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TPS40170
SLUS970B – NOVEMBER 2013 – REVISED DECEMBER 2014
TPS40170 4.5 V to 60 V, Wide-Input Synchronous PWM Buck Controller
1 Features
•
•
•
•
•
1
•
•
•
•
•
•
•
•
•
•
•
•
Wide Input Voltage Range from 4.5 V to 60 V
600 mV Reference Voltage with 1% Accuracy
Programmable UVLO and Hysteresis
Voltage Mode Control With Voltage Feed Forward
Programmable Frequency Between 100 kHz and
600 kHz
Bi-directional -Frequency Synchronization With
Master/Slave Option
Low-side FET Sensing Overcurrent Protection and
High-Side FET Sensing Short-Circuit Protection
With Integrated Thermal Compensation
Programmable Closed Loop Soft-Start
Supports Pre-Biased Outputs
Thermal Shutdown at 165°C with Hysteresis
Voltage Tracking
Powergood
ENABLE with 1-µA Low Current Shutdown
8.0-V and 3.3-V LDO Output
Integrated Bootstrap Diode
20-Pin 3.5 mm × 4.5 mm VQFN (RGY) Package
Create a Custom Design with WEBENCH Tools
2 Applications
•
•
POL Modules
Wide Input Voltage, High-Power Density DC - DC
Converters for Industrial, Networking and Telecom
Equipment
3 Description
TPS40170 is a full-featured, synchronous PWM buck
controller that operates at an input voltage between
4.5 V and 60 V and is optimized for high-power
density, high-reliability DC-DC converter applications.
The controller implements voltage-mode control with
input voltage feed-forward compensation that enables
instant response to input voltage change. The
switching frequency is programmable from 100 kHz to
600 kHz.
The TPS40170 has a complete set of system
protection and monitoring features such as
programmable
undervoltage
lockout
(UVLO),
programmable overcurrent protection (OCP) by
sensing the low-side FET, selectable short-circuit
protection (SCP) by sensing the high-side FET and
thermal shutdown. The ENABLE pin allows for
system shutdown in a low-current (1 µA typical)
mode. The controller supports pre-biased output,
provides an open-drain PGOOD signal, and has
closed-loop soft-start, output voltage tracking and
adaptive dead-time control.
Device Information(1)
PART NUMBER
PACKAGE
BODY SIZE (NOM)
TPS40170
VQFN (20)
3.50 mm × 4.50 mm
(1) For all available packages, see the orderable addendum at
the end of the datasheet.
Simplified Application
Efficiency vs. Load Current
100
VIN
ENABLE
20
UVLO
2
SYNC
3
M/S
BOOT 18
4
RT
HDRV 17
5
SS
SW 16
6
TRK
7
FB
8
COMP
9
AGND
VIN 19
VOUT
TRK
VDD
10
TPS40170
Efficiency (%)
95
1
ENABLE
90
85
80
VIN = 12 V
VIN = 24 V
VIN = 48 V
75
VBP 15
LDRV 14
70
0
PGND 13
1
2
3
4
Load Current (A)
5
6
GND
ILIM 12
PGOOD
11
1
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
TPS40170
SLUS970B – NOVEMBER 2013 – REVISED DECEMBER 2014
www.ti.com
Table of Contents
1
2
3
4
5
6
7
Features ..................................................................
Applications ...........................................................
Description .............................................................
Revision History.....................................................
Pin Configuration and Functions .........................
Specifications.........................................................
1
1
1
2
3
4
6.1
6.2
6.3
6.4
6.5
6.6
4
4
4
5
5
8
Absolute Maximum Ratings ......................................
Handling Ratings ......................................................
Recommended Operating Conditions.......................
Thermal Information ..................................................
Electrical Characteristics...........................................
Typical Characteristics ..............................................
Detailed Description ............................................ 11
7.1 Overview ................................................................. 11
7.2 Functional Block Diagram ....................................... 11
7.3 Feature Description................................................. 12
7.4 Device Functional Modes........................................ 27
8
Application and Implementation ........................ 29
8.1 Application Information............................................ 29
8.2 Typical Application ................................................. 30
9 Power Supply Recommendations...................... 37
10 Layout................................................................... 37
10.1 Layout Guidelines ................................................. 37
10.2 Layout Example .................................................... 37
11 Device and Documentation Support ................. 40
11.1
11.2
11.3
11.4
11.5
Custom Design with WEBENCH Tools.................
Device Support......................................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
40
40
40
40
40
12 Mechanical, Packaging, and Orderable
Information ........................................................... 40
4 Revision History
Changes from Revision B (December 2014) to Revision C
Page
Changes from Revision A (November 2013) to Revision B
Page
•
Added Handling Ratings table, Feature Description section, Device Functional Modes, Application and
Implementation section, Power Supply Recommendations section, Layout section, Device and Documentation
Support section, and Mechanical, Packaging, and Orderable Information section................................................................ 3
Changes from Original (March 2011) to Revision A
Page
•
Deleted Ordering Information table. Replaced with Package Option Addenda inserted after the last page of this data
sheet. ..................................................................................................................................................................................... 3
•
Added clarity to Figure 20..................................................................................................................................................... 16
•
Added significant clarity to and corrected typographic errors in DESIGN EXAMPLE ......................................................... 32
2
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SLUS970B – NOVEMBER 2013 – REVISED DECEMBER 2014
5 Pin Configuration and Functions
RGY PACKAGE
QFN-20
(Top View)
ENABLE
UVLO
1
20 19
SYNC
2
M/S
3
18
BOOT
RT
4
17
HDRV
SS
5
16
SW
VIN
TPS40170
TRK
6
15
VBP
FB
7
14
LDRV
COMP
8
13
PGND
AGND
9
11 12
10
VDD
ILIM
PGOOD
Pin Functions
PIN
I/O
DESCRIPTION
NAME
NO.
AGND
9
—
Analog signal ground. This pin must be electrically connected to power ground PGND externally.
BOOT
18
O
Boot capacitor node for high-side FET gate driver. The boot capacitor is connected from this pin to SW.
COMP
8
O
Output of the internal error amplifier. The feedback loop compensation network is connected from this pin
to the FB pin.
ENABLE
1
I
This pin must be high for the device to be enabled. If this pin is pulled low, the device is put in a lowpower consumption shutdown mode.
FB
7
I
Negative input to the error amplifier. The output voltage is fed back to this pin through a resistor divider
network.
HDRV
17
O
Gate driver output for the high-side FET.
ILIM
12
I
A resistor from this pin to PGND sets the overcurrent limit. This pin provides source current used for
overcurrent protection threshold setting.
LDRV
14
O
Gate driver output for the low-side FET. Also, a resistor from this pin to PGND sets the multiplier factor to
determine short-circuit current limit. If no resistor is present the multiplier defaults to 7 times the ILIM pin
voltage.
M/S
3
I
Master or slave mode selector pin for frequency synchronization. This pin must be tied to VIN for master
mode. In the slave mode this pin must be tied to AGND or left floating. If the pin is tied to AGND, the
device synchronizes with a 180° phase shift. If the pin is left floating, the device synchronizes with a 0°
phase shift.
PGND
13
—
Power ground. This pin must externally connect to the AGND at a single point.
PGOOD
11
O
Power good indicator. This pin is an open-drain output pin and a 10 kΩ pull-up resistor is recommended
to be connected between this pin and VDD.
RT
4
I
A resistor from this pin to AGND sets the oscillator frequency. Even if operating in slave mode, it is
required to have a resistor at this pin to set the free running switching frequency.
SS
5
I
Soft-start. A capacitor must be connected at this pin to AGND. The capacitor value sets the soft-start
time.
SW
16
I
This pin must connect to the switching node of the synchronous buck converter. The high-side and lowside FET current sensing are also done from this node.
