XR76121
20A Synchronous
Step-Down COT Regulators
Description
FEATURES
■■ 20A step-down regulator
4.5V to 5.5V low VIN operation
5V to 22V wide single input voltage
3V to 22V operation with external
5V bias
≥0.6V adjustable output voltage
■■ Proprietary constant on-time control
No loop compensation required
Ceramic output capacitor stable
operation
Programmable 70ns-1µs on-time
Constant 200kHz-1MHz frequency
Selectable CCM or CCM/DCM
operation
■■ Power-good flag with low impedance when
power removed
■■ Precision enable
■■ Programmable soft-start
■■ 5mm x 6mm QFN package
The XR76121 is a synchronous step-down regulator combining the
controller, drivers, bootstrap diode and MOSFETs in a single package
for point-of-load supplies. The XR76121 has a load current rating
of 20A. A wide 5V to 22V input voltage range allows for single supply
operation from industry standard 5V, 12V and 19.6V rails.
With a proprietary emulated current mode constant on-time (COT)
control scheme, the XR76121 provides extremely fast line and
load transient response using ceramic output capacitors. They
require no loop compensation, simplifying circuit implementation
and reducing overall component count. The control loop also
provides 0.1% load and 0.1% line regulation and maintains constant
operating frequency. A selectable power saving mode, allows the user
to operate in discontinuous mode (DCM) at light current loads thereby
significantly increasing the converter efficiency.
A host of protection features, including overcurrent, over temperature,
overvoltage, short-circuit, open feedback detect and UVLO, helps
achieve safe operation under abnormal operating conditions.
APPLICATIONS
■■ Servers
■■ Distributed power architecture
■■ Point-of-load converters
■■ FPGA, DSP and processor supplies
■■ Base stations, switches/routers
The XR76121 is available in a RoHS compliant, green/halogen-free
space-saving 5mm x 6mm QFN package.
Typical Application
VIN
EN
BST
VIN
SW
PVIN
ILIM
RLIM
POWER GOOD
VCC
XR76121
SS
FCCM
TON
VSNS
AGND
PGND
CSS
COUT
VOUT
R1
CVCC
R1
FB
R
RON
VOUT
CFF
RFF
PGOOD
CIN
L1
R2
R2
Efficiency (%)
CBST
ENABLE
100
98
96
94
92
90
88
86
84
82
80
78
76
74
72
70
600kHz
800kHz
5.0V
3.3V
2.5V
1.8V
1.5V
1.2V
1.0V
0.1
5.1
10.1
15.1
20.1
IOUT (A)
Figure 1. Typical Application
Figure 2. Efficiency
REV1D
1/18
XR76121
Absolute Maximum Ratings
Operating Conditions
These are stress ratings only and functional operation
of the device at these ratings or any other above those
indicated in the operation sections of the specifications
below is not implied. Stresses beyond those listed under
absolute maximum ratings may cause permanent damage
to the device. Exposure to any absolute maximum rating
condition for extended periods may affect device reliability
and lifetime.
PVIN.......................................................................3V to 22V
PVIN, VIN.......................................................................... -0.3V to 25V
Junction temperature range (TJ).................. -40°C to 125°C
VCC...................................................................................-0.3V to 6.0V
Package power dissipation max at 25°C...................... 4.1W
BST.................................................................-0.3V to 31V
Package thermal resistance θJA..................................... 24°C/W(4)
BST-SW.............................................................. -0.3V to 6V
NOTES:
1. No external voltage applied.
2. SW pin’s DC range is -1V, transient is -5V for less than 50ns.
3. Recommended.
4. Measured on MaxLinear evaluation board.
(1)
SW, ILIM......................................................... -1V to 25V(1)(2)
All other pins.......................................... -0.3V to VCC + 0.3V
VIN......................................................................4.5V to 22V
VCC....................................................................4.5V to 5.5V
SW, ILIM ...........................................................-1V to 22V(2)
PGOOD, TON, SS, EN..................................-0.3V to 5.5V(2)
Switching frequency.................................... 200kHz-1MHz(3)
Storage temperature..................................... -65°C to 150°C
Junction temperature.................................................. 150°C
Power dissipation....................................... Internally limited
Lead temperature (soldering, 10 second)................... 300°C
ESD rating (HBM – human body model)........................ 2kV
ESD rating (CDM – charged device model)................... 1kV
ESD rating (MM – machine model).............................. 200V
Electrical Characteristics
Specifications are for operating junction temperature of TJ = 25°C only; limits applying over the full operating junction
temperature range are denoted by a •. Typical values represent the most likely parametric norm at TJ = 25°C, and are
provided for reference purposes only. Unless otherwise indicated, VIN = 12V, SW = AGND = PGND = 0V, CVCC = 4.7uF.
Symbol
Parameter
Conditions
•
Min
Typ
Max
5
12
22
4.5
5.0
5.5
Units
Power Supply Characteristics
VCC regulating
VIN
Input voltage range
•
IVIN
VIN supply current
Not switching, VIN = 12V, VFB = 0.7V
•
0.8
1.3
mA
IVCC
VCC quiescent current
Not switching, VCC = VIN = 5V,
VFB = 0.7V
•
0.8
1.3
mA
IVIN
VIN supply current
f = 600kHz, RON = 49.9k,
VFB = 0.58V
17
mA
IOFF
Shutdown current
Enable = 0V, PVIN = VIN = 12V
1
μA
VCC tied to VIN
V
Enable and Undervoltage Lock-Out UVLO
VIH_EN
EN pin rising threshold
VEN_HYS
EN pin hysteresis
•
1.8
1.9
2.0
60
VCC UVLO start threshold, rising edge
•
4.00
4.25
VCC UVLO hysteresis
•
100
170
REV1D
V
mV
4.40
V
mV
2/18
XR76121
Electrical Characteristics (Continued)
Specifications are for operating junction temperature of TJ = 25°C only; limits applying over the full operating junction
temperature range are denoted by a •. Typical values represent the most likely parametric norm at TJ = 25°C, and are
provided for reference purposes only. Unless otherwise indicated, VIN = 12V, SW = AGND = PGND = 0V, CVCC = 4.7uF.
Symbol
Parameter
Conditions
•
Min
Typ
Max
Units
VIN = 5V - 22V, VCC regulating
0.597
0.600
0.603
V
VIN = 4.5V - 5.5V, VCC tied to VIN
0.596
0.600
0.604
V
0.594
0.600
0.606
V
Reference Voltage
VREF
Reference voltage
VIN = 5V - 22V, VCC regulating
VIN = 4.5V - 5.5V, VCC tied to VIN
DC load regulation
DC line regulation
•
CCM operation, closed loop,
applies to any COUT
±0.1
%
±0.1
%
Programmable Constant On-Time
On-time 1
RON = 5.90kΩ, VIN = 12V
f corresponding to on-time 1
VOUT = 1.0V
On-time 2
RON = 16.2kΩ, VIN = 12V
f corresponding to on-time 2
VOUT = 3.3V
On-time 3
RON = 3.01kΩ, VIN = 12V
Minimum off-time
•
•
•
170
200
230
ns
360
415
490
kHz
425
500
575
ns
478
550
647
kHz
90
110
135
ns
250
350
ns
•
Diode Emulation Mode
Zero crossing threshold
DC value measured during test
-2
mV
Soft-Start
ISS_CHARGE
Charge current
ISS_DISCHARGE
Discharge current
•
-14
-10
-6
µA
Fault present
•
1
3
VIN = 6V to 22V, ILOAD = 0 to 30mA
•
4.8
5.0
VIN = 5V, RON = 16.2kΩ,
fSW = 678kHz
•
4.6
4.8
-10
-7.5
-5
%
1
4
%
mA
VCC Linear Regulator
VCC
Output voltage
5.2
V
Power Good Output
Power good threshold
Power good hysteresis
Power good
Minimum ISINK = 1mA
0.2
V
Power good, unpowered
ISINK = 1mA
0.5
V
Power good assertion delay,
FB rising
2
ms
Power good de-assertion delay,
FB falling
65
µs
REV1D
3/18
XR76121
Electrical Characteristics (Continued)
Specifications are for operating junction temperature of TJ = 25°C only; limits applying over the full operating junction
temperature range are denoted by a •. Typical values represent the most likely parametric norm at TJ = 25°C, and are
provided for reference purposes only. Unless otherwise indicated, VIN = 12V, SW = AGND = PGND = 0V, CVCC = 4.7uF.
Symbol
Parameter
Conditions
•
Min
FCCM mode logic high threshold
FCCM rising
•
2.4
FCCM mode logic low threshold
FCCM falling
•
Typ
Max
Units
Mode Control (FCCM)
V
0.4
Input leakage current
100
V
nA
Open Feedback/OVP Detect (VSNS)
OVP trip high threshold
VSNS rising. Specified as % of VREF
•
OVP trip low threshold
VSNS falling. Specified as % of VREF
•
OVP comparator delay
VSNS rising
•
Delay to turn off power stage from an
overvoltage event
VSNS rising
•
115
120
125
115
0.5
1
%
%
3.5
µs
3.5
µs
Protection: OCP, OTP, Short-Circuit
Hiccup timeout
110
ILIM/RDS
14.5
ILIM current temperature coefficient
ILIM comparator offset
•
4.7
mV
-8.0
0
8.0
mV
Thermal hysteresis
•
%/°C
0
Rising temperature
Percent of VREF, short circuit is active.
After PGOOD asserts high.
µA/mΩ
-4.7
Current limit blanking
Feedback pin short-circuit threshold
18.0
0.4
ILIM comparator offset
Thermal shutdown threshold
16.2
ms
50
100
ns
138
°C
15
°C
60
70
%
Output Power Stage
High-side MOSFET RDS(ON)
IDS = 2A
7.7
10
mΩ
Low-side MOSFET RDS(ON)
IDS = 2A
3.1
3.5
mΩ
Maximum output current
•
REV1D
20
A
4/18
XR76121
AGND
TON
ILIM
PGOOD
1
2
3
4
5
6
7
BST 14
12
PVIN
AGND
SW
FCCM
BOTTOM VIEW
FB
TOP VIEW
Pin Configuration
13
11
PGND
8 VS
17
AGND
EN 15
9 VIN
SS 16
BST 14
10 VC
10 VCC
17
AGND
EN 15
9 VIN
SS 16
PVIN
13
8 VSNS
12
7
PGOOD
6
ILIM
5
TON
4
AGND
3
AGND
2
FCCM
FB
1
11
SW
Pin Functions
Pin Number
Pin Name
Type
1
FB
A
Feedback input to feedback comparator.
2
FCCM
I
Forcing this pin logic level high forces CCM operation.
AGND
A
Signal ground for control circuitry. Connect to AGND pad with a short trace.
5
TON
A
Constant on-time programming pin. Connect with a resistor to AGND.
6
ILIM
A
Overcurrent protection programming. Connect with a resistor to SW.
7
PGOOD
OD
8
VSNS
A
Sense pin for output OVP and open FB.
9
VIN
A
Supply input for the regulator’s LDO. Normally connected to PVIN.
10
VCC
A
The output of regulators LDO. It requires a 4.7µF VCC bypass capacitor. For operation
using a 5V rail, VCC should be tied to VIN.
11
PGND
PWR
Ground of the power stage. Internally connected to source of the low-side MOSFET.
12
SW
PWR
Switch node. Internally it connects source of the high-side MOSFET to drain of the
low-side MOSFET.
13
PVIN
PWR
Input voltage for power stage. Internally connected to drain of the high-side MOSFET.
14
BST
A
High-side driver supply pin. Connect a 0.1µF bootstrap capacitor between BST and SW.
15
EN
I
Precision enable pin. Pulling this pin above 2V will enable the regulator.
16
SS
A
Soft-start pin. Connect an external capacitor between SS and AGND to program the softstart rate based on the 10µA internal source current.
17
AGND PAD
A
Signal ground for control circuitry.
3
4
Description
Power-good output. Open drain to AGND. Low Z when IC unpowered.
NOTE:
A = Analog, I = Input, O = Output, OD = Open Drain, PWR = Power.
REV1D
5/18
PG
XR76121
Typical Performance Characteristics
100
98
96
94
92
90
88
86
84
82
80
78
76
74
72
70
600kHz
L = 0.4µH (1.0V, 1.2V, 1.5V, 1.8V)
L = 1µH (2.5V, 3.3V, 5.0V)
5.0V DCM
3.3V DCM
2.5V DCM
1.8V DCM
1.5V DCM
1.2V DCM
1.0V DCM
5.0V CCM
3.3V CCM
2.5V CCM
1.8V CCM
1.5V CCM
1.2V CCM
1.0V CCM
10.0
1.0
IOUT (A)
0.1
Efficiency (%)
Efficiency (%)
Efficiency and Package Thermal Derating
Unless otherwise specified: TAMBIENT = 25°C, no airflow, f = 800kHz. Efficiency data includes inductor losses, schematic
from the Application Information section of this datasheet.
100
98
96
94
92
90
88
86
84
82
80
78
76
74
72
70
600kHz
3.3V DCM
2.5V DCM
1.8V DCM
1.5V DCM
1.2V DCM
1.0V DCM
120
120
110
110
100
100
90
90
80
70
50
5.0V, CCM, 600kHz
2.5V, CCM, 800kHz
40
1.0V, CCM, 800kHz
80
70
60
3.3V, CCM, 600kHz
1.8V, CCM, 800kHz
1.0V, CCM, 800kHz
50
40
30
20
10.0
Figure 4. Efficiency, VIN = 5V, L = 0.4µH
TAMBIENT (ºC)
TAMBIENT (ºC)
Figure 3. Efficiency, VIN = 12V
60
1.0
IOUT (A)
0.1
3.3V CCM
2.5V CCM
1.8V CCM
1.5V CCM
1.2V CCM
1.0V CCM
30
4
6
8
10
12
14
16
18
20
20
IOUT (A)
12
IOUT (A)
Figure 5. Maximum TAMBIENT vs. IOUT,
VIN = 12V, No Airflow
Figure 6. Maximum TAMBIENT vs. IOUT,
VIN = 5V, No Airflow
REV1D
4
6
8
10
14
16
18
20
6/18
XR76121
Typical Performance Characteristics (Continued)
All data taken at VIN = 12V, VOUT = 1.8V, f = 800kHz, TA = 25°C, no airflow, forced CCM. (Unless otherwise specified).
Schematic from the Applications Information section of this datasheet.
SW
SW
13mVp-p
27mVp-p
VOUT
AC-coupled
20MHz
VOUT
AC-coupled
20MHz
IOUT
IOUT
Figure 7. Steady State, IOUT = 20A
Figure 8. Steady State, DCM, IOUT = 0A
VIN
VIN
EN
EN
VOUT
VOUT
IOUT
IOUT
Figure 9. Power-Up, IOUT = 20A
Figure 10. Power-Up, IOUT = 0A
SW
SW
VOUT AC-coupled
20MHz
-64mV
IOUT
4ms/div
4ms/div
90mV
VOUT AC-coupled
20MHz
82mV
-82mV
Di/Dt = 2.5A/μs
Di/Dt = 2.5A/μs
IOUT
10μs/div
Figure 11. Load Transient, Forced CCM,
0A-10A-0A
40μs/div
Figure 12. Load Transient, DCM,
1.8A-11.8A-1.8A
REV1D
7/18
XR76121
Typical Performance Characteristics (Continued)
All data taken at VIN = 12V, VOUT = 1.8V, f = 800kHz, TA = 25°C, no airflow, forced CCM. (Unless otherwise specified).
Schematic from the Applications Information section of this datasheet.
SW
EN
88mV
VOUT AC-coupled
20MHz
-62mV
VOUT
PGOOD
Di/Dt = 2.5A/μs
IOUT
10μs/div
IOUT
Figure 13. Load Transient, DCM or Forced CCM,
10A-20A-10A
4ms/div
Figure 14. Enable Functionality,
VIN = 12V
Pre-bias = 1.2V
VOUT
VOUT
PGOOD
IOUT
1ms/div
Figure 15. Power-Up with Pre-Bias Voltage,
IOUT = 0A
40ms/div
Figure 16. Short-Circuit Recovery,
IOUT = 20A
REV1D
8/18
XR76121
Typical Performance Characteristics (Continued)
1.850
1.850
1.840
1.840
1.830
1.830
1.820
1.820
1.810
1.810
VOUT (V)
VOUT (V)
All data taken at VIN = 12V, VOUT = 1.8V, f = 800kHz, TA = 25°C, no airflow, forced CCM. (Unless otherwise specified).
Schematic from the Applications Information section of this datasheet.
1.800
1.790
1.800
1.790
1.780
1.780
1.770
1.770
1.760
1.760
1.750
0
2
4
6
8
10
12
14
16
18
1.750
20
12
14
16
18
Figure 18. Line Regulation
20
22
20
22
20
22
Calculated
Typical
400
350
600
300
tON (ns)
700
500
400
300
250
200
200
150
100
0
10
5
15
20
RON (kΩ)
25
30
100
35
4
6
Figure 19. tON vs. RON
900
900
800
800
700
700
600
600
500
500
400
300
200
200
100
100
2
4
6
8
10
IOUT (A)
12
14
10
12
14
VIN (V)
16
18
400
300
0
8
Figure 20. tON vs. VIN, RON = 5.9kΩ
f (kHz)
f (kHz)
10
Figure 17. Load Regulation
Calculated
Typical
800
0
8
450
900
tON (ns)
6
VIN (V)
1,000
0
4
IOUT (A)
16
18
0
20
4
Figure 21. Frequency vs. IOUT
6
8
10
12
VIN (V)
14
16
18
Figure 22. Frequency vs. VIN
REV1D
9/18
XR76121
Typical Performance Characteristics (Continued)
All data taken at VIN = 12V, VOUT = 1.8V, f = 800kHz, TA = 25°C, no airflow, forced CCM. (Unless otherwise specified).
Schematic from the Applications Information section of this datasheet.
35
610
30
605
20
VREF (mV)
IOCP (A)
25
15
10
600
595
Calculated worst case
Typical
5
0
1
1.2
1.4
1.6
RLIM (kΩ)
1.8
2
590
-40
2.2
-20
0
20
40
60
TJ (°C)
80
100
120
Figure 24. VREF vs. Temperature
Figure 23. IOCP vs. RLIM
300
tON (ns)
250
200
150
100
-40
-20
0
20
40
TJ (˚C)
60
80
100
120
Figure 25. tON vs. Temperature, RON = 5.9k
REV1D
10/18
XR76121
Functional Block Diagram
VIN
VCC
PGOOD
VCC UVLO
4.25V
VCC
XR76121
LDO
10µA
VCC
THERMAL
SHUTDOWN
SS
0.6V
POWER GOOD
PVIN
HS
DRV
LEVEL
ENABLING SWITCHING
BST
SHIFT
AND
SW
NON
FB
VSNS
VH = 1.2 x VREF
VL = 1.15 x VREF
OVERLAP
COT CONTROL LOOP
0.555V
CONTROL
DELAY
SW
OVP
ZC
FB
0.36V
PGND
1.9V
EN
LS
DRV
VCC
SCCOMP
VCC
FCCM
PGND
HICCUP
ILIM
PGND
TON
EN
ILIM
AGND
Figure 26. Functional Block Diagram
REV1D
11/18
XR76121
Applications Information
Detailed Operation
The XR76121 uses a synchronous step-down proprietary
emulated current-mode Constant On-Time (COT) control
scheme. The on-time, which is programmed via RON,
is inversely proportional to VIN and maintains a nearly
constant frequency. The emulated current-mode control
allows the use of ceramic output capacitors.
