SLVS401 − AUGUST 2001
FEATURES
D Complete Power Management Solution for
D
D
D
D
D
D
D
D
D
DESCRIPTION
The TPS2149 incorporates two power distribution
switches and an LDO in one small package, providing
a USB bus-powered hub power management solution
that saves up to 60% in board space over typical
implementations.
USB Bus-Powered Hubs
3.3-V 200 mA Low-Dropout Voltage Regulator
Two 5-V 340-mΩ (Typ) High-Side MOSFETs
Independent Thermal- and Short-Circuit
Protection for LDO and Each Switch
Overcurrent Indicator With Transient Filter
2.9-V to 5.5-V Operating Range
CMOS- and TTL-Compatible Enable Inputs
75-µA (Typ) Supply Current
Available in 8-Pin MSOP (PowerPAD)
−40°C to 85°C Ambient Temperature Range
The TPS2149 meets USB 2.0 bus-powered hub
requirements. An integrated LDO regulates the 5-V bus
power down to 3.3 V for the USB controller. The two
MOSFET switches provide power to the downstream
ports. With independent enables, the downstream ports
remain unpowered until the hub completes
enumeration.
Each power-distribution switch is capable of supplying
200 mA of continuous current, and the independent
logic enables are compatible with 5-V logic and 3-V
logic. The switches and the LDO are designed with
controlled rise times and fall times to minimize current
surges.
APPLICATIONS
D USB Bus-Powered Hubs
− Keyboards
− Monitors
− Hub Boxes
The TPS2149 has active-low enables while the
TPS2159 has active-high enables.
LDO and dual switch family selection guide and schematics
TPS2145/55
TSSOP−14
VIN/SW1
LDO_EN
EN1
SW2
EN2
GND
LDO
TPS2147/57
MSOP−10
LDO_OUT
VIN/SW1
LDO_ADJ
LDO
VIN/SW1
OC1
OC1
OUT1
OUT1
OUT2
OC2
EN1
SW2
EN2
GND
LDO
LDO_OUT
OUT2
OC2
LDO_EN
EN2
EN1
GND
TPS2149/59
MSOP−8
TPS2148/58
MSOP−8
LDO_OUT
VIN
LDO
LDO_OUT
OUT2
OUT1
EN1
OUT1
OC
OUT2
EN2
GND
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
PowerPAD is a trademark of Texas Instruments.
!"#$% ! & '("") % $& ! *(+, '$% ! -$%)
"!-('%& '! !"# %! &*)' '$% ! & *)" %.) %)"#& ! )/$& &%"(#) %&
&%$ -$"- 0$""$ %1
"!-('% ! *"!')&& 2 -!)& !% )')&&$" ,1 ',(-)
%)&% 2 ! $,, *$"$#)%)"&
Copyright 2001, Texas Instruments Incorporated
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1
SLVS401 − AUGUST 2001
AVAILABLE OPTIONS
TA
PACKAGE
AND PIN
COUNT
DESCRIPTION
−40°C to 85°C
PACKAGED DEVICES
ACTIVE LOW
(SWITCH)
ACTIVE HIGH
(SWITCH)
Adjustable LDO with LDO enable
TSSOP-14
TPS2145IPWP
TPS2155IPWP
3.3-V fixed LDO
MSOP-10
TPS2147IDGQ
TPS2157IDGQ
3.3-V Fixed LDO with LDO enable and LDO output
switch
MSOP-8
TPS2148IDGN
TPS2158IDGN
3.3-V Fixed LDO, shared input with switches
MSOP-8
TPS2149IDGN
TPS2159IDGN
NOTE: All options available taped and reeled. Add an R suffix (e.g. TPS2145IPWPR)
TPS2149, TPS2159
MSOP (DGN) PACKAGE
(TOP VIEW)
OUT1
VIN
LDO_OUT
OUT2
1
8
2
7
3
6
4
5
EN1†
EN2†
OC
GND
† Pins 7 and 8 are active high for TPS2159.
