LTC1530CS8-2.5 Linear Technology, LTC1530CS8-2.5 Datasheet - Page 9

• Manufacturer Part Number: LTC1530CS8-2.5
• Description: IC SW REG CNTRLR SYNC 2.5V 8SOIC
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC1530CS8-2.5

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 2.5V
• 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
Typically, thermal shutdown is activated if the LTC1530’s
junction temperature exceeds 150 C. G1 and G2 resume
switching when the junction temperature drops below
100 C.
Soft-Start and Current Limit
Unlike other PWM parts, the LTC1530 includes an on-chip
soft-start capacitor that is used during start-up and cur-
rent limit operation. On power-up, an internal 4 A pull-up
at COMP brings the LTC1530 out of shutdown mode. An
internal current source then charges the internal C
capacitor. The COMP pin is clamped to one V
voltage on C
amplifier from forcing the loop to maximum duty cycle.
The LTC1530 operates at low duty cycle as the COMP pin
voltage increases above about 2.4V. The slew rate of the
soft-start capacitor is typically 0.4V/ms. As the voltage on
C
error amplifier regulates the output. The MIN comparator
is disabled if soft-start is active to prevent an override of
the soft-start function.
The LTC1530 includes another feedback loop to control
operation in current limit. Before each falling edge of G1,
the current comparator, CC, samples and holds the volt-
age drop across external MOSFET Q1 with the LTC1530’s
I
I
R
I
maximum desired level, CC pulls current out of C
cycle decreases and the output current is controlled. The
CC comparator pulls current out of C
voltage difference between I
overload conditions, the voltage at C
creating a time delay before current limit activates. Very
short, mild overloads may not affect the output voltage at
all. Significant overload conditions allow the voltage on
C
reduced voltage until the overload is removed. Serious
overloads generate a large overdrive and allow CC to pull
the C
the external components.
FB
MAX
MAX
SS
SS
DS(ON)
pin. CC compares the voltage at I
continues to increase, M
to reach a steady state and the output remains at a
, indicating that Q1’s drain current has exceeded the
SS
pin. As peak current rises, the voltage across the
voltage down quickly, thus preventing damage to
of Q1 increases. If the voltage at I
SS
during start-up. This prevents the error
U
U
SS
FB
eventually turns off and the
and I
W
FB
SS
to the voltage at the
in proportion to the
MAX
SS
FB
falls gradually,
. Under minor
GS
drops below
U
above the
SS
. Duty
SS
By using the R
current limit circuit eliminates the sense resistor that
would otherwise be required. This minimizes the number
of components in the high current power path. The current
limit circuitry is not designed to be highly accurate. It is
primarily meant to prevent damage to the power supply
circuitry during fault conditions. The exact current level
where current limiting takes effect will vary from unit to
unit as the R
Figure 5a illustrates the basic connections for the current
limit circuitry. For a given current limit level, the external
resistor from I
I
I
I
L
R
I
where
=
f
LMAX
LOAD
RIPPLE
IMAX
OSC
O
DS(ON)Q1
R
V
IN
IMAX
Inductor
f
OSC
Figure 5a. Current Limit Setting (Use Kelvin-Sense
Connections Directly at the Drain and Source of Q1)
LTC
CC
Maximum load current
200 A sink current
I
V
LOAD
LTC1530
Inductor ripple current
OUT
+
–
1530
L
DS(ON)
O
I
LMAX
O
DS(ON)
MAX
value
n-r
V
V
I
IN
200 A
OUT
oscillator frequency = 300kHz
RIPPLE
I
esis
IMAX
to V
of Q1 varies.
2
R
of Q1 to measure output current, the
DS ON Q
tance of Q1 at I
IN
I
MAX
I
FB
is determined by:
G1
G2
R
1
20
IMAX
V
IN
Q1
Q2
LMAX
L
O
LTC1530
+
+
C
C
IN
OUT
V
1530 F05
OUT
1530fa
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