LM5116WG/NOPB [TI]

100V 宽输入电压同步降压控制器 | NAR | 20 | -40 to 125;
LM5116WG/NOPB
型号: LM5116WG/NOPB
厂家: TEXAS INSTRUMENTS    TEXAS INSTRUMENTS
描述:

100V 宽输入电压同步降压控制器 | NAR | 20 | -40 to 125

控制器
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LM5116WG  
www.ti.com  
SNVS599D OCTOBER 2008REVISED FEBRUARY 2013  
LM5116WG Wide Range Synchronous Buck Controller  
Check for Samples: LM5116WG  
1
FEATURES  
DESCRIPTION  
The LM5116WG is a synchronous buck controller  
intended for step-down regulator applications from a  
high voltage or widely varying input supply. The  
control method is based upon current mode control  
utilizing an emulated current ramp. Current mode  
control provides inherent line feed-forward, cycle by  
cycle current limiting and ease of loop compensation.  
The use of an emulated control ramp reduces noise  
sensitivity of the pulse-width modulation circuit,  
allowing reliable control of very small duty cycles  
necessary in high input voltage applications. The  
operating frequency is programmable from 50 kHz to  
1 MHz. The LM5116WG drives external high-side and  
low-side NMOS power switches with adaptive dead-  
time control. A user-selectable diode emulation mode  
enables discontinuous mode operation for improved  
efficiency at light load conditions. A low quiescent  
current shutdown disables the controller and  
consumes less than 10 µA of total input current.  
2
Hermetic Package for Harsh Operating  
Environments  
Emulated Peak Current Mode  
Wide Operating Range up to 100V  
Low IQ Shutdown (< 10 µA)  
Drives Standard or Logic Level MOSFETs  
Robust 3.5A Peak Gate Drive  
Free-Run or Synchronous Operation to 1 MHz  
Optional Diode Emulation Mode  
Programmable Output from 1.215V to 80V  
Precision 1.5% Voltage Reference  
Programmable Current Limit  
Programmable Soft-Start  
Programmable Line Under-Voltage Lockout  
Automatic Switch to External Bias Supply  
CPGA-20 with No Thermal Shutdown  
Additional features include  
a high voltage bias  
regulator, automatic switch-over to external bias for  
improved efficiency, frequency synchronization, cycle  
by cycle current limit and adjustable line under-  
voltage lockout. The device is available in a CPGA-20  
high temperature ceramic package with the thermal  
shutdown feature disabled.  
Typical Application  
VIN  
VCC  
VIN  
LM5116WG  
C
VCC  
R
R
C
UV2  
IN  
HB  
UVLO  
V
IN  
UV1  
C
HB  
HO  
SW  
L
EN  
VOUT  
C
SYNC  
RT/SYNC  
C
OUT  
LO  
CS  
R
T
R
S
COMP  
FB  
CSG  
C
COMP  
DEMB  
C
HF  
R
COMP  
VOUT  
VCCX  
R
R
FB2  
SS  
RAMP  
C
AGND PGND  
RAMP  
C
SS  
FB1  
1
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of  
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.  
All trademarks are the property of their respective owners.  
2
PRODUCTION DATA information is current as of publication date.  
Products conform to specifications per the terms of the Texas  
Instruments standard warranty. Production processing does not  
necessarily include testing of all parameters.  
Copyright © 2008–2013, Texas Instruments Incorporated  
LM5116WG  
SNVS599D OCTOBER 2008REVISED FEBRUARY 2013  
www.ti.com  
Connection Diagram  
VIN  
UVLO  
RT/SYNC  
EN  
1
2
20  
19  
18  
17  
16  
15  
14  
13  
12  
11  
SW  
HO  
3
HB  
4
VCCX  
VCC  
LO  
RAMP  
AGND  
SS  
5
6
7
PGND  
CSG  
CS  
FB  
8
COMP  
VOUT  
9
10  
DEMB  
Figure 1. Top View  
See Package Number NAR0020A  
2
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LM5116WG  
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SNVS599D OCTOBER 2008REVISED FEBRUARY 2013  
PIN DESCRIPTIONS  
Pin  
1
Name  
Description  
VIN  
Chip supply voltage, input voltage monitor and input to the VCC regulator.  
2
UVLO  
If the UVLO pin is below 1.215V, the regulator will be in standby mode (VCC regulator running, switching regulator  
disabled). If the UVLO pin voltage is above 1.215V, the regulator is operational. An external voltage divider can be used  
to set an under-voltage shutdown threshold. There is a fixed 5 µA pull up current on this pin when EN is high. UVLO is  
pulled to ground in the event a current limit condition exists for 256 clock cycles.  
3
RT/SYN The internal oscillator is set with a single resistor between this pin and the AGND pin. The recommended frequency  
C
range is 50 kHz to 1 MHz. The internal oscillator can be synchronized to an external clock by AC coupling a positive  
edge onto this node.  
4
5
EN  
If the EN pin is below 0.5V, the regulator will be in a low power state drawing less than 10 µA from VIN. EN must be  
pulled above 3.3V for normal operation.  
RAMP Ramp control signal. An external capacitor connected between this pin and the AGND pin sets the ramp slope used for  
current mode control.  
6
7
AGND Analog ground. Connect directly to PGND under the LM5116WG.  
SS  
An external capacitor and an internal 10 µA current source set the soft start time constant for the rise of the error amp  
reference. The SS pin is held low during VCC < 4.5V, UVLO < 1.215V, or EN input low.  
8
9
FB  
Feedback signal from the regulated output. This pin is connected to the inverting input of the internal error amplifier. The  
regulation threshold is 1.215V.  
COMP Output of the internal error amplifier. The loop compensation network should be connected between this pin and the FB  
pin.  
10  
11  
VOUT  
Output monitor. Connect directly to the output voltage.  
DEMB Low-side MOSFET source voltage monitor for diode emulation. For start-up into a pre-biased load, tie this pin to ground  
at the CSG connection. For fully synchronous operation, use an external series resistor between DEMB and ground to  
raise the diode emulation threshold above the low-side SW on-voltage.  
12  
13  
CS  
Current sense amplifier input. Connect to the top of the current sense resistor or the drain of the low-sided MOSFET if  
RDS(ON) current sensing is used.  
CSG  
Current sense amplifier input. Connect to the bottom of the sense resistor or the source of the low-side MOSFET if  
RDS(ON) current sensing is used.  
14  
15  
16  
17  
PGND Power ground. Connect directly to AGND under the LM5116WG.  
LO  
Connect to the gate of the low-side synchronous MOSFET through a short, low inductance path.  
Locally decouple to PGND using a low ESR/ESL capacitor located as close to the controller as possible.  
VCC  
VCCX  
Optional input for an externally supplied VCC. If VCCX > 4.5V, VCCX is internally connected to VCC and the internal  
VCC regulator is disabled. If VCCX is unused, it should be connected to ground.  
18  
HB  
High-side driver supply for bootstrap gate drive. Connect to the cathode of the bootstrap diode and the positive terminal  
of the bootstrap capacitor. The bootstrap capacitor supplies current to charge the high-side MOSFET gate and should be  
placed as close to the controller as possible.  
19  
20  
HO  
SW  
Connect to the gate of the high-side synchronous MOSFET through a short, low inductance path.  
Switch node. Connect to the negative terminal of the bootstrap capacitor and the source terminal of the high-side  
MOSFET.  
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.  
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Absolute Maximum Ratings(1)(2)  
VIN to GND  
-0.3V to 100V  
-0.3 to 16V  
(3)  
VCC, VCCX, UVLO to GND  
SW, CS to GND  
HB to SW  
-3.0 to 100V  
-0.3 to 16V  
HO to SW  
-0.3 to HB+0.3V  
-0.3 to 100V  
-1V to 1V  
VOUT to GND  
CSG to GND  
LO to GND  
SS to GND  
FB to GND  
-0.3 to VCC+0.3V  
-0.3 to 7V  
-0.3 to 7V  
DEMB to GND  
RT to GND  
EN to GND  
ESD Rating  
-0.3 to VCC  
-0.3 to 7V  
-0.3 to 100V  
(4)  
HBM  
2 kV  
-55°C to +150°C  
+150°C  
Storage Temperature Range  
Junction Temperature  
(1) Absolute Maximum Ratings indicate limits beyond which damage to the component may occur.  
(2) If Military/Aerospace specified devices are required, please contact the TI Sales Office/Distributors for availability and specifications.  
(3) These pins must not exceed VIN.  
(4) The human body model is a 100 pF capacitor discharged through a 1.5 kresistor into each pin. LO, HO and HB are rated at 1 kV. 2  
kV rating for all pins except VIN which is rated for 1.5 kV.  
Operating Ratings(1)(2)  
VIN  
6V to 100V  
4.75V to 15V  
4.75V to 15V  
-0.3V to 2V  
VCC, VCCX  
HB to SW  
DEMB to GND  
Junction Temperature  
-40°C to +125°C  
(1) Operating Ratings are conditions under which operation of the device is intended to be functional. Operating Ratings do not imply  
guaranteed performance limits.  
