LTC1503CMS8-1.8 Linear Technology, LTC1503CMS8-1.8 Datasheet - Page 7

• Manufacturer Part Number: LTC1503CMS8-1.8
• Description: IC BUCK/SW CAP 1.8V .1A 8MSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck), Switched Capacitor (Charge Pump)r

Specifications of LTC1503CMS8-1.8

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 1.8V
• Current - Output: 100mA
• Frequency - Switching: 600kHz
• Voltage - Input: 2.4 ~ 6 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

APPLICATIO S I FOR ATIO
In 1-to-1 mode, switch S1 and S2 are connected in series
between V
regulation (see Figure 1c). The REG ENABLE signal from
the main comparator (COMP1) controls switches S1 and
S2 directly. Since all of the V
V
to that of a linear regulator.
Mode Selection and Mode Skipping
The optimal step-down conversion mode is chosen based
on V
tions. Two internal comparators are used to select the
default step-down mode based on the V
voltage. A separate comparator (COMP2) is used to sense
a droop on V
charge pump to skip to a higher output current mode to
IN
, the efficiency in 1-to-1 mode is approximately equal
IN
V
Figure 1b. Step-Down Charge Pump in 3-to-2 Mode
Figure 1c. Step-Down Charge Pump in 1-to-1 Mode
IN
to V
IN
V
OUT
IN
and V
OUT
differential voltage and output load condi-
due to a heavy output load and force the
S5
S7
OUT
2
2
U
S2
as needed to boost V
U
C1
C1
+
+
OUT
S2
S3
C1
C2
C2
GND
1
1
C1
C1
(EXTERNAL)
C2
(EXTERNAL)
C1
(EXTERNAL)
–
+
–
–
current is sourced from
S1
W
S4
S6
S1
2
2
1
1503-1.8/2 F01c
1503-1.8/2 F01b
V
OUT
IN
OUT
U
and V
V
back into
OUT
OUT
maintain regulation. This will only occur as V
a 3-to-2 or 1-to-1 transition point. For example, under light
load conditions, the LTC1503-X can operate in 2-to-1
mode when V
ciency. However, when the load is increased, the part can
no longer supply enough output current in 2-to-1 mode to
maintain regulation. This causes V
regulation point until COMP2 trips and forces the part to
skip from 2-to-1 mode to 3-to-2 mode. The COMP2
threshold is about 17mV (V
comparator regulation point. Hysteresis in COMP2 will
force the part to transition in and out of mode skipping.
This will result in a slight V
20mV under mode skipping conditions.
Shutdown/Soft-Start Operation
The SHDN/SS pin is used to implement both low current
shutdown and soft-start. The soft-start feature limits
inrush currents when the regulator is initially powered up
or taken out of shutdown. Forcing a voltage lower than
0.35V (typ) will put the part into shutdown mode. Shut-
down mode disables all control circuitry and forces the
charge pump V
up current on the SHDN/SS pin will force the part into
active mode if the pin is left floating or is driven with an
open-drain output that is in a high impedance state. If the
pin is not driven with an open-drain device, it must be
forced to a logic high voltage of 2.2V (min) to ensure
proper V
driven to a voltage higher than V
To implement soft-start, the SHDN/SS pin must be driven
with an open-drain device and a capacitor must be
connected from the SHDN/SS pin to GND. Once the open-
drain device is turned off, a 2 A pull-up current will begin
charging the external SS capacitor and force the voltage
on the pin to ramp towards V
threshold is reached (0.35V typ), the internal reference
voltage which controls the V
follow the ramp voltage on the SHDN/SS pin (minus a
0.35V offset to account for the SHDN threshold) until the
reference reaches its final band gap voltage. This occurs
when the voltage on the SHDN/SS pin reaches
OUT
regulation. The SHDN/SS pin should not be
LTC1503-1.8/LTC1503-2
IN
OUT
equals 4.1V with greater than 90% effi-
into a high impedance state. A 2 A pull-
OUT
OUT
decrease of approximately
IN
OUT
referred) below the main
IN
. As soon as the SHDN
OUT
.
regulation point will
to droop below the
IN
/V
OUT
nears
7