SYNC
2
I/O
Synchronization. This is a bi-directional pin used for frequency synchronization. In the master mode, it is
the SYNC output pin. In the slave mode, it is a SYNC input pin. If unused, this pin can be left open.
TRK
6
I
Tracking. External signal at this pin is used for output voltage tracking. This pin goes directly to the
internal error amplifier as a positive reference. The lesser of the voltages between VTRK and the internal
600 mV reference sets the output voltage. If not used, this pin should be pulled up to VDD.
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Pin Functions (continued)
PIN
I/O
DESCRIPTION
NAME
NO.
UVLO
20
I
Undervoltage lockout. A resistor divider on this pin from VIN to AGND can be used to set the UVLO
threshold.
VBP
15
O
8 V regulated output for gate driver. A ceramic capacitor with a value from 1 µF to 10 µF must be
connected from this pin to PGND and placed close to this pin.
VDD
10
O
3.3 V regulated output. A ceramic by-pass capacitor with a value from 0.1 µF to 1 µF must be connected
from this pin to AGND and placed close to this pin.
VIN
19
I
Input voltage for the controller which is also the input voltage for the DC/DC converter. A ceramic by-pass
capacitor with a value from 0.1 µF to 1 µF must be connected from this pin to PGND and placed close to
this pin.
6 Specifications
6.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted)
MIN
Input voltage
MAX
VIN
–0.3
62
M/S
–0.3
VIN
UVLO
–0.3
16
SW
–5
VVIN
SW (for duration less than 200 ns)
–10
VSW +
8.8
HDRV
VSW
BOOT
BOOT-SW, HDRV-SW (differential from BOOT or HDRV to SW)
–0.3
8.8
VBP, LDRV, COMP, RT, ENABLE, PGOOD, SYNC
–0.3
8.8
VDD, FB, TRK, SS, ILIM
–0.3
3.6
AGND-PGND, PGND-AGND
200
200
PowerPAD to AGND (must be electrically connected external to device)
0
Lead Temperature
Operating junction
temperature
V
VVIN
BOOT
Output voltage
UNIT
TJ
–40
V
mV
260
°C
125
°C
6.2 Handling Ratings
Tstg
Storage temperature
Human body model (HBM), per ANSI/ESDA/JEDEC JS-001, all pins
V(ESD)
(1)
(2)
Electrostatic discharge
MIN
MAX
UNIT
–55
150
°C
(1)
2000
Charged device model (CDM), per JEDEC specification JESD22-C101, all
pins (2)
1000
V
JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process.
6.3 Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted)
MIN
MAX
UNIT
VIN
Input voltage
4.5
60
V
TJ
Operating junction temperature range
-40
125
°C
4
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6.4 Thermal Information
TPS40170
THERMAL METRIC (1)
RGY
UNIT
20 PINS
RθJA
Junction-to-ambient thermal resistance
35.0
RθJC(top)
Junction-to-case(top) thermal resistance
36.7
RθJB
Junction-to-board thermal resistance
12.6
ψJT
Junction-to-top characterization parameter
0.4
ψJB
Junction-to-board characterization parameter
12.7
RθJC(bot)
Junction-to-case(bottom) thermal resistance
3.1
(1)
°C/W
For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953.
6.5 Electrical Characteristics
Unless otherwise stated, these specifications apply for -40ºC ≤ TJ ≤ 125ºC, VVIN=12 V
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
60
V
1
2.5
µA
4.5
mA
INPUT SUPPLY
VVIN
Input voltage range
ISD
Shutdown current
VENABLE < 100 mV
4.5
IQ
Operating current, drivers not switching
VENABLE ≥ 2 V, fSW = 300 kHz
ENABLE
VDIS
ENABLE pin voltage to disable the device
VEN
ENABLE pin voltage to enable the device
IENABLE
ENABLE pin source current
100
600
mV
300
nA
8.0
8.3
V
110
200
mV
3.30
3.42
V
8-V AND 3.3-V REGULATORS
VBP
8 V regulator output voltage
VENABLE ≥ 2 V, 8.2 V < VIN ≤ 60 V,
0 mA < IIN < 20 mA
VDO
8 V regulator dropout voltage,
VIN-BP
4.5 < VIN ≤ 8.2 V, VEN ≥ 2.0 V,
IIN = 10 mA
VVDD
3.3 V regulator output voltage
VENABLE ≥ 2 V, 4.5 V < VIN ≤ 60 V,
0 mA < IIN < 5 mA
7.8
3.22
FIXED AND PROGRAMMABLE UVLO
VUVLO
Programmable UVLO ON voltage (at UVLO pin)
VENABLE ≥ 2 V
878
900
919
mV
IUVLO
Hysteresis current out of UVLO pin
VENABLE ≥ 2 V , UVLO pin > VUVLO
4.06
5.00
6.20
µA
VBP(ON)
VBP turn-on voltage
VBP(OFF)
VBP turn-off voltage
VBP(HYS)
VBP UVLO Hysteresis voltage
VENABLE ≥ 2 V, UVLO pin > VUVLO
3.85
4.40
3.60
4.05
180
400
V
mV
REFERENCE
VREF
Reference voltage (+ input of the error amplifier)
TJ = 25°C, 4.5 V < VIN ≤ 60 V
594
600
606
–40°C ≤ TJ ≤ 125ºC, 4.5 V < VIN ≤ 60 V
591
600
609
Range (typical)
100
mV
OSCILLATOR
fSW
Switching frequency
VVALLEY
Valley voltage
KPWM (1)
PWM Gain (VIN / VRAMP)
600
RRT = 100 kΩ, 4.5 V 0.5 V
11.60
−40 −25 −10
95
Figure 8. UVLO Pin Hysteresis Current vs. Junction
Temperature
4.15
4.08
−40 −25 −10
5
20 35 50 65 80
Junction Temperature (°C)
5
20 35 50 65 80
Junction Temperature (°C)
95
110 125
Figure 11. Soft-Start Source Current vs. Junction
Temperature (VSS > 0.5 V)
VSS < 0.5 V
51.00
−40 −25 −10
5
20 35 50 65 80
Junction Temperature (°C)
95
110 125
Figure 12. Soft-Start Source Current vs. Junction
Temperature (VSS < 0.5 V)
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11.1
680
10.8
674
Soft−Start Initial Offset Voltage (mV)
ILIM Source Current (µA)
Typical Characteristics (continued)
10.5
10.2
9.9
9.6
9.3
9.0
8.7
8.4
−40 −25 −10
5
20 35 50 65 80
Junction Temperature (°C)
95
110 125
Figure 13. ILIM Source Current vs. Junction Temperature
668
662
656
650
644
638
632
626
620
614
−40 −25 −10
5
20 35 50 65 80
Junction Temperature (°C)
95
110 125
Figure 14. Soft-Start Initial Offset Voltage vs. Junction
Temperature
Power Good Threshold Voltage (mV)
675
650
625
Overvoltage
Undervoltage
600
575
550
525
−40 −25 −10
5
20 35 50 65 80
Junction Temperature (°C)
95
110 125
Figure 15. VOV/VUV Power Good Threshold Voltage
10
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7 Detailed Description
7.1 Overview
The TPS40170 is a synchronous PWM buck controller that accepts a wide range of input voltage from 4.5 V to
60 V and features voltage-mode control with input-voltage, feed-forward compensation. The switching frequency
is programmable from 100 kHz to 600 kHz.
The TPS40170 has a complete set of system protections such as programmable undervoltage lockout (UVLO),
programmable overcurrent protection (OCP), selectable short-circuit protection (SCP) and thermal shutdown. The
ENABLE pin allows for system shutdown in a low-current (1 µA typical) mode. The controller supports pre-biased
outputs, provides an open-drain PGOOD signal, and has closed loop programmable soft-start, output voltage
tracking and adaptive dead time control.
The TPS40170 provides accurate output voltage regulation via 1% specified accuracy.