(2) Note: RAMP, COMP are output pins. As such they are not specified to have an external voltage applied.  
Electrical Characteristics  
Limits in standard type are for TJ = 25°C only; limits in boldface type apply over the junction temperature range of -40°C to  
+125°C and are provided for reference only. Unless otherwise specified, the following conditions apply: VIN = 48V, VCC =  
7.4V, VCCX = 0V, EN = 5V, RT = 16 k, no load on LO and HO.  
Symbol  
VIN Supply  
Parameter  
Conditions  
Min  
Typ  
Max  
Units  
IBIAS  
IBIASX  
ISTDBY  
VIN Operating Current  
VIN Operating Current  
VIN Shutdown Current  
VCCX = 0V, VIN = 48V  
VCCX = 0V, VIN = 100V  
VCCX = 5V, VIN = 48V  
VCCX = 5V, VIN = 100V  
EN = 0V, VIN = 48V  
5
5.9  
1.2  
1.6  
1
7
mA  
mA  
mA  
mA  
µA  
8
1.7  
2.3  
10  
EN = 0V, VIN = 100V  
1
µA  
4
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LM5116WG  
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SNVS599D OCTOBER 2008REVISED FEBRUARY 2013  
Electrical Characteristics (continued)  
Limits in standard type are for TJ = 25°C only; limits in boldface type apply over the junction temperature range of -40°C to  
+125°C and are provided for reference only. Unless otherwise specified, the following conditions apply: VIN = 48V, VCC =  
7.4V, VCCX = 0V, EN = 5V, RT = 16 k, no load on LO and HO.  
Symbol  
VCC Regulator  
VCC(REG)  
Parameter  
Conditions  
Min  
Typ  
Max  
7.7  
6.0  
4.7  
6.2  
Units  
VCC Regulation  
7.1  
7.4  
10.6  
5.9  
V
V
VCC LDO Mode Turn-off  
VCC Regulation  
VIN = 6V  
5.0  
15  
V
VCC Sourcing Current Limit  
VCCX Switch Threshold  
VCCX Switch Hysteresis  
VCCX Switch RDS(ON)  
VCCX Leakage  
VCC = 0V  
VCCX Rising  
26  
mA  
V
4.3  
4.5  
0.25  
3.8  
V
ICCX = 10 mA  
VCCX = 0V  
VCCX = 3V  
VCC Rising  
-200  
100  
4.5  
nA  
kΩ  
V
VCCX Pull- down Resistance  
VCC Under-voltage Threshold  
VCC Under-voltage Hysteresis  
HB DC Bias Current  
4.3  
4.7  
200  
0.5  
0.2  
V
HB - SW = 15V  
125  
µA  
EN Input  
VIL max  
VIH min  
EN Input Low Threshold  
EN Input High Threshold  
EN Input Bias Current  
EN Input Bias Current  
EN Input Bias Current  
V
3.3  
-7.5  
-1  
V
VEN = 3V  
-3  
0
1
1
µA  
µA  
µA  
VEN = 0.5V  
VEN = 100V  
20  
90  
UVLO Thresholds  
UVLO Standby Threshold  
UVLO Threshold Hysteresis  
UVLO Pull-up Current Source  
UVLO Pull-down RDS(ON)  
UVLO Rising  
UVLO = 0V  
1.170  
1.215  
0.1  
1.262  
V
V
5.4  
µA  
80  
210  
14  
Soft Start  
SS Current Source  
SS = 0V  
8
11  
3
µA  
V
SS Diode Emulation Ramp Disable  
Threshold  
SS Rising  
SS to FB Offset  
FB = 1.25V  
160  
45  
mV  
mV  
SS Output Low Voltage  
Sinking 100 µA, UVLO = 0V  
Error Amplifier  
VREF  
FB Reference Voltage  
Measured at FB pin, FB =  
COMP  
1.195  
3
1.215  
15  
1.231  
500  
V
FB Input Bias Current  
COMP Sink/Source Current  
DC Gain  
FB = 2V  
nA  
mA  
dB  
AOL  
fBW  
80  
3
Unity Gain Bandwidth  
MHz  
PWM Comparators  
tHO(OFF)  
Forced HO Off-time  
320  
450  
100  
580  
ns  
ns  
tON(min)  
Minimum HO On-time  
VIN = 80V, CRAMP = 50 pF  
Oscillator  
fSW1  
Frequency 1  
RT = 16 kΩ  
RT = 5 kΩ  
180  
480  
200  
535  
220  
590  
kHz  
kHz  
V
fSW2  
Frequency 2  
RT output voltage  
RT sync positive threshold  
1.191  
3.0  
1.215  
3.5  
1.239  
4.0  
V
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SNVS599D OCTOBER 2008REVISED FEBRUARY 2013  
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Electrical Characteristics (continued)  
Limits in standard type are for TJ = 25°C only; limits in boldface type apply over the junction temperature range of -40°C to  
+125°C and are provided for reference only. Unless otherwise specified, the following conditions apply: VIN = 48V, VCC =  
7.4V, VCCX = 0V, EN = 5V, RT = 16 k, no load on LO and HO.  
Symbol  
Current Limit  
Parameter  
Conditions  
Min  
Typ  
Max  
Units  
VCS(TH)  
Cycle-by-cycle Sense Voltage Threshold VCCX = 0V, RAMP = 0V  
(CSG - CS)  
94  
105  
-1  
110  
122  
126  
139  
mV  
mV  
VCS(THX)  
Cycle-by-cycle Sense Voltage Threshold VCCX = 5V, RAMP = 0V  
(CSG - CS)  
CS Bias Current  
CS = 100V  
CS = 0V  
1
µA  
µA  
µA  
ms  
CS Bias Current  
90  
90  
125  
125  
CSG Bias Current  
Current Limit Fault Timer  
CSG = 0V  
RT = 16 k, (200 kHz), (256  
1.28  
clock cycles)  
RAMP Generator  
IR1  
IR2  
RAMP Current 1  
VIN = 60V, VOUT=10V  
VIN = 10V, VOUT = 10V  
VOUT = 36V  
235  
21  
285  
28  
335  
35  
µA  
µA  
µA  
mV  
RAMP Current 2  
VOUT Bias Current  
RAMP Output Low Voltage  
200  
265  
VIN = 60V, VOUT = 10V  
Diode Emulation  
SW Zero Cross Threshold  
DEMB Output Current  
DEMB Output Current  
DEMB Output Current  
-6  
2.7  
38  
65  
mV  
µA  
µA  
µA  
DEMB = 0V, SS = 1.25V  
DEMB =0V, SS = 2.8V  
1.6  
28  
45  
3.8  
48  
85  
DEMB = 0V, SS = Regulated  
by FB  
LO Gate Driver  
VOLL  
LO Low-state Output Voltage  
LO High-state Output Voltage  
ILO = 100 mA  
0.08  
0.25  
0.17  
V
V
VOHL  
ILO = -100 mA, VOHL = VCC  
VLO  
-
LO Rise Time  
C-load = 1000 pF  
C-load = 1000 pF  
VLO = 0V  
18  
12  
ns  
ns  
A
LO Fall Time  
IOHL  
IOLL  
Peak LO Source Current  
Peak LO Sink Current  
1.8  
3.5  
VLO = VCC  
A
HO Gate Driver  
VOLH  
HO Low-state Output Voltage  
HO High-state Output Voltage  
IHO = 100 mA  
0.17  
0.45  
0.27  
V
V
VOHH  
IHO = -100 mA, VOHH = VHB  
VHO  
-
HO Rise Time  
C-load = 1000 pF  
C-load = 1000 pF  
VHO = 0V  
19  
13  
1
ns  
ns  
A
HO High-side Fall Time  
Peak HO Source Current  
Peak HO Sink Current  
HB to SW under-voltage  
IOHH  
IOLH  
VHO = VCC  
2.2  
3
A
V
Switching Characteristics  
LO Fall to HO Rise Delay  
HO Fall to LO Rise Delay  
C-load = 0  
C-load = 0  
75  
70  
ns  
ns  
Thermal  
θJA  
Junction to Ambient  
Junction to Case  
115  
13  
°C/W  
°C/W  
θJC  
6
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Typical Performance Characteristics  
FB Reference Voltage vs Temperature  
FB Input Bias Current vs Temperature  
Figure 2.  
Figure 3.  
EN Input Threshold vs Temperature  
VIN Operating Current vs Temperature  
Figure 4.  
Figure 5.  
SS Current vs Temperature  
RAMP Current vs Temperature  
Figure 6.  
Figure 7.  
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Typical Performance Characteristics (continued)  
VCC UVLO vs Temperature  
VCC LDO Switch vs Temperature  
Figure 8.  
Figure 9.  
