MIC2544-1 MICREL [Micrel Semiconductor], MIC2544-1 Datasheet - Page 10

• Manufacturer Part Number: MIC2544-1
• Description: Programmable Current Limit High-Side Switch Preliminary Information
• Manufacturer: MICREL [Micrel Semiconductor]

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 (V
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:
To relate this to junction temperature, the following equation
can be used:
MIC2544/2548
(+)
(–)
P
Bold lines indicate
0.1" wide, 1-oz. copper
high-current traces.
NOTE: MSOP PACKAGE OPTION USES PIN 5 FOR I
PIN 4 IS NOT CONNECTED (NC).
5V
D
4.7µF
= R
V
D+
D–
GND
BUS
DS(on)
On/Off
On/Off
Figure 3. Supply Bypassing
NOTE: MSOP PACKAGE OPTION USES PIN 5 FOR I
PIN 4 IS NOT CONNECTED (NC).
IN max
× (I
LDO Regulator
MIC5203-3.3
IN
R
OUT
1
2
3
4
1.5k 2%
SET
= 6V) even for a short duration.
GND
MIC2548-1BM
EN
FLG
GND
ILIM
)2
OUT
LIM
OUT
OUT
.
NC
IN
4.0V to 5.5V
1.0
µF
8
7
6
5
3.3V USB Controller
V+
D+
D–
OVERCURRENT
0.1µF to 1µF
LIM
10k
GND
.
Power
Output
ON/OFF
Figure 4. USB Host Application
10
R
100k
SET
where:
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 (R
lel with R
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
R
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. R
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.
EN
FLG
GND
ILIM
MIC2544-2BM
SET
(optional)
R
C
SET(2)
T
T
T
θ
is 435Ω (510mA), an R
SET
JA
j
j
A
OUT
OUT
= junction temperature
= P
NC
IN
= ambient temperature
= is the thermal resistance of the package
SET
D
0.1µF
, as shown in Figure 4, allows the transient
× θ
JA
120µF
+ T
A
Ferrite
Bead
SET2
0.01µF
of 88Ω (2.5A) and C
GND
V
BUS
D+
D–
SET2
Downstream
500mA max.
4.75V min.
Port 1
June 2000
USB
) in paral-
Micrel
SET
SET
of