Application Note - NXP Semiconductors

AN10361
Philips BISS loadswitch solutions and the SOT666 BISS
loadswitch demo board
Rev. 01.00 — 20 June 2005
Application note
Document information
Info
Content
Keywords
BISS, loadswitch, high side switch, supply line switch, SOT666, low
VCEsat, RET
Abstract
This application note describes the Philips BISS loadswitch solutions
using improved bipolar technology and the SOT666 BISS loadswitch
demo board, complemented by selected measurement results.
AN10361
Philips Semiconductors
BISS loadswitch solutions
Revision history
Rev
Date
Description
<01>
<20050620>
Initial document
Contact information
For additional information, please visit: http://www.semiconductors.philips.com
For sales office addresses, please send an email to: sales.addresses@www.semiconductors.philips.com
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Application note
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
Rev. 01.00 — 20 June 2005
2 of 12
AN10361
Philips Semiconductors
BISS loadswitch solutions
1. Introduction
After the introduction into different loadswitch solutions the demo board will be described
and measurement results will be provided to allow the designer a more detailed view to
the loadswitch performance.
The SOT666 BISS loadswitch demo board is intended to be used for evaluation purpose
of the PBLS1501V – PBLS1503V and PBLS4001V – PBLS4003V BISS Loadswitches in
the SOT666 package.
Evaluation results can also be used for the PBLS1501Y – PBLS1503Y and PBLS4001Y
– PBLS4003Y BISS loadswitches in SOT363 (SC-88) due to the same electrical and
thermal specification and internal die construction.
2. The loadswitch circuit
A loadswitch – also referred to as high side switch or supply line switch – switches a
supply voltage to a load or a supply line. It is used to drive fans, relays or motors, to
switch sub-circuits like a mobile phone camera module or to build a voltage sequencing
circuit. A digital signal switches the load switch ON or OFF.
There are four alternatives to realize a loadswitch circuit as Fig 1 – Fig 4 show.
Fig 1. This loadswitch circuit uses bipolar transistors
Fig 2. Alternative circuit with a control N-MOSFET
Fig 3. Alternative circuit with a pass P-MOSFET
Fig 4. Alternative “pure” MOSFET solution
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Application note
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AN10361
Philips Semiconductors
BISS loadswitch solutions
The loadswitch circuit in Fig 1 consists of six components and uses bipolar transistors. If
a positive voltage is applied to the base of the control transistor Tr2 through R1, it
switches the pass transistor Tr1. A small base current of about a Milliampere switches up
to a few Amperes. The voltage drop across collector and emitter of the pass transistor
can be influenced by its base resistor R3. The lower R3, the higher Tr1’s base current
and the lower the voltage drop, i.e. the saturation voltage. But, the higher the base
current and the higher the input voltage the higher the power dissipation of this circuit,
mostly through R3.
Fig 2 - Fig 4 show circuit alternatives using MOSFET(s). Depending on cost and
performance requirements each alternative has its advantages and disadvantages as
Table 1: explains. Compared to MOSFET pass transistor alternatives the major
advantage of solutions with a bipolar pass transistor are the far lower costs, the major
disadvantage the higher power dissipation particularly for input voltages above 5 V due
to the required base current for Tr1 (Ptot = PC = Pdrive = VCEsat x IC + Vin x IB). The PMOSFET circuits are the most expensive ones and typically require an additional Zener
diode for ESD protection.
Table 1:
Cost and performance requirements determine the selection of loadswitch components
Pass transistor
Control transistor
PNP bipolar
NPN bipolar
PNP bipolar
N-MOSFET
P-MOSFET
NPN bipolar
P-MOSFET
N-MOSFET
Reference figure
Fig 1
Fig 2
Fig 3
Fig 4
Cost
+ cheap pass
transistor
+ cheap control
transistor
+ cheap pass
transistor
- expensive control
transistor
- expensive pass
transistor
+ cheap control
transistor
- expensive pass
transistor
- expensive control
transistor
Power dissipation
- fair
- fair
+ low
+ low
Control input current
• low
+ no
• low
+ no
Threshold voltage
+ low
- high
+ low
- high
Reverse blocking
+ yes
+ yes
- no
- no
ESD sensitive
+ no
+ no
- yes
- yes
3. Bipolar transistor products for loadswitch applications
Philips offers a wide variety of product alternatives to realize a loadswitch allowing to
build a discrete, a partly integrated or a fully integrated solution.
