参数资料
| 型号： | SP6121CN-L |
| 厂商： | Exar Corporation |
| 文件页数： | 5/16页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM VM 8NSOIC |
| 标准包装： | 98 |
| PWM 型： | 电压模式 |
| 输出数： | 1 |
| 频率 - 最大： | 560kHz |
| 占空比： | 100% |
| 电源电压： | 3 V ~ 5.5 V |
| 降压： | 是 |
| 升压： | 无 |
| 回扫： | 无 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | 0°C ~ 70°C |
| 封装/外壳： | 8-SOIC（0.154"，3.90mm 宽） |
| 包装： | 管件 |
THEORY OF OPERATION
value is selected to match the MOSFET charac-
teristics. When the over-current threshold is
exceeded, the over-current comparator sets the
fault latch and terminates the output pulses. The
controller stops switching and goes through a
hiccup sequence. This prevents excessive power
dissipation in the external power MOSFETs
during an overload condition. An internal delay
circuit prevents that very short and mild over-
load conditions, that could occur during a load
transient, activate the current limit circuit.
A low power sleep mode can be invoked in the
SP6121 by externally forcing the COMP pin
below 0.3V. Quiescent supply current in sleep
mode is typically less than 25 μ A. An internal
5 μ A pull-up current at the COMP pin brings the
SP6121 out of shutdown mode.
The SP6121 also includes under-voltage lock-
out and over-voltage protection. Output over-
voltage protection is achieved by turning off the
high side switch, and turning on the low side N-
channel MOSFET full time.
Enable
Low quiescent mode or “Sleep Mode” is initi-
ated by pulling the COMP pin below 0.3V with
an external open-drain or open-collector tran-
sistor. Supply current is reduced to 25 μ A (typi-
cal) in shutdown. On power-up, assuming that
V CC has exceeded the UVLO start threshold
(2.79V), an internal 5 μ A pull-up current at the
COMP pin brings the SP6121 out of shutdown
mode and ensures start-up. During normal oper-
ating conditions and in absence of a fault, an
internal clamp prevents the COMP pin from
swinging below 0.6V. This guarantees that dur-
ing mild transient conditions, due either to line
or load variations, the SP6121 does not enter
shutdown unless it is externally activated.
If no faults are present, the SP6121 will initiate
a soft start when V CC exceeds 2.79V.
Hysteresis (about 100mV) in the UVLO com-
parator provides noise immunity at start-up.
Soft Start
Soft start is required on step-down controllers to
prevent excess inrush current through the power
train during start-up. Typically this is managed
by sourcing a controlled current into a timing
capacitor and then using the voltage across this
capacitor to slowly ramp up either the error amp
reference or the error amp output (COMP). The
control loop creates narrow width driver pulses
while the output voltage is low and allows these
pulses to increase to their steady-state duty
cycle as the output voltage increases to its regu-
lated value. As a result of controlling the induc-
tor volt*second product during startup, inrush
current is also controlled.
In the SP6121 the duration of the soft-start is
controlled by an internal timing circuit that
provides a 0.4V/ms slew-rate, which is used
during start-up and over-current to set the hic-
cup time. The SP6121 implements soft-start by
ramping up the error amplifier reference voltage
providing a controlled slew-rate of the output
voltage, thereby preventing overshoot and in-
rush current at power up.
The presence of the output capacitor creates
extra current draw during startup. Simply stated,
dV OUT /dt requires an average sustained current
in the output capacitor and this current must be
considered while calculating peak inrush cur-
rent and over current thresholds. An approxi-
mate expression to determine the excess inrush
current due to the dV OUT /dt of the output capaci-
tor C OUT is:
During Sleep Mode, the high side and low side
MOSFETs are turned off and the internal soft
IC OUT = C OUT *(0.4 V/ms) *
V OUT
1.25
start voltage is held low.
UVLO
Assuming that there is not shutdown condition
present, then the voltage on the V CC pin deter-
mines operation of the SP6121. As V CC rises,
the UVLO block monitors V CC and keeps the
high side and low side MOSFETS off and the
internal SS voltage low until V CC reaches 2.79V.
As Figure 1 shows, the SS voltage controls a
variety of signals. First, provided all the exter-
nal fault conditions are removed, an internal
5 μ A pull-up at the COMP pin brings the SP6121
out of shutdown mode. The internal timing
circuit is then activated and controls the ramp-
up of the error amp reference voltage. The
COMP pin is pulled to 0.7V by the internal
Date: 11/29/04
SP6121 Low Voltage, Synchronous Step Down PWM Controller
5
? Copyright 2004 Sipex Corporation
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相关代理商/技术参数 |
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|---|---|
| SP6121CN-L/TR | 功能描述:电压模式 PWM 控制器 Low Voltage, 8 Pin Synchronous, Cntrllr RoHS:否 制造商:Texas Instruments 输出端数量:1 拓扑结构:Buck 输出电压:34 V 输出电流: 开关频率: 工作电源电压:4.5 V to 5.5 V 电源电流:600 uA 最大工作温度:+ 125 C 最小工作温度:- 40 C 封装 / 箱体:WSON-8 封装:Reel |
| SP6121EB | 功能描述:电压模式 PWM 控制器 Low Voltage, 8 Pin Sync Buck Controller RoHS:否 制造商:Texas Instruments 输出端数量:1 拓扑结构:Buck 输出电压:34 V 输出电流: 开关频率: 工作电源电压:4.5 V to 5.5 V 电源电流:600 uA 最大工作温度:+ 125 C 最小工作温度:- 40 C 封装 / 箱体:WSON-8 封装:Reel |
| SP6122 | 制造商:SIPEX 制造商全称:Sipex Corporation 功能描述:Low Voltage, Micro 8, PFET, Buck Controller Ideal for 1A to 5A, Small Footprint, DC-DC Power Converters |
| SP6122_04 | 制造商:SIPEX 制造商全称:Sipex Corporation 功能描述:Low Voltage, Micro 8, PFET, Buck Controller Ideal for 1A to 5A, Small Footprint, DC-DC Power Converters |
| SP6122ACU | 制造商:Rochester Electronics LLC 功能描述: 制造商:Exar Corporation 功能描述: |
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