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MAX1946ETA-T [MAXIM]

Power Supply Support Circuit, Fixed, 1 Channel, BICMOS, 3 X 3 MM, 0.80 MM HEIGHT, EXPOSED PAD, THIN, MO-220, QFN-8;
MAX1946ETA-T
型号： MAX1946ETA-T
厂家： MAXIM INTEGRATED PRODUCTS    MAXIM INTEGRATED PRODUCTS
描述：

Power Supply Support Circuit, Fixed, 1 Channel, BICMOS, 3 X 3 MM, 0.80 MM HEIGHT, EXPOSED PAD, THIN, MO-220, QFN-8

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文件： 总13页 (文件大小：435K)
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19-2550; Rev 1; 1/03  
Single USB Switch with Autoreset and  
Fault Blanking in Tiny QFN  
General Description  
Features  
The MAX1946 single current-limited switch with auto-  
reset supplies a guaranteed 500mA load in accordance  
with USB specifications. The MAX1946 operates from a  
2.7V to 5.5V input supply and consumes only 40µA of  
quiescent current when operating and only 3µA in shut-  
down. Selectable active-high/active-low control logic  
and shutdown control provide additional flexibility. An  
autoreset feature latches the switch off in the event of a  
short circuit, saving system power. The switch reacti-  
vates upon removal of the shorted condition.  
o Single USB Switch in 3mm x 3mm Package  
o Autoreset Feature Saves System Power  
o Guaranteed 500mA Load Current  
o Built-In 20ms Fault-Blanking Circuitry  
o Active-High or Active-Low Control Logic  
o Fully Compliant to USB Specifications  
o 2.7V to 5.5V Input Voltage Range  
o Fault-Indicator Output  
The MAX1946 provides several safety features to pro-  
tect the USB port. Built-in thermal-overload protection  
turns off the switch when the die temperature exceeds  
+160 C. Accurate internal current-limiting circuitry pro-  
tects the input supply against both overload and short-  
circuit conditions. An open-drain fault signal, (FAULT),  
notifies the microprocessor (µP) when a thermal over-  
load, current-limit, undervoltage lockout (UVLO), or  
short-circuit fault occurs. A 20ms fault-blanking feature  
enables the circuit to ignore momentary faults, such as  
those caused when hot-swapping a capacitive load,  
preventing false alarms to the host system. The fault-  
blanking feature prevents fault signals from being  
issued when the device powers up the load.  
o Thermal-Overload Protection  
o UL Certification Pending  
Ordering Information  
The MAX1946 is available in a space-saving 8-pin thin  
QFN package and operates over the extended (-40 C  
to +85 C) temperature range.  
PART  
TEMP RANGE  
-40°C to +85°C  
PIN-PACKAGE  
8 Thin QFN 3mm x 3mm  
MAX1946ETA  
Applications  
USB Ports and USB Hubs  
Notebook and Desktop Computers  
PDAs and Palmtop Computers  
Digital Cameras  
Docking Stations  
Typical Operating Circuit  
Pin Configuration  
INPUT  
2.7V TO 5.5V  
TOP VIEW  
IN  
SEL  
ON  
IN  
FAULT  
GND  
OUT  
1
2
3
4
8
7
6
5
IN  
FAULT  
OUT  
MAX1946  
ON  
SEL  
ACTIVE HIGH  
ACTIVE LOW  
SELECTABLE  
MAX1946  
GND  
OUT  
OUT  
IN  
QFN  
________________________________________________________________ Maxim Integrated Products  
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at  
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.  
Single USB Switch with Autoreset and  
Fault Blanking in Tiny QFN  
ABSOLUTE MAXIMUM RATINGS  
IN, ON, OUT, SEL to GND........................................-0.3V to +6V  
Continuous Power Dissipation (T = +70 C)  
A
FAULT to GND.............................................-0.3V to (V + 0.3V)  
Exposed Pad Must be Soldered to PC Board  
IN  
IN to OUT..................................................................-0.3V to +6V  
OUT Continuous Switch Current (internally limited)..............1.3A  
FAULT DC Current..............................................................10mA  
8-Pin QFN (derate 24.4mW/ C above +70 C) ...........1951mW  
Operating Temperature Range ...........................-40 C to +85 C  
Junction Temperature......................................................+150 C  
Storage Temperature Range.............................-65 C to +150 C  
Lead Temperature (soldering, 10s) .................................+300 C  
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional  
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to  
absolute maximum rating conditions for extended periods may affect device reliability.  
