UCC28220, UCC28221
SLUS544A 鈭?SEPTEMBER 2003 鈭?REVISED AUGUST 2004
APPLICATION INFORMATION
LINE Over Voltage and Under Voltage
Three pins are provided to turn-off the output drivers and reset the soft-start capacitor when the converter input
voltage is outside a prescribed range. The under-voltage set point and under-voltage hysteresis are accurately
set via external resistors. The over-voltage set point is also accurately set via a resistor ratio, but the hysteresis
is fixed by the same resistor that sets the u*nder-voltage hysteresis.
Figure 1 and 2 show detailed functional diagram and operation of the under voltage lockout (UVLO) and
over-voltage lockout (OVLO) features. The equations for setting the thresholds defined in Figure 2 are:
V1
+
1.26
V2
+
1.26
V4
+
1.26
R1
)
1.26
(R2
)
R3)
(R1
)
Rx)
, where Rx
+
R4 (R2
)
R3)
Rx
(R1
)
R2
)
R3)
R3
R1
R4
(1)
(2)
(3)
(4)
V3
+
V4
*
1.26
The UVLO hysteresis and the OVLO hysteresis can then be calculated as V2 鈭?V1 and V4 鈭?V3, respectively.
By examining the design equations it becomes apparent that the value of R4 sets the amount of hysteresis at
both thresholds. By realizing this fact, the designer can then set the value of R4 based on the most critical
hysteresis specification either at high line or at low line. In most designs the value of R4 will be determined by
the desired amount of hysteresis around the UVLO threshold. As an example consider a telecom power supply
with the following input UVLO and OVLO design specifications:
鈥?/div>
鈥?/div>
鈥?/div>
鈥?/div>
Then,
V1 = 32.0 V
V2 = 34.0 V
V3 = 83.0 V
V4 = 84.7 V
鈥?/div>
鈥?/div>
鈥?/div>
and
R1 = 976 k鈩?/div>
R2 = 24.9 k鈩?/div>
R3 = 15.0 k鈩?/div>
鈥?/div>
R4 = 604 k鈩?/div>
www.ti.com
9
prev
next
UCC28220 PDF文件相關型號
UCC28221
UCC28220相關型號PDF文件下載
-
型號
版本
描述
廠商
下載
-
英文版
Low Dropout 3 Ampere Linear Regulator Family
TI
-
英文版
Low Dropout 3 Ampere Linear Regulator Family
TI [Texas ...
-
英文版
Low Dropout 1 Ampere Linear Regulator Family
TI [Texas ...
-
英文版
Low Dropout 0.5A Negative Linear Regulator
TI [Texas ...
-
英文版
HID Lamp Controller
TI
-
英文版
HID Lamp Controller
TI [Texas ...
-
英文版
HIGH EFFICIENCY SECONDARY SIDE SYNCHRONOUS BUCK PWM CONTROLL...
TI
-
英文版
HIGH EFFICIENCY SECONDARY SIDE SYNCHRONOUS BUCK PWM CONTROLL...
TI [Texas ...
-
英文版
HIGH-EFFICIENCY SYNCHRONOUS BUCK PWM CONTROLLER
TI [Texas ...
-
英文版
Low Power Pulse Width Modulator
TI
-
英文版
Low Power Pulse Width Modulator
TI [Texas ...
-
英文版
Micropower Voltage Mode PWM
TI
-
英文版
Micropower Voltage Mode PWM
TI [Texas ...
-
英文版
Switch Mode Secondary Side Post Regulator
TI
-
英文版
Switch Mode Secondary Side Post Regulator
TI [Texas ...
-
英文版
Low Voltage Synchronous Buck Controller
TI
-
英文版
Low Voltage Synchronous Buck Controller
TI [Texas ...
-
英文版
Brushless DC Motor Controller
TI
-
英文版
Brushless DC Motor Controller
TI [Texas ...
-
英文版
Source Ringer Controller
TI