MIC2546 Datasheet, PDF (11/12 Pages) Micrel Semiconductor – Dual Programmable Current Limit Switch Preliminary Information

MIC2546/2547
Applications Information
Supply Filtering
A 0.1µF to 1µF 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_{IN max} = 6V) even for a short duration.
4.0V to 5.5V
0.1 to 1µF
MIC2546-1BM
1 _INA
OUTA ¹⁶
2 _{OUTA ILIMA} 15
3 _{ENA GNDA} 14
4 _NC
FLGB ¹³
5 _FLGA
12
ENB
6 _{GNDB OUTB} 11
7 _ILIMB
NC ¹⁰
8 _{OUTB INB} ⁹
R_SETB
R_SETA
.
0.1 to 1µF
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:
Micrel
P_D = R_DS(on) × (I_OUT)2
To relate this to junction temperature, the following equation
can be used:
T_j = P_D × θ_JA + T_A
where:
T_j = junction temperature
T_A = ambient temperature
θ_JA = 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 (R_SET2) in paral-
lel with R_SET, as shown in Figure 3, 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
R_SET is 435Ω (510mA), an R_SET2 of 88Ω (2.5A) and C_SET of
1µF (RC = 100µs) allows transient surge of 3A to pass for
100µs 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_SET
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.
5V
(+)
4.7µF
(–)
V_BUS
D+
D–
GND
1.5k 2%
MIC5203-3.3
LDO Regulator
IN
OUT
GND
Bold lines indicate
0.1" wide, 1-oz. copper
high-current traces.
10k
10k
3.3V USB Controller
V+
ON/OFF
OVERCURRENT
D+
D– _GND
100k
R_SET
R_SET(2)
C_SET
(optional)
MIC2546-2BM
INA OUTA
OUTA ILIMA
ENA GNDA
NC FLGB
FLGA ENB
GNDB OUTB
ILIMB NC
OUTB INB
100k
Ferrite Bead
R_SET
120µF
0.01µF
V_BUS
D+
D–
GND
120µF
0.01µF
V_BUS
D+
D–
GND
Ferrite Bead
Downstream
USB
Port 1
4.75V min.
500mA max.
Downstream
USB
Port 2
4.75V min.
500mA max.
Figure 3. USB Host Application
June 2000
11
MIC2546/2547