ELECTRICAL CHARACTERISTICS  
(V = 5V, C = 0.1µF, C  
= 1µF, T = 0°C to +85°C, unless otherwise noted. Typical values are at T = +25°C.) (Note1)  
IN  
IN  
OUT  
A
A
PARAMETER  
SYMBOL  
CONDITIONS  
MIN  
TYP  
MAX  
5.5  
90  
UNITS  
Supply Voltage Range  
Switch On-Resistance  
Standby Supply Current  
V
2.7  
V
IN  
V
V
V
= 5, T = +25°C  
75  
IN  
IN  
IN  
A
R
ON  
= 5V  
= 3.3V  
110  
125  
10  
m
Switch disabled  
Switch enabled, I  
3
µA  
µA  
Quiescent Supply Current  
I
IN  
= 0  
OUT  
40  
60  
Switch disabled, V  
Switch disabled, V  
= 0, T = +25°C  
0.01  
0.2  
2.5  
1
OUT  
OUT  
A
OUT Off-Leakage Current  
I
µA  
LKG  
= 0, T = +85°C  
A
Undervoltage Lockout Threshold  
Continuous Load Current  
Continuous Current Limit  
V
Rising edge, 3% hysteresis  
2.3  
500  
0.74  
0.8  
2.7  
V
mA  
A
ULVO  
I
V
V
- V = 0.5V  
OUT  
1.1  
1.2  
0.35  
1
1.20  
1.6  
LIM  
IN_  
A
PK  
Short-Circuit Current Limit  
I
= 0 (I  
pulsing)  
SC  
OUT  
OUT  
A
RMS  
V
Short-Circuit Detect Threshold  
(Note 2)  
Continuous Current-Limit  
Blanking Timeout Period  
From continuous current-limit condition to  
FAULT asserted  
10  
7.5  
20  
18  
35  
ms  
ms  
Short-Circuit Blanking Timeout  
Period  
From short-circuit current-limit condition to  
FAULT asserted  
35.0  
1.50  
R
= 10 , time from ON to 10% of V  
,
,
OUT  
OUT  
Turn-On Delay  
Output Rise Time  
Turn-Off Delay  
t
0.25  
0.6  
1.2  
0.8  
ms  
ms  
ms  
ON  
does not include rise time  
t
R
R
= 10 , from 10% to 90% of V  
OUT  
RISE  
OUT  
= 10 , time from ON to 90% of V  
OUT  
OUT  
t
2
OFF  
does not include fall time  
= 10 , from 90% to 10% of V  
OUT  
Output Fall Time  
t
R
3
ms  
FALL  
OUT  
Thermal-Shutdown Threshold  
15oC hysteresis  
160  
°C  
2
_______________________________________________________________________________________  
Single USB Switch with Autoreset and  
Fault Blanking in Tiny QFN  
ELECTRICAL CHARACTERISTICS (continued)  
(V = 5V, C = 0.1µF, C  
= 1µF, T = 0°C to +85°C, unless otherwise noted. Typical values are at T = +25°C.) (Note1)  
IN  
IN  
OUT  
A
A
PARAMETER  
SYMBOL  
CONDITIONS  
= 2.7V to 4V  
MIN  
1.6  
2
TYP  
MAX  
UNITS  
V
V
V
V
V
IN  
IN  
IN  
IN  
ON, SEL Input High Level  
ON, SEL Input Low Level  
V
V
IH  
= 4V to 5.5V  
= 2.7V to 4V  
= 4V to 5.5V  
0.6  
0.8  
+1  
V
V
IL  
ON, SEL Input Leakage Current  
, V  
ON SEL  
= 0 or V , T = +25°C  
-1  
µA  
V
IN  
A
FAULT Output Low Voltage  
V
I
= 1mA, V = 2.7V  
0.5  
OL  
SINK  
IN  
FAULT Output High Leakage  
Current  
V
= V  
= 5.5V  
FAULT  
1
µA  
IN  
OUT Output Current Autoreset  
Mode  
In latched off state, V  
= 0  
10  
25  
45  
mA  
OUT  
OUT Autoreset Threshold  
In latched off state, V  
In latched off state, V  
rising  
0.4  
10  
0.5  
20  
0.6  
35  
V
OUT  
OUT  
OUT Autoreset Blanking Time  
> 0.5V  
ms  
ELECTRICAL CHARACTERISTICS  
(V = 5V, C = 0.1µF, C  
= 1µF, T = -40°C to +85°C, unless otherwise noted.) (Note1)  
A
IN  
IN  
OUT  
PARAMETER  
SYMBOL  
CONDITIONS  
MIN  
TYP  
MAX  
5.5  
90  
UNITS  
Supply Voltage Range  
Switch On-Resistance  
Standby Supply Current  
V
2.7  
V
IN  
V
V
V
= 5, T = +25°C  
A
IN  
IN  
IN  
R
ON  
= 5V  
= 3.3V  
110  
125  
10  