absolute maximum ratings over operating free-air temperature (unless otherwise noted)†
Input voltage range: VI(VIN),VI(ENx), . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . −0.3 V to 6 V
Output voltage range: VO(OUTx), VO(LDO_OUT), VO(OC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . −0.3 V to 6 V
Maximum output current, IO(OC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ±10 mA
Continuous output current, IO(OUT), IO(LDO_OUT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Internally limited
Continuous total power dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . See Dissipation Rating Table
Operating virtual-junction temperature range, TJ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . −40°C to 110°C
Storage temperature range, Tstg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . −65°C to 150°C
Lead temperature soldering 1,6 mm (1/16 inch) from case for 10 seconds . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260°C
Electrostatic discharge (ESD) protection: Human body model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 kV
Charged device model (CDM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 kV
† 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 under “recommended operating conditions” is not
implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
‡ All voltages are with respect to GND.
DISSIPATION RATING TABLE
2
PACKAGE
TA ≤ 25°C
POWER RATING
DERATING FACTOR
ABOVE TA = 25°C
TA = 70°C
POWER RATING
TA = 85°C
POWER RATING
MSOP8
1455.5 mW
17.1 mW/°C
684.9 mW
428.08 mW
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SLVS401 − AUGUST 2001
recommended operating conditions
VI(VIN)
VI(ENx)
Input voltage
Continuous output current, IO
Output current limit, IO(LMT)
MIN
MAX
2.9
5.5
0
5.5
LDO_OUT
200
OUT1, OUT2
150
UNIT
V
mA
LDO_OUT
250
450
OUT1, OUT2
200
400
−40
100
°C
MAX
UNIT
VI(ENx) = 5 V (inactive),
VO(LDO_OUT) = no load,
VO(OUTx) = no load
100
µA
VI(ENx) = 5 V (inactive),
VO(LDO_OUT) = no load,
VO(OUTx) = 0 V
(measured from outputs to
ground)
1
µA
ENx = on (active)
150
µA
ENx = off (inactive)
100
µA
MAX
UNIT
Operating virtual-junction temperature range, TJ
mA
electrical characteristics over recommended operating junction-temperature range,
2.9 V ≤ VI(VIN) ≤ 5.5 V, TJ = −40°C to 100°C (unless otherwise noted)
general
PARAMETER
TEST CONDITIONS
Off-state supply current
VI(VIN) = 5 V
Forward leakage current (power
switches only)
II
Total input current at VIN
VI(VIN) = 5 V,
No load on OUTx,
No load on LDO_OUT
MIN
TYP
power switches
PARAMETER
rDS(on)
Ilkg(R)
IOS
Static drain-source
on-state resistance,
VIN to OUTx
Reverse leakage current at OUTx
TEST CONDITIONS
MIN
TYP
IO(LDO_OUT) = 200 mA,
IOUT1 and IOUT2 = 150 mA, TJ = −40°C to 100°C
680
mΩ
IO(LDO_OUT) = 200 mA,
IOUT1 and IOUT2 = 150 mA, TJ = 25°C
VO(OUTx) = 5 V
340
VI(ENx) = 5 V, VI(ENx) = 0 V,
VI(VIN) = 5 V
10
VI(ENx) = 5 V, VI(ENx) = 0 V,
VI(VIN) = 2.9 V
10
VI(ENx) = 5 V, VI(ENx) = 0 V,
VI(VIN) = 0 V
10
µA
Short circuit output current
OUTx connected to GND, device enabled into short
circuit
Delay time for asserting OC flag
From IOUTx at 95% of current limit level to 50% OC.
5.5
ms
Delay time for deasserting OC flag
From IOUTx at 95% of current limit level to 50% OC.
10.5
ms
0.2
0.4
A
NOTE 1: Specified by design, not tested in production.