Additionally, the controller implements a novel scheme of bidirectional synchronization with one controller acting
as the master other downstream controllers acting as slaves, synchronized to the master in-phase or 180° out-ofphase. Slave controllers can be synchronized to an external clock within ±30% of the internal switching
frequency.
7.2 Functional Block Diagram
ENABLE
VIN
UVLO
1
19
20
TPS40170
8-V
Regulator
VBP
Input and
Regulators OK
Run
3.3-V
Regulator
Gate Drivers
VDD 10
RT
4
SYNC
2
M/S
3
TRK
6
FB
7
COMP
8
AGND
9
18 BOOT
VBP
VIN
17 HDRV
CLK
Oscillator
and
Synchronization
16 SW
PWM Logic
Anti-Cross
Conduction
RAMP
+
15 VBP
PWM
Comparator
Run
+
+
+
SSEAMP
VREF
Error
Amplifier
14 LDRV
Run
13 PGND
Fault
Run
Run
TJ
Over-Temperature
Fault Controller
CLK
VIN
LDRV
CLK
11 PGOOD
FAULT
FAULT
Reset
Soft-Start
and
Fault Logic
Overcurrent
Fault Controller
OC_FAULT
Run
Power Good
Controller
Run
Run
SW
ILIM 12
FB
VREF
T_FAULT
5
SS
SSEAMP
Run
UDG-09218
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7.3 Feature Description
7.3.1 LDO Linear Regulators and Enable
The TPS40170 has two internal low-drop-out (LDO) linear regulators. One has a nominal output voltage of VVBP
and is present at the VBP pin. This is the voltage that is mainly used for the gate-driver output. The other linear
regulator has an output voltage of VVDD and is present at the VDD pin. This voltage can be used in external lowcurrent logic circuitry. The maximum allowable current drawn from the VDD pin must not exceed 5 mA.
The TPS40170 has a dedicated device enable pin (ENABLE). This simplifies user level interface design because
no multiplexed functions exist. If the ENABLE pin of the TPS40170 is higher than VEN, then the LDO regulators
are enabled. To ensure that the LDO regulators are disabled, the ENABLE pin must be pulled below VDIS. By
pulling the ENABLE pin below VDIS, the device is completely disabled and the current consumption is very low
(nominally, 1 µA). Both LDO regulators are actively discharged when the ENABLE pin is pulled below VDIS. A
functionally equivalent circuit to the enable circuitry on the TPS40170 is shown in Figure 16.
VIN
19
TPS40170
Always Active
ISD= 1 mA
ENABLE
1
+
DISABLE
+
VDIS
AGND
9
UDG-09147
Figure 16. TPS40170 Enable Functional Block
The ENABLE pin must not be allowed to float. If the ENABLE function is not needed for the design, then it is
suggested that the ENABLE pin be pulled up to VIN by a high value resistor ensuring that the current into the
ENABLE pin does not exceed 10 µA. If it is not possible to meet this clamp current requirement, then it is
suggested that a resistor divider from VIN to GND be used to connect to ENABLE pin. The resistor divider should
be such that the ENABLE pin should be higher than VEN and lower than 8 V.
NOTE
To avoid potential erroneous behavior of the enable function, the ENABLE signal applied
must have a minimum slew rate of 20 V/s.
7.3.2 Input Undervoltage Lockout (UVLO)
The TPS40170 has both fixed and programmable input undervoltage lockout (UVLO). In order for the device to
turn ON, all of the following conditions must be met:
• The ENABLE pin voltage must be greater than VEN
• The VBP voltage (at VBP pin) must be greater than VBP(on)
• The UVLO pin must be greater than VUVLO
In order for the device to turn OFF, any one of the following conditions must be met:
• The ENABLE pin voltage must be less than VDIS
• The VBP voltage (at VBP pin) must be less than VBP(off)
• The UVLO pin must be less than VUVLO
12
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Feature Description (continued)
Programming the input UVLO can be accomplished using the UVLO pin. A resistor divider from the input voltage
(VIN pin) to GND sets the UVLO level. Once the input voltage reaches a value that meets the VUVLO level at the
UVLO pin, then a small hysteresis current, IUVLO at the UVLO pin is switched in. The programmable UVLO
function is shown in Figure 17.
VIN
TPS40170
IUVLO
R1
UVLO
+
20
R2
VIN_OK
1 nF
+
VUVLO
AGND
9
UDG-09199
Figure 17. UVLO Functional Block Schematic
7.3.2.1 Equations for Programming the Input UVLO:
Components R1 and R2 represent external resistors for programming UVLO and hysteresis and can be
calculated in Equation 1 and Equation 2 respectively.
V - VOFF
R1 = ON
IUVLO
(1)
VUVLO
R2 = R1 ´
(VON - VUVLO )
where
•
•
•
•
VON is the desired turn-on voltage of the converter
VOFF is the desired turn-off voltage for the converter
IUVLO is the hysteresis current generated by the device, 5.0 µA (typ)
VUVLO is the UVLO pin threshold voltage, 0.9 V (typ)
(2)
NOTE
If the UVLO pin is connected to a voltage greater than 0.9 V, the programmable UVLO is
disabled and the device defaults to an internal UVLO (VBP(on) and VBP(off)). For example,
the UVLO pin can be connected to VDD or the VBP pin to disable the programmable
UVLO function.
A 1 nF ceramic by-pass capacitor must be connected between the UVLO pin and GND.
7.3.3 Oscillator and Voltage Feed-Forward
TPS40170 implements an oscillator with input-voltage feed-forward compensation that enables instant response
to input voltage changes. Figure 18 shows the oscillator timing diagram for the TPS40170. The resistor from the
RT pin to GND sets the free running oscillator frequency. The voltage VRT on the RT pin is made proportional to
the input voltage (see Equation 3).
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Feature Description (continued)
VRT =
VIN
KPWM
where
•
KPWM = 15
(3)
The resistor at the RT pin sets the current in the RT pin. The proportional current charges an internal 100-pF
oscillator capacitor. The ramp voltage on this capacitor is compared with the RT pin voltage, VRT. Once the ramp
voltage reaches VRT, the oscillator capacitor is discharged. The ramp that is generated by the oscillator (which is
proportional to the input voltage) acts as voltage feed-forward ramp to be used in the PWM comparator.
The time between the start of the discharging oscillator capacitor and the start of the next charging cycle is fixed
at 170 ns (typical). During the fixed discharge time, the PWM output is maintained as OFF. This is the minimum
OFF-time of the PWM output.
VIN
Minimum OFF Time
RAMP
VCOMP
VCLK
PWM
t – Time
UDG-09200
Figure 18. Feed-Forward Oscillator Timing Diagram
7.3.3.1 Calculating the Timing Resistance (RRT)
æ 104
RRT = ç
ç fSW
è
ö
÷ - 2 (kW )
÷
ø
where
•
•
fSW is the switching frequency in kHz
RRT is the resistor connected from RT pin to GND in kΩ
(4)
NOTE
The switching frequency can be adjusted between 100 kHz and 600 kHz. The maximum
switching frequency before skipping pulses is determined by the input voltage, output
voltage, FET resistances, DCR of the inductor, and the minimum on time of the
TPS40170. Use Equation 5 to determine the maximum switching frequency. For further
details, please see application note SLYT293.
fSW (max ) =
14
(
)
VOUT(min ) + IOUT(min ) ´ (RDS2 + RLOAD )
(
)
tON(min ) ´ VIN(max ) - IOUT(min ) ´ (RDS1 - RDS2 )
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Feature Description (continued)
where
•
•
•
•
•
•
•
fSW(max) is the maximum switching frequency
VOUT(min) is the minimum output voltage
VIN(max) is the maximum input voltage
IOUT(min) is the minimum output current
RDS1 is the high-side FET resistance
RDS2 is the low-side FET resistance
and RLOAD is the inductor series resistance
(5)
7.3.4 Overcurrent Protection and Short-Circuit Protection (OCP and SCP)
The TPS40170 has the capability to set a two-level overcurrent protection. The first level of overcurrent
protection (OCP) is the normal overload setting based on low-side MOSFET voltage sensing. The second level
of protection is the heavy overload setting such as short-circuit based on the high-side MOSFET voltage sensing.