VCC Regulation vs Temperature  
VCC Current Limit vs Temperature  
Figure 10.  
Figure 11.  
VCCX Switch Threshold vs Temperature  
VCCX Switch RDS(ON) vs Temperature  
Figure 12.  
Figure 13.  
8
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Typical Performance Characteristics (continued)  
Frequency vs Temperature  
Frequency vs Temperature  
Figure 14.  
Figure 15.  
RT/SYNC Threshold vs Temperature  
RT/SYNC Hysteresis vs Temperature  
Figure 16.  
Figure 17.  
Forced HO Off-Time vs Temperature  
DEMB Output Current vs Temperature  
Figure 18.  
Figure 19.  
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Typical Performance Characteristics (continued)  
Current Limit Threshold vs Temperature  
HO UVLO vs Temperature  
Figure 20.  
Figure 21.  
CS & CSG Input Bias Current vs Temperature  
HO & LO Delay vs Temperature  
Figure 22.  
Figure 23.  
CS Input Bias Current vs Temperature  
HB Input Bias Current vs Temperature  
Figure 24.  
Figure 25.  
10  
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Block Diagram and Typical Application Circuit  
VCCX  
17  
VCCX  
C
VCCX  
LM5116WG  
+
-
4.5V  
V
IN  
6V-100V  
VCC  
1
4
2
16  
VIN  
7. 4 V  
REGULATOR  
UVLO  
R
C
EN  
VCC  
D1  
C
IN  
SLEEP  
MODE  
SHUTDOWN  
EN  
EN  
STANDBY  
1.215V  
D2  
HB 18  
R
R
5 mA  
UV2  
UV1  
UVLO  
UVLO  
LOGIC  
C
FT  
DIS  
C
HB  
HICCUP FAULT TIMER  
256 CLOCK CYCLES  
UVLO  
V
IN  
DRIVER  
HO 19  
CLK  
Q1  
10 mA  
S
R
Q
Q
L1  
SS  
ADAPTIVE  
TIMER  
7
8
VOUT  
3V  
1V  
SW 20  
PWM  
C
SS  
VCC  
DRIVER  
1.215V  
FB  
Q2  
C
CURRENT  
LIMIT  
SNUB  
LO 15  
C
OUT  
R
SNUB  
12  
CS  
TRACK  
SAMPLE  
and  
C
ERROR  
AMP  
COMP  
1.6V  
10 x RS V/A  
0.5V  
A=10  
C
HF  
R
S
HOLD  
R
COMP  
13  
CSG  
COMP  
9
+
CLK  
DIODE  
EMULATION  
CONTROL  
SW  
11  
DEMB  
SS  
VOUT 10  
VIN  
CLK  
C
SYNC  
SYNC  
RT/SYNC  
3
OSCILLATOR  
R
FB2  
RAMP GENERATOR  
= 5mA/V x (VIN - VOUT) + 25 mA  
I
R
R
T
IR  
R
FB1  
RAMP  
AGND  
PGND  
5
6
14  
C
RAMP  
Figure 26.  
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DETAILED OPERATING DESCRIPTION  
The LM5116WG high voltage switching regulator features all of the functions necessary to implement an efficient  
high voltage buck regulator using a minimum of external components. This easy to use regulator integrates high-  
side and low-side MOSFET drivers capable of supplying peak currents of 2 Amps. The regulator control method  
is based on current mode control utilizing an emulated current ramp. Emulated peak current mode control  
provides inherent line feed-forward, cycle by cycle current limiting and ease of loop compensation. The use of an  
emulated control ramp reduces noise sensitivity of the pulse-width modulation circuit, allowing reliable processing  
of the very small duty cycles necessary in high input voltage applications. The operating frequency is user  
programmable from 50 kHz to 1 MHz. An oscillator/synchronization pin allows the operating frequency to be set  
by a single resistor or synchronized to an external clock. Fault protection features include current limiting and  
remote shutdown capability. An under-voltage lockout input allows regulator shutdown when the input voltage is  
below a user selected threshold, and an enable function will put the regulator into an extremely low current  
shutdown via the enable input.  
High Voltage Start-Up Regulator  
The LM5116WG contains a dual mode internal high voltage startup regulator that provides the VCC bias supply  
for the PWM controller and a boot-strap gate drive for the high-side buck MOSFET. The input pin (VIN) can be  
connected directly to an input voltage source as high as 100 volts. For input voltages below 10.6V, a low dropout  
switch connects VCC directly to VIN. In this supply range, VCC is approximately equal to VIN. For VIN voltages  
greater than 10.6V, the low dropout switch is disabled and the VCC regulator is enabled to maintain VCC at  
approximately 7.4V. The wide operating range of 6V to 100V is achieved through the use of this dual mode  
regulator.  
Upon power-up, the regulator sources current into the capacitor connected to the VCC pin. When the voltage at  
the VCC pin exceeds 4.5V and the UVLO pin is greater than 1.215V, the output switch is enabled and a soft-start  
sequence begins. The output switch remains enabled until VCC falls below 4.5V, EN is pulled low or the UVLO  
pin falls below 1.215V.  
VCCX  
C
VCCX  
V
OUT  
SW  
L
C
OUT  
Figure 27. VCCX Bias Supply with Additional Inductor Winding  
An output voltage derived bias supply can be applied to the VCCX pin to reduce the IC power dissipation. If the  
bias supply voltage is greater than 4.5V, the internal regulator will essentially shut off, reducing the IC power  
dissipation. The VCC regulator series pass transistor includes a diode between VCC and VIN that should not be  
forward biased in normal operation. For an output voltage between 5V and 15V, VOUT can be connected directly  
to VCCX. For VOUT < 5V, a bias winding on the output inductor can be added to VOUT. If the bias winding can  
supply VCCX greater than VIN, an external blocking diode is required from the input power supply to the VIN pin  
to prevent VCC from discharging into the input supply.  
The output of the VCC regulator is current limited to 15 mA minimum. The VCC current is determined by the  
MOSFET gate charge, switching frequency and quiescent current (see MOSFETs section in the Application  
Information). If VCCX is powered by the output voltage or an inductor winding, the VCC current should be  
evaluated during startup to ensure that it is less than the 15 mA minimum current limit specification. IF VCCX is  
powered by an external regulator derived from VIN, there is no restriction on the VCC current.  
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V
IN  
1
6
VIN  
0.1 mF  
AGND  
Figure 28. Input Blocking Diode for VCCX > VIN  
In high voltage applications extra care should be taken to ensure the VIN pin does not exceed the absolute  
maximum voltage rating of 100V. During line or load transients, voltage ringing on the VIN line that exceeds the  
Absolute Maximum Ratings can damage the IC. Both careful PC board layout and the use of quality bypass  
capacitors located close to the VIN and GND pins are essential.  
Enable  
The LM5116WG contains an enable function allowing a very low input current shutdown. If the enable pin is  
pulled below 0.5V, the regulator enters shutdown, drawing less than 10 µA from the VIN pin. Raising the EN  
input above 3.3V returns the regulator to normal operation. The maximum EN transition time for proper operation  
is one switching period. For example, the enable rise time must be less than 4 μs for 250 kHz operation.  
A 1 Mpull-up resistor to VIN can be used to interface with an open collector control signal. At low input voltage  
the pull-up resistor may be reduced to 100 kto speed up the EN transition time. The EN pin can be tied directly  
to VIN if this function is not needed. It must not be left floating. If low-power shutdown is not needed, the UVLO  
pin should be used as an on/off control.  
Internal 5V rail  
3 mA  
EN  
6V  
Figure 29. Enable Circuit  
Figure 30. EN Bias Current vs Voltage  
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UVLO  
An under-voltage lockout pin is provided to disable the regulator without entering shutdown. If the UVLO pin is  
pulled below 1.215V, the regulator enters a standby mode of operation with the soft-start capacitor discharged  
and outputs disabled, but with the VCC regulator running. If the UVLO input is pulled above 1.215V, the  
controller will resume normal operation. A voltage divider from input to ground can be used to set a VIN threshold  
to disable the supply in brown-out conditions or for low input faults. The UVLO pin has a 5 µA internal pull up  
current that allows this pin to left open if the input under-voltage lockout function is not needed. For applications  
which require fast on/off cycling, the UVLO pin with an open collector control signal may be used to ensure  
proper start-up sequencing.  
The UVLO pin is also used to implement a “hiccup” current limit. If a current limit fault exists for more than 256  
consecutive clock cycles, the UVLO pin will be internally pulled down to 200 mV and then released. A capacitor  
to ground connected to the UVLO pin will set the timing for hiccup mode current limit. When this feature is used  
in conjunction with the voltage divider, a diode across the top resistor may be used to discharge the capacitor in  
the event of an input under-voltage condition. There is a 5 µs filter at the input to the fault comparator. At higher  
switching frequency (greater than approximately 250 kHz) the hiccup timer may be disabled if the fault capacitor  
is not used.  