Programming the On-Time
The on-time tON is programmed via resistor RON according
to following equation:
Each switching cycle begins with the high-side (switching)
FET turning on for a preprogrammed time. At the end
of the on-time, the high-side FET is turned off and the
low-side (synchronous) FET is turned on for a preset
minimum time (250ns nominal). This parameter is termed
the minimum off-time. After the minimum off-time the voltage
at the feedback pin FB is compared to an internal voltage
ramp at the feedback comparator. When VFB drops below
the ramp voltage, the high-side FET is turned on and the
cycle repeats. This voltage ramp constitutes an emulated
current ramp and allows for the use of ceramic capacitors,
in addition to other capacitor types, for output filtering.
A graph of tON versus RON, using the above equation,
is compared to typical test data in Figure 19. The graph
VOUT
shows that calculated
data matches typical test data
– (2.5 × 10-8)]
IN × x[tfON
within 3%.tON = V xV1.06
x Eff.
RONIN=
10-10
The tON corresponding to3.45
a ×
particular
set of operating
conditions can be calculated based on empirical data from:
Enable
The enable input provides precise control for startup.
Where bus voltage is well regulated, the enable input
can be derived from this voltage with a suitable resistor
divider. This ensures that XR76121 does not turn on
until bus voltage reaches the desired level. Therefore the
enable feature allows implementation of undervoltage
lockout for the bus voltage PVIN. Simple sequencing can
be implemented by using the PGOOD signal as the enable
input of a succeeding XR76121. Sequencing can also
be achieved by using an external signal to control the
enable pin.
Selecting the Forced CCM Mode
A voltage higher than 2.4V at the FCCM pin forces the
XR76121 to operate in continuous conduction mode (CCM).
Note that discontinuous conduction mode (DCM) is always
on during soft-start. DCM will persist following soft-start
until a sufficient load is applied to transition the regulator
to CCM. Magnitude of the load required to transition
to CCM is ΔIL/2, where ΔIL is peak-to-peak inductor
current ripple. Once the regulator transitions to CCM it will
continue operating in CCM regardless of the load magnitude.
Selecting the DCM/CCM Mode
The DCM will always be available if a voltage less
than 0.4V is applied to the FCCM pin. XR76121 will
operate in either DCM or CCM depending on the
load magnitude. At light loads DCM significantly increases
efficiency as seen in Figures 3 and 4. A preload of 10mA
is recommended for DCM operation. This helps improve
voltage regulation when external load is less then 10mA
and may reduce voltage ripple.
RON =
Where:
VIN × [tON – (2.5 × 10-8)]
3.45 × 10-10
VOUT VOUT
-8
VIN =× [tON
– (2.5 ×
)]× 10-8) x VIN]
tON
– 10
[(2.5
1.06VxINf xx 1.06
Eff. x f x Eff.
RON =
RON =
3.45 ×(3.45
10-10× 10-10)
■■ f
is the desired switching frequency at
nominal IOUT. VOUT
VOUT
tON =
– [(2.5 × 10-8) x V ]
■■ Eff. is
the Vconverter
1.06
xxfEff.
x Eff. correspondingINto
x
1.06
x
fefficiency
IN
∆
IL))
(I
+
(0.5
×
RON .OCP
=
nominal IOUT
(3.45 +× 0.16kΩ
10-10)
RLIM =
ILIM
Substituting for tON in the
first equation we get:
RDS
VOUT
– [(2.5 × 10-8) x VIN]
1.06 x f x Eff.