This protection takes effect immediately. The second level is termed short-circuit protection (SCP).
The OCP level is set by the ILIM pin voltage. A current (IILIM) is sourced into the ILIM pin from which a resistor
RILIM is connected to GND. Resistor RILIM sets the first level of overcurrent limit. The OCP is based on the lowside FET voltage at the switch-node (SW pin) when the LDRV is ON after a blanking time, which is the product of
inductor current and low-side FET turn-on resistance RDS(on). The voltage is inverted and compared to ILIM pin
voltage. If it is greater than the ILIM pin voltage, then a 3-bit counter inside the device increments the fault-count
by 1 at the start of the next switching cycle. Alternatively, if it is less than the ILIM pin voltage, then the counter
inside the device decrements the fault-count by 1. When the fault-count reaches 7, an overcurrent fault
(OC_FAULT) is declared and both the HDRV and LDRV are turned OFF. The resistor RILIM can be calculated by
the following Equation 6.
IOC ´ RDS(on) IOC ´ RDS(on)
RILIM =
=
IILIM
9.0 mA
(6)
The SCP level is set by a multiple of the ILIM pin voltage. The multiplier has three discrete values, 3, 7 or 15
times, which can be selected by respectively choosing a 10-kΩ, open circuit, or 20 kΩ resistor from LDRV pin to
GND. This multiplier AOC information is translated during the tCAL time, which starts after the enable and UVLO
conditions are met.
The SCP is based on sensing the high-side FET voltage drop from VVIN to VSW when the HDRV is ON after a
blanking time, which is product of inductor current and high-side FET turn-on resistance RDS(on). The voltage is
compared to the product of multiplier and the ILIM pin voltage. If it exceeds the product, then the fault-count is
immediately set to 7 and the OC_FAULT is declared. The HDRV is terminated immediately without waiting for
the duty cycle to end. When an OC_FAULT is declared, both the HDRV and LDRV are turned OFF. The
appropriate multiplier (A), can be selected using Equation 7.
ISC ´ RDS(on)HS
A=
IOC ´ RDS(on)LS
(7)
Figure 19 shows the functional block of the two-level overcurrent protection.
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Feature Description (continued)
A
10
3
OPEN
7
20
15
HDRV On
tBLNK
VIN
(A x VILIM)
3-Bit
State
Machine
+
+
RLDRV (kW)
19
HDRV
R
tBLNK
17
LDRV On
SW
R
Q0
OC_FAULT
+
Q1
Q2
16
+
LDRV
VDD
14
CLK
RLDRV
IILIM
ILIM
12
PGND
RILIM
13
UDG-09198
Figure 19. OCP and SCP Protection Functional Block Diagram
NOTE
Both OCP and SCP are based on low-side and high-side MOSFET voltage sensing at the
SW node. Excessive ringing on the SW node can have negative impact on the accuracy of
OCP and SCP. Adding an RC snubber from the SW node to GND helps minimize the
potential impact.
7.3.5 Soft-Start and Fault-Logic
A capacitor from the SS pin to GND defines the SS time, tSS. The TPS40170 enters into soft-start immediately
after completion of the overcurrent calibration. The SS pin goes through the device's internal level-shifter circuit
before reaching one of the positive inputs of the error amplifier. The SS pin must reach approximately 0.65 V
before the input to the error amplifier begins to rise above 0 V. To charge the SS pin from 0 V to 0.65 V faster, at
the beginning of the soft-start in addition to the normal charging current, (11.6 µA, typ.), an extra charging current
(40.4 µA, typ.) is switched-in to the SS pin. As the SS capacitor reaches 0.5 V, the extra charging current is
turned off and only the normal charging current remains. Figure 20 shows the soft-start function block.
16
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Feature Description (continued)
TPS40170
VDD
40.4 µA
11.6 µA
SS
Soft-Start
Charge/Discharge
Control
5
CSS
1.05 µA
VDD
TRK
VOUT
SS_EAmp
R1
VREF
FB
+
+
+
SS Error
Amplifier
COMP
FB
7
R2
UDG-09202
Figure 20. Soft-Start Schematic Block
As the SS pin voltage approaches 0.65 V, the positive input to the error amplifier begins to rise (see Figure 21).
The output of the error amplifier (the COMP pin) starts rising. The rate of rise of the COMP voltage is mainly
limited by the feedback loop compensation network. Once VCOMP reaches the valley of the PWM ramp, the
switching begins. The output is regulated to the error amplifier input through the FB pin in the feedback loop.
Once the FB pin reaches the 600 mV reference voltage, the feedback node is regulated to the reference voltage,
VREF. The SS pin continues to rise and is clamped to VDD.
The SS pin is discharged through an internal switch during the following conditions:
• Input (VIN) undervoltage lock out UVLO pin less than VUVLO
• Overcurrent protection calibration time (tCAL)
• VBP less than threshold voltage (VBP(off))
Because it is discharged through an internal switch, the discharging time is relatively fast compared with the
discharging time during the fault restart which is discussed in the Soft-Start During Overcurrent Fault section.
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Feature Description (continued)
Internal Logic RUN
Clamped at VDD
SS
tCAL
SS_EAMP
1.1 V
0.5 V
VREF = 0.6 V
0.65 V
VSS
tSS
VVALLEY
VCOMP
(2)
(1)
VOUT
t – Time
UDG-09203
Figure 21. Soft-Start Waveforms
NOTE
Referring to Figure 21
• (1) VREF dominates the positive input of the error amplifier
• (2) SS_EAMP dominates the positive input of the error amplifier
For 0 < VSS_EAMP < VREF
VOUT = VSS(EAMP) ´
(R1 + R2 )
R2
(8)
For VSS_EAMP > VREF
VOUT = VREF ´
(R1 + R2 )
R2
(9)
7.3.5.1 Soft-Start During Overcurrent Fault
The soft-start block also has a role to controls the fault-logic timing. If an overcurrent fault (OC_FAULT) is
declared, the soft-start capacitor is discharged internally through the device by a small current ISS(sink) (1.05 µA,
typ.). Once the SS pin capacitor is discharged to below VSS(flt,low) (300 mV, typ.), the soft-start capacitor begins
charging again. If the fault is persistent, a fault is declared which is determined by the overcurrent protection
state machine. If the soft-start capacitor is below VSS(flt,high) (2.5 V, typ.), then the soft-start capacitor continues to
charge until it reaches VSS(flt,high) before a discharge cycle is initiated. This ensures that the re-start time-interval
is always constant. Figure 22 shows the restart timing.
18
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Feature Description (continued)
Persistent FAULT
OC_FAULT
FAULT Reset
FAULT Set
tRS
2.5 V
VSS
300 mV
t – Time
UDG-09204
Figure 22. Overcurrent Fault Restart Timing
NOTE
For the feedback to be regulated to the SS_EAMP voltage, the TRK pin must be pulled up
high directly or through a resistor to VDD.
7.3.5.2 Equations for Soft-Start and Restart Time
The soft-start time (tSS) is defined as the time taken for the internal SS_EAMP node to go from 0 V to the 0.6 V,
VREF voltage. The SS_EAMP starts rising as the SS pin goes beyond 0.65 V. The offset voltage between the SS
and the SS_EAMP starts increasing as the SS pin voltage starts rising. Figure 21, shows that the SS time can be
defined as the time taken for the SS pin voltage to change by 1.05 V (see Equation 10).