m
Switch disabled  
Switch enabled, I  
µA  
µA  
µA  
V
Quiescent Supply Current  
OUT Off-Leakage Current  
Undervoltage Lockout Threshold  
Continuous Load Current  
Continuous Current Limit  
Short-Circuit Current Limit  
I
IN  
= 0  
60  
OUT  
OUT  
I
Switch disabled, V  
= 0, T = -40°C to +25°C  
1
LKG  
A
V
Rising edge, 3% hysteresis  
2.3  
500  
0.6  
0.8  
2.7  
ULVO  
mA  
A
I
V
V
- V = 0.5V  
OUT  
1.3  
1.6  
LIM  
IN_  
I
= 0 (I  
pulsing)  
A
PK  
SC  
OUT  
OUT  
Continuous Current-Limit  
Blanking Timeout Period  
From continuous current-limit condition to  
FAULT asserted  
10  
7.5  
35  
ms  
ms  
ms  
Short-Circuit Blanking Timeout  
Period  
From short-circuit current-limit condition to  
FAULT asserted  
35.0  
1.50  
R
= 10 . Time from ON to 10% of V  
.
OUT  
OUT  
Turn-On Delay  
t
0.25  
ON  
Does not include rise time.  
_______________________________________________________________________________________  
3
Single USB Switch with Autoreset and  
Fault Blanking in Tiny QFN  
ELECTRICAL CHARACTERISTICS (continued)  
(V = 5V, C = 0.1µF, C  
= 1µF, T = -40°C to +85°C, unless otherwise noted.) (Note1)  
A
IN  
IN  
OUT  
PARAMETER  
SYMBOL  
CONDITIONS  
MIN  
TYP  
MAX  
UNITS  
R
= 10 , time from ON to 90% of V  
,
OUT  
OUT  
Turn-Off Delay  
t
2
ms  
OFF  
does not include fall time  
V
V
V
V
V
= 2.7V to 4V  
= 4V to 5.5V  
= 2.7V to 4V  
= 4V to 5.5V  
1.6  
2
V
V
IN  
IN  
IN  
IN  
ON, SEL Input High Level  
ON, SEL Input Low Level  
V
IH  
0.6  
0.8  
+1  
V
V
IL  
V
ON, SEL Input Leakage Current  
, V  
ON SEL  
= 0 or V  
-1  
µA  
V
IN  
FAULT Output Low Voltage  
V
I
= 1mA, V = 2.7V  
0.5  
OL  
SINK  
IN  
OUT Output Current Autoreset  
Mode  
In latched off state, V  
= 0  
10  
45  
mA  
OUT  
OUT Autoreset Threshold  
In latched off state, V  
In latched off state, V  
rising  
0.4  
10  
0.6  
35  
V
OUT  
OUT  
OUT Autoreset Blanking Time  
> 0.5V  
ms  
Note 1: All parts are 100% tested at T = +25 C. Limits over the operating temperature range are guaranteed by design.  
A
Note 2: Short-circuit detect threshold is the output voltage at which the device transitions from short-circuit current limit to continuous  
current limit.  
Typical Operating Characteristics  
(Circuit of Figure 2, V = 5V, C = 0.1µF, C  
= 1µF, ON = SEL, T = +25°C, unless otherwise noted.)  
A
IN  
IN  
OUT  
QUIESCENT SUPPLY CURRENT  
vs. INPUT VOLTAGE  
QUIESCENT SUPPLY CURRENT  
vs. TEMPERATURE  
SHUTDOWN SUPPLY CURRENT  
vs. TEMPERATURE  
50  
40  
30  
20  
10  
0
45  
42  
39  
36  
33  
30  
3.4  
3.3  
3.2  
3.1  
3.0  
2.9  
2.8  
2.7  
2.6  
V
= V = GND  
ON  
SEL  
V
= V = GND  
ON  
SEL  
ON = GND, V = 5V  
SEL  
V
= 5.5V  
= 5V  
IN  
V
IN  
V
= 2.7V  
IN  
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5  
INPUT VOLTAGE (V)  
-40  
-15  
10  
35  
60  
85  
-40  
-15  
10  
35  
60  
85  
TEMPERATURE ( C)  
TEMPERATURE ( C)  
4
_______________________________________________________________________________________  
Single USB Switch with Autoreset and  
Fault Blanking in Tiny QFN  
Typical Operating Characteristics (continued)  
(Circuit of Figure 2, V = 5V, C = 0.1µF, C  
= 1µF, ON = SEL, T = +25°C, unless otherwise noted.)  