The widest flexibility and lowest voltage drop provides the discrete solution. The
availability of various low VCEsat (BISS) transistors1 (PBSS-series) enables to select the
best fitting transistor for the application. To limit the higher number of components the
use of resistor-equipped transistors (RETs, PDTC-, PDTD-series) is recommended.
These are standard transistors with built-in resistors making external resistors R1 and R2
obsolete.
If the current to be switched is less than 100 mA and if there are no tight voltage drop
requirements the number of components can be reduced to one if a double NPN/PNP
RETs (PIMD-, PUMD-, PEMD-series) is used. The circuit parameter can be set be
selecting the most appropriate type out of 13 different combinations of resistance values.
1.
see also AN10116 “Breakthrough In Small Signal - Low VCEsat (BISS) Transistors and their Applications”
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Application note
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AN10361
Philips Semiconductors
BISS loadswitch solutions
A partly integrated solution features a low voltage drop and a reduced number of
components. The BISS loadswitch contains a PNP low VCEsat (BISS) transistor as pass
transistor and a NPN resistor-equipped transistor as control transistor in a 6pin package.
The current portfolio (June 2005) includes 0.5 A and 1 A types with different breakdown
voltages to meet different application requirements (e.g. VCEO = 60 V for automotive
applications) and different integrated resistors to set the control transistor’s base current
depending on the control input voltage. An external resistor (R3) is used to set the base
current of the pass transistor. The voltage drop (= transistor’s saturation voltage)
decreases with increasing base current, whereas the power dissipation of the loadswitch
circuit increases.
Table 2: summarizes the three alternatives of realizing a bipolar loadswitch circuit.
Table 2:
The partly integrated solution features a low voltage drop while the number of components could be
reduced.
Solution
Discrete
Partly integrated
Fully integrated
Component count
4–6
2–3
1
Voltage drop
very low
low
higher
Flexibility
broadest portfolio
ability to balance low saturation
voltage vs. low base current
large number of available types
to meet application requirements
Collector current (IC)
0.5 – 5 A
0.5 – 1 A
100 mA
Breakdown voltage
(VCEO)
15 – 100 V
15 – 60 V
50 V
Types
PBSS-series (pass transistor)
PDTC-, PDTD-series (control
transistor)
PBLS-series
PIMD-, PUMD-, PEMD-series
4. The SOT666 BISS loadswitch demo board
The SOT666 BISS loadswitch demo board contains six loadswitch circuits as shown in
Fig 5 – Fig 7. Each of the six circuits contains the BISS loadswitch Q – which includes
the PNP pass transistor, the NPN control transistor and its two associated resistors – and
two resistors R1 and R2 in size 0603. Additional space is given for optional 1206 sized
input and output capacitors C1 and C2. The top row contains the 15 V types PBLS1501V
through PBLS1503V whereas the bottom row is assembled with the 40 V types
PBLS4001V through PBLS4003V. The difference between PBLSxx01V – PBLSxx03V
types is the value of the internal resistors of the control transistor.
Table 3: contains the bill of material for the full board.
The connection of the demo board is done by soldering wires from the related pad to the
application circuit or test setup.
Grooves allow to break the circuit into single loadswitch circuits which simplifies their use
in the final application.