The restart time (tRS) is defined in Equation 11 as the time taken for the soft-start capacitor (CSS) to discharge
from 2.5 V to 0.3 V and to then recharge up to 2.5 V.
t
CSS = SS
0.09
(10)
tRS » 2.28 ´ CSS
where
•
•
•
CSS is the soft-start capacitance in nF
tSS is the soft-start time in ms
tRS is the re-start time in ms
(11)
NOTE
During soft-start (VSS < 2.5 V), the overcurrent protection limit is 1.5 times normal
overcurrent protection limit. This allows higher output capacitance to fully charge without
activating overcurrent protection.
7.3.6 Over-Temperature Fault
Figure 23 shows the over-temperature protection scheme. If the junction temperature of the device reaches the
thermal shutdown limit of tSD(set) (165°C, typ) and SS charging is completed, an over-temperature FAULT is
declared. The soft-start capacitor begins to be discharged. During soft-start discharging period, the PWM
switching is terminated; therefore both HDRV and LDRV are driven low, turning off both MOSFETs.
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Feature Description (continued)
The soft-start capacitor begins to charge and over-temperature fault is reset whenever the soft-start capacitor is
discharged below VSS(flt,low) (300 mV, typ.). During each restart cycle, PWM switching is turned on. When SS is
fully charged, PWM switching is terminated. These restarts repeat until the temperature of the device has fallen
below the thermal reset level, tSD(reset) (135°C typ). PWM switching continues and system returns to normal
regulation.
Persistent FAULT
TS_FAULT
FAULT Reset
FAULT Set
tRS
2.5 V
300 mV
VSS
t – Time
UDG-09205
Figure 23. Over-Temperature Fault Restart Timing
The soft-start timing during over-temperature fault is the same as the soft-start timing during overcurrent fault.
See the Equations for Soft-Start and Restart Time section.
7.3.7 Tracking
The TRK pin is used for output voltage tracking. The output voltage is regulated so that the FB pin equals the
lowest of the internal reference voltage (VREF) or the level-shifted SS pin voltage (SSEAMP) or the TRK pin
voltage. Once the TRK pin goes above the reference voltage, then the output voltage is no longer governed by
the TRK pin, but it is governed by the reference voltage.
If the voltage tracking function is used, then it should be noted that the SS pin capacitor must remain connected
as the SS pin and is also used for FAULT timing. For proper tracking using the TRK pin, the tracking voltage
should be allowed to rise only after SSEAMP has exceeded VREF, so that there is no possibility of the TRK pin
voltage being higher than the SSEAMP voltage. From Figure 21, for SSEAMP = 0.6 V, the SS pin voltage is typically
1.7 V.
The maximum slew rate on the TRK pin should be determined by the output capacitance and feedback loop
bandwidth. A higher slew rate can possibly trip overcurrent protection.
Figure 24 shows the tracking functional block. For SSEAMP voltages greater than TRK pin voltage, the VOUT is
given by Equation 12 and Equation 13.
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Feature Description (continued)
.
For 0 V < VTRK < VREF
TPS40170
TRK
TRK
.
TRK IN
VOUT = VTRK ´
(R1 + R2 )
R2
(12)
6
VOUT
SSEAMP
.
For VTRK > VREF
R1
.
VOUT = VREF ´
(R1 + R2 )
R2
+
+
+
FB
COMP
VREF
7
FB
(13)
R2
UDG-09208
Figure 24. Tracking Functional Block
There are three potential applications for the tracking function.
• simultaneous voltage tracking
• ratiometric voltage tracking
• sequential startup mode
The tracking function configurations and waveforms are shown in Figure 25, Figure 27, and Figure 29
respectively.
In simultaneous voltage tracking shown in Figure 25, tracking signals, VTRK1 and VTRK2, of two modules, POL1
and POL2, start up at the same time and their output voltages VOUT1 initial and VOUT2 initial are approximately the
same during initial startup. Since VTRK1 and VTRK2 are less than VREF (0.6 V, typ), Equation 12 is used. As a
result, components selection should meet Equation 14.
æ (R3 + R 4 ) ö
æ (R1 + R2 ) ö
R
÷ ´ VTRK2 Þ 5
ç
÷ ´ VTRK1 = ç
ç
÷
ç
÷
R1
R3
R6
è
ø
è
ø
ææ
ö
ö
R1
çç
÷
÷
ç çè (R1 + R2 ) ÷ø
÷
=ç
- 1÷
ö ÷
R3
çæ
ç çç (R + R ) ÷÷ ÷
4 ø
èè 3
ø
(14)
After the lower output voltage setting reaches output voltage VOUT1 set point, where VTRK1 increases above VREF,
the output voltage of the other one (VOUT2) continues increasing until it reaches its own set point, where VTRK2
increases above VREF. At that time, Equation 13 is used. As a result, the resistor settings should meet
Equation 15 and Equation 16.
æ (R1 + R2 ) ö
VOUT1 = ç
÷ ´ VREF
ç
÷
R1
è
ø
VOUT2
(15)
æ (R3 + R 4 ) ö
=ç
÷ ´ VREF
ç
÷
R3
è
ø
(16)
Equation 14 can be simplified into Equation 17 by replacing with Equation 15 and Equation 16
æ R5 ö æ æ VOUT2 ö ö
ç
÷ = çç ç
÷ - 1÷÷
è R6 ø è è VOUT1 ø ø
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Feature Description (continued)
If 5 V = VOUT2 and 2.5 V = VOUT1 are required, according to Equation 15, Equation 16 and Equation 17, the
selected components can be as following:
• R5 = R6 = R4 = R2 = 10 kΩ
• R1 = 3.16 kΩ
• R3 = 1.37 kΩ
VIN
External
Tracking
Input
VTRK1
VOUT1
VTRK1
POL1
R2
VTRK2
0.6
Voltage
R1
R5
VIN
VOUT2
VOUT2
VTRK2
POL2
VOUT1
R4
R6
R3
0
t – Time
UDG-09210
UDG-09209
Figure 25. Simultaneous Voltage Tracking
Schematic
22
Figure 26. Simultaneous Voltage Tracking
Waveform
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Feature Description (continued)
In ratiometric voltage tracking shown in Figure 27, the two tracking voltages, VTRK1 and VTRK2, for two modules,
POL1 and POL2, are the same. Their output voltage, VOUT1 and VOUT2, are different with different voltage divider
R2/R1 and R4/R3. VOUT1 and VOUT2 increase proportionally and reach their output voltage set points at about the
same time.
VIN
VTRK2
VOUT1
VTRK1
VTRK1
POL1
External
Tracking
Input
0.6
R2
Voltage
R1
VIN
VOUT2
VOUT2
VTRK2
POL2
VOUT1
R4
R3
0
t – Time
UDG-09212
UDG-09211
Figure 27. Ratiometric Voltage Tracking Schematic
Figure 28. Ratiometric Voltage Tracking Waveform
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Feature Description (continued)
Sequential startup is shown in Figure 29. During start-up of the first module, POL1, its PGOOD1 is pulled to low.
Since PGOOD1 is connected to soft-start SS2 of the second module, POL2, is not able to charge its soft-start
capacitor. After output voltage VOUT1 of POL1 reaches its setting point, PGOOD1 is released. POL2 starts
charging its soft-start capacitor. Finally, output voltage VOUT2 of POL2 reaches its setting point.
VIN
VOUT1
VOUT1
VSS2, VPGOOD1
PGOOD1
POL1
R2
Voltage
R1
VIN
VOUT2
VOUT2
SS2
POL2
VPGOOD2
R4
CSS
R3
0
t – Time
UDG-09214
UDG-09213
Figure 29. Sequential Start-Up Schematic
Figure 30. Sequential Start-Up Waveform
NOTE
The TRK pin has high impedance, so it is a noise sensitive terminal. If the tracking
function is used, a small RC filter is recommended at the TRK pin to filter out highfrequency noise.