Oscillator and Sync Capability  
The LM5116WG oscillator frequency is set by a single external resistor connected between the RT/SYNC pin  
and the AGND pin. The resistor should be located very close to the device and connected directly to the pins of  
the IC (RT/SYNC and AGND). To set a desired oscillator frequency (fSW), the necessary value for the resistor  
can be calculated from the following equation:  
T - 450 ns  
RT =  
284 pF  
(1)  
Where T = 1 / fSW and RT is in ohms. 450 ns represents the fixed minimum off time.  
The LM5116WG oscillator has a maximum programmable frequency that is dependent on the VCC voltage. If  
VCC is above 6V, the frequency can be programmed up to 1 MHz. If VCCX is used to bias VCC and VCCX <  
6V, the maximum programmable oscillator frequency is 750 kHz.  
The RT/SYNC pin can be used to synchronize the internal oscillator to an external clock. The external clock must  
be a higher frequency than the free-running frequency set by the RT resistor. The internal oscillator can be  
synchronized to an external clock by AC coupling a positive edge into the RT/SYNC pin. The voltage at the  
RT/SYNC pin is nominally 1.215V and must exceed 4V to trip the internal synchronization pulse detection. A 5V  
amplitude signal and 100 pF coupling capacitor are recommended. The free-running frequency should be set  
nominally 15% below the external clock. Synchronizing above twice the free-running frequency may result in  
abnormal behavior of the pulse width modulator.  
Error Amplifier and PWM Comparator  
The internal high-gain error amplifier generates an error signal proportional to the difference between the  
regulated output voltage and an internal precision reference (1.215V). The output of the error amplifier is  
connected to the COMP pin allowing the user to provide loop compensation components, generally a type II  
network. This network creates a pole at very low frequency, a mid-band zero, and a noise reducing high  
frequency pole. The PWM comparator compares the emulated current sense signal from the RAMP generator to  
the error amplifier output voltage at the COMP pin.  
Ramp Generator  
The ramp signal used in the pulse width modulator for current mode control is typically derived directly from the  
buck switch current. This switch current corresponds to the positive slope portion of the inductor current. Using  
this signal for the PWM ramp simplifies the control loop transfer function to a single pole response and provides  
inherent input voltage feed-forward compensation. The disadvantage of using the buck switch current signal for  
PWM control is the large leading edge spike due to circuit parasitics that must be filtered or blanked. Also, the  
current measurement may introduce significant propagation delays. The filtering, blanking time and propagation  
delay limit the minimal achievable pulse width. In applications where the input voltage may be relatively large in  
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comparison to the output voltage, controlling small pulse widths and duty cycles is necessary for regulation. The  
LM5116WG utilizes a unique ramp generator which does not actually measure the buck switch current but rather  
reconstructs the signal. Representing or emulating the inductor current provides a ramp signal to the PWM  
comparator that is free of leading edge spikes and measurement or filtering delays. The current reconstruction is  
comprised of two elements, a sample-and-hold DC level and an emulated current ramp.  
t
ON  
(5 mA/V x (VIN-VOUT) + 25 mA) x  
C
RAMP  
RAMP  
Sample and Hold  
DC Level  
10 x R V/A  
S
t
ON  
Figure 31. Composition of Current Sense Signal  
The sample-and-hold DC level is derived from a measurement of the recirculating current through either the low-  
side MOSFET or current sense resistor. The voltage level across the MOSFET or sense resistor is sampled and  
held just prior to the onset of the next conduction interval of the buck switch. The current sensing and sample-  
and-hold provide the DC level of the reconstructed current signal. The positive slope inductor current ramp is  
emulated by an external capacitor connected from the RAMP pin to the AGND and an internal voltage controlled  
current source. The ramp current source that emulates the inductor current is a function of the VIN and VOUT  
voltages per the following equation:  
IR = 5 µA/V x (VIN - VOUT) + 25 µA  
(2)  
Proper selection of the RAMP capacitor (CRAMP) depends upon the value of the output inductor (L) and the  
current sense resistor (RS). For proper current emulation, the DC sample and hold value and the ramp amplitude  
must have the same dependence on the load current. That is:  
gm x L  
, so  
RS x A =  
CRAMP  
gm x L  
A x RS  
CRAMP  
=
(3)  
Where gm is the ramp generator transconductance (5 µA/V) and A is the current sense amplifier gain (10 V/V).  
The ramp capacitor should be located very close to the device and connected directly to the pins of the IC  
(RAMP and AGND).  
The difference between the average inductor current and the DC value of the sampled inductor current can  
cause instability for certain operating conditions. This instability is known as sub-harmonic oscillation, which  
occurs when the inductor ripple current does not return to its initial value by the start of next switching cycle.  
Sub-harmonic oscillation is normally characterized by observing alternating wide and narrow pulses at the switch  
node. Adding a fixed slope voltage ramp (slope compensation) to the current sense signal prevents this  
oscillation. The 25 µA of offset current provided from the emulated current source adds the optimal slope  
compensation to the ramp signal for a 5V output. For higher output voltages, additional slope compensation may  
be required. In these applications, a resistor is added between RAMP and VCC to increase the ramp slope  
compensation.  
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SW  
LO  
CS  
R
R
G
G
CSG  
DEMB  
R
DEMB  
Figure 32. RDS(ON) Current Sensing without Diode Emulation  
The DC current sample is obtained using the CS and CSG pins connected to either a source sense resistor (RS)  
or the RDS(ON) of the low-side MOSFET. For RDS(ON) sensing, RS = RDS(ON) of the low-side MOSFET. In this case  
it is sometimes helpful to adjust the current sense amplifier gain (A) to a lower value in order to obtain the  
desired current limit. Adding external resistors RG in series with CS and CSG, the current sense amplifier gain A  
becomes:  
10k  
A ,  
1k + RG  
(4)  
Current Limit  
The LM5116WG contains a current limit monitoring scheme to protect the circuit from possible over-current  
conditions. When set correctly, the emulated current sense signal is proportional to the buck switch current with a  
scale factor determined by the current limit sense resistor. The emulated ramp signal is applied to the current  
limit comparator. If the emulated ramp signal exceeds 1.6V, the current cycle is terminated (cycle-by-cycle  
current limiting). Since the ramp amplitude is proportional to VIN - VOUT, if VOUT is shorted, there is an immediate  
reduction in duty cycle. To further protect the external switches during prolonged current limit conditions, an  
internal counter counts clock pulses when in current limit. When the counter detects 256 consecutive clock  
cycles, the regulator enters a low power dissipation hiccup mode of current limit. The regulator is shut down by  
momentarily pulling UVLO low, and the soft-start capacitor discharged. The regulator is restarted with a full soft-  
start cycle once UVLO charges back to 1.215V. This process is repeated until the fault is removed. The hiccup  
off-time can be controlled by a capacitor to ground on the UVLO pin. In applications with low output inductance  
and high input voltage, the switch current may overshoot due to the propagation delay of the current limit  
comparator. If an overshoot should occur, the sample-and-hold circuit will detect the excess recirculating current.  
If the sample-and-hold DC level exceeds the internal current limit threshold, the buck switch will be disabled and  
skip pulses until the current has decayed below the current limit threshold. This approach prevents current  
runaway conditions due to propagation delays or inductor saturation since the inductor current is forced to decay  
following any current overshoot.  
CURRENT SENSE  
AMPLIFIER  
CURRENT LIMIT  
COMPARATOR  
1.6V  
10k  
CS  
1k  
R
G
LO  
-
+
-
R
I
L
S
+
gm x (VIN - VOUT) + 25 mA  
1k CSG  
R
G
10k  
0.5V  
10k  
1k + R  
HO  
A =  
RAMP  
G
C
RAMP  
Figure 33. Current Limit and Ramp Circuit  
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Using a current sense resistor in the source of the low-side MOSFET provides superior current limit accuracy  
compared to RDS(ON) sensing. RDS(ON) sensing is far less accurate due to the large variation of MOSFET RDS(ON)  
with temperature and part-to-part variation. The CS and CSG pins should be Kelvin connected to the current  
sense resistor or MOSFET drain and source.  
The peak current which triggers the current limit comparator is:  
x tON  
CRAMP  
A x RS  
25 mA  
-
1.1V  
1.1V  
A x RS  
IPEAK  
=
,
(5)  
Where tON is the on-time of the high-side MOSFET. The 1.1V threshold is the difference between the 1.6V  
reference at the current limit comparator and the 0.5V offset at the current sense amplifier. This offset at the  
current sense amplifier allows the inductor ripple current to go negative by 0.5V / (A x RS) when running full  
synchronous operation.  
Current limit hysteresis prevents chatter around the threshold when VCCX is powered from VOUT. When 4.5V <  
VCC < 5.8V, the 1.6V reference is increased to 1.72V. The peak current which triggers the current limit  
comparator becomes:  
x tON  
CRAMP  
A x RS  
25 mA  
-
1.22V  
1.22V  
A x RS  
IPEAK  
=
,
(6)  
This has the effect of a 10% fold-back of the peak current during a short circuit when VCCX is powered from a  
5V output.  