A
IN  
IN  
OUT  
NORMALIZED ON-RESISTANCE  
vs. TEMPERATURE  
CONTINUOUS CURRENT-LIMIT  
THRESHOLD vs. TEMPERATURE  
SWITCH OFF-LEAKAGE  
vs. TEMPERATURE  
1.3  
1.2  
1.1  
1.0  
0.9  
0.8  
0.7  
1090  
1080  
1070  
1060  
1050  
1040  
1030  
1000  
100  
10  
ON = OUT = GND, V = 5V  
SEL  
V
= 5.5V  
IN  
V
= 5.0V  
IN  
1
0.1  
0.01  
V = 2.7V  
IN  
-40  
-15  
10  
35  
60  
85  
-40  
-40  
-40  
-15  
10  
35  
60  
85  
85  
85  
-40  
-15  
10  
35  
60  
85  
TEMPERATURE ( C)  
TEMPERATURE ( C)  
TEMPERATURE ( C)  
FAULT-BLANKING TIME  
vs. TEMPERATURE  
TURN-ON TIME  
TURN-OFF TIME vs. TEMPERATURE  
vs. TEMPERATURE (t + t  
)
(t  
+ t  
)
ON  
RISE  
OFF  
FALL  
21.0  
20.8  
20.6  
20.4  
20.2  
4.0  
3.5  
3.0  
2.5  
2.0  
1.5  
1.0  
3.8  
3.5  
3.2  
2.9  
2.6  
2.3  
2.0  
R
= 10  
R
= 10  
OUT  
OUT  
V
= 5.5V  
IN  
V
= 2.7V  
IN  
V
= 5V  
IN  
V
V
= 2.7V  
= 5V  
IN  
V
= 5V  
V
IN  
20.0  
19.8  
19.6  
19.4  
IN  
V
= 2.7V  
10  
IN  
= 5.5V  
IN  
V
= 5.5V  
IN  
19.2  
19.0  
-40  
-15  
10  
35  
60  
85  
-40  
-15  
10  
35  
60  
85  
-15  
35  
60  
TEMPERATURE ( C)  
TEMPERATURE ( C)  
TEMPERATURE ( C)  
FAULT OUTPUT LOW VOLTAGE  
vs. TEMPERATURE  
AUTORESET CURRENT  
vs. TEMPERATURE  
AUTORESET CURRENT  
vs. INPUT VOLTAGE  
345  
325  
305  
285  
265  
40  
35  
30  
25  
20  
15  
10  
5
35  
31  
27  
23  
19  
15  
11  
7
I
= 1mA  
SINK  
V
= 5.5V  
IN  
V
= 2.7V  
IN  
T
= -40 C  
A
V
= 5V  
IN  
245  
225  
205  
185  
T
= +25 C  
A
V
= 5V  
10  
IN  
V
IN  
= 2.7V  
T
= +85 C  
V
= 5.5V  
A
IN  
165  
145  
-40  
-15  
35  
60  
85  
-15  
10  
35  
60  
3.5  
3.9  
4.3  
4.7  
5.1  
5.3  
5.5  
3.7  
4.1  
4.5  
4.9  
TEMPERATURE ( C)  
TEMPERATURE ( C)  
INPUT VOLTAGE (V)  
_______________________________________________________________________________________  
5
Single USB Switch with Autoreset and  
Fault Blanking in Tiny QFN  
Typical Operating Characteristics (continued)  
(Circuit of Figure 2, V = 5V, C = 0.1µF, C  
= 1µF, ON = SEL, T = +25°C, unless otherwise noted.)  
