Texas Instruments | Improve the TPIC74100 Load Transient Performance with Suitable Inductor and Capa | Application notes | Texas Instruments Improve the TPIC74100 Load Transient Performance with Suitable Inductor and Capa Application notes

Texas Instruments Improve the TPIC74100 Load Transient Performance with Suitable Inductor and Capa Application notes
Application Report
SLIA092 – June 2019
Improve the TPIC74100-Q1 Load Transient Performance
with Suitable Inductor and Capacitor
Jasper Li
ABSTRACT
The application report firstly introduces the control method used in TPIC74100-Q1 to reduce the output
voltage undershoot. Then the output voltage waveforms at different conditions are measured to verify the
impact of the external components. Finally suitable inductor and capacitor are suggested to get good load
transient performance.
1
2
3
4
Contents
Introduction ...................................................................................................................
Special Control Circuit in BUCK Mode ....................................................................................
Impact of the External Components ......................................................................................
Conclusion ....................................................................................................................
1
Simplified Control Circuit of the TPIC74100-Q1 ......................................................................... 2
2
Load Transient Performance of the TPIC74100EVM ................................................................... 3
3
Load transient performance with ceramic capacitor
1
2
3
5
List of Figures
4
5
6
7
8
9
10
11
....................................................................
Load transient performance at 14-V input ................................................................................
Load transient performance at 26-V input ................................................................................
Load transient performance at L1=33µH .................................................................................
Load transient performance at L1=22µH ................................................................................
Load transient performance with small ESR .............................................................................
Load transient performance with large ESR .............................................................................
Load transient performance with one GRM32ER61A107ME20 .......................................................
Load transient performance with three GRM32ER61A107ME20 in parallel .........................................
3
3
3
4
4
4
4
4
4
List of Tables
1
External components suggestion .......................................................................................... 5
Trademarks
All trademarks are the property of their respective owners.
1
Introduction
The TPCI74100-Q1 is voltage control mode buck-boost converter. It regulates the output voltage to 5V for
a wide input voltage range. When the device operates in BUCK mode, it integrates a special circuit to
reduce the output voltage undershoot when the loading suddenly increases. The application report
introduces the control method of the special circuit and suggests suitable inductor and capacitor to fully
utilize this function
SLIA092 – June 2019
Submit Documentation Feedback
Improving the TPIC74100-Q1 Load Transient Performance with Suitable
Inductor and Capacitor
Copyright © 2019, Texas Instruments Incorporated
1
Special Control Circuit in BUCK Mode
2
www.ti.com
Special Control Circuit in BUCK Mode
The power stage and simplified control circuit are shown in Figure 1. In BUCK mode, the Q3 is always on
and the Q4 is always off. The Q1 and Q2 turn on and off alternatively to regulate the output voltage
VOUT. When the load is stable, the output voltage is controlled by the error amplifier EA. The duty cycle
of the BUCK is proportional to the EA output voltage. If the output current suddenly increases, the VOUT
will drop down because of the response time of the EA and the inductor current. Once the VOUT
decreases more than 90mV, the comparator Comp will outputs logic high signal. This logic high signal will
force the high side MOSFET Q1 on, ignoring the EA output signal. The inductor current linearly increases
when the Q1 turns on. The VOUT starts to increase after the inductor current is higher than the loading.
The comparator will be logic low again when the VOUT is only 40mV (typical) lower than the setting
voltage 5V (typical).The duty cycle of the Q1 is controlled by EA output voltage once comparator output
low logic. However, the duty cycle may be still too low to support loading. The VOUT could drop down to
90mA again and repeat the above process. During the repeating process, the EA voltage slowly increases
as the average output voltage is lower than 5V (typical). The comparator will not be triggered after the EA
is high enough.
VIN
Q1
L1
VOUT
C1
Q3
Q4
Q2
ESR
+
Comp
VREF1
±
PWM
Controller
Circuit
±
EA
VREF2
+
Figure 1. Simplified Control Circuit of the TPIC74100-Q1
The Figure 2 shows the transient performance of the TPIC74100EVM when the loading increase from 50
mA to 500mA. The output capacitor in the TPIC74100 is a tantalum capacitor 594D476X0016C2T, which
has 47µF effective capacitance and approximately 110mΩ ESR. From the waveform, the inductor quickly
increases to reduce the output voltage undershoot when the special circuit is triggered. The VOUT drops
down again if the special circuit exits. The process repeats several times until the EA is higher enough to
support the loading.
