参数资料
型号: SP6127EK1-L
厂商: Exar Corporation
文件页数: 6/12页
文件大小: 0K
描述: IC REG CTRLR BUCK PWM VM 6TSOT
标准包装: 1
PWM 型: 电压模式
输出数: 1
频率 - 最大: 1.05MHz
占空比: 100%
电源电压: 4.5 V ~ 29 V
降压:
升压:
回扫:
反相:
倍增器:
除法器:
Cuk:
隔离:
工作温度: -40°C ~ 125°C
封装/外壳: SOT-23-6 细型,TSOT-23-6
包装: 散装
其它名称: 1016-1392
______________________________________________________ GENERAL OVERVIEW
for Rs in the range of 0.5k
to 3k . For Rs larger
Overcurrent Protection (OCP)
SP6127
Vin
than 3k , test results are lower than those
predicted by (5), due to circuit parasitics.
Therefore the maximum value of Rs should be
limited to 3k .
Ov er-Current Comparator
Gate
LX
Rs
Q1
Note that in order to safeguard against false
overcurrent trigger due to transients, there is a
150ns delay between the turn on of the MOSFET
and when OCP circuit is activated. As a
consequence at very high Vo/V IN ratio, where
Vin - 0.3V
30uA
Ds
MOSFET on-time is less than 150ns, the OCP
circuit will not detect overcurrent.
Using the ON/OFF Function
Figure 3 Overcurrent protection circuit
The overcurrent protection (OCP) circuit
functions by monitoring the voltage across the
high-side FET Q1. When this voltage exceeds
0.3V, the overcurrent comparator triggers and
the controller enters hiccup mode. For example
if Q1 has R DS ( ON )=0.1 , then the overcurrent
will trigger at I = 0.3V/0.1 =3A. To program a
lower overcurrent use a resistor Rs as shown in
figure 1. Calculate Rs from:
The Feedback pin serves a dual role of ON/OFF
control. The MOSFET driver is disabled when a
voltage greater than 1V is applied at the FB pin.
Maximum voltage rating of this pin is 5.5V. The
controlling signal should be applied through a
small signal diode as shown on page 1.
Please note that an optional 10k bleeding
resistor across the output helps keep the output
capacitor discharged under no load condition.
Programming the Output Voltage
Rs =
0 . 3 ? ( 1 . 15 × Iout × Rds ( on ) × Kt )
30 uA
...(5)
To program the output voltage, calculate R2
using the following equation:
? ?
? 1 ? ?
Where:
1.15 is used to calculate peak inductor current
which is nominally 15% higher than average
R 2 =
R 1
? Vout
? Vref
?
?
output current
R DS ( ON ) is MOSFET ON-resistance rating
Kt is a multiplier that accounts for increase in
R DS ( ON ) due to temperature
Example: A switching MOSFET used with
SP6127 has R DS ( ON ) of 0.08 and Kt is 1.5.
Program the over-current circuit so that
maximum output is 2A.
Where:
V REF =0.6 is the reference voltage of the SP6127
R1=200k is a fixed-value resistor that, in
addition to being a voltage divider, it is part of the
compensation network. In order to simplify
compensation calculations, R1 is fixed at 200k .
Rs =
Rs=800
0 . 3 ? ( 1 . 15 × 2 A × 0 . 08 Ohm × 1 . 5 )
30 uA
Soft Start
Soft Start is preset internally to 5ms (nominal).
Internal Soft Start eliminates the need for the
Using the above equation there is good
agreement between calculated and test results
external capacitor CSS that is commonly used to
program this function.
Jan28-08 RevE
SP6127 TSOT-6 PFET Buck Controller
Page 6
? 2007 Exar Corporation
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