(IOCP + (0.5 × ∆IL))
RON =
(3.45 × 10-10)
RLIM =
+ 0.16kΩ
ILIM
R
DS
VOUT
– 1in terms of operating
= R2
Now RONR1
can
bexcalculated
0.6
conditions VIN, VOUT, f and efficiency using the
above equation. (I
OCP + (0.5 × ∆IL))
10µA
RLIM
=
+ 0.16kΩ
CSS f==tSS
x ILIMI
At VIN = 12V,
800kHz,
= 20A and using the
OUT
0.6V
RDS
VOUT 3 we get the following RON:
efficiency numbers
from
–1
R1 = R2
x Figure
0.6
1
VOUT (V)
f (kHz)
RON (kΩ)
CFF = Eff. (%)
2 x π x R1 x 5 x fLC
5.0
0.95
600
23.12
10µA
CSS = tSS x
0.6V
3.3
0.93
600
15.30
VOUT
1– 1
R1f= R2
x
=
0.6
2.5 LC
0.91
800
8.52
2 x π x √ L x 1COUT
CFF = 0.89
1.8
800
6.04
2 x π x R1 x 5 x fLC
10µA
1.5 C
0.87
800
5.02
SS = tSS x 0.6V
1
1.2 RFF =
0.84
800
4.01
2 x=π x f x CFF 1
fLC
1.0
0.81
800
3.35
21x π x √ L x COUT
CFF =
2 x π x R1 x 5 x fLC
XR76121 RON for common output voltages,
VIN = 12V,
1 IOUT = 20A
RFF =
1
2 x π x f x CFF
fLC =
2 x π x √ L x COUT
REV1D
12/18
RON =
VIN × [tON – (2.5 × 10-8)]
3.45 × 10-10
RON =
VIN × [tON – (2.5 × 10-8)]XR76121
3.45 × 10-10
Applications Information
VOUT (Continued)
tON =
VIN x(OCP)
1.06 x f x Eff.
Overcurrent Protection
If the load current exceeds the programmed overcurrent
threshold IOCP for four consecutive switching cycles,
the regulator enters the hiccup mode of operation.
In hiccup mode the MOSFET
off for 110ms
VOUT gates are turned
– [(2.5 timeout
× 10-8) x VaIN]soft-start
(hiccup timeout). Following
the
hiccup
1.06 x f x Eff.
is attempted.RON
If =
OCP persists, hiccup-10timeout will repeat.
(3.45 × mode
10 ) until load current
The regulator will remain in hiccup
is reduced below the programmed IOCP. In order to program
overcurrent protection use the following equation:
(IOCP + (0.5 × ∆IL))
RLIM =
+ 0.16kΩ
ILIM
RDS
Where:
■■ RLIM
is resistor value in kΩ for programming IOCP
■■ IOCP
is the overcurrent value to be programmed
VOUT inductor current ripple
is the
peak-to-peak
–1
R1 =
R2 x
0.6
■■ ILIM/RDS is the minimum value of the parameter
specified in the tabulated data
Overvoltage Protection (OVP)VOUT
tON =
The output OVP function
overvoltage condition
VINdetects
x 1.06 x an
f x Eff.
on VOUT of the regulator. OVP is achieved by
comparing
VIN × [tON – (2.5 × 10-8)]
the voltage at VSNS
pin
to
an
OVP
threshold
voltage
RON =
3.45 ×voltage
10-10
set at 1.2 x VREF. When VSNS
exceeds the
OVP threshold, an internal overvoltage signal asserts after
1us (typical). This OVP signalVOUT
latches off
the ×
high-side
– [(2.5
10-8) x V FET,
]
1.06and
x f xalso
Eff. asserts PGOODIN low.
turns on the low-side FET
VOUT
RON =
The low-side FET tON
remains
on (3.45
to discharge
=
× 10-10) the output
VIN x 1.06
x f xbelow
Eff. 1.15 x VREF.
capacitor until VSNS voltage
drops
Then low-side FET turns off to prevent complete discharge
of VOUT. The high-side and low-side FETs remain latched
off until VIN or EN is recycled. In order to use this feature,
(IOCP a+Vresistor
(0.5 × ∆IL))
connect VSNS to VOUT with
divider as shown in
OUT
– [(2.5
× 10-8) xvalue
VIN]
the application circuit.
the ILIM
same
resistor
divider
RLIM = Use 1.06
+ 0.16kΩ
x f x Eff.