Soft-Start and Diode Emulation  
The soft-start feature allows the regulator to gradually reach the initial steady state operating point, thus reducing  
start-up stresses and surges. The LM5116WG will regulate the FB pin to the SS pin voltage or the internal  
1.215V reference, whichever is lower. At the beginning of the soft-start sequence when SS = 0V, the internal 10  
µA soft-start current source gradually increases the voltage of an external soft-start capacitor (CSS) connected to  
the SS pin resulting in a gradual rise of FB and the output voltage.  
DIODE EMULATION  
COMPARATOR  
R
DEMB  
S
SW  
+
-
R
DEMB  
1.215V  
5V  
40k  
SS Latch  
+
SS  
-
Figure 34. Diode Emulation Control  
During this initial charging of CSS to the internal reference voltage, the LM5116WG will force diode emulation.  
That is, the low-side MOSFET will turn off for the remainder of a cycle if the sensed inductor current becomes  
negative. The inductor current is sensed by monitoring the voltage between SW and DEMB. As the SS capacitor  
continues to charge beyond 1.215V to 3V, the DEMB bias current will increase from 0 µA up to 40 µA. With the  
use of an external DEMB resistor (RDEMB), the current sense threshold for diode emulation will increase resulting  
in the gradual transition to synchronous operation. Forcing diode emulation during soft-start allows the  
LM5116WG to start up into a pre-biased output without unnecessarily discharging the output capacitor. Full  
synchronous operation is obtained if the DEMB pin is always biased to a higher potential than the SW pin when  
LO is high. RDEMB = 10 kwill bias the DEMB pin to 0.45V minimum, which is adequate for most applications.  
The DEMB bias potential should always be kept below 2V. At very light loads with larger values of output  
inductance and MOSFET capacitance, the switch voltage may fall slowly. If the SW voltage does not fall below  
the DEMB threshold before the end of the HO fall to LO rise dead-time, switching will default to diode emulation  
mode. When RDEMB = 0, the LM5116WG will always run in diode emulation.  
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Once SS charges to 3V the SS latch is set, increasing the DEMB bias current to 65 µA. An amplifier is enabled  
that regulates SS to 160 mV above the FB voltage. This feature can prevent overshoot of the output voltage in  
the event the output voltage momentarily dips out of regulation. When a fault is detected (VCC under-voltage,  
UVLO pin < 1.215, or EN = 0V) the soft-start capacitor is discharged. Once the fault condition is no longer  
present, a new soft-start sequence begins.  
HO Ouput  
The LM5116WG contains a high current, high-side driver and associated high voltage level shift. This gate driver  
circuit works in conjunction with an external diode and bootstrap capacitor. A 1 µF ceramic capacitor, connected  
with short traces between the HB pin and SW pin, is recommended. During the off-time of the high-side  
MOSFET, the SW pin voltage is approximately -0.5V and the bootstrap capacitor charges from VCC through the  
external bootstrap diode. When operating with a high PWM duty cycle, the buck switch will be forced off each  
cycle for 450 ns to ensure that the bootstrap capacitor is recharged.  
The LO and HO outputs are controlled with an adaptive deadtime methodology which insures that both outputs  
are never enabled at the same time. When the controller commands HO to be enabled, the adaptive block first  
disables LO and waits for the LO voltage to drop below approximately 25% of VCC. HO is then enabled after a  
small delay. Similarly, when HO turns off, LO waits until the SW voltage has fallen to ½ of VCC. LO is then  
enabled after a small delay. In the event that SW does not fall within approximately 150 ns, LO is asserted high.  
This methodology insures adequate dead-time for appropriately sized MOSFETs.  
In some applications it may be desirable to slow down the high-side MOSFET turn-on time in order to control  
switching spikes. This may be accomplished by adding a resistor is series with the HO output to the high-side  
gate. Values greater than 10should be avoided so as not to interfere with the adaptive gate drive. Use of an  
HB resistor for this function should be carefully evaluated so as not cause potentially harmful negative voltage to  
the high-side driver, and is generally limited to 2.2maximum.  
Thermal Protection  
For high temperature applications in the CPGA-20, the internal thermal shutdown circuitry is disabled.  
Application Information  
EXTERNAL COMPONENTS  
The procedure for calculating the external components is illustrated with the following design example. The Bill of  
Materials for this design is listed in Table 1. The circuit shown in Figure 41 is configured for the following  
specifications:  
Output voltage = 5V  
Input voltage = 7V to 60V  
Maximum load current = 7A  
Switching frequency = 250 kHz  
Simplified equations are used as a general guideline for the design method. Comprehensive equations are  
provided at the end of this section.  
TIMING RESISTOR  
RT sets the oscillator switching frequency. Generally, higher frequency applications are smaller but have higher  
losses. Operation at 250 kHz was selected for this example as a reasonable compromise for both small size and  
high efficiency. The value of RT for 250 kHz switching frequency can be calculated as follows:  
1
- 450 ns  
250 kHz  
= 12.5 kW  
RT =  
284 pF  
(7)  
The nearest standard value of 12.4 kwas chosen for RT.  
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OUTPUT INDUCTOR  
The inductor value is determined based on the operating frequency, load current, ripple current and the input and  
output voltages.  
I
I
PP  
O
0
1
T =  
f
SW  
Figure 35. Inductor Current  
Knowing the switching frequency (fSW), maximum ripple current (IPP), maximum input voltage (VIN(MAX)) and the  
nominal output voltage (VOUT), the inductor value can be calculated:  
VOUT  
VOUT  
VIN(MAX)  
1 -  
x
L =  
IPP x fSW  
(8)  
The maximum ripple current occurs at the maximum input voltage. Typically, IPP is 20% to 40% of the full load  
current. When running diode emulation mode, the maximum ripple current should be less than twice the  
minimum load current. For full synchronous operation, higher ripple current is acceptable. Higher ripple current  
allows for a smaller inductor size, but places more of a burden on the output capacitor to smooth the ripple  
current for low output ripple voltage. For this example, 40% ripple current was chosen for a smaller sized  
inductor.  
5V  
5V  
1 -  
x
= 6.5mH  
L =  
60V  
0.4 x 7A x 250kHz  
(9)  
The nearest standard value of 6 µH will be used. The inductor must be rated for the peak current to prevent  
saturation. During normal operation, the peak current occurs at maximum load current plus maximum ripple.  
During overload conditions with properly scaled component values, the peak current is limited to VCS(TH) / RS  
(See next section). At the maximum input voltage with a shorted output, the valley current must fall below VCS(TH)  
/ RS before the high-side MOSFET is allowed to turn on. The peak current in steady state will increase to VIN(MAX)  
x tON(min) / L above this level. The chosen inductor must be evaluated for this condition, especially at elevated  
temperature where the saturation current rating may drop significantly.  
CURRENT SENSE RESISTOR  
The current limit is set by the current sense resistor value (RS).  
VCS(TH)  
ILIM  
=
RS  
(10)  
For a 5V output, the maximum current sense signal occurs at the minimum input voltage, so RS is calculated  
from:  
VCS(TH)  
RS  
Ç
VOUT  
VOUT  
x 1 +  
IO  
+
VIN(MIN)  
2 x L x fSW  
(11)  
(12)  
For this example VCCX = 0V, so VCS(TH) = 0.11V. The current sense resistor is calculated as:  
0.11V  
0.011W  
Ç
RS Ç  
5V  
5V  
7V  
x
1 +  
7A +  
2 x 6 mH x 250 kHz  
The next lowest standard value of 10 mwas chosen for RS.  
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RAMP CAPACITOR  
With the inductor and sense resistor value selected, the value of the ramp capacitor (CRAMP) necessary for the  
emulation ramp circuit is:  
gm x L  
CRAMP  
,
A x RS  
(13)  
Where L is the value of the output inductor in Henrys, gm is the ramp generator transconductance (5 µA/V), and  
A is the current sense amplifier gain (10 V/V). For the 5V output design example, the ramp capacitor is  
calculated as:  
5 mA/V x 6 mH  
= 300 pF  
CRAMP  
=
10V/V x 10 mW  
(14)  
The next lowest standard value of 270 pF was selected for CRAMP. A COG type capacitor with 5% or better  
tolerance is recommended.  
OUTPUT CAPACITORS  
The output capacitors smooth the inductor ripple current and provide a source of charge for transient loading  
conditions. For this design example, five 100 µF ceramic capacitors where selected. Ceramic capacitors provide  
very low equivalent series resistance (ESR), but can exhibit a significant reduction in capacitance with DC bias.  
