SC198AMLTRT Semtech, SC198AMLTRT Datasheet - Page 10

• Manufacturer Part Number: SC198AMLTRT
• Description: IC DUAL DC-DC BUCK CONV 20-MLPQ
• Manufacturer: Semtech
• Type: Step-Down (Buck)r

Specifications of SC198AMLTRT

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Voltage - Output: Programmable
• Current - Output: 800mA
• 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: SC198AMLTR

When selecting output fi lter components, the LC product
should not vary over a wide range. The practical lower
limit for the inductor value is 4.7μH to ensure system sta-
bility. Selection of smaller inductor and capacitor values
will shift the corner frequency higher, which may impact
stability. The internal compensation is designed to
operate with a single-pole output fi lter where L = 4.7μH
and COUT = 10μF.
Application Information
Detailed Description
The SC198A 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 oscil-
lator 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 feed-
back 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 feed-
back loop uses an internal feedback divider. The on-time
is determined by comparing the summed current feed-
back and the output of the error amplifi er. The period is
set by the onboard oscillator or by an external clock
attached to the MODE/SYNC pin. When synchronizing to
an external frequency, the SC198A operates in PWM mode
only. The device has an internal synchronous NMOS recti-
fi 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 SC198A converter also has internal loop compensa-
tion. The internal compensation is designed to work with
a specifi c output fi lter corner frequency defi ned by the
equation
f
C
2
L
1
C
OUT
NOT RECOMMENDED FOR NEW DESIGN
Programmable Output Voltage
The SC198A has three control pins per output to allow
selection of a voltage level from eight predetermined
output voltage levels (see Table 1). CAUTION — All CTL
pins much be pulled high or low for proper operation
(they must not be allowed to fl oat). The output voltage
can be selected while the device is enabled and loaded.
Continuous Conduction and Oscillator
Synchronization
The SC198A is designed to operate in continuous con-
duction mode, where it maintains a fixed frequency.
When the MODE/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 con-
necting a clock signal to the MODE/SYNC pin. The part
synchronizes to the rising edge of the clock.
Power-Save Mode Operation
The SC198A has a power-save mode (PSAVE) which may
be selected by tying the MODE/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 device will automatically
detect the load current at which it should enter PSAVE
mode. The device is optimized to track maximum
effi ciency.
CTLA2/B2 CTLA1/B1 CTLA0/B0
0
0
0
0
1
1
1
1
Table 1 — Output Voltage Options
Programmable Output Voltage
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
Nominal Output
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.8
A
Voltage (V)
SC198A
1.8
2.2
2.5
2.7
2.8
2.9
3.0
3.3
B
10