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MIC2537
Micrel
MIC2537
Quad Power Distribution Switch Final Information
General Description
The MIC2537 is a cost-effective high-side power switch with four independently controlled channels, optimized for buspowered Universal Serial Bus (USB) applications. Few external components are necessary to satisfy USB requirements. The MIC2537 satisfies the following USB requirements: each switch channel supplies up to 100mA as required by USB bus-powered downstream devices; fault current is limited to typically 250mA, well below the UL 25VA safety requirements; and a flag output is available to indicate fault conditions to the local USB controller. Soft start eliminates the momentary voltage drop on the upstream port that may occur when the switch is enabled in bus-powered applications. Additional features include thermal shutdown to prevent catastrophic switch failure from high-current loads and 3.3V and 5V logic compatible enable inputs. The MIC2537 is available in active-high and active-low versions in a 16-lead SOP package.
Features
* * * * * * * * * * * * Compliant to USB specifications 3V to 5.5V input 100mA minimum continuous load current per port 425m typical on-resistance < 400mA current limit Individual open-drain fault flag leads 3V/5V-compatible enable inputs Active-high (-1) and active-low (-2) versions 100A max. on-state supply current <1A typical off-state supply current 16-lead SOP package -40C to 85C operation
Applications
* * * * * * USB keyboards USB bus-powered docking stations Notebook docking stations Notebook PCs PDA General power distribution
Typical Application
Upstream VBUS 4.75V to 5.25V 500mA max. 10k MIC5207-3.3 LDO Regulator IN 4.7 F OUT 1F GND 3.3V USB Controller V+ EN OC EN OC EN D+ D- Bold lines indicate 0.1" wide, 1-oz. copper high-current traces. GND OC EN OC Ferrite Bead 10k 10k 10k MIC2537 ENA FLGA ENB FLGB ENC FLGC END FLGD IN NC OUTA OUTB OUTC OUTD NC GND VBUS 33F* * 33F, 16V tantalum or 100F, 10V electrolytic per port 0.01F D+ D- GND Downstream USB Port 3 100mA max. 0.1 F 33F* 0.01F 33F* 0.01F VBUS D+ D- GND Downstream USB Port 1 100mA max.
VBUS D+ D- GND Downstream USB Port 2 100mA max.
VBUS 33F* 0.01F D+ D- GND Downstream USB Port 4 100mA max.
Typical Bus-Powered Hub
UL Recognized Component Micrel, Inc. * 1849 Fortune Drive * San Jose, CA 95131 * USA * tel + 1 (408) 944-0800 * fax + 1 (408) 944-0970 * http://www.micrel.com
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MIC2537
MIC2537
Micrel
Ordering Information
Part Number MIC2537-1BM MIC2537-2BM Enable Active High Active Low Temperature Range -40C to +85C -40C to +85C Package 16-Lead SOP 16-Lead SOP
Pin Configuration
MIC2537-x
FLGA ENA OUTA GND NC OUTB ENB FLGB 1 2 3 4 5 6 7 8 16 FLGD 15 END 14 OUTD 13 IN 12 NC 11 OUTC 10 ENC 9 FLGC
16-Lead SOP (M)
Pin Description
Pin Number 1 2 3 4 5, 12 6 7 8 9 10 11 13 14 15 16 Pin Name FLGA ENA OUTA GND NC OUTB ENB FLGB FLGC ENC OUTC IN OUTD END FLGD Pin Function Flag A: (Output): Channel A open-drain fault flag output. Enable A (Input): Channel A control input. Output A: Channel A switch output. Ground: Supply return. Connect both leads to ground. Not internally connected Output B: Channel B switch output. Enable B (Input): Channel B control input. Flag B (Output): Channel B open-drain fault flag output. Flag C (Output): Channel C open-drain fault flag output. Enable C (Input): Channel C control input. Output C: Channel C switch output. Positive Supply Input Output D: Channel D switch output. Enable D (Input): Channel D control input. Flag D (Output): Channel D open-drain fault flag output.
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MIC2537
MIC2537
Micrel
Absolute Maximum Ratings (Note 1)
Supply Voltage (VIN) .....................................................+6V Fault Flag Voltage (VFLG) .............................................. +6V Fault Flag Current (IFLG) ............................................ 25mA Output Voltage (VOUT) .................................................. +6V Output Current (IOUT) ............................... Internally Limited Control Input (VEN) ......................................... -0.3V to 12V Storage Temperature (TS) ....................... -65C to +150C Lead Temperature (Soldering 5 sec.) ....................... 260C ESD Rating, Note 3 ....................................................... 2kV
Operating Ratings (Note 2)
Supply Voltage (VIN) ...................................... +3V to +5.5V Ambient Operating Temperature (TA) ........ -40C to +85C Thermal Resistance SOP (JA) .......................................................... 120C/W
Electrical Characteristics
VIN = +5V; TA = 25C; unless noted. Parameter Supply Current Condition Note 4, switch off, OUTA-D = open Note 4, all switches on, OUTA-D = open Enable Input Threshold low-to-high transition high-to-low transition, Note 4 Enable Input Current VEN = VOH(min) = 2.4V VEN = VOL(max) = 0.8V Enable Input Capacitance Switch Resistance Output Turn-On Delay Output Turn-On Rise Time Output Turnoff Delay Output Turnoff Fall Time Output Leakage Current Current Limit Threshold Continuous Load Current Short Circuit Current Limit Overtemperature Shutdown Threshold Error Flag Output Resistance single switch, 100mA load RL = 50, CL = 1F, Note 5 RL = 50, CL = 1F, Note 5 RL = 50, CL = 1F, Note 5 RL = 50, CL = 1F, Note 5 each output (switch off) ramped load applied to enable output, Note 6 each output, FLG not active each output (enabled into load), VOUT = 4.0V TJ increasing TJ decreasing VIN = 5V, IL = 10mA VIN = 3.3V, IL = 10mA Error Flag Off Current
Note 1. Note 2. Note 3. Note 4. Note 5. Note 6.
Min
Typ 0.75 70 1.8
Max 5 100 2.4
Units A A V V A A pF
0.8
1.6 0.01 0.01 1 425 0.51 700 1 1
m ms ms s s A mA mA
0.2
0.5 150 148 1 300 300 300 10 500
100 150 250 135 125 10 12 0.01 1 400
mA C C A
VFLAG = 5V
Exceeding the absolute maximum rating may damage the device. The device is not guaranteed to function outside its operating rating. Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5k in series with 100pF. Off is 0.8V and on is 2.4V for the MIC2537-1. Off is 2.4V and on is 0.8V for the MIC2537-2. The enable input has approximately 200mV of hysteresis. See control threshold charts. See "Timing Diagrams." See "Functional Characteristics: Current-Limit Response" graph.
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MIC2537
MIC2537
Micrel
Typical Characteristics
Supply Current vs. Supply Voltage
100 SUPPLY CURRENT (A)
ON-RESISTANCE (m)
Supply Current vs. Temperature
VIN = 5V
100 SUPPLY CURRENT (A) 80 60 40
500 400 300 200
Ouput On-Resistance Variation vs. Supply Voltage
80 60 40 20
TA = 25C 20 0 RL =
VIN = 3.3V RL =
TA = 25C 100 0 2 IL = 100mA
2
3 4 5 SUPPLY VOLTAGE (V)
6
0 -40 -20 0 20 40 60 80 100 TEMPERATURE (C)
3 4 5 SUPPLY VOLTAGE (V)
6
Output On-Resistance Variation vs. Temperature
500 ON RESISTANCE (m) 400
Overcurrent Threshold and Current Limit vs. Supply Voltage
300 250 CURRENT (mA) 200 150 100 50 0 2 TA = 25C ILIM ITHR CURRENT (mA)
300 250 200 150 100
Overcurrent Threshold and Current Limit vs. Temperature
ITHR
300 200 100 VIN = 5V IL = 100mA
ILIM
50 0 -40 -20
VIN = 5V
0 -40 -20 0 20 40 60 80 100 TEMPERATURE (C)
3 4 5 SUPPLY VOLTAGE (V)
6
0
20
40
60
80 100
TEMPERATURE (C)
Control Threshold vs. Supply Voltage
2.0
THRESHOLD VOLTAGE (V) 2.0
Control Threshold vs. Temperature
500 VIH 400 VIL TIME (s) 300 200 100
Output Rise Time vs. Temperature
VIH ENABLE VOLTAGE (V) 1.5 VIL 1.0
1.5
1.0
0.5
TA = 25C
0.5
VIN = 5V
VIN = 5V CL = 0.01F RL = 44
0
2
3 4 5 SUPPLY VOLTAGE (V)
6
0 -40 -20 0 20 40 60 80 100 TEMPERATURE (C)
0 -40 -20 0 20 40 60 80 100 TEMPERATURE (C)
1.5
Output Fall Time vs. Temperature
TIME (s)
1.0
0.5
VIN = 5V CL = 0.01F RL = 44
0 -40 -20 0 20 40 60 80 100 TEMPERATURE (C)
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MIC2537
MIC2537
Micrel
Functional Characteristics
Input Voltage Response (Input Voltage Rising: MIC2537-2)
VOUT VFLG VIN IOUT (100mA/div.) (2V/div.) (2V/div.) (2V/div.)
Input Voltage Response (Input Voltage Decreasing: MIC2537-2)
VOUT VFLG VIN IOUT (100mA/div.) (2V/div.) (2V/div.) (2V/div.)
EN = 0V RL = 24
EN = 0V RL = 24
TIME (25ms/div.)
TIME (25ms/div.)
Current Limit Transient Response (Heavy Load Applied to Output: MIC2537-2)
VOUT VFLG VEN (5V/div.) (10V/div.)(5V/div.)
Current Limit Response (Ramped Load: MIC2537-2)
VOUT VFLG VEN (5V/div.) (10V/div.)(5V/div.)
1V
1V 250mA Current Limit Threshold 180mA Short Circuit Current Limit VIN = 5V
VIN = 5V
IOUT (500mA/div.)
TIME (25s/div.)
IOUT (100mA/div.)
TIME (5ms/div.)
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MIC2537
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Test Circuit
VOUT Device Under OUT Test RL CL
Timing Diagrams
tR VOUT 10% 90% 90% 10% tF
Output Rise and Fall Times
VEN
50% tOFF tON
VOUT
90% 10%
Active-Low Switch Delay Times (MIC2537-2)
VEN
50% tOFF tON
VOUT
90% 10%
Active-Low Switch Delay Times (MIC2537-1)
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MIC2537
MIC2537
Micrel
Functional Diagram
FLGA
OUTA ENA CHARGE PUMP GATE CONTROL CURRENT LIMIT FLG B
ENB CHARGE PUMP
GATE CONTROL CURRENT LIMIT
OUTB
OSC.
