SC198MLTRT Semtech, SC198MLTRT Datasheet - Page 7

• Manufacturer Part Number: SC198MLTRT
• Description: IC DUAL DC-DC BUCK CONV 20-MLPQ
• Manufacturer: Semtech
• Type: Step-Down (Buck)r

Specifications of SC198MLTRT

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Voltage - Output: Programmable
• Current - Output: 600mA
• Frequency - Switching: 1MHz
• Voltage - Input: 2.7 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 20-MLPQ
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Other names: SC198MLTR

SC198 Detailed Description
The SC198 is a dual step-down, pulse-width modulated
DC-DC converter with programmable output voltage
and power-save mode. This device has a 1MHz internal
oscillator that can be used during forced PWM mode or
power-save mode (PSAVE).
Operation
During normal operation, the PMOS switch is activated
on each rising edge of the internal oscillator. Current
feedback for the switching regulator is through the PMOS
current path, and it is amplifi ed and summed with
the internal slope compensation network. The voltage
feedback loop uses an internal feedback divider. The on-
time is determined by comparing the summed current
feedback and the output of the error amplifi er. The period
is set by the onboard oscillator or by an external clock
attached to the SYNC/PWM pin. When synchronizing
to an external frequency, the SC198 operates in PWM
mode only. The device has an internal synchronous
NMOS rectifi er and does not require a Schottky diode on
the LX pin. The device is designed to operate as a buck
converter in PWM mode with a fi xed frequency of 1MHz.
At light loads the part can enter PSAVE mode to maximize
effi ciency.
Output Filter
The SC198 converter also has internal loop compensa-
tion. The internal compensation is designed to work with
a certain output fi lter corner frequency defi ned by the
equation:
When selecting output fi lter components, the LC product
should not vary over a wide range. Selection of smaller
inductor and capacitor values will move the corner fre-
quency, potentially impacting system stability. Due to
this issue the practical lower limit for the inductor value
is 4.7μH. The internal compensation is designed to oper-
ate with a single-pole output fi lter, L = 4.7μH and C
10μF.
POWER MANAGEMENT
Applications Information
© 2007 Semtech Corp.
f
C
= —————
2 √ L×C
———
1
NOT RECOMMENDED FOR NEW DESIGN
OUT
=
7
Programmable Output Voltage
The SC198 has three control pins per output to allow the
user to select a voltage level from eight predetermined
output voltage levels (see Table A, Output Voltage Options
below). The output voltage can be selected at any time,
including while the output is enabled and loaded.
Table A — Output Voltage Options
Continuous Conduction and Oscillator Synchronization
The SC198 is designed to operate in a continuous
conduction mode, where it maintains a fi xed frequency.
When the SYNC pin is tied high, the part runs under
control of the internal oscillator in PWM mode. The part
can be synchronized to an external clock by connecting a
clock signal to the SYNC pin. The part synchronizes to the
rising edge of the clock.
Power-Save Mode Operation
The SC198 has a power-save mode (PSAVE) which may be
selected by tying the SYNC pin to GND. Selecting PSAVE
mode enables automatic activation of PSAVE mode at
light loads, thus maximizing effi ciency across the full
load range. The SC198 will automatically detect the load
current at which it should enter PSAVE mode. The SC198
is optimized to track maximum effi ciency with respect to
V
CTLA2/B2
IN
.
0
0
0
0
1
1
1
1
Programmable Output Voltage
CTLA1/B1
0
0
1
1
0
0
1
1
CTLA0/B0
0
1
0
1
0
1
0
1
Nominal Output
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Voltage (V)
SC198
1.375
1.575
1.875
1.2
1.4
1.5
1.8
1