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Application note
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
Rev. 01.00 — 20 June 2005
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AN10361
Philips Semiconductors
BISS loadswitch solutions
Fig 5. The SOT666 BISS loadswitch demo board
Fig 6. Demo board layout
Fig 7. Demo board circuit
Table 3:
Bill of materials
Part reference
Qty Type, Value
Package
Vendor
Remark
Q
1
PBLS1501V (2k2 / 2k2)
SOT666
Philips
1
PBLS1502V (4k7 / 4k7)
Counted from the top
left to the bottom right
1
PBLS1503V (10k / 10k)
1
PBLS4001V (2k2 / 2k2)
1
PBLS4002V (4k7 / 4k7)
1
PBLS4003V (10k / 10k)
R1
1
220R
0603[1]
R2
1
10k
0603
C1, C2
[1]
1206
not mounted
Note: R1 of the bottom right loadswitch circuit is 1206 sized to improve power dissipation capability
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BISS loadswitch solutions
5. Measurement results
This chapter discusses selected test results. Measurements were done for the 40 V-type
PBLS4001V and the 15 V-type PBLS1501V. The internal resistance values are 2.2 kΩ
for both types. Opposed to the demo board configuration described above, R1 was set to
100 Ω, 220 Ω and 470 Ω, respectively. R2 was kept open. Table 4: through Table 6:
contain the measured values. The following paragraphs reflect the outcome.
BISS loadswitches with a lower breakdown voltage (VCEO) feature a lower voltage drop
and power dissipation. Comparing the 40 V PBLS4001V and the 15 V PBLS1501V
(Table 4: and Table 6:) results in VCEsat = 214 mV, PC = 88 mW compared to
VCEsat = 127 mV, PC = 52 mW of the latter one. As a guidance the user should select the
lowest possible VCEO value.
The lower the forced current gain IC/IB the lower the voltage drop VCEsat. Table 5:
exemplarily shows that VCEsat decreases from 159 mV to 127 mV if IC/IB decreases from
46 to 10. In turn, the circuit needs more drive power (Pdrive = Vin x IB) which reduces the
efficiency. As a consequence the user needs to balance voltage drop and acceptable
power dissipation by selecting R1. If the Vdrop requirement can not be met by using a
500 mA BISS loadswitch the 1 A versions in SOT457 (SC-74) with lower saturation
voltage values might be an alternative (see Table 7: below).
The collector-emitter saturation resistance depends on the collector current. Opposed to
the RDS(on) of MOSFETs the RCEsat of bipolar transistors depends on the collector current.
This can be seen in Table 6: where RCEsat decreases with increasing collector current
operating with constant forced current gain IC/IB.
The total power dissipation sums up from drive and collector power dissipation. As Fig 9
shows the total power dissipation Ptot can be reduced by reducing the drive power
dissipation Pdrive, i.e. the PNP transistor’s base current. However, the saturation voltage
increase – indicated by the increasing collector power dissipation PC – must be watched
to meet the Vdrop requirement. If the 500 mA PBLS-series is not sufficient, check the 1 A
PBLS-series (see Table 7: below).