From the manufacturer’s data, the ESR at 250 kHz is 2 m/ 5 = 0.4 m, with a 36% reduction in capacitance at  
5V. This is verified by measuring the output ripple voltage and frequency response of the circuit. The  
fundamental component of the output ripple voltage is calculated as:  
2
1
ESR2 +  
DVOUT = IPP  
x
With typical values for the 5V design example:  
8 x fSW x COUT  
(15)  
2
1
DVOUT = 3A x 0.4 mW2 +  
8 x 250 kHz x 320 mF  
DVOUT = 4.8 mV  
(16)  
INPUT CAPACITORS  
The regulator supply voltage has a large source impedance at the switching frequency. Good quality input  
capacitors are necessary to limit the ripple voltage at the VIN pin while supplying most of the switch current  
during the on-time. When the buck switch turns on, the current into the switch steps to the valley of the inductor  
current waveform, ramps up to the peak value, and then drops to zero at turn-off. The input capacitors should be  
selected for RMS current rating and minimum ripple voltage. A good approximation for the required ripple current  
rating is IRMS > IOUT / 2.  
Quality ceramic capacitors with a low ESR were selected for the input filter. To allow for capacitor tolerances and  
voltage rating, four 2.2 µF, 100V ceramic capacitors were used for the typical application circuit. With ceramic  
capacitors, the input ripple voltage will be triangular and peak at 50% duty cycle. Taking into account the  
capacitance change with DC bias, the input ripple voltage is approximated as:  
IOUT  
7A  
DVIN  
=
=
= 1V  
4 x 250 kHz x 7 mF  
4 x fSW x CIN  
(17)  
When the converter is connected to an input power source, a resonant circuit is formed by the line impedance  
and the input capacitors. If step input voltage transients are expected near the maximum rating of the  
LM5116WG, a careful evaluation of the ringing and possible overshoot at the device VIN pin should be  
completed. To minimize overshoot make CIN > 10 x LIN. The characteristic source impedance and resonant  
frequency are:  
LIN  
1
fS  
=
ZS  
=
2p  
CIN  
LIN x CIN  
(18)  
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The converter exhibits a negative input impedance which is lowest at the minimum input voltage:  
2
VIN  
ZIN = -  
POUT  
(19)  
(20)  
The damping factor for the input filter is given by:  
ZS  
RIN + ESR  
ZS  
1
2
d =  
+
ZIN  
where RIN is the input wiring resistance and ESR is the series resistance of the input capacitors. The term ZS/ZIN  
will always be negative due to ZIN.  
When δ = 1, the input filter is critically damped. This may be difficult to achieve with practical component values.  
With δ < 0.2, the input filter will exhibit significant ringing. If δ is zero or negative, there is not enough resistance  
in the circuit and the input filter will sustain an oscillation. When operating near the minimum input voltage, an  
aluminum electrolytic capacitor across CIN may be needed to damp the input for a typical bench test setup. Any  
parallel capacitor should be evaluated for its RMS current rating. The current will split between the ceramic and  
aluminum capacitors based on the relative impedance at the switching frequency.  
VCC CAPACITOR  
The primary purpose of the VCC capacitor (CVCC) is to supply the peak transient currents of the LO driver and  
bootstrap diode (D1) as well as provide stability for the VCC regulator. These current peaks can be several  
amperes. The recommended value of CVCC should be no smaller than 0.47 µF, and should be a good quality, low  
ESR, ceramic capacitor located at the pins of the IC to minimize potentially damaging voltage transients caused  
by trace inductance. A value of 1 µF was selected for this design.  
BOOTSTRAP CAPACITOR  
The bootstrap capacitor (CHB) between the HB and SW pins supplies the gate current to charge the high-side  
MOSFET gate at each cycle’s turn-on as well as supplying the recovery charge for the bootstrap diode (D1).  
These current peaks can be several amperes. The recommended value of the bootstrap capacitor is at least 0.1  
µF, and should be a good quality, low ESR, ceramic capacitor located at the pins of the IC to minimize potentially  
damaging voltage transients caused by trace inductance. The absolute minimum value for the bootstrap  
capacitor is calculated as:  
Qg  
CHB  
í
DVHB  
(21)  
Where Qg is the high-side MOSFET gate charge and ΔVHB is the tolerable voltage droop on CHB, which is  
typically less than 5% of VCC. A value of 1 µF was selected for this design.  
SOFT-START CAPACITOR  
The capacitor at the SS pin (CSS) determines the soft-start time, which is the time for the reference voltage and  
the output voltage to reach the final regulated value. The soft-start time tSS should be substantially longer than  
the time required to charge COUT to VOUT at the maximum output current. To meet this requirement:  
tSS > VOUT x COUT / (ICURRENT LIMIT IOUT  
)
(22)  
The value of CSS for a given time is determined from:  
tSS x 10 mA  
CSS  
=
1.215V  
(23)  
For this application, a value of 0.01 µF was chosen for a soft-start time of 1.2 ms.  
OUTPUT VOLTAGE DIVIDER  
RFB1 and RFB2 set the output voltage level, the ratio of these resistors is calculated from:  
RFB2  
VOUT  
- 1  
=
RFB1  
1.215V  
(24)  
RFB1 is typically 1.21 kfor a divider current of 1 mA. The divider current can be reduced to 100 µA with  
RFB1=12.1 k. For the 5V output design example used here, RFB1 = 1.21 kand RFB2 = 3.74 k.  
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UVLO DIVIDER  
A voltage divider and filter can be connected to the UVLO pin to set a minimum operating voltage VIN(MIN) for the  
regulator. If this feature is required, the following procedure can be used to determine appropriate resistor values  
for RUV2, RUV1 and CFT.  
1. RUV2 must be large enough such that in the event of a current limit, the internal UVLO switch can pull UVLO  
< 200mV. This can be guaranteed if:  
RUV2 > 500 x VIN(MAX)  
where  
VIN(MAX) is the maximum input voltage and RUV2 is in ohms.  
2. With an appropriate value for RUV2, RUV1 can be selected using the following equation:  
RUV2  
RUV1 = 1.215 x  
VIN(MIN) + (5 mA x RUV2) - 1.215  
where  
VIN(MIN) is the desired shutdown voltage.  
3. Capacitor CFT provides filtering for the divider and determines the off-time of the “hiccup” duty cycle during  
current limit. When CFT is used in conjunction with the voltage divider, a diode across the top resistor should  
be used to discharge CFT in the event of an input under-voltage condition.  
RUV1 x RUV2  
RUV1 + RUV2  
1.215 x (RUV1 + RUV2  
VIN x RUV1  
)
x CFT x ln  
tOFF = -  
1 -  
If under-voltage shutdown is not required, RUV1 and RUV2 can be eliminated and the off-time becomes:  
1.215V  
tOFF = CFT  
x
5 mA  
(25)  
The voltage at the UVLO pin should never exceed 16V when using an external set-point divider. It may be  
necessary to clamp the UVLO pin at high input voltages. For the design example, RUV2 = 102 kand RUV1 = 21  
kfor a shut-down voltage of 6.6V. If sustained short circuit protection is required, CFT 1 µF will limit the short  
circuit power dissipation. D2 may be installed when using CFT with RUV1 and RUV2  
.
MOSFETs  
Selection of the power MOSFETs is governed by the same tradeoffs as switching frequency. Breaking down the  
losses in the high-side and low-side MOSFETs is one way to determine relative efficiencies between different  
devices. When using discrete SO-8 MOSFETs the LM5116WG is most efficient for output currents of 2A to 10A.  
Losses in the power MOSFETs can be broken down into conduction loss, gate charging loss, and switching loss.  
Conduction, or I2R loss PDC, is approximately:  
PDC(HO-MOSFET) = D x (IO2 x RDS(ON) x 1.3)  
PDC(LO-MOSFET) = (1 - D) x (IO2 x RDS(ON) x 1.3)  
(26)  
(27)  
Where D is the duty cycle. The factor 1.3 accounts for the increase in MOSFET on-resistance due to heating.  
Alternatively, the factor of 1.3 can be ignored and the on-resistance of the MOSFET can be estimated using the  
RDS(ON) vs Temperature curves in the MOSFET datasheet. Gate charging loss, PGC, results from the current  
driving the gate capacitance of the power MOSFETs and is approximated as:  
PGC = n x VCC x Qg x fSW  
(28)  
Qg refer to the total gate charge of an individual MOSFET, and ‘n’ is the number of MOSFETs. If different types  
of MOSFETs are used, the ‘n’ term can be ignored and their gate charges summed to form a cumulative Qg.  
Gate charge loss differs from conduction and switching losses in that the actual dissipation occurs in the  
LM5116WG and not in the MOSFET itself. Further loss in the LM5116WG is incurred as the gate driving current  
is supplied by the internal linear regulator. The gate drive current supplied by the VCC regulator is calculated as:  
IGC = (Qgh + Qgl) x fSW  
(29)  
Where Qgh + Qgl represent the gate charge of the HO and LO MOSFETs at VGS = VCC. To ensure start-up, IGC  
should be less than the VCC current limit rating of 15 mA minimum when powered by the internal 7.4V regulator.  