If the tracking function is not used, the TRK pin must be pulled up directly or through a
resistor (with a value between 10 kΩ and 100 kΩ) to VDD.
7.3.8 Adaptive Drivers
The drivers for the external high-side and low-side MOSFETs are capable of driving a gate-to-source voltage,
VBP. The LDRV driver for the low-side MOSFET switches between VBP and PGND, while the HDRV driver for
the high-side MOSFET is referenced to SW and switches between BOOT and SW. The drivers have nonoverlapping timing that is governed by an adaptive delay circuit to minimize body diode conduction in the
synchronous rectifier.
7.3.9 Start-Up into Pre-Biased Output
The TPS40170 contains a circuit to prevent current from being pulled out of the output during startup in case the
output is pre-biased. When the soft-start commands a voltage higher than the pre-bias level (internal soft-start
becomes greater than feedback voltage [VFB]), the controller slowly activates synchronous rectification by starting
the first LDRV pulses with a narrow on-time (see Figure 31), where:
• VIN = 5 V
• VOUT = 3.3 V
• VPRE = 1.4 V
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Feature Description (continued)
•
•
fSW = 300 kHz
L = 0.6 µH
It then increments the on-time on a cycle-by-cycle basis until it coincides with the time dictated by (1-D), where D
is the duty cycle of the converter. This scheme prevents the initial sinking of the pre-bias output, and ensures
that the output voltage (VOUT) starts and ramps up smoothly into regulation and the control loop is given time to
transition from pre-biased startup to normal mode operation with minimal disturbance to the output voltage. The
time from the start of switching until the low-side MOSFET is turned on for the full (1-D) interval is between
approximately 20 and 40 clock cycles.
Figure 31. Start-Up Switching Waveform during Pre-Biased Condition
If the output is pre-biased to a voltage higher than the voltage commanded by the reference, then the PWM
switching does not start.
NOTE
When output is pre-biased at VPRE-BIAS, that voltage also applies to the SW node during
start-up. When the pre-bias circuitry commands the first few high-side pulses before the
first low-side pulse is initiated, the gate voltage for the high-side MOSFET is as described
in Equation 18. Alternatively, If pre-bias level is high, it is possible that SCP can be tripped
due to high turn-on resistance of the high-side MOSFET with low gate voltage. Once
tripped, the device resets and then attempts to re-start. The device may not be able to
start up until output is discharged to a lower voltage level by either an active load or
through feedback resistors.
In the case of a high pre-bias level, a low gate-threshold voltage rated device is
recommended for the high-side MOSFET and increasing the SCP level also helps
alleviate the problem.
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Feature Description (continued)
VGATE(hs ) =
(VBP -
VDFWD - VPRE-BIAS )
where
•
•
•
VGATE(hs) is the gate voltage for the high-side MOSFET
VBP is the BP regulator output
VDFWD is bootstrap diode forward voltage
(18)
7.3.10 Powergood (PGOOD)
The TPS40170 provides an indication that the output voltage of the converter is within the specified limits of the
regulation as measured at the FB pin. The PGOOD pin is an open-drain signal and pulls low when any condition
exists that would indicate that the output of the supply might be out of regulation. These conditions include:
• VFB is not within the PGOOD threshold limits.
• Soft-start is active, i.e., SS pin voltage is below VSS,FLT,HIGH limit.
• An undervoltage condition exists for the device.
• An overcurrent or short-circuit fault is detected.
• An over-temperature fault is detected.
Figure 32 shows a situation where no fault is detected during the startup, (the normal PGOOD situation). It
shows that PGOOD goes high tPGD (20 µs, typ.) after all the conditions (listed above) are met.
VDD
Track
VSS, steady-state
VSS, FLT, HI
VSS
VOV
VUV
VFB
tPGD
VPGOOD
t – Time
UDG-09215
Figure 32. PGOOD Signal
When there is no power to the device, PGOOD is not able to pull close to GND if an auxiliary supply is used for
the power good indication. In this case, a built-in resistor connected from drain to gate on the PGOOD pull-down
device allows the PGOOD pin to operate like as a diode to GND.
7.3.11 PGND and AGND
TPS40170 provides separate signal ground (AGND) and power ground (PGND) pins. PGND is primarily used for
gate driver ground return. AGND is an internal logic signal ground return. These two ground signals are internally
loosely connected by two anti-parallel diodes. PGND and AGND must be electrically connected externally.
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7.4 Device Functional Modes
7.4.1 Frequency Synchronization
The TPS40170 has three modes.
• Master mode: In this mode the master/slave selector pin, (M/S) is connected to VIN. The SYNC pin emits a
stream of pulses at the same frequency as the PWM switching frequency. The pulse stream at the SYNC pin
is at 50% duty cycle and the same amplitude as VVBP. Also, the falling edge of the voltage on SYNC pin is
synchronized with the rising edge of the HDRV.
• Slave-180° mode: In this mode the M/S pin is connected to GND. The SYNC pin of the TPS40170 accepts a
synchronization clock signal, and the HDRV is synchronized with the rising edge of the incoming
synchronization clock.
• Slave-0° mode: In this mode, the M/S pin is left open. The SYNC pin of the TPS40170 accepts a
synchronization clock signal, and the HDRV is synchronized with the falling edge of the incoming
synchronization clock.
The two slave modes can be synchronized to an external clock through the SYNC pin. They are shown in
Figure 33. The synchronization frequency should be within ±30% of its programmed free running frequency.
Master Mode (SYNC as an output pin)
VHDRV
VSYNC
t – Time
Slave 180 Mode (SYNC as an input pin)
VSYNC
VHDRV
t – Time
Slave 0 Mode (SYNC as an input pin)
VSYNC
VHDRV
t – Time
UDG-09206
Figure 33. Frequency Synchronization Waveforms In Different Modes
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Device Functional Modes (continued)
TPS40170 provides a smooth transition for the SYNC clock signal loss at slave mode. In slave mode, a
synchronization clock signal is provided externally through the SYNC pin to the device. The switching frequency
is synchronized to the external SYNC clock signal. If for some reason the external clock signal is missing, the
device switching frequency is automatically overridden by a transition frequency which is 0.7 times its
programmed free running frequency. This transition time is approximately 20 μs. After that, the device switching
frequency is changed to its programmed free running frequency. Figure 34 shows this process.
SYNC clock pulse missing
VSYNC
VHDRV
Synchronized duration
fS = SYNC clock frequency
20-ms transition duration
Free running duration .
fS = 0.7 x running frequency
fS = free running frequency
UDG-09207
Figure 34. Transition for Sync Clock Signal Missing (For Slave-180 Mode)
NOTE
When the device is operating in the master mode with duty ratio around 50%, PWM
jittering may occur. Always configure the device into the slave mode by either connecting
the M/S pin to GND or leaving it floating if master mode is not used.
When an external SYNC clock signal is used for synchronization, limit maximum slew rate
of the clock signal to 10 V/µs to avoid potential PWM jittering and connect the SYNC pin
to the external clock signal via a 5-kΩ resistor.
7.4.2 Operation Near Minimum VIN (VVIN ≤ 4.5 V)
The TPS40170 is designed to operate with input voltages above 4.5 V. With voltages below 4.5 V if the EN pin is
above its 600 mV turn on threshold the VDD and VBP internal regulators are active. These regulators will
operate in drop out and output the highest voltage possible for the given VIN. The EN pin voltage must be below
100 mV to disable the VDD and VBP regulators. Switching is disabled while the VBP output voltage is below the
VBP turn-on voltage of 4.4 V maximum. When there is sufficient VIN voltage to regulate the VBP voltage above
4.4 V the final condition for switching to begin is the UVLO pin voltage must be above its 900 mV typical
threshold. Once all three conditions are met the TPS40170 will begin switching and the soft-start sequence is
initiated. The device starts at the soft-start time determined by the external capacitance at the SS/TR pin. If a
design requires operation near the minimum VIN voltage, due to lower VBP voltage when operating in dropout,
lower gate threshold MOSFETs are recommended
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8 Application and Implementation
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
8.1 Application Information
The wide input TPS40170 controller can function in a very wide range of applications. The WEBENCH software
uses an iterative design procedure and accesses a comprehensive database of components when generating a
design. This section presents a simplified discussion of the design process.
