LTC1682-3.3 LINER [Linear Technology], LTC1682-3.3 Datasheet - Page 10

• Manufacturer Part Number: LTC1682-3.3
• Description: Doubler Charge Pumps with Low Noise Linear Regulator
• Manufacturer: LINER [Linear Technology]

LTC1682/LTC1682-3.3/LTC1682-5
APPLICATIONS
Power-On Reset
Upon initial power-up, a power-on reset circuit ensures
that the internal functions are correctly initialized when
power is applied. Once V
power-on reset circuit will enable the part as long as the
SHDN pin is held high.
Thermal Considerations
The power handling capability of the device will be limited
by the maximum rated junction temperature (125 C). The
device power dissipation P
V
through its pins, especially GND (Pin 4). Thermal resis-
tance to ambient can be optimized by connecting GND to
a large copper region on the PCB, which serves as a heat
sink. Applications which operate the LTC1682 near maxi-
mum power levels should maximize the copper area at all
pins except C
some airflow over the part to carry away excess heat.
10
IN
(4mA). The device dissipates the majority of its heat
POWER SUPPLY
LOW NOISE DC
+
BATTERY OR
, C
–
R
U
GROUND TERMINAL E5
and FILT/FB and ensure that there is
LOAD
OUTPUT CAPACITOR
CONNECT BNC AND
GROUND TO THE
IN
INFORMATION
U
LTC1682
reaches approximately 1V, the
BOARD
DEMO
D
OR COUPLERS
BNC CABLES
= I
V
OUT
OUT
W
CAPACITOR IN SHIELDED
Figure 6. LTC1682 Noise Measurement Test Setup
BOX WITH COAXIAL
(2V
PLACE COUPLING
R
CONNECTOR
CAPACITOR
LOAD
COUPLING
SHDN
IN
C
FILT
– V
C2
U
V
OUT
GND
OUT
1
2
3
4
) +
R*
LTC1682-3.3/5
Figure 5
R*
+
–
*50 TERMINATIONS
PREAMPLIFIER
General Layout Considerations
Due to the high switching frequency and high transient
currents produced by the device, careful board layout is a
must. A clean board layout using a ground plane and short
connections to all capacitors will improve noise perfor-
mance and ensure proper regulation (Figure 5).
The FILT pin on the LTC1682-3.3/LTC1682-5 is a high
impedance node. Leakage currents at this pin must be
minimized.
Measuring Output Noise
Measuring the LTC1682 low noise levels requires care.
Figure 6 shows a test setup for taking the measurement.
Good connection and signal handling technique should
yield about 500 V
measurement involves AC coupling the LTC1682 output
into the test setup’s input and terminating this connection
with 50 . Coaxial connections must be maintained to
preserve measurement integrity.
20dB
HP-11048C OR
EQUIVALENT
1822
C1
8
7
6
5
V
IN
C3
R*
C4
1682 F05
NOTE: KEEP BNC CONNECTIONS
BANDWIDTH
P-P
FILTER
AS SHORT AS POSSIBLE
over a 2.5MHz bandwidth. The noise
PLACE BANDWIDTH FILTER
COMPONENTS IN SHIELDED BOX
WITH COAXIAL CONNECTORS
INPUT
OSCILLOSCOPE
1682 F06