LTC1159CG-5#PBF Linear Technology, LTC1159CG-5#PBF Datasheet - Page 10

• Manufacturer Part Number: LTC1159CG-5#PBF
• Description: IC SW REG STEP-DOWN 5V 20-SSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC1159CG-5#PBF

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 5V
• 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: Lead free / RoHS Compliant
• Power - Output: -

APPLICATIO S I FOR ATIO
C
In continuous mode, the source current of the P-channel
MOSFET is a square wave of duty cycle V
To prevent large voltage transients, a low ESR input
capacitor sized for the maximum RMS current must be
used. The maximum RMS capacitor current is given by:
This formula has a maximum at V
I
monly used for design because even significant deviations
do not offer much relief. Note that capacitor manufacturer’s
ripple current ratings are often based on only 2000 hours
of life. This makes it advisable to further derate the
capacitor, or to choose a capacitor rated at a higher
temperature than required. Several capacitors may be
paralleled to meet size or height requirements in the
design. An additional 0.1 F ceramic capacitor may also be
required on V
The selection of C
series resistance (ESR). The ESR of C
twice the value of R
LTC1159:
Optimum efficiency is obtained by making the ESR equal to
R
Sprague should be considered for high performance ca-
pacitors. The OS-CON semiconductor dielectric capacitor
available from Sanyo has the lowest ESR for its size at a
somewhat higher price. Once the ESR requirement for
C
exceeds the I
In surface mount applications, multiple capacitors may
have to be paralleled to meet the capacitance, ESR or RMS
current handling requirements of the application. Alumi-
num electrolytic and dry tantalum capacitors are both
available in surface mount configurations. In the case of
tantalum, it is critical that the capacitors are surge tested
for use in switching power supplies. An excellent choice is
the AVX TPS series of surface mount tantalums, available
in case heights ranging from 2mm to 4mm. For example,
LTC1159
LTC1159-3.3/LTC1159-5
10
RMS
IN
OUT
SENSE
C
C
and C
IN
OUT
= I
has been met, the RMS current rating generally far
Required I
. Manufacturers such as Nichicon, Chemicon, and
MAX
Required ESR < 2R
OUT
/2. This simple worst-case condition is com-
RIPPLE(P-P)
IN
Selection
for high frequency decoupling.
RMS
OUT
U
SENSE
is driven by the required effective
requirement.
I
U
MAX
SENSE
for proper operation of the
[V
OUT
W
OUT
IN
(V
V
IN
IN
must be less than
= 2V
– V
OUT
OUT
U
OUT
, where
)]
1/2
/V
IN
.
if 200 F/10V is called for in an application requiring 3mm
height, two AVX 100 F/10V (P/N TPSD107K010) could be
used. Consult the manufacturer for other specific recom-
mendations.
At low supply voltages, a minimum value of C
suggested to prevent an abnormal low frequency operating
mode (see Figure 4). When C
ripple at low frequencies will be large enough to trip the
voltage comparator. This causes the Burst Mode operation
to be activated when the LTC1159 would normally be in
continuous operation. The effect is most pronounced with
low values of R
higher frequencies with lower values of L. The output
remains in regulation at all times.
Load Transient Response
Switching regulators take several cycles to respond to a
step in DC (resistive) load current. When a load step
occurs, V
where ESR is the effective series resistance of C
also begins to charge or discharge C
loop adapts to the current change and returns V
steady-state value. During this recovery time V
monitored for overshoot or ringing which would indicate a
stability problem. The I
the Figure 1 circuit will provide adequate compensation for
most applications.
A second, more severe transient is caused by switching in
loads with large (>1 F) supply bypass capacitors. The
1000
OUT
800
400
200
600
0
Figure 4. Minimum Suggested C
0
shifts by an amount equal to I
SENSE
R
SENSE
1
L = 50 H
(V
= 0.05
and can be improved by operating at
IN
TH
– V
L = 50 H
R
L = 25 H
R
2
OUT
SENSE
SENSE
external components shown in
) VOLTAGE (V)
OUT
= 0.02
= 0.02
3
is too small, the output
OUT
LTC1159 • TPC04
4
until the regulator
OUT
5
LOAD
OUT
OUT
OUT
. I
OUT
• ESR,
can be
to its
LOAD
is