A
IN  
IN  
OUT  
OVERLOAD RESPONSE INTO 2.5  
(EXPANDED TIME SCALE)  
OVERLOAD RESPONSE INTO 2.5  
MAX1946 toc14  
MAX1946 toc13  
A
0
A
B
0
0
B
0
0
C
C
D
0
0
D
0
400 s/div  
10ms/div  
A: V , 5V/div  
FAULT  
A: V , 5V/div  
FAULT  
OUT  
OUT  
B: V , 5V/div  
B: V  
, 5V/div  
C: I , 1A/div  
C: I , 1A/div  
IN  
IN  
D: I , 1A/div  
D: I , 1A/div  
OUT  
OUT  
SHORT-CIRCUIT RESPONSE INTO 0  
(EXPANDED TIME SCALE)  
SHORT-CIRCUIT RESPONSE INTO 0  
MAX1946 toc16  
MAX1946 toc15  
A
B
0
0
A
B
0
0
C
D
0
0
CURRENT TRANSIENT FROM  
SHORTING OUTPUT CAPACITANCE  
C
D
0
0
400 s/div  
10ms/div  
A: V , 5V/div  
FAULT  
A: V , 5V/div  
FAULT  
OUT  
OUT  
B: V  
, 5V/div  
B: V  
, 5V/div  
C: I , 2A/div  
C: I , 1A/div  
IN  
IN  
D: I , 10A/div  
D: I , 1A/div  
OUT  
OUT  
6
_______________________________________________________________________________________  
Single USB Switch with Autoreset and  
Fault Blanking in Tiny QFN  
Typical Operating Characteristics (continued)  
(Circuit of Figure 2, V = 5V, C = 0.1µF, C  
= 1µF, ON = SEL, T = +25°C, unless otherwise noted.)  
A
IN  
IN  
OUT  
SWITCH TURN-ON TIME  
(t + t  
SWITCH TURN-OFF TIME  
(t + t  
)
RISE  
)
FALL  
ON  
OFF  
MAX1946 toc17  
MAX1946 toc18  
C
R
= 1 F  
= 10  
C
R
= 1 F  
= 10  
OUT  
OUT  
OUT  
OUT  
A
B
A
B
0
0
0
0
1ms/div  
1ms/div  
A: V , 2V/div  
ON  
A: V , 2V/div  
ON  
B: V , 2V/div  
B: V , 2V/div  
OUT  
OUT  
STARTUP WAVEFORMS  
= 1 F  
STARTUP WAVEFORMS  
= 330 F  
C
C
OUT  
OUT  
MAX1946 toc19  
MAX1946 toc20  
C
R
= 1 F  
= 10  
C
R
= 330 F  
= 10  
OUT  
OUT  
OUT  
OUT  
A
A
0
0
0
B
0
B
C
C
0
0
0
0
D
D
400 s/div  
1ms/div  
A: V , 5V/div  
OUT  
A: V , 5V/div  
OUT  
B: V  
, 5V/div  
B: V  
, 5V/div  
FAULT  
FAULT  
C: V , 2V/div  
C: V , 2V/div  
OUT  
OUT  
D: I , 500mA/div  
D: I , 500mA/div  
OUT  
OUT  
_______________________________________________________________________________________  
7
Single USB Switch with Autoreset and  
Fault Blanking in Tiny QFN  
Typical Operating Characteristics (continued)  
(Circuit of Figure 2, V = 5V, C = 0.1µF, C  
= 1µF, ON = SEL, T = +25°C, unless otherwise noted.)  
A
IN  
IN  
OUT  
STARTUP WAVEFORMS  
= 100 F  
UVLO RESPONSE  
C
OUT  
MAX1946 toc22  
MAX1946 toc21  
C
= 100 F  
= 10  
OUT  
OUT  
A
R
0
0
A
B
0
0
B
C
0
0
C
0
D
10ms/div  
1ms/div  
A: V , 2V/div  
IN  
A: V , 5V/div  
FAULT  
OUT  
B: V , 2V/div  
OUT  
C: V  
B: V  
, 5V/div  
, 2V/div  
FAULT  
C: V , 2V/div  
OUT  
D: I , 500mA/div  
OUT  
Pin Description  
PIN  
NAME  
FUNCTION  
Fault-Indicator Output Switch. Open-drain output asserts low when switch enters thermal shutdown,  
undervoltage lockout, or a sustained (>20ms) current-limit or short-circuit condition.  
1
2
FAULT  
GND  
Ground  
Switch Power Output. Connect OUT pins together at the device and bypass with a 1µF ceramic  
capacitor. Load conditions may require additional bulk capacitance. When disabled, OUT goes into  
a high-impedance state.  
3, 4  
5, 6  
OUT  
IN  
Switch Power Input. Connect IN pins together at the device and bypass with a 0.1µF ceramic  
capacitor to GND. Input conditions may require additional bulk capacitance to prevent pulling the  
input supply down.  
ON/OFF Control Input. The active polarity of ON is set by SEL. Connect SEL high to make ON active  
high. Connect SEL to GND to make ON active low.  
