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PDF MAX1940 Data sheet ( Hoja de datos )
| Número de pieza | MAX1940 | |
| Descripción | Triple USB Switch with Autoreset and Fault Blanking | |
| Fabricantes | Maxim Integrated | |
| Logotipo |  |
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19-2497; Rev 0; 7/02
Triple USB Switch with Autoreset and
Fault Blanking
General Description
The MAX1940 triple current-limited switch with auto-
reset supplies a guaranteed 500mA load per channel in
accordance with USB specifications. The MAX1940
operates from a 4V to 5.5V input supply and consumes
only 60µA of quiescent current when operating and only
3µA in standby. Selectable active-high/active-low con-
trol logic and independent shutdown controls for each
channel provide additional flexibility. An autoreset fea-
ture latches the switch off in the event of a short circuit,
saving system power. The switch reactivates upon
removal of the shorted condition.
The MAX1940 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. Independent open-drain fault signals
(FAULTA, FAULTB, and FAULTC) notify the micro-
processor when a thermal-overload, current-limit,
undervoltage lockout (UVLO), or short-circuit fault
occurs. A 20ms fault-blanking feature enables the cir-
cuit 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
also prevents fault signals from being issued when the
device powers up the load.
The MAX1940 is available in a space-saving 16-pin
QSOP package and operates over the extended (-40°C
to +85°C) temperature range.
Applications
USB Ports
USB Hubs
Notebook Computers
PDAs and Palmtop
Computers
Docking Stations
Desktop Computers
Pin Configuration
TOP VIEW
ONA 1
IN1 2
IN2 3
IN3 4
ONB 5
IN4 6
IN5 7
ONC 8
MAX1940
QSOP
16 FAULTA
15 OUTA
14 GND
13 OUTB
12 FAULTB
11 SEL
10 OUTC
9 FAULTC
Features
o Triple USB Switch in Tiny 16-Pin QSOP Package
o Autoreset Feature Saves System Power
o Guaranteed 500mA Load Current per Channel
o Built-In 20ms Fault-Blanking Circuitry
o Active-High/Active-Low Control Logic
o Fully Compliant to USB Specifications
o 4V to 5.5V Input Voltage Range
o Independent Shutdown Control
o Independent Fault Indicator Outputs
o Thermal-Overload Protection
o 3µA Standby Current
o UL Certification Pending
PART
MAX1940EEE
Ordering Information
TEMP RANGE
-40°C to +85°C
PIN-PACKAGE
16 QSOP
Typical Operating Circuit
INPUT
4V TO 5.5V
ACTIVE-HIGH/ACTIVE-LOW
SELECTABLE
MAX1940
IN1 FAULTA
IN2 FAULTB
IN3 FAULTC
IN4
IN5 OUTA
ONA
ONB OUTB
ONC
SEL OUTC
GND
USB
PORT A
USB
PORT B
USB
PORT C
________________________________________________________________ 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.
1 page  
Triple USB Switch with Autoreset and
Fault Blanking
Typical Operating Characteristics (continued)
(Circuit of Figure 2, VIN_ = 5V, CIN_ = 0.1µF, COUT_ = 1µF, ON_ = SEL, TA = +25°C, unless otherwise noted.)