Vdrop = VCEsat
mW
300
IB
250
200
150
Pdrive
100
Rint
PC
50
0
100R
Rint
Fig 8. Parameter definition for chapter 5
470R
PBLS1501V
Fig 9. Total power dissipation as a result of drive
power dissipation Pdrive and collector power
dissipation PC
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© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
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AN10361
Philips Semiconductors
BISS loadswitch solutions
Table 4:
PBLS4001V, IC/IB = constant
VCEO = 40 V, Rint = 2.2 kΩ, R2 = open
IC
VCEsat
RCEsat
IB
IC/IB
R1
PC
Ptot
412 mA
214 mV
519 Ω
41 mA
10
100 Ω
88 mW
293 mW
232 mA
133 mV
573 Ω
19 mA
12
220 Ω
31 mW
126 mW
105 mA
72 mV
686 Ω
9 mA
11
470 Ω
8 mW
53 mW
Table 5:
PBLS1501V, IC = constant
VCEO = 15 V, Rint = 2.2 kΩ, R2 = open
IC
VCEsat
RCEsat
IB
IC/IB
R1
PC
Ptot
412 mA
127 mV
308 Ω
41 mA
10
100 Ω
52 mW
257 mW
412 mA
140 mV
340 Ω
19 mA
22
220 Ω
58 mW
153 mW
412 mA
159 mV
386 Ω
9 mA
46
470 Ω
66 mW
111 mW
Table 6:
PBLS1501V, IC/IB = constant
VCEO = 15 V, Rint = 2.2 kΩ, R2 = open
IC
VCEsat
RCEsat
IB
IC/IB
R1
PC
Ptot
412 mA
127 mV
308 Ω
41 mA
10
100 Ω
52 mW
257 mW
232 mA
77 mV
332 Ω
19 mA
12
220 Ω
18 mW
113 mW
105 mA
39 mV
371 Ω
9 mA
12
470 Ω
4 mW
49 mW
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BISS loadswitch solutions
6. Calculating and selecting BISS loadswitches
Typically, there are three application based parameters: Maximum input voltage, switch
current and maximum voltage drop. Further, there might be a limitation for Tr2’s base
current and for the maximum power dissipation of the loadswitch circuit (parameter
definition refers to Fig 1).
Selection criteria:
• VCEO (Tr1) ≥ Vin
determining breakdown voltage (Tr1)
• IC (Tr1) ≥ I
determining collector current (Tr1)
• IB (Tr1) = IC (Tr1) / (IC/IB) (Tr1)
setting base current (Tr1), IC/IB := 10 – 100
• R3 = (Vin - VBEsat (Tr1) - VCEsat (Tr2)) / IB
calculating resulting resistance value (R3)
• PR3 = IB² x R3
calculating resistor’s power dissipation (R3)
• (IC/IB) (Tr2) = IB (Tr1) / IB (Tr2)
IC/IB ≤ 100, transistor saturated?
• R1 = (Vctrl - VBEsat (Tr2)) / IB (Tr2)
calculating base resistor (R1)
The data sheet contains all relevant information like limiting values and VCEsat curves.
Example:
Vin = 5 V; I = 200 mA; Vctrl = 3,3 V; Ictrl = 0,5 mA; Vdrop = 100 mV typical
• VCEO (Tr1) := 15 V
• IC (Tr1) := 0.5 A
Î PBLS15xxV
• IB (Tr1) = 200 mA / 20 = 10 mA
Î IC/IB = 20 sufficient for Vdrop requirement
• R3 = (5 V – 1 V – 0.5 V) / 10 mA = 350 Ω
• PR3 = (10 mA)² x 330 Ω = 33 mW
Î 330 Ω (next lower E24 value), size 0603
• (IC/IB) (Tr2) = 10 mA / 0.5 mA = 20
• R1 = (3.3 V – 0.8 V) / 0.5 mA = 5 kΩ
Î PBLS1502V (R1 = 4.7 kΩ)
This example is based on nominal values and yet disregards parameter spread of the
resistance values and saturation voltage.
Table 7: gives an overview about the released BISS loadswitch types (June 2005).
Table 7:
The BISS loadswitch portfolio contains 0,5 A and 1 A types
IC Tr1
VCEO Tr1
0.5 A
1A
[2]
SOT457
(SC-74)
SOT363
(SC-88)
SOT666
VCEsat
@ IC = 0,5 A
15 V
PBLS15xxY
PBLS15xxV
250 mV
40 V
PBLS40xxY
PBLS40xxV
350 mV
20 V
PBLS20xxD
150 mV
40 V
PBLS40xxD
170 mV
60 V
PBLS60xxD
180 mV
Note: “xx” indicates a sequential number used to distinguish between different internal resistance values
R1 and R2: 01 – 2.2 kΩ, 02 – 4.7 kΩ, 03 – 10 kΩ, 04 – 22 kΩ
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BISS loadswitch solutions
7. Applications for BISS loadswitches
Beside standard applications like a supply line switch (e.g. camera module in a mobile phone)
in Fig 10 or as high side switch (e.g. fan driver in a notebook) in Fig 11 the BISS loadswitches
can be used to realize a voltage selector or a switchable constant current source.
