LTC1530CS8 Linear Technology, LTC1530CS8 Datasheet - Page 11

• Manufacturer Part Number: LTC1530CS8
• Description: IC SW REG CNTRLR SYNC ADJ 8-SOIC
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC1530CS8

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 1.3 ~ 3.5 V
• Current - Output: 20A
• Frequency - Switching: 300kHz
• Voltage - Input: 3.3V, 5V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

APPLICATIO S I FOR ATIO
In order for the current limit circuit to operate properly and
to obtain a reasonably accurate current limit threshold, the
I
source pins. A 0.1 F decoupling capacitor can also be
connected across R
tion, LTC recommends that the voltage drop across the
R
or ringing at Q1’s source can cause the actual current limit
to be greater than the desired current limit set point.
MOSFET Gate Drive
The PV
voltage, V
efficient operation. This higher voltage can be supplied
with a separate supply, or it can be generated using a
simple charge pump as shown in Figure 7. The 86%
maximum duty cycle ensures sufficient off-time to refresh
the charge pump during each cycle.
As PV
age lockout circuit prevents G1 and G2 from pulling high
until PV
R
PV
PV
thermal shutdown, the driver logic is designed to hold G2
low until G1 first goes high.
1N5243B
MAX
IMAX
DS(ON)
CC
CC
OPTIONAL FOR
13V
V
and I
IN
is slewing, the current limit circuit is disabled until
CC
is 8V. In addition, on start-up or recovery from
resistor be set to 100mV. Otherwise, noise spikes
> 6.5V
CC
from triggering the current limit comparator while
CC
is powered up from 0V, the LTC1530 undervolt-
FB
IN
supply must be greater than the input supply
+
LTC1530
, by at least one power MOSFET V
reaches about 3.5V. To prevent Q1’s high
pins must be Kelvin sensed at Q1’s drain and
Figure 7. Doubling Charge Pump
10 F
U
IMAX
PV
MBR0530T1 MBR0530T1
CC
to filter switching noise. In addi-
U
G1
G2
0.22 F
W
V
IN
Q1
Q2
L
O
U
GS(ON)
+
+
C
C
IN
O
V
1530 F07
for
OUT
Power MOSFETs
Two N-channel power MOSFETs are required for synchro-
nous LTC1530 circuits. They should be selected based
primarily on threshold voltage and on-resistance consid-
erations. Thermal dissipation is often a secondary con-
cern in high efficiency designs. The required MOSFET
threshold should be determined based on the available
power supply voltages and/or the complexity of the gate
drive charge pump scheme. In 5V input designs where a
12V supply is used to power PV
with R
good results. The current drawn from the 12V supply
varies with the MOSFETs used and the LTC1530’s operat-
ing frequency, but is generally less than 50mA.
LTC1530 applications that use a 5V V
doubling charge pump to generate PV
enough gate drive voltage to fully enhance standard
power MOSFETs. Under this condition, the effective
MOSFET R
tion in the FETs and reducing efficiency. In addition,
power supply start-up problems can occur with standard
power MOSFETs. These start-up problems can occur for
two reasons. First, if the MOSFET is not fully enhanced,
the higher effective R
vate current limit at a much lower level than the desired
trip point. Second, standard MOSFETs have higher GATE
threshold voltages than logic level MOSFETs, thereby
increasing the PV
MOSFET whose R
necessarily have a logic level MOSFET GATE threshold
voltage. Logic level FETs are the recommended choice for
5V-only systems. Logic level FETs can be fully enhanced
with a doubler charge pump and will operate at maximum
efficiency. Note that doubler charge pump designs run-
ning from supplies higher than 6.5V should include a
Zener diode clamp at PV
exceeding the absolute maximum rating of the pin.
After the MOSFET threshold voltage is selected, choose
the R
allowable power dissipation and maximum output cur-
rent. In a typical LTC1530 buck converter circuit, operat-
ing in continuous mode, the average inductor current is
equal to the output load current. This current flows through
DS(ON)
DS(ON)
DS(ON)
based on the input voltage, the output voltage,
specified at V
CC
may be quite high, raising the dissipa-
DS(ON)
voltage required to turn them on. A
DS(ON)
is rated at V
CC
GS
causes the LTC1530 to acti-
= 5V or 6V can be used with
to prevent transients from
CC
, standard MOSFETs
GS
CC
IN
= 4.5V does not
LTC1530
do not provide
voltage and a
11
1530fa