THERMAL SHUTDOWN
1.2V REFERENCE
IN
CURRENT LIMIT CHARGE PUMP ENC GATE CONTROL
OUTC FLGC
CHARGE PUMP END GATE CONTROL
CURRENT LIMIT
OUTD FLGD
MIC2537 GND
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MIC2537
MIC2537
Micrel
Current Sensing and Limiting The current-limit threshold is preset internally. The preset level prevents damage to the output MOSFET and external load but allows a minimum current of 0.15A through the output MOSFET of each channel. The current-limit circuit senses a portion of the output FET switch current. The current sense resistor shown in the block diagram is virtual and has no voltage drop. The reaction to an overcurrent condition varies with the following three scenarios:
Functional Description
The MIC2537-1 and MIC2537-2 are quad high-side switches with active-high and active-low enable inputs, respectively. Fault conditions turn off or inhibit turn-on of one or more of the output transistors, depending upon the type of fault, and activate the open-drain error flag transistors making them sink current to ground. Input and Output IN (input) is the power supply connection to the logic circuitry and the drain of each output MOSFET. OUTx (output) is the source of each respective MOSFET. In a typical circuit, current flows through the switch from IN to OUTx toward the load. If VOUT is greater than VIN, current will flow from OUT to IN since the MOSFET is bidirectional when on. The output MOSFET and driver circuitry are also designed to allow the MOSFET source to be externally forced to a higher voltage than the drain (VOUTx > VIN) when the output is off. In this situation, the MIC2537 prevents reverse current flow. Thermal Shutdown Thermal shutdown shuts off the affected output MOSFET and signals the corresponding fault flags if the die temperature exceeds 135C. 10C of hysteresis prevents the switch from turning on until the die temperature drops to 125C. Overtemperature detection functions only when at least one switch is enabled. Current-Limit Induced Thermal Shutdown Internal circuitry increases the output MOSFET on-resistance until the series combination of the MOSFET on-resistance and the load impedance limits output current to approximately 200mA. The resulting increase in power dissipation may cause the shorted channel to go into thermal shutdown. In addition, even though individual channels are thermally isolated, it is possible they may shut down when an adjacent channel is shorted. When this is undesirable, shutdown of the channels not shorted can be avoided by externally responding to the fault and disabling the current limited channel before the shutdown temperature is reached. The delay between the flag indication of a current limit fault and thermal shutdown will vary with ambient temperature, board layout, and load impedance, but is typically several seconds. The USB controller must therefore recognize a fault and disable the appropriate channel within this time.
Switch Enabled into Short Circuit If a switch is powered on or enabled into an excessive load or short circuit, the switch immediately goes into a constantcurrent mode, slowly increasing the output voltage. The fault flag goes low until the load is reduced. Short Circuit Applied to Output When a heavy load or short circuit is applied to an enabled switch, a large transient current may flow until the currentlimit circuitry responds. Once this occurs, the device limits current to less than the short circuit current-limit specification. See the "Functional Characteristics: Current-Limit Transient Response graph for details. Current-Limit Response The MIC2537 current-limit profile exhibits a small foldback effect of approximately 100mA. Once this current-limit threshold is exceeded the device enters constant-current mode. This constant current is specified as the short-circuit current limit in the "Electrical Characteristics" table. It is important to note that the MIC2537 will deliver load current up to the current-limit threshold. See the "Functional Characteristics: Current-Limit Response" graph for details. Fault Flag FLGx is an open-drain N-channel MOSFET output. Fault flags are active (low) for current limit or thermal shutdown. Each flag output MOSFET is capable of sinking a 10mA load to approximately 200mV above ground. Several FLGx pins may be wired-NOR connected to a common pull-up resistor.
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MIC2537
MIC2537
Micrel
In USB applications it is required that output bulk capacitance shown in "Typical Application" is utilized to meet transient regulation requirements during hot-plug events. When the MIC2537 is enabled, the flag will go active for about 5ms depending on output capacitance. Additionally, during hotplug events, inrush currents may cause the flag to go active for approximately 30s. If these "false" overcurrent indications are a system problem, they can be masked by an RC filter on the flag output (see Figure 2). Alternatively, a 15ms debounce routine may be programmed into the USB logic controller to eliminate the need for an RC filter. Bus-Powered Hub Port Switching The USB Specification requires that bus-powered hubs implement port switching on either a ganged or individual basis. The specific implementation must be reported via the Hub Descriptor Status Register. Individual port switching has advantages in that a fault on one port will not prevent the other ports from operating correctly. In addition, a soft-start circuit must be included in order to reduce inrush currents when the switch is enabled. To meet this requirement, the MIC2537 has been designed to slowly ramp its output. Suspend Current For hubs, Universal Serial Bus Specification Revision 1.1 section 7.2.3, stipulates that the maximum suspend current for a configured hub is 2.5mA. This number is derived by allocating 500A for up to four downstream ports plus 500A for the hub's internal functions. A nonconfigured hub is considered a low-power device and cannot consume more than 500A. In a nonconfigured state all downstream devices will be switched off. In most cases, a nonconfigured hub is not a practical state for the system. Therefore, the 2.5mA specification is the applicable target specification for the suspend state. In a bus-powered hub with less than 4 ports, the hub may use the additional current for internal functions. The 500A worst case suspend current must be further divided among the data port termination resistors and internal functions. The termination resistors will consume 3.6V / (16.5K - 5%) = 230A. This leaves only 270A for internal functions. Assuming 100A as the maximum USB controller suspend current, 170A remains for the rest of the system. The MIC2537 will consume 100A maximum, leaving a margin of 70A.