Failure to observe this rating may result in excessive MOSFET heating and potential damage. The IGC run  
current may exceed 15 mA when VCC is powered by VCCX.  
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Switching loss occurs during the brief transition period as the MOSFET turns on and off. During the transition  
period both current and voltage are present in the channel of the MOSFET. The switching loss can be  
approximated as:  
PSW = 0.5 x VIN x IO x (tR + tF) x fSW  
(30)  
Where tR and tF are the rise and fall times of the MOSFET. Switching loss is calculated for the high-side  
MOSFET only. Switching loss in the low-side MOSFET is negligible because the body diode of the low-side  
MOSFET turns on before the MOSFET itself, minimizing the voltage from drain to source before turn-on. For this  
example, the maximum drain-to-source voltage applied to either MOSFET is 60V. VCC provides the drive  
voltage at the gate of the MOSFETs. The selected MOSFETs must be able to withstand 60V plus any ringing  
from drain to source, and be able to handle at least VCC plus ringing from gate to source. A good choice of  
MOSFET for the 60V input design example is the Si7850DP. It has an RDS(ON) of 20 m, total gate charge of 14  
nC, and rise and fall times of 10 ns and 12 ns respectively. In applications where a high step-down ratio is  
maintained for normal operation, efficiency may be optimized by choosing a high-side MOSFET with lower Qg,  
and low-side MOSFET with lower RDS(ON)  
.
For higher voltage MOSFETs which are not true logic level, it is important to use the UVLO feature. Choose a  
minimum operating voltage which is high enough for VCC and the bootstrap (HB) supply to fully enhance the  
MOSFET gates. This will prevent operation in the linear region during power-on or power-off which can result in  
MOSFET failure. Similar consideration must be made when powering VCCX from the output voltage. For the  
high-side MOSFET, the gate threshold should be considered and careful evaluation made if the gate threshold  
voltage exceeds the HO driver UVLO.  
MOSFET SNUBBER  
A resistor-capacitor snubber network across the low-side MOSFET reduces ringing and spikes at the switching  
node. Excessive ringing and spikes can cause erratic operation and couple spikes and noise to the output.  
Selecting the values for the snubber is best accomplished through empirical methods. First, make sure the lead  
lengths for the snubber connections are very short. Start with a resistor value between 5and 50. Increasing  
the value of the snubber capacitor results in more damping, but higher snubber losses. Select a minimum value  
for the snubber capacitor that provides adequate damping of the spikes on the switch waveform at high load.  
ERROR AMPLIFIER COMPENSATION  
RCOMP, CCOMP and CHF configure the error amplifier gain characteristics to accomplish a stable voltage loop gain.  
One advantage of current mode control is the ability to close the loop with only two feedback components, RCOMP  
and CCOMP. The voltage loop gain is the product of the modulator gain and the error amplifier gain. For the 5V  
output design example, the modulator is treated as an ideal voltage-to-current converter. The DC modulator gain  
of the LM5116WG can be modeled as:  
DC Gain(MOD) = RLOAD / (A x RS)  
(31)  
The dominant low frequency pole of the modulator is determined by the load resistance (RLOAD) and output  
capacitance (COUT). The corner frequency of this pole is:  
fP(MOD) = 1 / (2π x RLOAD x COUT  
)
(32)  
For RLOAD = 5V / 7A = 0.714and COUT = 320 µF (effective) then fP(MOD) = 700 Hz  
DC Gain(MOD) = 0.714/ (10 x 10 m) = 7.14 = 17 dB  
For the 5V design example the modulator gain vs. frequency characteristic was measured as shown in Figure 36.  
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Figure 36. Modulator Gain and Phase  
Components RCOMP and CCOMP configure the error amplifier as a type II configuration. The DC gain of the  
amplifier is 80 dB which has a pole at low frequency and a zero at fZEA = 1 / (2π x RCOMP x CCOMP). The error  
amplifier zero cancels the modulator pole leaving a single pole response at the crossover frequency of the  
voltage loop. A single pole response at the crossover frequency yields a very stable loop with 90° of phase  
margin. For the design example, a target loop bandwidth (crossover frequency) of one-tenth the switching  
frequency or 25 kHz was selected. The compensation network zero (fZEA) should be selected at least an order of  
magnitude less than the target crossover frequency. This constrains the product of RCOMP and CCOMP for a  
desired compensation network zero 1 / (2π x RCOMP x CCOMP) to be 2.5 kHz. Increasing RCOMP, while  
proportionally decreasing CCOMP, increases the error amp gain. Conversely, decreasing RCOMP while  
proportionally increasing CCOMP, decreases the error amp gain. For the design example CCOMP was selected as  
3300 pF and RCOMP was selected as 18 k. These values configure the compensation network zero at 2.7 kHz.  
The error amp gain at frequencies greater than fZEA is: RCOMP / RFB2, which is approximately 4.8 (13.6 dB).  
Figure 37. Error Amplifier Gain and Phase  
The overall voltage loop gain can be predicted as the sum (in dB) of the modulator gain and the error amp gain.  
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Figure 38. Overall Voltage Loop Gain and Phase  
If a network analyzer is available, the modulator gain can be measured and the error amplifier gain can be  
configured for the desired loop transfer function. If a network analyzer is not available, the error amplifier  
compensation components can be designed with the guidelines given. Step load transient tests can be  
performed to verify acceptable performance. The step load goal is minimum overshoot with a damped response.  
CHF can be added to the compensation network to decrease noise susceptibility of the error amplifier. The value  
of CHF must be sufficiently small since the addition of this capacitor adds a pole in the error amplifier transfer  
function. This pole must be well beyond the loop crossover frequency. A good approximation of the location of  
the pole added by CHF is: fP2 = fZEA x CCOMP / CHF. The value of CHF was selected as 100 pF for the design  
example.  
PCB BOARD LAYOUT and THERMAL CONSIDERATIONS  
In a buck regulator the primary switching loop consists of the input capacitor, MOSFETs and current sense  
resistor. Minimizing the area of this loop reduces the stray inductance and minimizes noise and possible erratic  
operation. The input capacitor should be placed as close as possible to the MOSFETs, with the VIN side of the  
capacitor connected directly to the high-side MOSFET drain, and the GND side of the capacitor connected as  
close as possible to the low-side source or current sense resistor ground connection. A ground plane in the PC  
board is recommended as a means to connect the quiet end (input voltage ground side) of the input filter  
capacitors to the output filter capacitors and the PGND pin of the regulator. Connect all of the low power ground  
connections (CSS, RT, CRAMP) directly to the regulator AGND pin. Connect the AGND and PGND pins together  
through to a topside copper area covering the entire underside of the device. Place several vias in this underside  
copper area to the ground plane.  
The highest power dissipating components are the two power MOSFETs. The easiest way to determine the  
power dissipated in the MOSFETs is to measure the total conversion losses (PIN - POUT), then subtract the power  
losses in the output inductor and any snubber resistors. The resulting power losses are primarily in the switching  
MOSFETs.  
If a snubber is used, the power loss can be estimated with an oscilloscope by observation of the resistor voltage  
drop at both turn-on and turn-off transitions. Assuming that the RC time constant is << 1 / fSW  
.
P = C x V2 x fSW  
(33)  
Selecting MOSFETs with exposed pads will aid the power dissipation of these devices. Careful attention to  
RDS(ON) at high temperature should be observed. Also, at 250 kHz, a MOSFET with low gate capacitance will  
result in lower switching losses.  
Comprehensive Equations  
CURRENT SENSE RESISTOR AND RAMP CAPACITOR  
T = 1 / fSW, gm = 5 µA/V, A = 10 V/V. IOUT is the maximum output current at current limit.  
General Method for VOUT < 5V:  
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VCS(TH)  
RS  
=
5 - VOUT  
VIN(MIN)  
1 +  
1 +  
VOUT x T  
2 x L  
VOUT  
VOUT x T  
L
IOUT  
-
x 1 -  
x
+
VIN(MIN)  
5 - VOUT  
VIN(MAX)  
(34)  
(35)  
5 - VOUT  
VIN(MAX)  
gm x L  
A x RS  
x
1 +  
CRAMP  
=
General Method for 5V < VOUT < 7.5V:  
VCS(TH)  
RS  
=
VOUT x T  
2 x L  
VOUT  
VOUT x T  
L
IOUT  
-
1 -  
x
+
VIN(MIN)  
(36)  
(37)  
gm x L  
A x RS  
5 - VOUT  
VIN(MIN)  
x
1 +  
CRAMP  
=
Best Performance Method:  
This minimizes the current limit deviation due to changes in line voltage, while maintaining near optimal slope  
compensation.  
Calculate optimal slope current, IOS = (VOUT / 3) x 10 µA/V. For example, at VOUT = 7.5V, IOS = 25 µA.  
VCS(TH)  
IOS x L  
RS  
=
CRAMP =  
VOUT x A x RS  
VOUT x T  
IOUT  
+
L
(38)  
(39)  
(40)  
Calculate VRAMP at the nominal input voltage.  