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3
SLVS401 − AUGUST 2001
electrical characteristics over recommended operating junction-temperature range,
2.9 V ≤ VI(VIN) ≤ 5.5 V, TJ = −40°C to 100°C (unless otherwise noted)
timing parameters, power switches
PARAMETER
TEST CONDITIONS
ton
Turnon time, OUTx switch, (see Note 1)
CL = 100 µF
CL = 1 µF
RL = 33 Ω
toff
Turnoff time, OUTx switch (see Note 1)
CL = 100 µF
CL = 1 µF
RL = 33 Ω
tr
Rise time, OUTx switch (see Note 1)
tf
CL = 100 µF
CL = 1 µF
CL = 100 µF
Fall time, OUTx switch (see Note 1)
CL = 1 µF
RL = 33 Ω
RL = 33 Ω
MIN
TYP
MAX
0.5
6
0.1
3
5.5
10
0.05
2
0.5
5
0.1
2
5.5
9
0.05
1.2
UNIT
ms
NOTE 1. Specified by design, not tested in production.
undervoltage lockout at VIN
PARAMETER
TEST CONDITIONS
UVLO Threshold
MIN
TYP
2.2
Hysteresis (see Note 1)
MAX
2.85
260
Deglitch (see Note 1)
UNIT
V
mV
µs
50
NOTE 1. Specified by design, not tested in production.
electrical characteristics over recommended operating junction-temperature range,
2.9 V ≤ VI(VIN) ≤ 5.5 V, VI(ENx) = 0 V, VI(LDO_EN) = 5 V, CL(LDO_OUT) = 10 µF, TJ = −40°C to 100°C
(unless otherwise noted)
3.3 V LDO
PARAMETER
VO
TEST CONDITIONS†
Output voltage, dc
VI(VIN) = 4.25 V to 5.25 V,
IO(LDO_OUT) = 0.5 mA to 200 mA
Dropout voltage
VI(VIN) = 3.2 V, IO(OUT1) = 150 mA,
IO(LDO_OUT) = 200 mA
Line regulation voltage (see Note 1)
Load regulation voltage (see Note 1)
IOS
Short-circuit current limit
Ilkg(R)
Reverse leakage current into
LDO_OUT
MIN
TYP
MAX
UNIT
3.20
3.3
3.40
V
0.35
V
0.1
%/V
VI(VIN) = 4.25 V to 5.25 V, IO(LDO_OUT) = 5 mA
VI(VIN) = 4.25 V, IO(LDO_OUT) = 5 mA to 200 mA
VI(VIN) = 4.25 V, LDO_OUT connected to GND
VO(LDO_OUT) = 3.3 V, VI(IN) = 0 V
0.275
0.4
1%
0.33
0.55
A
10
µA
VO(LDO_OUT) = 5.5 V, VI(IN) = 0 V
10
µA
Power supply rejection
f = 1 kHz, CL(LDO_OUT) = 4.7 µF, ESR = 0.25 Ω,
IO = 5 mA, VINp−p = 100 mV
50
dB
Ramp-up time, LDO_OUT (0% to 90%)
VIN ramping up from 10% to 90% in 0.1 ms,
RL = 16 Ω, CL(LDO_OUT) = 10 µF
0.1
1
ms
† Pulse-testing techniques maintain junction temperature close to ambient temperature; thermal effects must be taken into account separately.
NOTES: 1. Specified by design, not tested in production.
4
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SLVS401 − AUGUST 2001
electrical characteristics over recommended operating junction-temperature range,
2.9 V ≤ VI(VIN) ≤ 5.5 V, VI(ENx) = 0 V, TJ = −40°C to 100°C (unless otherwise noted)
enable input, ENx (active low)
PARAMETER
VIH
VIL
High-level input voltage
II
Input current, pullup (source)
TEST CONDITIONS
MIN
TYP
MAX
2
UNIT
V
Low-level input voltage
VI(ENx) = 0 V
0.8
V
5
µA
enable input, ENx (active high)
PARAMETER
VIH
VIL
High-level input voltage
II
Input current, pulldown (sink)
TEST CONDITIONS
MIN
TYP
MAX
2
UNIT
V
Low-level input voltage
VI(ENx) = 5 V
0.8
V
5
µA
logic output, OC
PARAMETER
TEST CONDITIONS
Current sinking at VO = 0.4 V
MIN
TYP
MAX
1
UNIT
mA
thermal shutdown characteristics
PARAMETER
First thermal shutdown (shuts down switch or regulator
in overcurrent)
TEST CONDITIONS
Occurs at or above specified temperature
when overcurrent is present.
Recovery from thermal shutdown
Second thermal shutdown (shuts down all switches and
regulator)
MIN
TYP
Second thermal shutdown hysteresis
UNIT
120
110
Occurs on rising temperature, irrespective of
overcurrent.