8.1.1 Bootstrap Resistor
A small resistor in series with the bootstrap capacitor reduces the turn-on speed of the high-side MOSFET,
thereby reducing the rising edge ringing of the SW node and reduces short through induced by dv/dt. A bootstrap
resistor value that is too large delays the turn-on time of the high-side switch and may trigger an apparent SCP
fault.
8.1.2 SW Node Snubber Capacitor
Observable voltage ringing at the SW node is caused by fast switching edges and parasitic inductance and
capacitance. If the ringing results in excessive voltage on the SW node, or erratic operation of the converter, an
RC snubber may be used to dampen the ringing and ensure proper operation over the full load range. See
design example.
8.1.3 Input Resistor
The TPS40170 has a wide input voltage range which allows for the device input to share power source with
power stage input. Power stage switching noise may pollute the device power source if the layout is not
adequate in minimizing noise. It may trigger short-circuit fault. If so, adding a small resistor between the device
input and power stage input is recommended. This resistor composites an RC filter with the device input
capacitor and filter out the switching noise from power stage. See R1 in the design example.
8.1.4 LDRV Gate Capacitor
Power device selection is important for proper switching operation. If the low-side MOSFET has low gate
capacitance CGS (if CGS 2 x VOUT, use overshoot to calculate minimum output capacitance. If VIN(min) < 2 x VOUT, use
undershoot to calculate minimum output capacitance.
2
COUT(min )
ITRAN(max) ) ´ L (3 )2 ´ 8.2 mH
(
=
=
= 59 mF
VOUT ´ VOVER
5 ´ 250mV
(23)
With a minimum capacitance, the maximum allowable ESR is determined by the maximum ripple voltage and is
approximated Equation 24.
æ
ö
IRIPPLE
æ
ö
1.86 A
VRIPPLE(tot) - ç
÷ 100mV - ç
÷
VRIPPLE(tot) - VRIPPLE(cap)
è 8 ´ COUT ´ fSW ø =
è 8 ´ 59 mF ´ 300kHz ø = 47mW
ESRMAX =
=
IRIPPLE
IRIPPLE
1.86 A
(24)
Two 1210, 22 µF, 16 V X7R ceramic capacitors plus two 0805 10 µF, 16 V X7R ceramic capacitors are selected
to provide more than 59 µF of minimum capacitance (including tolerance and DC bias derating) and less than
47 mΩ of ESR (parallel ESR of approximately 4 mΩ).
8.2.2.6 Peak Current Rating of Inductor
With output capacitance, it is possible to calculate the charge current during start-up and determine the minimum
saturation current rating for the inductor. The start-up charging current is approximated in Equation 25.
´ COUT 5 V ´ (2 ´ 22 mF + 2 ´ 10 mF )
V
=
= 0.08 A
ICHARGE = OUT
tSS
4ms
(25)
IL(peak ) = IOUT(max) + (12 ´ IRIPPLE )+ ICHARGE = 6 A +
(26)
1
2 ´ 1.86 A + 0.08 A = 7.01A
An IHLP5050FDER8R2M01 8.2 µH is selected. This 10-A, 16-mΩ inductor exceeds the minimum inductor ratings
in a 13 mm × 13 mm package.
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8.2.2.7 Input Capacitor Selection (C1, C6)
The input voltage ripple is divided between capacitance and ESR. For this design VRIPPLE(cap) = 400 mV and
VRIPPLE(ESR) = 100 mV. The minimum capacitance and maximum ESR are estimated by:
ILOAD ´ VOUT
6A´5V
=
= 25 mF
CIN(min) =
VRIPPLE(cap) ´ VIN ´ fSW
400mV ´ 10 V ´ 300kHz
(27)
VRIPPLE(esr)
ESRMAX =
ILOAD +
=
1 ´I
2 RIPPLE
100mV
= 14.4mW
6.93A
(28)
The RMS current in the input capacitors is estimated in Equation 29.
IRMS(cin ) = ILOAD ´ D ´ (1 - D ) = 6 A ´ 0.5 ´ (1 - 0.5) = 3.0 A
(29)
To achieve these values, four 1210, 2.2 µF, 100 V, X7R ceramic capacitors plus a 120 µF electrolytic capacitor
are combined at the input. This provides a smaller size and overall cost than 10 ceramic input capacitors or an
electrolytic capacitor with the ESR required.
Table 3. Inductor Summary
PARAMETER
VALUE
UNIT
L
Inductance
8.2
µH
IL(rms)
RMS current (thermal rating)
6.02
A
IL(peak)
Peak current (saturation rating)
7.01
A
8.2.2.8 MOSFET Switch Selection (Q1, Q2)
Using the J/K method for MOSFET optimization, apply Equation 30 through Equation 33.
High-side gate (Q1):
ö
Q
-9 æ V ´ I
J = (10 ) ´ ç IN OUT + G ´ VDRIVE ÷ ´ fSW
QSW
è IDRIVE
ø
-3
K = (10 )
((I
OUT
)2 + 112 ´ (IP-P )2
(W nC)
(30)
)´ æçè VV ö÷ø (W mW)
(31)
)´ æçè1- VV ö÷ø (W mW)
(32)
OUT
IN
Low-side gate (Q2):
-3
K = (10 )
((I
OUT
)2 + 112 ´ (IP-P )2
OUT
IN
æ V ´I
ö
Q
J = 10-9 ç FD OUT + G ´ VDRIVE ÷ ´ fSW W
nC
QSW
è IDRIVE
ø
(
)
(33)
Optimizing for 300 kHz, 24 V input, 5 V output at 6 A, calculate ratios of 5.9 mΩ/nC and 0.5 mΩ/nC for the highside and low-side FETS respectively. BSC110N06NS2 (Ratio 1.2) and BSC076N06NS3 (Ratio 0.69) MOSFETS
are selected.
8.2.2.9 Timing Resistor (R7)
The switching frequency is programmed by the current through RRT to GND. The RRT value is calculated using
Equation 34.
RRT =
(10 )4
fSW
- 2kW =
(10 )4
300kHz
- 2 = 31.3kW » 31.6kW
(34)
8.2.2.10 UVLO Programming Resistors (R2, R6)
The UVLO hysteresis level is programmed by R2 using Equation 35.
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RUVLO(hys ) =
VUVLO(on ) - VUVLO(off )
IUVLO
=
www.ti.com
9V -8V
= 200kW
5.0 mA
(35)
VUVLO(max)
0.919 V
RUVLO(set ) > RUVLO(hys )
= 200kW
= 22.7kW » 22.1kW
(9.0 V - 0.919 V )
VUVLO _ ON(min) - VUVLO(max)
(
)
(36)
8.2.2.11 Boot-Strap Capacitor (C7)
A bootstrap capacitor with a value between 0.1 µF and 0.22 µF must be placed between the BOOT pin and the
SW pin. It should be 10 times higher than MOSFET gate capacitance. To ensure proper charging of the highside FET gate, limit the ripple voltage on the boost capacitor to less than 250 mV.
QG1
25nC
=
= 100nF
CBOOST =
VBOOT(ripple ) 250mV
(37)
8.2.2.12 VIN Bypass Capacitor (C18)
Place a capacitor with a value of 1.0 µF. Select a capacitor with a value from 0.1 µF to 1.0 µF, X5R or better
ceramic bypass capacitor for VIN as specified in Recommended Operating Conditions. For this design a 1.0-µF,
100-V, X7R capacitor has been selected.
