LTC1159CG#TR Linear Technology, LTC1159CG#TR Datasheet - Page 11

• Manufacturer Part Number: LTC1159CG#TR
• Description: IC REG SW STPDWN SYNC ADJ 20SSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC1159CG#TR

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: Adjustable
• Current - Output: 50mA
• Frequency - Switching: 250kHz
• Voltage - Input: 4 ~ 40 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 20-SSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

APPLICATIO S I FOR ATIO
discharged bypass capacitors are effectively put in parallel
with C
deliver enough current to prevent this problem if the load
switch resistance is low and it is driven quickly. The only
solution is to limit the rise time of the switch drive so that
the load rise time is limited to approximately 25 • C
Thus a 10 F capacitor would require a 250 s rise time,
limiting the charging current to about 200mA.
Line Transient Response
The LTC1159 has better than 60dB line rejection and is
generally impervious to large positive or negative line
voltage transients. However, one rarely occurring condi-
tion can cause the output voltage to overshoot if the proper
precautions are not observed. This condition is a negative
V
positive transition of greater than 0.5V/ s slew rate.
The reason this condition rarely occurs is because it takes
tens of amps to slew the regulator input capacitor at this
rate! The solution is to add a diode between the cap and V
pins of the LTC1159 as shown in several of the typical
application circuits. If you think your system could have
this problem, add the diode. Note that in surface mount
applications it can be combined with the P-gate diode by
using a low cost common cathode dual diode.
EXTV
The LTC1159 contains an internal PNP switch connected
between the EXTV
supplies the V
in voltage than the 4.5V internal regulator. This allows the
IN
transition of several volts followed within 100 s by a
LTC1159-3.3
CC
OUT
V
IN
Pin Connection
Figure 5a. Inductive Boost Circuit for EXTV
, causing a rapid drop in V
P-DRIVE
N-GATE
EXTV
P-GATE
P-GND
CC
CC
power whenever the EXTV
CC
U
and V
V
IN
U
P-CH
N-CH
+
CC
pins. The switch closes and
C
IN
•
1:1
W
L
OUT
BAT85
•
3
. No regulator can
1
R
SENSE
CC
C
1 F
OUT
pin is higher
2
CC
U
+
4
+
LTC1159 • F05a
LOAD
V
OUT
IN
.
MOSFET driver and control power to be derived from the
output during normal operation and from the internal
regulator when the output is out of regulation (start-up,
short circuit).
Significant efficiency gains can be realized by powering V
from the output, since the V
driver and control currents will be scaled by a factor of
(Duty Cycle)/(Efficiency). For 5V regulators this simply
means connecting the EXTV
ever, for 3.3V and other low voltage regulators, additional
circuitry is required to derive V
The following list summarizes the four possible connec-
tions for EXTV
1. EXTV
only from the internal 4.5V regulator resulting in reduced
MOSFET gate drive levels and an efficiency penalty of up to
10% at high input voltages.
2. EXTV
connection for a 5V regulator and provides the highest
efficiency.
3. EXTV
work. For 3.3V and other low voltage regulators, efficiency
gains can still be realized by connecting EXTV
output-derived voltage which has been boosted to greater
than 4.5V. This can be done either with the inductive boost
winding shown in Figure 5a or the capacitive charge pump
shown in Figure 5b. The charge pump has the advantage of
simple magnetics and generally provides the highest effi-
ciency at the expense of a slightly higher parts count.
LTC1159-3.3
V
IN
CC
CC
CC
Figure 5b. Capacitive Charge Pump for EXTV
P-DRIVE
N-GATE
P-GATE
EXTV
Connected Directly to V
Left Open. This will cause V
P-GND
Connected to an Output-Derived Boost Net-
CC
CC
LTC1159-3.3/LTC1159-5
:
+
1 F
V
IN
P-CH
N-CH
CC
IN
+
CC
current resulting from the
pin directly to V
BAT85
power from the output.
C
OUT
IN
VN2222LL
L
. This is the normal
0.22 F
CC
LTC1159 • F05b
to be powered
LTC1159
R
SENSE
OUT
BAT85
BAT85
CC
CC
11
+
. How-
to an
V
C
CC
OUT
OUT