MAX
°C
155
10
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5
SLVS401 − AUGUST 2001
TPS2149 functional block diagram
3.3 V / 200 mA
LDO
VIN
LDO_OUT
CS
Charge
Pump
OUT1
Current
Limit
Driver
OC
EN1
Thermal
Sense
OUT2
CS
Current
Limit
Driver
EN2
Thermal
Sense
GND
Terminal Functions
TERMINAL
NAME
NO.
TPS2149
EN1
EN1
I/O
DESCRIPTION
TPS2159
8
I
Logic level enable to transfer power to OUT1
7
I
Logic level enable to transfer power to OUT2
8
EN2
EN2
7
GND
5
5
LDO_OUT
3
3
O
LDO output
OC
6
6
O
Overcurrent status flag for OUT1 and OUT2. Open drain output.
OUT1
1
1
O
Switch 1 output
OUT2
4
4
VIN
2
2
6
Ground
Switch 2 output
I
Input for LDO switch 1 and switch 2; device supply voltage
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SLVS401 − AUGUST 2001
detailed description
VIN
The VIN serves as the input to the internal LDO and as the input to both N-channel MOSFETs. The 3.3-V LDO
has a dropout voltage of 0.35 V and is rated for 200 mA of continuous current. The power switches are N-channel
MOSFETs with a maximum on-state resistance of 580 mΩ per switch. Configured as high-side switches, the
power switches prevent current flow from OUT to IN and IN to OUT when disabled. The power switches are rated
at 150 mA, continuous current.
OUTx
OUT1 and OUT2 are the outputs from the internal power-distribution switches.
LDO_OUT
LDO_OUT is the output of the internal 200-mA LDO.
enable (ENx, ENx)
The logic enable disables the power switch. Both switches have independent enables and are compatible with
both TTL and CMOS logic.
overcurrent (OC)
The OC open drain output is asserted (active low) when an overcurrent or overtemperature condition is
encountered. The output will remain asserted until the overcurrent or overtemperature condition is removed.
current sense
A sense FET monitors the current supplied to the load. Current is measured more efficiently by the sense FET
than by conventional resistance methods. When an overload or short circuit is encountered, the current-sense
circuitry sends a control signal to the driver. The driver in turn reduces the gate voltage and drives the power
FET into its saturation region, which switches the output into a constant-current mode and holds the current
constant while varying the voltage on the load.
thermal sense
A dual-threshold thermal trip is implemented to allow fully independent operation of the power distribution
switches. In an overcurrent or short-circuit condition, the junction temperature rises. When the die temperature
rises to approximately 120°C, the internal thermal sense circuitry determines which power switch is in an
overcurrent condition and turns off that switch, thus isolating the fault without interrupting operation of the
adjacent power switch. Because hysteresis is built into the thermal sense, the switch turns back on after the
device has cooled approximately 10 degrees. The switch continues to cycle off and on until the fault is removed.
undervoltage lockout
A voltage sense circuit monitors the input voltage. When the input voltage is below approximately 2.5 V, a control
signal turns off the power switch.