2
Improving the TPIC74100-Q1 Load Transient Performance with Suitable
Inductor and Capacitor
Copyright © 2019, Texas Instruments Incorporated
SLIA092 – June 2019
Submit Documentation Feedback
Impact of the External Components
www.ti.com
ICOIL 500mA/div
VOUT 100mV/div
VIN=14V
IOUT=50mA~500mA
L1=33µH
C1=47µF
ESR=110mŸ
100µs/div
Figure 2. Load Transient Performance of the TPIC74100EVM
Improper external components could lead to overshoot in the VOUT after the special circuit exits. If the
overshoot is so large that the average voltage of the VOUT is equal to 5V (typical). The EA output can’t
increase to the voltage level required by the loading. So the special circuit will be repeatedly triggered,
which will result in large output voltage ripple. The behavior is shown in Figure 3. The waveform is tested
by changing the TPIC74100EVM output tantalum capacitor to ceramic capacitor GRM32ER61A107ME20.
The effective capacitance of the GRM32ER61A107ME20 is approximately 46µF at 5-V bias condition. The
ESR of a ceramic capacitor is much smaller than tantalum capacitor.
ICOIL 500mA/div
VOUT 100mV/div
VIN=14V
IOUT=50mA~500mA
L1=33µH
C1=46µF
ESR=1mŸ
100µs/div
Figure 3. Load transient performance with ceramic capacitor
3
Impact of the External Components
To avoid the behavior as in Figure 3, the overshoot in the VOUT should be limited. The overshoot of
VOUT is impacted by the input voltage, inductor L1, output capacitor C1 and its ESR.
• High input voltage increase the overshoot as more energy flowing to the output capacitor.
• High inductance increase the overshoot as the inductor stores more energy before the comparator
outputs logic low.
• High output capacitance reduces the overshoot.
• High ESR of the output capacitor reduces the overshoot. Because the voltage drop on the ESR helps
to change the comparator output to logic low quickly. However, large ESR also increase the output
ripple at stable condition.
The Figure 4 and Figure 5 are the load transient performance at 14-V and 26-V input voltage respectively.
the inductor current is higher at 26 V condition which results in higher overshoot in the VOUT.
SLIA092 – June 2019
Submit Documentation Feedback
Improving the TPIC74100-Q1 Load Transient Performance with Suitable
Inductor and Capacitor
Copyright © 2019, Texas Instruments Incorporated
3
Impact of the External Components
www.ti.com
ICOIL 500mA/div
ICOIL 500mA/div
VOUT 100mV/div
VOUT 100mV/div
VIN=14V
IOUT=50mA~500mA
L1=33µH
C1=47µF
ESR=110mŸ
VIN=26V
IOUT=50mA~500mA
L1=33µH
C1=47µF
ESR=110mŸ
100µs/div
100µs/div
Figure 5. Load transient performance at 26-V input
Figure 4. Load transient performance at 14-V input
The Figure 6 and Figure 7 show the load transient performance at 33µH and 22µH inductor respectively.
With 33µH inductor, the inductor stores more energy before the special circuit exits. The energy causes a
little higher overshoot in the VOUT.
ICOIL 500mA/div
ICOIL 500mA/div
VOUT 100mV/div
VOUT 100mV/div
VIN=14V
IOUT=50mA~1A
L1=33µH
C1=47µF
ESR=110mŸ
VIN=14V
IOUT=50mA~1A
L1=22µH
C1=47µF
ESR=110mŸ
100µs/div
Figure 6. Load transient performance at L1=33µH
100µs/div
Figure 7. Load transient performance at L1=22µH
The Figure 8 shows the load transient performance when output capacitor is pure ceramic capacitor
GRM32ER61A107ME20 of which the ESR is only 1mΩ. Without enough ESR, the inductor increases to
high level before the special circuit exits. The high current in the inductor causes high overshoot in the
VOUT. With 82mΩ resistor in series with the output capacitor, the inductor peak current greatly decreases,
so the VOUT overshoot is much smaller in Figure 9.
