鈩?/div>
R2
+
310k
Circuit Description
Instead of charging the capacitor in a short period of time, the
idea is to charge the capacitor in a long period of time by
limiting the charge current. The circuit in Figure 1 uses the
MIC2545A-2 and the MIC2778. The MIC2545A-2 is a pro-
grammable current limit high-side switch that is capable of
having current-limit up to 2.5A. The current-limit is set by the
external resistor. In this circuit, there are two current-limits,
100mA and 500mA. USB specifications limit the device
current to 100mA prior to enumeration. After enumeration, a
high-powered device can request no more than 500mA. This
circuit will guarantee these limits are not exceeded. The
MIC2778 is a voltage monitor with adjustable hysteresis and
that operate down to 1.5V. The high and low thresholds are
set at 4V and 2V respectively. The equation below shows how
to calculate the resistors鈥?value for the two thresholds and the
two current-limits.
R2
=
310k
R1
=
1M
鈩?鈭?/div>
310k
鈭?/div>
310k
=
380k
Current-limit
Current limit =
230
R
SET
where:
Current factor = 230
100mA
=
R
SET1
=
230
R
SET
230
鈮?/div>
2.2k
100mA
500mA
=
230
R
SET1
|| R
SET2
(continued)
C1
R1
4.7碌F 380k
R2
310k
R3
310k
MIC2778
VDD
LTH
HTH
/RST
GND
R4
100k
MIC2545A-2
IN
OUT
IN
OUT
EN
ILIM
GND FLG
Load
C
L
500碌F
R
L
10鈩?/div>
R
SET1
600鈩?/div>
R
SET2
2.2k
Q1
VN1206
Figure 1. Dual Current-Limiting Switch
Micrel, Inc. 鈥?1849 Fortune Drive 鈥?San Jose, CA 95131 鈥?USA 鈥?tel + 1 (408) 944-0800 鈥?fax + 1 (408) 944-0970 鈥?http://www.micrel.com
February 2000
1
Application Note 32
APPNOTE32相關(guān)型號PDF文件下載
-
型號
版本
描述
廠商
下載
-
英文版
Universal Serial Bus Power Management
ETC
-
英文版
Universal Serial Bus Power Management
-
英文版
Dual Current-Limiting Switch for USB Applications
ETC
-
英文版
Dual Current-Limiting Switch for USB Applications
-
英文版
Electroluminescent Display Drivers
ETC
-
英文版
Electroluminescent Display Drivers
-
英文版
Understanding the Power Rating of Caddock MP9100 Resistors
ETC
-
英文版
Understanding the Power Rating of Caddock MP9100 Resistors
ETC [ETC]
1
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