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SLVS401 − AUGUST 2001
PARAMETER MEASUREMENT INFORMATION
50%
VI(ENx)
50%
tpd(off)
ton
toff
tpd(on)
90%
VO(OUTx)
90%
10%
10%
tr
tf
90%
VO(OUTx)
90%
10%
10%
TIMING
Figure 1. Timing and Internal Voltage Regulator Transition Waveforms
TYPICAL CHARACTERISTICS
SWITCH TURNON DELAY AND RISE TIME
WITH 1-µF LOAD
SWITCH TURNOFF DELAY AND FALL TIME
WITH 1-µF LOAD
VI(EN)
(5 V/div)
VI(EN)
(5 V/div)
VO(OUT)
(2 V/div)
VO(OUT)
(2 V/div)
VI = 5 V
TA = 25°C
CL = 1 µF
RL = 25 Ω
VI = 5 V
TA = 25°C
CL = 1 µF
RL = 25 Ω
0
0.4
0.8 1.2
1.6 2 2.4 2.8
t − Time − ms
3.2
3.6
4.2
Figure 2
8
0
0.4
0.8 1.2
1.6 2 2.4 2.8
t − Time − ms
Figure 3
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3.2
3.6
4.2
SLVS401 − AUGUST 2001
TYPICAL CHARACTERISTICS
SWITCH TURNOFF DELAY AND FALL TIME
WITH 120-µF LOAD
SWITCH TURNON DELAY AND RISE TIME
WITH 120-µF LOAD
VI(EN)
(5 V/div)
VI(EN)
(5 V/div)
VO(OUT)
(2 V/div)
VO(OUT)
(2 V/div)
VI = 5 V
TA = 25°C
CL = 120 µF
RL = 25 Ω
VI = 5 V
TA = 25°C
CL = 120 µF
RL = 25 Ω
0
2
4
6
8 10 12 14
t − Time − ms
16
18
0
20
4
Figure 4
8
12
16 20 24 28
t − Time − ms
32
36
40
Figure 5
SHORT-CIRCUIT CURRENT, SWITCH
ENABLED INTO A SHORT
LDO TURNON DELAY AND RISE TIME
WITH 4.7-µF LOAD
VI(EN)
(5 V/div)
VI = 5 V
TA = 25°C
CL = 4.7 µF
RL = 13.2 Ω
VI(LDO_EN)
(5 V/div)
VO(LDO_OUT)
(1 V/div
IO(OUT)
(100 mA/div)
0
1
2
3
4
5
6
t − Time − ms
7
8
9
10
Figure 6
0
0.4
0.8 1.2
1.6 2 2.4 2.8
t − Time − ms
3.2
3.6 4.2
Figure 7
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SLVS401 − AUGUST 2001
TYPICAL CHARACTERISTICS
LOAD TRANSIENT RESPONSE
LINE TRANSIENT RESPONSE
IO(LDO_OUT)
5.25 V
VI(VIN)
4.25 V
(200 mA/div)
∆VO(LDO_OUT)
(100 mV/div)
∆VO(LDO_OUT)
(0.05 V/div)
TA = 25°C
CL(LDO_OUT) = 4.7 µF
ESR = 1 Ω
IO(LDO_OUT) = 200 mA
0
TA = 25°C
CL(LDO_OUT) = 4.7 µF
ESR = 1 Ω
0
100 200 300 400 500 600 700 800 900 1000
t − Time − µs
100 200 300 400 500 600 700 800 900 1000
t − Time − µs
Figure 9
Figure 8
SUPPLY CURRENT
vs
SUPPLY VOLTAGE
140
140
120
120
I DD − Supply Current − µ A
I DD − Supply Current − µ A
SUPPLY CURRENT
vs
JUNCTION TEMPERATURE
100
80
60
40
−20
0
20
40
60
80
100
TJ − Temperature − °C
Figure 10
10
80
60
40
20
20
0
−40
100
0
2.5
3
3.5
4
4.5
VCC − Supply Voltage − V
Figure 11
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5
5.5
SLVS401 − AUGUST 2001
rDS(on) − Static Drain-Source On-State Resistance − Ω
STATIC DRAIN-SOURCE ON-STATE RESISTANCE
vs
JUNCTION TEMPERATURE
0.6
0.55
0.5
0.45
SW1
0.4
SW2
0.35
0.3
0.25
0.2
0.15
0.1
−40
−20
0
20
40
60
80
TJ − Junction Temperature − °C
100
rDS(on) − Static Drain-Source On-State Resistance − Ω
TYPICAL CHARACTERISTICS
STATIC DRAIN-SOURCE ON-STATE RESISTANCE
vs
SUPPLY VOLTAGE
0.38
0.37
0.36
0.35
SW1
0.34
SW2
0.33
0.32
0.31
0.3
2.5
3
Figure 12
380
380
360
360
Short Circuit Current − mA
Short Circuit Current − mA
400
340
320
SW1
280
SW2
260
5
5.5
340
320
SW1
300
280
240
220
220
0
20
40
60
80
TJ − Free-Air Temperature − °C
100
Figure 14
SW2
260
240
−20
5.5
SHORT CIRCUIT CURRENT
vs
SUPPLY VOLTAGE
400
200
−40
5
Figure 13
SHORT CIRCUIT CURRENT
vs
JUNCTION TEMPERATURE
300
3.5
4
4.5
VCC − Supply Voltage
200
2.5
3
3.5
4
4.5
VCC − Supply Voltage
Figure 15
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SLVS401 − AUGUST 2001
TYPICAL CHARACTERISTICS
UNDERVOLTAGE LOCKOUT
vs
JUNCTION TEMPERATURE
2.9
UVLO − Undervoltage Lockout − V
2.8
Rising
2.7
2.6
2.5
Falling
2.4
2.3
2.2
2.1
−40 −25 −10
5 20 35 50 65 80
TJ − Junction Temperature − °C
95 110
Figure 16
APPLICATION INFORMATION
external capacitor requirements on power lines
A ceramic bypass capacitor (0.01-µF to 0.1-µF) between VIN and GND, close to the device, is recommended
to improve load transient response and noise rejection.
A bulk capacitor (4.7-µF ) between VIN and GND is also recommended, especially if load transients in the
hundreds of milliamps with fast rise times are anticipated.
A 66-µF bulk capacitor is recommended from OUTx to ground, especially when the output load is heavy. This
precaution helps reduce transients seen on the power rails. Additionally, bypassing the outputs with a 0.1-µF
ceramic capacitor improves the immunity of the device to short-circuit transients.
LDO output capacitor requirements
Stabilizing the internal control loop requires an output capacitor connected between LDO_OUT and GND. The
minimum recommended capacitance is a 4.7 µF with an ESR value between 200 mΩ and 10 Ω. Solid tantalum
electrolytic, aluminum electrolytic, and multilayer ceramic capacitors are all suitable, provided they meet the
ESR requirements.
overcurrent
A sense FET is used to measure current through the device. Unlike current-sense resistors, sense FETs do not
increase the series resistance of the current path. When an overcurrent condition is detected, the device
maintains a constant output current. Complete shut down occurs only if the fault is present long enough to
activate thermal limiting.
Three possible overload conditions can occur. In the first condition, the output is shorted before the device is
enabled or before VIN has been applied. The TPS2149 and TPS2159 sense the short and immediately switches
to a constant-current output.
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SLVS401 − AUGUST 2001
APPLICATION INFORMATION
overcurrent (continued)
In the second condition, the short occurs while the device is enabled. At the instant the short occurs, very high
currents may flow for a very short time before the current-limit circuit can react. After the current-limit circuit has
tripped (reached the overcurrent trip threshold), the device switches into constant-current mode.
In the third condition, the load has been gradually increased beyond the recommended operating current. The
current is permitted to rise until the current-limit threshold is reached or until the thermal limit of the device is
exceeded. The TPS2149 and TPS2159 are capable of delivering current up to the current-limit threshold without
damaging the device. Once the threshold has been reached, the device switches into its constant-current mode.
OC response
The OC open-drain output is asserted (active low) when an overcurrent condition is encountered. The output
will remain asserted until the overcurrent condition is removed. Connecting a heavy capacitive load to an
enabled device can cause momentary false overcurrent reporting from the inrush current flowing through the
device, charging the downstream capacitor. The TPS2149 and TPS2159 are designed to reduce false
overcurrent reporting. An internal overcurrent transient filter eliminates the need for external components to
remove unwanted pulses. Using low-ESR electrolytic capacitors on OUTx lowers the inrush current flow through
the device during hot-plug events by providing a low-impedance energy source, also reducing erroneous
overcurrent reporting.
power dissipation and junction temperature
The main source of power dissipation for the TPS2149 and TPS2159 comes from the internal voltage regulator
and the N-channel MOSFETs. Checking the power dissipation and junction temperature is always a good
design practice and it starts with determining the rDS(on) of the N-channel MOSFET according to the input voltage
and operating temperature. As an initial estimate, use the highest operating ambient temperature of interest and
read rDS(on) from the graphs shown in the Typical Characteristics section of this data sheet. Using this value,
the power dissipation per switch can be calculated using:
P D + r DS(on)
I2
(1)
Multiply this number by two to get the total power dissipation coming from the N-channel MOSFETs.
