MIC2546 Micrel Semiconductor, MIC2546 Datasheet - Page 11

• Manufacturer Part Number: MIC2546
• Description: Dual Programmable Current Limit Switch Preliminary Information
• Manufacturer: Micrel Semiconductor

Applications Information
Supply Filtering
A 0.1 F to 1 F bypass capacitor from INX to GND, located
near the MIC2546 and MIC2547, 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:
June 2000
MIC2546/2547
(+)
(–)
Bold lines indicate
0.1" wide, 1-oz. copper
high-current traces.
5V
0.1 to 1 F
4.7 F
V
D+
D–
GND
BUS
IN max
Supply Bypassing
1
2
3
4
LDO Regulator
5
6
7
8
R
MIC5203-3.3
IN
SETB
MIC2546-1BM
INA
OUTA
ENA
NC
FLGA
GNDB
ILIMB
OUTB
1.5k 2%
= 6V) even for a short duration.
GND
OUT
GNDA
OUTB
OUTA
ILIMA
FLGB
ENB
INB
NC
16
15
14
13
12
11
10
9
3.3V USB Controller
V+
D+
D–
OVERCURRENT
4.0V to 5.5V
10k
10k
GND
.
ON/OFF
R
0.1 to 1 F
Figure 3. USB Host Application
SETA
(optional)
R
C
SET(2)
100k
SET
R
SET
11
To relate this to junction temperature, the following equation
can be used:
where:
Transient Overcurrent Filter
The inrush current from the connection of a heavy capacitive
load may cause the fault flag to fall for 10 s to 200 s 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 10 s to 20 s. If
R
1 F (RC = 100 s) allows transient surge of 3A to pass for
100 s without tripping the overcurrent flag (FLG).
USB Power Distribution
The MIC2546 is ideal for meeting USB power distribution
requirements. Figure 3 depicts a USB Host application. R
should be set to a value providing a current-limit >500mA.
The accurate current-limit of the MIC2546 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 MIC2546/47 are ideal inrush current-limiters suitable for
hot-plug applications. Due to the integrated charge pump,
the MIC2546/47 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.
SET
MIC2546-2BM
INA
OUTA ILIMA
ENA
NC
FLGA
GNDB
ILIMB
OUTB
P
T
T
T
is 435 (510mA), an R
JA
j
j
A
GNDA
OUTB
D
OUTA
FLGB
= junction temperature
= P
ENB
= ambient temperature
INB
NC
= R
= is the thermal resistance of the package
SET
D
DS(on)
, as shown in Figure 3, allows the transient
JA
100k
R
+ T
SET
120 F
120 F
(I
OUT
A
)2
Ferrite Bead
Ferrite Bead
SET2
0.01 F
0.01 F
of 88 (2.5A) and C
GND
GND
V
V
BUS
BUS
D+
D–
D+
D–
MIC2546/2547
SET2
500mA max.
Downstream
500mA max.
Downstream
4.75V min.
4.75V min.
Port 1
Port 2
USB
USB
) in paral-
SET
Micrel
SET
of