7
8
ON  
Logic Input Polarity Select. SEL sets the active polarity of the ON input. Connect SEL high to make  
ON active high. Connect SEL to GND to make ON active low.  
SEL  
A built-in current limit of 1.1A limits the output current in  
Detailed Description  
the event of an overload condition. A built-in short-circuit  
detection circuit pulses the output current if the output  
voltage falls below 1V. This lowers RMS output current  
and reduces power dissipation during continuous short  
conditions.  
The MAX1946 includes output current limiting, short-cir-  
cuit protection, thermal shutdown, an enable input, and  
fault indicator (see the Functional Diagram). A logic  
input at SEL sets the active polarity of the enable input.  
The fault indicator notifies the system when the current-  
limit, short-circuit, undervoltage lockout, or thermal-  
shutdown threshold is exceeded.  
An internal micropower charge pump generates a high-  
side supply that drives the gate of an internal 75m  
NMOS switch.  
The MAX1946 operates from a 2.7V to 5.5V input  
supply and supplies a minimum output current of 740mA.  
8
_______________________________________________________________________________________  
Single USB Switch with Autoreset and  
Fault Blanking in Tiny QFN  
IN  
ON  
CHARGE  
PUMP  
SEL  
IN  
FAULT  
OUT  
MAX1946  
ILIM  
THERMAL  
SHUTDOWN  
25mA  
FAULT LOGIC  
20ms TIMERS  
OSC  
25kHz  
BIAS  
UVLO  
REF  
GND  
Figure 1. Functional Diagram  
On/Off Control and Undervoltage  
Lockout (UVLO)  
SEL sets the active polarity of the logic input of the  
MAX1946. Connect ON to the same voltage as SEL to  
enable OUT. Connect ON to the opposite voltage as  
SEL to disable OUT (see Table 1). The output enters a  
high-impedance state when disabled.  
Table 1. On/Off Control  
SEL  
ON  
OUT BEHAVIOR  
GND  
ON  
OFF  
OFF  
ON  
GND  
V
IN  
GND  
V
IN  
V
IN  
The MAX1946 includes a UVLO circuit to prevent erro-  
neous switch operation when the input voltage goes  
low during startup and brownout conditions. Input volt-  
ages less than 2.5V inhibit operation of the device.  
FAULT asserts low during a UVLO condition.  
The MAX1946 detects short-circuit removal by sourcing  
25mA from the output and monitoring the output volt-  
age. When the voltage at the output exceeds 0.5V for  
20ms, the fault flag resets, the output turns back on,  
and the 25mA current source turns off.  
Output Fault Protection and Autoreset  
The MAX1946 senses the switch output voltage and  
selects continuous current limiting for V  
greater  
OUT  
OUT  
Thermal Shutdown  
When the MAX1946 die temperature exceeds +160°C  
the switch turns off and FAULT goes low. Thermal shut-  
down does not utilize the 20ms fault-blanking timeout  
period. When the junction temperature cools by 15°C  
the switch turns on again and FAULT returns high.The  
switch cycles on and off if the overload condition per-  
sists, resulting in a pulsed output that reduces the aver-  
age system load.  
than 1V or short-circuit current limiting for V  
less  
than 1V. When V  
is greater than 1V, the device  
OUT  
operates in a continuous current-limit mode that limits  
output current to 1.1A. When V is less than 1V, the  
OUT  
device operates in short-circuit current-limit mode,  
sourcing 1.2A pulses to the load. When either fault con-  
dition persists for 20ms, the output turns off and the  
fault flag asserts. The output automatically restarts  
20ms after the short or overload is removed.  
_______________________________________________________________________________________  
9
Single USB Switch with Autoreset and  
Fault Blanking in Tiny QFN  
blanked. Thermal-overload faults and input voltage  
Fault Indicator  
The MAX1946 provides an open-drain fault output,  
FAULT. Connect FAULT to IN through a 100k pullup  
resistor for most applications. FAULT asserts low when  
any of the following conditions occur:  
drops below the UVLO threshold immediately turn the  
switch off and assert FAULT low.  
Fault blanking allows the MAX1946 to handle USB  
loads that may not be fully compliant with the USB  
specification. The MAX1946 successfully powers USB  
loads with additional bypass capacitance and/or large  
startup currents while protecting the upstream power  
source. No fault is reported if the switch brings up the  
load within the 20ms blanking period. See Table 2 for a  
summary of current limit and fault behavior.  
•
•
The input voltage is below the UVLO threshold.  
The switch junction temperature exceeds the  
+160°C thermal-shutdown temperature limit.  
