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](http://pdffile.icpdf.com/pdf2/p00262/img/icpdf/MAX1946ETA-T_1578653_icpdf.jpg)
型号: | MAX1946ETA-T |
厂家: | ![]() |
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 信息通信管理 |
文件: | 总13页 (文件大小:435K) |
中文: | 中文翻译 | 下载: | 下载PDF数据表文档文件 |
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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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