Applications Information
Supply Filtering A 0.1F to 1F bypass capacitor from IN to GND, located at the device, 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 or output transients must not exceed the absolute maximum supply voltage (VIN(max) = 6V) even for a short duration.
VIN 3V to 5.5V 0.1F to 1F MIC2537 FLGA ENA FLGB ENB
OUTA OUTB GND NC IN NC
OUTC OUTD ENC FLGC END FLGD
Figure 1. Supply Bypassing Enable Input EN must be driven logic high or logic low for a clearly defined input. Floating the input may cause unpredictable operation. EN should not be allowed to go negative with respect to GND. Soft Start The MIC2537 presents a high impedance when off and slowly becomes a low impedance as it turns on. This reduces inrush current and related voltage drop that results from charging a capacitive load, satisfying the USB voltage droop requirements. Transient Overcurrent Fault-Flag Filter When the MIC2537 is enabled, large values of capacitance at the output of the device will cause inrush currents to flow that exceed the short circuit current-limit threshold of the device and cause the flag to activate. The duration of this time depends on the size of the output capacitance. See "Functional Characteristics: Switch Turn-On and Turnoff Charcteristics" for details. During the charging time, the device enters into constant-current mode and the flag is activated. As the capacitance is charged the current decreases below the short circuit current-limit threshold and the flag will be deasserted.
10k FLGA 50k FLGB FLGC FLGD
USB Controller OVERCURRENT
0.3F
Figure 2. Transient Filter
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MIC2537
USB Voltage Regulation USB specifications require a minimum downstream voltage supply of 4.40V from a bus-powered hub port (See Application Note 17 for details). The USB specification allows for a 100mV drop across the hub, leaving 250mV for PCB, upstream cable, and connector resistance. Therefore, the onresistance of the switch for each port, not including PCB resistance, must be about 100mV / 100mA = 1. The MIC2537 has a maximum on-resistance of 700m, which easily satisfies this requirement. Overcurrent Indication
Micrel
The USB Specification does not require bus-powered hubs to report overcurrent conditions to the host since the hub is already current-limited at the upstream port. However, if it is desired to report overcurrent, the Hub Descriptor Status Register must be programmed to indicate this. The MIC2537 provides a flag output for this application.
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MIC2537
MIC2537
Micrel
Package Information
PIN 1
0.157 (3.99) 0.150 (3.81)
DIMENSIONS: INCHES (MM)
0.020 (0.51) REF 0.050 (1.27) BSC
0.020 (0.51) 0.013 (0.33) 0.0098 (0.249) 0.0040 (0.102)
45 0-8 0.050 (1.27) 0.016 (0.40) 0.244 (6.20) 0.228 (5.79)
0.0648 (1.646) 0.0434 (1.102)
0.394 (10.00) 0.386 (9.80)
SEATING PLANE
16-Lead SOP (M)
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MIC2537
MIC2537
Micrel
MICREL INC. 1849 FORTUNE DRIVE SAN JOSE, CA 95131
TEL
USA
+ 1 (408) 944-0800
FAX
+ 1 (408) 944-0970
WEB
http://www.micrel.com
This information is believed to be accurate and reliable, however no responsibility is assumed by Micrel for its use nor for any infringement of patents or other rights of third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent right of Micrel Inc. (c) 1999 Micrel Incorporated
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MIC2537

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