MIC2544(2000) Ver la hoja de datos (PDF) - Micrel
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MIC2544 Datasheet PDF : 12 Pages
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MIC2544/2548
Applications Information
Supply Filtering
A 0.1µF to 1µF bypass capacitor from IN to GND, located near
the MIC2544 and MIC2548, is strongly recommended to
control supply transients. Without a bypass capacitor, an
output short may cause sufficient ringing on the input (from
supply lead inductance) to damage internal control circuitry.
Input transients must not exceed the absolute maximum
supply voltage (VIN max = 6V) even for a short duration.
4.0V to 5.5V
On/Off
MIC2548-1BM
1 EN
OUT 8
2 FLG
IN 7
3 GND OUT 6
4 ILIM
NC 5
RSET
Power
Output
0.1µF to 1µF
NOTE: MSOP PACKAGE OPTION USES PIN 5 FOR ILIM.
PIN 4 IS NOT CONNECTED (NC).
Figure 3. Supply Bypassing
Power Dissipation
The device's junction temperature depends on several fac-
tors such as the load, PCB layout, ambient temperature and
package type. Equations that can be used to calculate power
dissipation and junction temperature are found below.
Calculation of power dissipation can be accomplished by the
following equation:
PD = RDS(on) × (IOUT)2
To relate this to junction temperature, the following equation
can be used:
Micrel
Tj = PD × θJA + TA
where:
Tj = junction temperature
TA = ambient temperature
θJA = is the thermal resistance of the package
Transient Overcurrent Filter
The inrush current from the connection of a heavy capacitive
load may cause the fault flag to fall for 10µs to 200µs while the
switch is in a constant-current mode, charging the capaci-
tance.
Adding an optional series resistor-capacitor (RSET2) in paral-
lel with RSET, as shown in Figure 4, allows the transient
current-limit to be set to a different value than steady state. A
typical USB hot-plug inrush is 2A to 3A for 10µs to 20µs. If
RSET is 435Ω (510mA), an RSET2 of 88Ω (2.5A) and CSET of
1µF (RC = 100µs) allows transient surge of 3A to pass for
100µs without tripping the overcurrent flag (FLG).
USB Power Distribution
The MIC2544 is ideal for meeting USB power distribution
requirements. Figure 4 depicts a USB Host application. RSET
should be set to a value providing a current-limit >500mA.
The accurate current-limit of the MIC2544 will reduce power
supply current requirements. Also, fast reaction to short
circuit faults prevent voltage droop in mobile PC applications.
Printed Circuit Board Hot-Plug
The MIC2544/48 are ideal inrush current-limiters suitable for
hot-plug applications. Due to the integrated charge pump,
the MIC2544/48 presents a high impedance when off and
slowly becomes a low impedance as it turns on. This “soft-
start” feature effectively isolates power supplies from highly
capacitive loads by reducing inrush current during hot-plug
events. Figure 5 shows how the MIC2544 may be used in a
hot-plug application.
5V
(+)
4.7µF
(–)
VBUS
D+
D–
GND
1.5k 2%
MIC5203-3.3
LDO Regulator
IN
OUT
GND
10k
3.3V USB Controller
V+
ON/OFF
1.0 OVERCURRENT
µF
Bold lines indicate
0.1" wide, 1-oz. copper
high-current traces.
D+
D– GND
100k
MIC2544-2BM
EN
OUT
FLG
IN
GND OUT
ILIM
NC
RSET
RSET(2)
CSET
(optional)
120µF
0.1µF
NOTE: MSOP PACKAGE OPTION USES PIN 5 FOR ILIM.
PIN 4 IS NOT CONNECTED (NC).
Figure 4. USB Host Application
Ferrite
Bead
0.01µF
VBUS
D+
D–
GND
Downstream
USB
Port 1
4.75V min.
500mA max.
MIC2544/2548
10
June 2000
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