Fig 12 shows a voltage selector which switches either 3.3 V or 5 V to Vout depending on
the logic signal at Vsel as it could be used to manage 3.3 V and 5 V SIM cards. The
voltage drop of both input rails is minimized by applying a BISS loadswitch for the 5 V rail
and a low VF (MEGA) Schottky rectifier2 or a low VF small signal Schottky diode for the
3.3 V rail. If other voltages are used, please note that always the higher voltage needs to
be connected to the Schottky diode.
A generic constant current source is given in Fig 13. R1 sets the current through D1 and
D2, which must be much higher than the base current through Tr1 to achieve an
unloaded voltage divider. R2 is used to set the output current Iout. The output current can
be switched off by connecting Ven to ground.
Relays
or fan
(1) Tr1, Tr2, Rint: 1x PBLS-series
R1:
1x standard resistor
(2) Tr1, Tr2, Rint: 1x PBLS-series
R1:
1x standard resistor
Fig 10. Supply line switch uses only two components
Fig 11. Two component loadswitch
Iout = 0.7 V / R4
(3) Tr1, Tr2, Rint: 1x PBLS-series
D1:
1x PMEG-series or 1x BAT754
R1:
1x standard resistor
Fig 12. Voltage selector needs only three instead of
six single components
2.
(4) Tr1, Tr2, Rint: 1x PBLS-series
D1, D2:
1x BAV99W
R1, R2:
2x standard resistors
Fig 13. Switchable constant current source only requires four instead of eight single components
see also AN10230: “The PMEG1020EA and PMEG2010EA MEGA Schottky diodes – a pair designed
for high efficiency rectification”
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BISS loadswitch solutions
8. Disclaimers
Life support — These products are not designed for use in life support
appliances, devices, or systems where malfunction of these products can
reasonably be expected to result in personal injury. Philips Semiconductors
customers using or selling these products for use in such applications do so
at their own risk and agree to fully indemnify Philips Semiconductors for any
damages resulting from such application.
Right to make changes — Philips Semiconductors reserves the right to
make changes in the products - including circuits, standard cells, and/or
software - described or contained herein in order to improve design and/or
performance. When the product is in full production (status ‘Production’),
relevant changes will be communicated via a Customer Product/Process
Change Notification (CPCN). Philips Semiconductors assumes no
responsibility or liability for the use of any of these products, conveys no
licence or title under any patent, copyright, or mask work right to these
products, and makes no representations or warranties that these products
are free from patent, copyright, or mask work right infringement, unless
otherwise specified.
Application information — Applications that are described herein for any of
these products are for illustrative purposes only. Philips Semiconductors
make no representation or warranty that such applications will be suitable for
the specified use without further testing or modification.
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BISS loadswitch solutions
9. Contents
1.
Introduction .........................................................3
2.
The loadswitch circuit.........................................3
3.
Bipolar transistor products for loadswitch
applications .........................................................4
4.
The SOT666 BISS loadswitch demo board .......5
5.
Measurement results ..........................................7
6.
Calculating and selecting BISS loadswitches ..9
7.
Applications for BISS loadswitches ................10
8.
Disclaimers ........................................................11
9.
Contents.............................................................12
© Koninklijke Philips Electronics N.V. 2005
All rights are reserved. Reproduction in whole or in part is prohibited without the prior
written consent of the copyright owner. The information presented in this document does
not form part of any quotation or contract, is believed to be accurate and reliable and may
be changed without notice. No liability will be accepted by the publisher for any
consequence of its use. Publication thereof does not convey nor imply any license under
patent- or other industrial or intellectual property rights.
Date of release:20 June 2005
Document number: <12NC>
Published in Germany