参数资料
型号: UCC28250RGPR
厂商: Texas Instruments
文件页数: 21/53页
文件大小: 0K
描述: IC REG CTRLR PWM CM/VM 20-QFN
标准包装: 3,000
PWM 型: 电流/电压模式
输出数: 1
频率 - 最大: 1MHz
占空比: 100%
电源电压: 4.7 V ~ 17 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: 20-VFQFN 裸露焊盘
包装: 带卷 (TR)
SLUSA29C – APRIL 2010 – REVISED JULY 2011
For primary-side control, the internal error amplifier is connected as a buffer stage. In other words, the COMP pin
is shorted to the FB/EA- pin, and the output of an external error amplifier is connected to the REF/EA+ pin
through an optical coupler ( Figure 14 ). In this case, the output start-up is an open loop soft start because the
COMP follows the soft-start voltage instead of the voltage loop output. The soft-start time is still determined by
external capacitor C SS and the 27- μ A internal charge current. The voltage depends on the value of final COMP
voltage which corresponds to the regulated primary output duty cycle. According to the desired soft start time and
COMP pin voltage level at steady state, the SS pin capacitor can be calculated as:
C SS =
27 m A T SS
V COMP _ final
(10)
After soft start, the voltage at SS pin is eventually clamped at around 4 V. Under fault conditions (UVLO, internal
thermal shut down, OVP/OTP, hiccup mode), or when externally disabled, SS pin is pulled down to ground
quickly by an internal switch with 2 k Ω on resistance to prepare for re-start. Pulling SS pin to ground externally
shuts down the controller as well.
VOUT
UCC28250
R Z3
C Z3
R O2
R Z2
+
C P1
C Z2
VSENSE
VREF
COMP
FB/EA-
R O1
REF/EA+
+
+
SS
External
Reference
C SS
Figure 14. Error Amplifier EAMP Connections for primary-side Control
Copyright ? 2010 – 2011, Texas Instruments Incorporated
Product Folder Link(s): UCC28250
21
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