VOUT ((VIN œ VOUT) x gm + IOS) x T  
x
VRAMP  
=
VIN  
CRAMP  
For VOUT > 7.5V, install a resistor from the RAMP pin to VCC.  
VCC - VRAMP  
RRAMP  
=
IOS - 25 mA  
VCC  
R
RAMP  
RAMP  
C
RAMP  
Figure 39. RRAMP to VCC for VOUT > 7.5V  
For VOUT < 7.5V, a negative VCC is required. This can be made with a simple charge pump from the LO gate  
output. Install a resistor from the RAMP pin to the negative VCC.  
VCC œ 0.5V + VRAMP  
RRAMP  
=
25 mA - IOS  
(41)  
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LO  
10 nF  
1N914  
10 nF  
R
RAMP  
RAMP  
-VCC  
RAMP  
C
Figure 40. RRAMP to -VCC for VOUT < 7.5V  
If a large variation is expected in VCC, say for VIN < 11V, a Zener regulator may be added to supply a constant  
voltage for RRAMP  
.
MODULATOR TRANSFER FUNCTION  
The following equations can be used to calculate the control-to-output transfer function:  
s
wZ  
1 +  
RLOAD  
1
VOUT  
x
x
=
s
wP  
s
s2  
A x RS  
VCOMP  
RLOAD  
x
1 +  
1 +  
+
1 +  
2
wn x Q  
wn  
Km x A x RS  
(42)  
1
Km  
=
(D œ 0.5) x A x RS x T  
VSL  
+ (1 - 2 x D) x KSL  
+
L
VIN  
(43)  
(44)  
gm x T  
IOS x T  
CRAMP  
VSL  
=
KSL  
=
CRAMP  
p
T
1
1
1
1
x
+
wn =  
wP =  
wZ =  
Km x A x RS  
COUT x ESR  
COUT  
RLOAD  
(45)  
(VIN œ VOUT) x KSL + VSL  
VIN x A x RS  
L
Se =  
Sn =  
T
1
Se  
mC =  
Sn  
Q =  
p x (mC œ 0.5)  
(46)  
Km is the effective DC gain of the modulating comparator. The duty cycle D = VOUT / VIN. KSL is the proportional  
slope compensation term. VSL is the fixed slope compensation term. Slope compensation is set by mc, which is  
the ratio of the external ramp to the natural ramp. The switching frequency sampling gain is characterized by ωn  
and Q, which accounts for the high frequency inductor pole.  
For VSL without RRAMP, use IOS = 25 µA  
For VSL with RRAMP to VCC, use IOS = 25 µA + VCC/RRAMP  
For VSL with RRAMP to -VCC, use IOS = 25 µA - VCC/RRAMP  
ERROR AMPLIFIER TRANSFER FUNCTION  
The following equations are used to calculate the error amplifier transfer function:  
1
VCOMP  
-GEA(S) x  
=
GEA(S)  
KFB  
VOUT(FB)  
1
s
1 +  
1 +  
+
x
AOL  
wBW  
(47)  
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s
wZEA  
1 +  
RFB1  
KFB  
=
GEA(S)  
=
RFB1 + RFB2  
s
wHF  
s
wO  
1 +  
x
(48)  
1
1
wO  
=
wZEA  
=
CCOMP x RCOMP  
(CHF + CCOMP) x RFB2  
(CHF + CCOMP  
)
wHF  
=
CHF x CCOMP x RCOMP  
(49)  
Where AOL = 10,000 (80 dB) and ωBW = 2π x fBW. GEA(S) is the ideal error amplifier gain, which is modified at DC  
and high frequency by the open loop gain of the amplifier and the feedback divider ratio.  
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Figure 41. 5V 7A Typical Application Schematic  
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Table 1. Bill of Materials for 7V-60V Input, 5V 7A Output, 250kHz  
ID  
C1, C2, C14  
C3  
Part Number  
Type  
Size  
0805  
0603  
0603  
0603  
Parameters  
1µF, 25V, X7R  
Qty  
3
Vendor  
TDK  
C2012X7R1E105K  
VJ0603Y103KXAAT  
VJ0603A271JXAAT  
Capacitor, Ceramic  
Capacitor, Ceramic  
Capacitor, Ceramic  
Capacitor, Ceramic  
0.01µF, 50V, X7R  
270pF, 50V, COG, 5%  
100pF, 50V, X7R  
1
Vishay  
Vishay  
Vishay  
C4  
1
C5, C15  
VJ0603Y101KXAT  
W1BC  
2
C6  
C7  
VJ0603Y332KXXAT  
Capacitor, Ceramic  
Capacitor, Ceramic  
Capacitor, Ceramic  
0603  
0603  
1812  
3300pF, 25V, X7R  
Not Used  
1
0
4
Vishay  
TDK  
C8, C9, C10,  
C11  
C4532X7R2A225M  
2.2µF, 100V X7R  
C12  
C13  
C3225X7R2A105M  
C2012X7R2A104M  
C4532X6S0J107M  
Capacitor, Ceramic  
Capacitor, Ceramic  
Capacitor, Ceramic  
1210  
0805  
1812  
1µF, 100V X7R  
0.1µF, 100V X7R  
1
1
5
TDK  
TDK  
TDK  
C16, C17, C18,  
C19, C20  
100µF, 6.3V, X6S, 105°C  
C21, C22  
C23  
Capacitor, Tantalum  
Capacitor, Ceramic  
Diode, Switching  
D Case  
0805  
Not Used  
Not Used  
0
0
1
D1  
CMPD2003  
CMPD2003  
SOT-23  
200mA, 200V  
Central  
Semi  
D2  
Diode, Switching  
SOT-23  
Not Used  
0
Central  
Semi  
JMP1  
L1  
Connector, Jumper  
Inductor  
2 pin sq. post  
6µH, 16.5A  
1
1
4
5
2
HC2LP-6R0  
1514-2  
Cooper  
Keystone  
Keystone  
P1-P4  
TP1-TP5  
Q1, Q2  
Turret Terminal  
Test Point  
.090” dia.  
.040” dia.  
5012  
Si7850DP  
N-CH MOSFET  
SO-8 Power PAK  
10.3A, 60V  
Vishay  
Siliconix  
R1  
R2  
CRCW06031023F  
CRCW06032102F  
CRCW06033741F  
CRCW06031211F  
Resistor  
Resistor  
Resistor  
Resistor  
Resistor  
Resistor  
Resistor  
Resistor  
Resistor  
Resistor  
0603  
0603  
0603  
0603  
0603  
0603  
0603  
0603  
0603  
2010  
102k, 1%  
21.0k, 1%  
3.74k, 1%  
1.21k, 1%  
Not Used  
0Ω  
1
1
1
1
0
2
1
1
1
1
Vishay  
Vishay  
Vishay  
Vishay  
R3  
R4  
R5  
R6, R7  
R8  
CRCW06030R0J  
CRCW0603103J  
CRCW06031242F  
CRCW0603183J  
Vishay  
Vishay  
Vishay  
Vishay  
IRC  
10k, 5%  
12.4k, 1%  
18k, 5%  
0.010, 1%  
R9  
R10  
R11  
LRC-LRF2010-01-  
R010-F  
R12  
R13  
R14  
U1  
Resistor  
Resistor  
Resistor  
0603  
0603  
Not Used  
1M, 5%  
Not Used  
0
1
0
1
CRCW0603105J  
LM5116WG  
Vishay  
TI  
1206  
Synchronous Buck  
Controller  
CPGA-20  
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Page  
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Changes from Revision B (February 2013) to Revision C  
Changed layout of National Data Sheet to TI format .......................................................................................................... 30  
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PACKAGE OPTION ADDENDUM  
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10-Dec-2020  
PACKAGING INFORMATION  
Orderable Device  
Status Package Type Package Pins Package  
Eco Plan  
Lead finish/  
Ball material  
MSL Peak Temp  
Op Temp (°C)  
Device Marking  
Samples  
Drawing  
Qty  
(1)  
(2)  
(3)  
(4/5)  
(6)  
LM5116WG/NOPB  
ACTIVE  
CFP  
NAR  
20  
30  
RoHS-Exempt  
& Green  
Call TI  
Level-1-NA-UNLIM  
-40 to 125  
LM5116WG  
(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 <=1000ppm threshold. Antimony trioxide based  
flame retardants must also meet the <=1000ppm threshold requirement.  
(3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.  
(4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.  
(5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation  
of the previous line and the two combined represent the entire Device Marking for that device.  
(6)  
Lead finish/Ball material - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead finish/Ball material values may wrap to two  
lines if the finish value exceeds the maximum column width.  
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information  
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and  
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.  
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.  
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.  
Addendum-Page 1  
MECHANICAL DATA  
NAR0020A  
WG20A (Rev D)  
www.ti.com  
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 © 2020, Texas Instruments Incorporated  

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