LT1738_15 Datasheet, PDF (1/20 Pages) Linear Technology – Slew Rate Controlled Ultralow Noise DC/DC Controller

LT1738
Slew Rate Controlled
Ultralow Noise DC/DC Controller
FEATURES
s _{Greatly Reduced Conducted and Radiated EMI}
s _{Low Switching Harmonic Content}
s _{Independent Control of Output Switch Voltage and}
Current Slew Rates
s _{Greatly Reduced Need for External Filters}
s _{Single N-Channel MOSFET Driver}
s _{20kHz to 250kHz Oscillator Frequency}
s _{Easily Synchronized to External Clock}
s _{Regulates Positive and Negative Voltages}
s _{Easier Layout Than with Conventional Switchers}
U
APPLICATIO S
s _{Power Supplies for Noise Sensitive Communication}
Equipment
s _{EMI Compliant Offline Power Supplies}
s _{Precision Instrumentation Systems}
s _{Isolated Supplies for Industrial Automation}
s _{Medical Instruments}
s _{Data Acquisition Systems}
DESCRIPTIO
The LT^®1738 is a switching regulator controller designed
to lower conducted and radiated electromagnetic interfer-
ence (EMI). Ultralow noise and EMI are achieved by
controlling the voltage and current slew rates of an exter-
nal N-channel MOSFET switch. Current and voltage slew
rates can be independently set to optimize harmonic
content of the switching waveforms vs efficiency. The
LT1738 can reduce high frequency harmonic power by as
much as 40dB with only minor losses in efficiency.
The LT1738 utilizes a current mode architecture opti-
mized for single switch topologies such as boost, flyback
and Cuk. The IC includes gate drive and all necessary
oscillator, control and protection circuitry. Unique error
amp circuitry can regulate both positive and negative
voltages. The internal oscillator may be synchronized to
an external clock for more accurate placement of switch-
ing harmonics.
Protection features include gate drive lockout for low V_IN,
soft-start, output current limit, short-circuit current limit-
ing, gate drive overvoltage clamp and input supply
undervoltage lockout.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
Ultralow Noise 5V to 12V Converter
5V
V_IN
+
100µF
1.3nF
16.9k
25k 3.3k
25k 3.3k
22nF
0.22µF
1.5k
22µH
P3
17
3
V_IN
GCL
5pF
14
SHDN
5
V5
6
SYNC
2
CAP
7
C_T
1
GATE
8
R_T
LT1738
16
R_VSL
4
CS
15
R_CSL
20
PGND
12
V_C
9
FB
SS GND NFB
13 11 10
10nF
MBRD620
B
+
4 × 150µF
OSCON
10µH
150µF ⁺
OSCON
OPTIONAL
A _12V
1A
POINT A
ON SCHEMATIC
500µV/DIV
Si9426
25mΩ
21.5k
POINT B
ON SCHEMATIC
50mV/DIV
2.5k
1738 TA01
12V Output Noise
(Bandwidth = 100MHz)
400µV_P-P
5µs/DIV
1738 TA01a
1738fa
1