LTC3704
Wide Input Range, No R
SENSE
TM
Positive-to-Negative DC/DC Controller
FEATURES
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DESCRIPTIO
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High Efficiency Operation (No Sense
Resistor Required)
Wide Input Voltage Range: 2.5V to 36V
Current Mode Control Provides Excellent Transient
Response
High Maximum Duty Cycle (Typ 92%)
±1%
Internal Voltage Reference
±2%
RUN Pin Threshold with 100mV Hysteresis
Micropower Shutdown: I
Q
= 10µA
Programmable Switching Frequency
(50kHz to 1MHz) with One External Resistor
Synchronizable to an External Clock Up to 1.3
×
f
OSC
User-Controlled Pulse Skip or Burst Mode
®
Operation
Internal 5.2V Low Dropout Voltage Regulator
Capable of Operating with a Sense Resistor for High
Output Voltage Applications (V
DS
>36V)
Small 10-Lead MSOP Package
The LTC
®
3704 is a wide input range, current mode,
positive-to-negative DC/DC controller that drives an
N-channel power MOSFET and requires very few external
components. Intended for low to high power applications,
it eliminates the need for a current sense resistor by
utilizing the power MOSFET’s on-resistance, thereby maxi-
mizing efficiency.
The IC’s operating frequency can be set with an external
resistor over a 50kHz to 1MHz range, and can be synchro-
nized to an external clock using the MODE/SYNC pin.
Burst Mode operation at light loads, a low minimum
operating supply voltage of 2.5V and a low shutdown
quiescent current of 10µA make the LTC3704 ideally
suited for battery-operated systems.
For applications requiring constant frequency operation,
the Burst Mode operation feature can be defeated using
the MODE/SYNC pin. Higher than 36V switch voltage
applications are possible with the LTC3704 by connecting
the SENSE pin to a resistor in the source of the power
MOSFET.
The LTC3704 is available in the 10-lead MSOP package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
No R
SENSE
is a trademark of Linear Technology Corporation.
APPLICATIO S
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SLIC Power Supplies
Telecom Power Supplies
Portable Electronic Equipment
Cable and DSL Modems
Router Supplies
TYPICAL APPLICATIO
R1
1M
1
2
RUN
I
TH
LTC3704
R
C
3k
3
4
5
C
C1
4.7nF
R
T
80.6k
1%
R
FB1
1.21k
1%
R
FB2
3.65k
1%
NFB
FREQ
MODE/SYNC
INTV
CC
GATE
GND
SENSE
V
IN
•
L1*
10
9
C
DC
47µF
V
IN
5V to 15V
V
OUT
–5.0V
3A to 5A
L2*
•
EFFICIENCY (%)
8
7
6
D1
C
VCC
4.7µF
C
IN
47µF
M1
C
OUT
100µF
(X2)
GND
3704 TA01
C
IN
, C
DC
: TDK C5750X5R1C476M
C
OUT
: TDK C5750X5R0J107M
C
VCC
: TAIYO YUDEN LMK316BJ475ML
D1: MBRD835L (ON SEMICONDUCTOR)
L1, L2: BH ELECTRONICS BH510-1009
M1: Si4884 (SILICONIX/VISHAY)
Figure 1. High Efficiency Positive to Negative Supply
sn3704 3704fs
U
Conversion Efficiency
100
90
80
70
60
V
IN
= 10V
50
40
30
20
0.001
0.01
1.0
0.1
OUTPUT CURRENT (A)
10
3704 TA01b
U
U
V
IN
= 5V
V
IN
= 15V
1
LINER [ LINEAR TECHNOLOGY ]