FAULT OUTPUT LOW VOLTAGE
vs. TEMPERATURE
250
240 RPU = 4.7kΩ
230
220
210 VIN_ = 5.5V
200
190
180
170
160
150
140
130
120
110
100
-40 -15
VIN_ = 5V
VIN_ = 4.5V
10 35
60
TEMPERATURE (°C)
85
OVERLOAD RESPONSE INTO 2.5Ω
MAX1940 toc13
A 5V
AUTORESET CURRENT
vs. TEMPERATURE
38
36
34 VIN_ = 5.5V
32 VIN_ = 5V
30
28
26
24
22
20 VIN_ = 4.5V
18
-40
-15 10 35 60
TEMPERATURE (°C)
85
OVERLOAD RESPONSE INTO 2.5Ω
(EXPANDED TIME SCALE)
MAX1940 toc14
A 5V
AUTORESET CURRENT
vs. INPUT VOLTAGE
40
35
TA = +25°C
30 TA = -40°C
25
20
15
TA = +85°C
10
5
0
3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5
INPUT VOLTAGE (V)
SHORT-CIRCUIT RESPONSE INTO 0Ω
MAX1940 toc15
A 5V
B
0
C
0
D
A: VIN_ 5V/div
B: VOUT_ 5V/div
10ms/div
C: VFAULT_ 5V/div
D: IOUT_ 1A/div
0
SHORT-CIRCUIT RESPONSE INTO 0Ω
(EXPANDED TIME SCALE)
MAX1940 toc16
A 5V
B
0
C 5V
B
0
C 5V
D
A: VIN_ 5V/div
B: VOUT_ 5V/div
400µs/div
C: VFAULT_ 5V/div
D: IOUT_ 1A/div
0
SWITCH TURN-ON TIME (tON + tRISE)
MAX1940 toc17
VSEL = 5V
ROUT_ = 10Ω
COUT_ = 1µF
A
5V
5V
B
5V
B
C 5V
D
A: VIN_ 5V/div
B: VOUT_ 5V/div
10ms/div
C: VFAULT_ 5V/div
D: IOUT_ 1A/div
0
SWITCH TURN-ON TIME (tON + tFALL)
MAX1940 toc18
VSEL = 5V
ROUT_ = 10Ω
COUT_ = 1µF
A
5V
B
D
A: VIN_ 5V/div
B: VOUT_ 5V/div
400µs/div
C: VFAULT_ 5V/div
D: IIN_ 2A/div
0
A: VON_ 5V/div
B: VOUT_ 2V/div
1ms/div
A: VON_ 5V/div
B: VOUT_ 2V/div
1ms/div
0
_______________________________________________________________________________________ 5
5 Page 
Triple USB Switch with Autoreset and
Fault Blanking
INPUT
4V TO 5.5V
O.1µF
OFF
ON
MAX1940
IN1 FAULTA
IN2 FAULTB
IN3 FAULTC
IN4
IN5 OUTA
ONA
ONB OUTB
ONC
SEL OUTC
GND
100kΩ
100kΩ
100kΩ
USB
PORT A
1µF*
USB
PORT B
1µF*
USB
PORT C
1µF*
*USB APPLICATIONS MAY REQUIRE
ADDITIONAL BULK CAPACITANCE
Figure 2. Typical Application Circuit
power bus with short traces. Wide power bus planes at
IN_ and OUT provide superior heat dissipation as well.
An active switch dissipates little power with minimal
change in package temperature. Calculate the power
dissipation for this condition as follows:
P = (IOUT_)2 x RON
At the normal operating current (IOUT_ = 0.5A) and the
maximum on-resistance of the switch (135mΩ), the
power dissipation is:
P = (0.5A)2 x 0.135Ω = 34mW per switch.
The worst-case power dissipation occurs when the output
current is just below the current-limit threshold (1.2A max)
with an output voltage greater than 1V. In this case, the
power dissipated in each switch is the voltage drop
across the switch multiplied by the current limit:
P = ILIM x (VIN - VOUT)
For a 5V input and 1V output, the maximum power dis-
sipation per switch is:
P = 1.2A x (5V - 1V) = 4.8W
Because the package power dissipation is 667mW, the
MAX1940 die temperature exceeds the +160°C thermal
shutdown threshold, and the switch output shuts down
until the junction temperature cools by +15°C. The duty
cycle and period are strong functions of the ambient
temperature and the PC board layout (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 MAX1940 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:
P = 0.025A x 5V = 0.125W
Chip Information
TRANSISTOR COUNT: 4259
PROCESS: BiCMOS
______________________________________________________________________________________ 11
11 Page | ||
| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet MAX1940.PDF ] | |
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