•
The switch is in current-limit or short-circuit current-  
limit mode for more than 20ms.  
The FAULT output deasserts after a 20ms delay once  
the fault condition is removed. Ensure that the  
MAX1946 input bypass capacitance is sufficiently large  
to prevent load glitches from triggering the FAULT out-  
put. Limit the input voltage slew rate to 0.2V/µs to pre-  
vent erroneous FAULT indications.  
Applications Information  
Typical Application Circuit  
Input Power Supply and Capacitance  
Connect both IN inputs together. IN powers the internal  
control circuitry and charge pump for the switch.  
Bypass IN to GND with a 0.1µF ceramic capacitor.  
When driving inductive loads or operating from induc-  
tive sources, which may occur when the MAX1946 is  
powered by long leads or PC traces, larger input  
bypass capacitance is required to prevent voltage  
spikes from exceeding the MAX1946’s absolute maxi-  
mum ratings during short-circuit events.  
To differentiate large capacitive loads from short cir-  
cuits or sustained overloads, the MAX1946 has a fault-  
blanking circuit. When a load transient causes the  
device to enter current limit, an internal counter moni-  
tors the duration of the fault. For load faults exceeding  
the 20ms fault-blanking time, the switch turns off,  
FAULT asserts low, and the device enters autoreset  
mode (see the Output Fault Protection and Autoreset  
section). Only current-limit and short-circuit faults are  
Table 2. Current Limiting and Fault Behavior  
CONDITION  
MAX1946 BEHAVIOR  
• If a short is detected at the output, the switch turns off, and the blanking timer begins. FAULT  
remains high during the blanking timeout period.  
• If the short persists during the fault-blanking period, the output pulses at 0.35A  
. If the short is  
RMS  
removed before the 18ms short-circuit blanking timeout period, the next ramped current pulse soft  
starts the output. FAULT remains high.  
• If the short circuit persists after the fault-blanking period, FAULT goes low, autoreset mode  
begins, and the output sources 25mA.  
Output Short Circuit  
(V < 1V)  
OUT  
• If the output voltage rises above 0.5V for 20ms, the switch resets, the output turns on, and FAULT  
goes high (see Short-Circuit Response in the Typical Operating Characteristics.)  
• Output current regulates at I  
and the blanking timer turns on. FAULT remains high during  
LIM  
the blanking timeout period.  
• Continuous current at I  
persists until either the 20ms blanking period expires or a thermal  
LIM  
fault occurs.  
Output Overload Current  
(V > 1V)  
• If overcurrent persists after 20ms, FAULT goes low, autoreset mode is enabled, and the output  
sources 25mA.  
OUT  
• If the output voltage rises above 0.5V for 20ms, the switch resets, the output turns on, and FAULT  
goes high (see Short Overload Response in the Typical Operating Characteristics.)  
• A junction temperature of +160°C immediately asserts FAULT low (the blanking timeout period  
does not apply for thermal faults) and turns off the switch. When the junction cools by 15 C,  
the thermal fault is cleared and FAULT goes high. Note that if other fault conditions are present  
when a thermal fault clears, those fault states then take effect.  
Thermal Fault  
(T > +160oC)  
J
10 ______________________________________________________________________________________  
Single USB Switch with Autoreset and  
Fault Blanking in Tiny QFN  
Place input and output capacitors no more than 5mm  
from device leads. Connect IN and OUT to the power  
bus with short traces. The exposed pad on the QFN  
package underside must be soldered to the PC board in  
order to realize the rated package dissipation.  
INPUT  
2.7V TO 5.5V  
IN  
100k  
IN  
FAULT  
OUT  
0.1 F  
OFF  
An active switch dissipates little power with minimal  
change in package temperature. Calculate the power  
dissipation for this condition as follows:  
ON  
SEL  
MAX1946  
GND  
ON  
OUT  
1 F  
2
✕
P = (I  
)
R
ON  
OUT  
At the normal operating current (I  
maximum on-resistance of the switch (90m ), the  
power dissipation is:  
= 0.5A) and the  
OUT  
*USB APPLICATIONS MAY REQUIRE  
ADDITIONAL BULK CAPACITANCE  
Figure 2. Typical Application Circuit  
P = (0.5A)2 0.09 = 22.5mW  
✕
Output Capacitor  
The worst-case power dissipation occurs when the out-  
put current is just below the current-limit threshold  
(1.2A max) with an output voltage just greater than 1V.  
In this case, the power dissipated is the voltage drop  
across the switch multiplied by the current limit:  
Bypass OUT to GND with a 1µF ceramic capacitor for  
local decoupling. Additional bulk capacitance (up to  
470µF) reduces output-voltage transients under dynamic  
load conditions. Using output capacitors greater than  
470µF can assert FAULT if the current limit cannot  
charge the output capacitor within the 20ms fault-  
blanking period. In addition to bulk capacitance, small-  
value (0.1µF or greater) ceramic capacitors improve  
the output’s resilience to electrostatic discharge (ESD).  
✕
P = I  
(V - V  
IN  
)
OUT  
LIM  
For a 5V input and 1V output, the maximum power dis-  
sipation per switch is:  
Driving Inductive Loads  
A wide variety of devices (mice, keyboards, cameras, and  
printers) typically connect to the USB port with cables,  
which can add an inductive component to the load. This  
inductance causes the output voltage at the USB port to  
oscillate during a load step. The MAX1946 drives induc-  
tive loads, but avoid exceeding the device’s absolute  
maximum ratings. The load inductance is usually relatively  
small, and the MAX1946 input typically includes substan-  
tial bulk capacitance from an upstream regulator as well  
as local bypass capacitors, limiting overshoot. If severe  
ringing occurs due to large load inductance, clamp the  
MAX1946 output below +6V and above -0.3V.  
✕
P = 1.2A (5V - 1V) = 4.8W  
Since the package power dissipation is 1951mW for the  
8-pin thin QFN, the MAX1946 die temperature exceeds  
the +160 C thermal-shutdown threshold. The switch  
output shuts down until the junction temperature cools  
by 15°C. The duty cycle and period are strong func-  
tions of the ambient temperature and the PC board lay-  
out (see the Thermal Shutdown section).  
If the output current exceeds the current-limit threshold,  
or the output voltage is pulled below the short-circuit  
detect threshold, the MAX1946 enters a fault state after  
20ms, at which point autoreset mode is enabled and  
25mA is sourced by the output. For a 5V input, OUT  
short-circuited to GND, and autoreset mode active, the  
power dissipation is as follows:  
Turn-On and Turn-Off Behavior  
When turned on, the MAX1946 output ramps up over  
1.2ms to eliminate load transients on the upstream  
power source. When turned off, the output ramps down  
for 3ms. Under fault conditions, the output of the  
MAX1946 turns off rapidly to provide maximum safety  
for the upstream power source and downstream  
devices. Internal blocks shut down to minimize supply  
current when the switch is off.  
✕
P = 0.025A 5V = 0.125W  
Chip Information  
TRANSISTOR COUNT: 2004  
PROCESS: BiCMOS  
Layout and Thermal Dissipation  
Keep all traces as short as possible to reduce the effect  
of undesirable parasitic inductance, and to optimize the  
switch response time to output short-circuit conditions.  
______________________________________________________________________________________ 11  
Single USB Switch with Autoreset and  
Fault Blanking in Tiny QFN  
Package Information  
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,  
go to www.maxim-ic.com/packages.  
PACKAGE OUTLINE, 6, 8 & 10L,  
QFN THIN (DUAL), EXPOSED PAD, 3x3x0.80 mm  
21-0137  
C
12 ______________________________________________________________________________________  
Single USB Switch with Autoreset and  
Fault Blanking in Tiny QFN  
Package Information (continued)  
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,  
go to www.maxim-ic.com/packages.  
COMMON DIMENSIONS  
SYMBOL  
MIN.  
0.70  
2.90  
2.90  
0.00  
0.20  
MAX.  
0.80  
3.10  
3.10  
0.05  
0.40  
A
D
E
A1  
L
k
0.25 MIN  
0.20 REF.  
A2  
PACKAGE VARIATIONS  
PKG. CODE  
T633-1  
N
6
D2  
E2  
e
JEDEC SPEC  
MO229 / WEEA  
MO229 / WEEC  
b
[(N/2)-1] x e  
1.90 REF  
1.95 REF  
1.50–0.10 2.30–0.10 0.95 BSC  
1.50–0.10 2.30–0.10 0.65 BSC  
0.40–0.05  
0.30–0.05  
T833-1  
8
T1033-1  
10  
1.50–0.10 2.30–0.10 0.50 BSC MO229 / WEED-3 0.25–0.05 2.00 REF  
PACKAGE OUTLINE, 6, 8 & 10L,  
QFN THIN (DUAL), EXPOSED PAD, 3x3x0.80 mm  
21-0137  
C
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are  
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.  
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 13  
© 2003 Maxim Integrated Products  
Printed USA  
is a registered trademark of Maxim Integrated Products.  

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