ICOIL 500mA/div
ICOIL 500mA/div
VOUT 100mV/div
VOUT 100mV/div
VIN=14V
IOUT=50mA~500mA
L1=22µH
C1=46µF
ESR=1mŸ
VIN=14V
IOUT=50mA~500mA
L1=22µH
C1=46µF
ESR=82mŸ
100µs/div
Figure 8. Load transient performance with small ESR
100µs/div
Figure 9. Load transient performance with large ESR
The Figure 10 is measured with a ceramic capacitor GRM32ER61A107ME20 and a 82mΩ ESR. While in
Figure 11, the output capacitor increases to three GRM32ER61A107ME20 in parallel and the ESR is still
82mΩ. The waveforms show that larger capacitance also help to reduce the overshoot of the VOUT.
4
Improving the TPIC74100-Q1 Load Transient Performance with Suitable
Inductor and Capacitor
Copyright © 2019, Texas Instruments Incorporated
SLIA092 – June 2019
Submit Documentation Feedback
Conclusion
www.ti.com
ICOIL 500mA/div
ICOIL 500mA/div
VOUT 100mV/div
VOUT 100mV/div
VIN=26V
IOUT=50mA~500mA
L1=22µH
C1=46µF
ESR=82mŸ
VIN=26V
IOUT=50mA~1mA
L1=22µH
C1=138µF
ESR=82mŸ
100µs/div
Figure 10. Load transient performance with one
GRM32ER61A107ME20
100µs/div
Figure 11. Load transient performance with three
GRM32ER61A107ME20 in parallel
Based on above measurements, following external components are suggested to improve the load
transient performance of the TPS74100-Q1.
Table 1. External components suggestion
4
Input Voltage VIN
Inductor L1
Effective output capacitance C1
ESR of the output capacitor
VIN < 18V
22µH
100µF ≤ C1 ≤ 470µF
50mΩ ≤ ESR ≤ 150mΩ
VIN < 26V
22µH
150µF ≤ C1 ≤ 470µF
100mΩ ≤ ESR ≤ 150mΩ
Conclusion
The application report introduces the special control circuit of the TPIC74100-Q1 in BUCK mode. This
control circuit is designed to reduce the undershoot of the VOUT when the loading is suddenly applied.
However, improper selection of the external components would result in high output ripple after the load
transient. To overcome this issue, the application report investigate the impact of each external
component and finally suggest the suitable components for different input condition.
SLIA092 – June 2019
Submit Documentation Feedback
Improving the TPIC74100-Q1 Load Transient Performance with Suitable
Inductor and Capacitor
Copyright © 2019, Texas Instruments Incorporated
5
IMPORTANT NOTICE AND DISCLAIMER
TI PROVIDES TECHNICAL AND RELIABILITY DATA (INCLUDING DATASHEETS), DESIGN RESOURCES (INCLUDING REFERENCE
DESIGNS), APPLICATION OR OTHER DESIGN ADVICE, WEB TOOLS, SAFETY INFORMATION, AND OTHER RESOURCES “AS IS”
AND WITH ALL FAULTS, AND DISCLAIMS ALL WARRANTIES, EXPRESS AND IMPLIED, INCLUDING WITHOUT LIMITATION ANY
IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT OF THIRD
PARTY INTELLECTUAL PROPERTY RIGHTS.
These resources are intended for skilled developers designing with TI products. You are solely responsible for (1) selecting the appropriate
TI products for your application, (2) designing, validating and testing your application, and (3) ensuring your application meets applicable
standards, and any other safety, security, or other requirements. These resources are subject to change without notice. TI grants you
permission to use these resources only for development of an application that uses the TI products described in the resource. Other
reproduction and display of these resources is prohibited. No license is granted to any other TI intellectual property right or to any third
party intellectual property right. TI disclaims responsibility for, and you will fully indemnify TI and its representatives against, any claims,
damages, costs, losses, and liabilities arising out of your use of these resources.
TI’s products are provided subject to TI’s Terms of Sale (www.ti.com/legal/termsofsale.html) or other applicable terms available either on
ti.com or provided in conjunction with such TI products. TI’s provision of these resources does not expand or otherwise alter TI’s applicable
warranties or warranty disclaimers for TI products.
Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265
Copyright © 2019, Texas Instruments Incorporated
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertising