参数资料
| 型号： | SC198MLTRT |
| 厂商： | Semtech |
| 文件页数： | 7/16页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK SYNC PROG .6A 20MLPQ |
| 标准包装： | 1 |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 2 |
| 输出电压： | 可编程 |
| 输入电压： | 2.7 V ~ 5.5 V |
| 频率 - 开关： | 1MHz |
| 电流 - 输出： | 600mA |
| 同步整流器： | 是 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 20-MLPQ |
| 包装： | 标准包装 |
| 供应商设备封装： | 20-MLPQ（4x4） |
| 产品目录页面： | 1358 (CN2011-ZH PDF) |
| 其它名称： | SC198MLDKR |
POWER MANAGEMENT
Applications Information
NOT RECOMMENDED FOR NEW DESIGN
SC198
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
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
Programmable Output Voltage
current path, and it is ampli ? 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 ampli ? 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 recti ? 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 ? xed frequency of 1MHz.
At light loads the part can enter PSAVE mode to maximize
ef ? ciency.
CTLA2/B2
0
0
0
0
1
1
1
1
CTLA1/B1
0
0
1
1
0
0
1
1
CTLA0/B0
0
1
0
1
0
1
0
1
Nominal Output
Voltage (V)
1
1.2
1.375
1.4
1.5
1.575
1.8
1.875
f C = —————
2 √ L×C
OutputFilter
The SC198 converter also has internal loop compensa-
tion. The internal compensation is designed to work with
a certain output ? lter corner frequency de ? ned by the
equation:
1
———
When selecting output ? 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 4.7 μ H. The internal compensation is designed to oper-
ate with a single-pole output ? lter, L = 4.7 μ H and C OUT =
10 μ F.
? 2007 Semtech Corp.
7
Continuous Conduction and Oscillator Synchronization
The SC198 is designed to operate in a continuous
conduction mode, where it maintains a ? 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 ef ? 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 ef ? ciency with respect to
V IN .
www.semtech.com
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