
Dual 2-Phase,
No R_SENSE^TM Low V_IN
Synchronous Controller
FEATURES
n _{No Current Sense Resistors Required}
n _{Out-of-Phase Controllers Reduce Required Input}
Capacitance
n _{All N-Channel Synchronous Drive}
n _{VIN Range: 2.75V to 4.5V}
n _{Constant-Frequency Current Mode Operation}
n _{0.6V ±1.5% Voltage Reference}
n _{Low Dropout Operation: 97% Duty Cycle}
n _{True PLL for Frequency Locking or Adjustment}
n _{Selectable Pulse-Skipping/Continuous Operation}
n _{Tracking Function}
n _{Internal Soft-Start Circuitry}
n _{Power Good Output Voltage Monitor}
n _{Output Overvoltage Protection}
n _{Micropower Shutdown: IQ = 6.5μA}
n _{Tiny Low Profile (4mm × 5mm) QFN and Narrow}
SSOP Packages
APPLICATIONS
n _{General Purpose 3.3V to 1.X Supplies}
n _{Single Lithium-Ion Powered Devices}
n _{Distributed DC Power Systems}
L, LT, LTC, LTM, Linear Technology, Burst Mode, OPTI-LOOP and the Linear logo are
registered trademarks and No R_SENSE is a trademark of Linear Technology Corporation. All other
trademarks are the property of their respective owners. Protected by U.S. Patents including
5481178, 5929620, 6144194, 6304066, 6498466, 6580258, 6611131.
DESCRIPTION
The LTC^®3836 is a 2-phase dual output synchronous
step-down switching regulator controller with tracking
that drives external N-channel power MOSFETs using few
external components. The constant-frequency current
mode architecture with MOSFET V_DS sensing eliminates
the need for sense resistors and improves efficiency.
The power loss and noise due to the ESR of the input
capacitance are minimized by operating the two control-
lers out-of-phase. Pulse-skipping operation provides high
efficiency at light loads. The 97% duty cycle capability
provides low dropout operation, extending operating time
in battery-powered systems.
The operating frequency is selectable from 300kHz to
750kHz, allowing the use of small surface mount induc-
tors and capacitors. For noise sensitive applications, the
LTC3836 operating frequency can be externally synchro-
nized from 250kHz to 850kHz.
The LTC3836 features an internal 1ms soft-start that can
be extended with an external capacitor. A tracking input al-
lows the second output to track the first during start-up.
The LTC3836 is available in the tiny thermally enhanced
(4mm × 5mm) QFN and 28-lead narrow SSOP packages.
TYPICAL APPLICATION
High Efficiency, 2-Phase, Dual Synchronous DC/DC Step-Down Converter
V_OUT1
1.8V AT
15A
V_IN
SBEONOSSET11⁺ SBEONOSSET22⁺
TG1
TG2
0.47μH
SW1
SW2
LTC3836
BG1
BG2
118k
100μF
×2
PGND
820pF
V_FB1
V_FB2
I_TH1
I_TH2
SGND
59k 15k
820pF
15k
V_IN
22μF
3.3V
×3
0.47μH
59k
59k
V_OUT2
1.2V AT
15A
100μF
×2
3836 TA01
Efficiency/Power Loss vs Load Current
100
3.3V-1.8V
90
EFFICIENCY
10000
80 3.3V-1.2V
EFFICIENCY
70
1000
60
50
100
3.3V-1.2V
40
POWER LOSS
30 _3.3V-1.8V
20 ^{POWER LOSS}
10
10
0
10
CIRCUIT OF FIGURE 15
1
100
1000 10000 100000
LOAD CURRENT (mA)
3836 TA01b
3836fb
1