8.2.2.13 VBP Bypass Capacitor (C19)
Select a capacitor with a value from 1.0 µF to 10 µF, X5R or better ceramic bypass capacitor for VBP as
specified in Recommended Operating Conditions. It should be at least 10 times higher than the bootstrap
capacitance. For this design a 4.7-µF, 16-V capacitor has been selected.
8.2.2.14 VDD Bypass Capacitor (C16)
Select a capacitor with a value between 0.1 µF and 1 µF, X5R or better ceramic bypass capacitor for VDD as
specified in Recommended Operating Conditions. For this design a 1-µF, 16-V capacitor has been selected.
8.2.2.15 SS Timing Capacitor (C15)
The soft-start capacitor provides smooth ramp of the error amplifier reference voltage for controlled start-up. The
soft-start capacitor is selected by using Equation 38.
t
4ms
CSS = SS =
= 44nF » 47nF
0.09 0.09
(38)
8.2.2.16 ILIM Resistor (R9, C17)
The TPS40170 use the negative drop across the low-side FET at the end of the "OFF" time to measure the
inductor current. Allowing for 30% over the minimum current limit for transient recovery and 20% rise in RDS(on)Q2
for self-heating of the MOSFET, the voltage drop across the low-side FET at current limit is given by
Equation 39.
((
) (
VOC = 1.3 ´ IOCP(min) + 21 ´ IRIPPLE
))´ 1.25 ´ RDS(on)G2 = (1.3 ´ 8 A + 21 ´ 1.86 A) ´ 1.25 ´ 7.6mW = 107.6mV
(39)
The internal current limit temperature coefficient helps compensate for the MOSFET RDS(on) temperature
coefficient, so the current limit programming resistor is selected by Equation 40.
VOC
107.6mV
=
= 12.0kW » 12.1kW
RILIM =
IOCSET(min )
9.0 mA
(40)
A 1000 pF capacitor is placed in parallel to improve noise immunity of the current limit set-point.
8.2.2.17 SCP Multiplier Selection (R5)
The TPS40170 controller uses a multiplier (AOC) to translate the low-side over-current protection into a high-side
RDS(on) pulse-by-pulse short circuit protection. Ensure that Equation 41 is true.
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A OC >
(21 ´ IRIPPLE )´ RDS(on)Q1 = 8 A + 21 ´ 1.86 A ´ 11 mW = 1.45
IOCP(min) + (21 ´ IRIPPLE ) RDS(on )Q2 8 A + 21 ´ 1.86 A 7.6 mW
IOCP(min) +
(41)
AOC = 3 is selected as the next greater AOC. The value of R5 is set to 10 kΩ.
8.2.2.18 Feedback Divider (R10, R11)
The TPS40170 controller uses a full operational amplifier with an internally fixed 0.6 V reference. The value of
R11 is selected between 10 kΩ and 50 kΩ for a balance of feedback current and noise immunity. With the value
of R11 set to 20 kΩ, the output voltage is programmed with a resistor divider given by Equation 42.
VFB ´ R11
0.600 V ´ 20.0kW
R10 =
=
= 2.73kW » 2.74kW
(VOUT - VFB ) (5.0 V - 0.600 V )
(42)
8.2.2.19 Compensation: (R4, R13, C13, C14, C21)
Using the TPS40k Loop Stability Tool for a 60 kHz bandwidth and a 50° phase margin with an R11 value of
20.0 kΩ, the following values are obtained. The tool is available from the TI website, SLUC263.
• C21 = C1 = 1500 pF
• C13 = C2 = 8200 pF
• C14 = C3 = 220 pF
• R13 = R2 = 511 Ω
• R4 = R3 = 3.83 kΩ
8.2.3 Application Curves
Figure 36 shows an input from 10 V to 60 V for an output of 5.0 V at 6 A, efficiency graph for this design.
Figure 37 shows an input of 24 V for an output of 5.0 V at 6 A, loop response where VIN = 24V and IOUT = 6A,
yielding 58 kHz bandwidth, 51° phase margin. Figure 38 shows the output ripple 20 mV/div, 2 µs/div, 20 MHz
bandwidth.
100
100
225
80
180
60
135
40
90
20
45
0
0
85
VIN = 10 V
VIN = 12 V
VIN = 24 V
VIN = 36 V
VIN = 48 V
VIN = 60 V
80
75
70
0
1
2
3
4
Load Current (A)
5
−20
−40
−60
0.1
6
Figure 36. Efficiency vs. Load Current
−45
−90
Gain
Phase
1
10
Frequency (kHz)
100
−135
1000
Figure 37. Loop Response
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Phase (°)
90
Gain (dB)
Efficiency (%)
95
35
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Figure 38. Output Ripple Waveform
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9 Power Supply Recommendations
The TPS40170 is designed for operation from an input voltage supply range between 4.5 V and 60 V. Good
regulation of this input supply is essential. If the input supply is more distant than a few inches from the
TPS40170 and the buck power stage, the circuit may require additional bulk capacitance in addition to ceramic
bypass capacitors. An electrolytic capacitor with a value of 120 µF is a typical choice.
10 Layout
10.1 Layout Guidelines
Figure 39 illustrates an example layout. For the controller, it is important to carefully connect noise sensitive
signals such as RT, SS, FB, and comp as close to the IC as possible and connect to AGND as shown. The
PowerPad should be connected to any internal PCB ground planes using multiple vias directly under the IC. The
AGND and PGND should be connected at a single point.
When using high-performance FETs such as NexFET™ from Texas Instruments, careful attention to the layout is
required. Minimize the distance between positive node of the input ceramic capacitor and the drain pin of the
control (high-side) FET. Minimize the distance between the negative node of the input ceramic capacitor and the
source pin of the syncronization (low-side) FET. Becasue of the large gate drive, smaller gate charge, and faster
turn-on times of the high-performance FETs, it is recommended to use a minimum of 4, 10 µF ceramic input
capacitors such as TDK #C3216X5R1A106M. Ensure the layout allows a continuous flow of the power planes.
The layout of the HPA578 EVM is shown in Figure 39 through Figure 42 for reference.
10.2 Layout Example
Figure 39. Top Copper, Viewed From Top
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Layout Example (continued)
Figure 40. Bottom Copper, Viewed From Bottom
Figure 41. Internal Layer 1, Viewed from Top
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Layout Example (continued)
Figure 42. Internal Layer 2, Viewed from Top
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11 Device and Documentation Support
11.1 Custom Design with WEBENCH Tools
Create a Custom Design with WEBENCH Tools
11.2 Device Support
11.2.1 Third-Party Products Disclaimer
TI'S PUBLICATION OF INFORMATION REGARDING THIRD-PARTY PRODUCTS OR SERVICES DOES NOT
CONSTITUTE AN ENDORSEMENT REGARDING THE SUITABILITY OF SUCH PRODUCTS OR SERVICES
OR A WARRANTY, REPRESENTATION OR ENDORSEMENT OF SUCH PRODUCTS OR SERVICES, EITHER
ALONE OR IN COMBINATION WITH ANY TI PRODUCT OR SERVICE.
11.2.2 Related Devices
The following device has characteristics similar to the TPS40170 and may be of interest.
DEVICE
TPS40057
DESCRIPTION
Wide Input Synchronous Buck Controller
11.3 Trademarks
WEBENCH is a registered trademark of Texas Instruments.
11.4 Electrostatic Discharge Caution
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
11.5 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
12 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
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PACKAGE OPTION ADDENDUM
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10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
TPS40170RGYR
ACTIVE
VQFN
RGY
20
3000
RoHS & Green
NIPDAU
Level-2-260C-1 YEAR
-40 to 125
40170
TPS40170RGYT
ACTIVE
VQFN
RGY
20
250
RoHS & Green
NIPDAU
Level-2-260C-1 YEAR
-40 to 125
40170
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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