The power dissipation for the internal voltage regulator is calculated using:
ǒ
P D + V –V
I O(min)
Ǔ
I
O
(2)
The total power dissipation for the device becomes:
P D(total) + P
D(voltage regulator)
ǒ
) 2
P
D(switch)
Ǔ
(3)
Finally, calculate the junction temperature:
TJ + PD
R qJA ) T A
(4)
Where:
TA = Ambient temperature °C
RθJA = Thermal resistance °C/W, equal to inverting the derating factor found on the power dissipation
table in this datasheet.
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13
SLVS401 − AUGUST 2001
APPLICATION INFORMATION
Compare the calculated junction temperature with the initial estimate. If they do not agree within a few degrees,
repeat the calculation, using the calculated value as the new estimate. Two or three iterations are generally
sufficient to get a reasonable answer.
thermal protection
Thermal protection prevents damage to the IC when heavy-overload or short-circuit faults are present for
extended periods of time. The faults force the TPS2149 and TPS2159 into constant-current mode at first, which
causes the voltage across the high-side switch to increase; under short-circuit conditions, the voltage across
the switch is equal to the input voltage. The increased dissipation causes the junction temperature to rise to high
levels.
The protection circuit senses the junction temperature of the switch and shuts it off. Hysteresis is built into the
thermal sense circuit, and after the device has cooled approximately 10 degrees, the switch turns back on. The
switch continues to cycle in this manner until the load fault or input power is removed.
The TPS2149 and TPS2159 implement a dual thermal trip to allow fully independent operation of the power
distribution switches. In an overcurrent or short-circuit condition the junction temperature will rise. Once the die
temperature rises to approximately 120°C, the internal thermal sense circuitry checks which power switch is
in an overcurrent condition and turns that power switch off, thus isolating the fault without interrupting operation
of the adjacent power switch. Should the die temperature exceed the first thermal trip point of 120°C and reach
155°C, the device will turn off.
undervoltage lockout (UVLO)
An undervoltage lockout ensures that the device (LDO and switches) is in the off state at power up. The UVLO
will also keep the device from being turned on until the power supply has reached the start threshold (see
undervoltage lockout table), even if the switches are enabled. The UVLO will also be activated whenever the
input voltage falls below the stop threshold as defined in the undervoltage lockout table. This facilitates the
design of hot-insertion systems where it is not possible to turn off the power switches before input power is
removed. Upon reinsertion, the power switches will be turned on with a controlled rise time to reduce EMI and
voltage overshoots.
universal serial bus (USB) applications
The universal serial bus (USB) interface is a multiplexed serial bus operating at either 12 Mb/s, or 1.5 Mb/s for
USB 1.1, or 480 Mb/s for USB 2.0. The USB interface is designed to accommodate the bandwidth required by
PC peripherals such as keyboards, printers, scanners, and mice. The four-wire USB interface was conceived
for dynamic attach-detach (hot plug-unplug) of peripherals. Two lines are provided for differential data, and two
lines are provided for 5-V power distribution.
USB data is a 3.3-V level signal, but power is distributed at 5 V to allow for voltage drops in cases where power
is distributed through more than one hub or across long cables. Each function must provide its own regulated
3.3 V from the 5-V input or its own internal power supply.
The USB specification defines the following five classes of devices, each differentiated by power-consumption
requirements:
•
•
•
•
•
14
Hosts/self-powered hubs (SPH)
Bus-powered hubs (BPH)
Low-power, bus-powered functions
High-power, bus-powered functions
Self-powered functions
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SLVS401 − AUGUST 2001
APPLICATION INFORMATION
universal serial bus (USB) applications (continued)
The TPS2149 and TPS2159 are well suited for USB bus-powered hub applications. The internal LDO can be
used to provide the 3.3 V power needed by the controller while the dual switches distribute power to the
downstream functions.
USB power distribution requirements
USB can be implemented in several ways, and, regardless of the type of USB device being developed, several
power-distribution features must be implemented.
•
Hosts/self-powered hubs must:
−
−
Current-limit downstream ports
Report overcurrent conditions on USB VBUS
D Bus-powered hubs must:
−
−
−
Enable/disable power to downstream ports
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