RON =
that was used for programming
OUT.
RV
DS
(3.45 × 10-10)
Programming the Output Voltage
Use a voltage divider as shown in Figure 1 to program the
output voltage VOUT.
■■ ΔIL
R1R=LIM
R2 =x
■■ ILIM/RDS
= 14.5uA/mΩ
10µA
CSS = tSS x
■■ 0.16kΩ accounts for 0.6V
OCP comparator offset
The above equation is for worst-case analysis and
1
safeguards against
CFF = premature OCP. Typical value of IOCP,
R1 higher
x 5 x fLC than that predicted by
x π xbe
for a given RLIM, 2will
the above equation. Graph of calculated IOCP vs. RLIM is
compared to typical IOCP in Figures 23.
1
LC =
Short-Circuit fProtection
(SCP)
2 x π x √ L x COUT
If the output voltage drops below
60% of its programmed
value (i.e., FB drops below 0.36V), the regulator will enter
hiccup mode. Hiccup mode will persist until short-circuit
is removed. The SCP circuit
becomes active at the end
1
R =
of soft-start. FFHiccup
mode
2 x π x f x CFF and short-circuit recovery
waveform is shown in Figure 16.
Over Temperature Protection (OTP)
OTP triggers at a nominal controller temperature of 138°C.
The gates of the switching FET and the synchronous FET
are turned off. When controller temperature cools down to
123°C, soft-start is initiated and regular operation resumes.
(IOCP + (0.5 × ∆IL))
VOUT
+ 0.16kΩ
I– 1
0.6 LIM
RDS
The recommended value for R2 is 2kΩ.
10µA
CSS = tSS x
Programming the Soft-Start
0.6V
Place a capacitor CSS between the SS and AGND pins to
program the soft-start. In order to program a soft-start time
VOUT
1
–1
R1 ==required
R2 x
of tSS, calculate Cthe
capacitance
CSS from the
FF
0.6x 5 x fLC
2 x π x R1
following equation:
10µA
1
fLCCSS
= = tSS x 0.6V
2 x π x √ L x COUT
1
Pre-Bias Startup C =
FF 2 x π x R1 x 5 x f
XR76121 has the capability
to startup LC
into a pre-charged
1
output. Typical pre-bias
startup
waveforms
are shown in
RFF =
2 x π x f x CFF
Figure 15.
1
=
Maximum AllowablefLC
Voltage
Ripple at FB Pin
π x √ L atx COUT
The steady-state voltage2 xripple
feedback pin FB
(VFB,RIPPLE) must not exceed 50mV in order for the regulator
to function correctly. If VFB,RIPPLE is larger than 50mV then
COUT and/or L should be increased
1 as necessary in order to
FF = 2 50mV.
keep the VFB,RIPPLERbelow
x π x f x CFF
REV1D
13/18
RDS× ∆IL))
(IOCP + (0.5
+ 0.16kΩ
ILIM
VOUT
R
DS
tON =
VIN x 1.06 x f x Eff.
RLIM =
XR76121
VOUT (Continued)
ApplicationsR1Information
–1
= R2 x
0.6
V)
Feed-Forward CapacitorV(CFF
– [(2.5 × 10-8) x VIN]
OUT OUT
–fisx1 Eff.
R1 =capacitor
R2 x 1.06
x
The feed-forward
C
used
to set the necessary
FF
RON = 0.6 10µA
phase margin when
using ceramic
(3.45 × output
10-10) capacitors.
CSS = tSS x
0.6V equation:
Calculate CFF from
the following
10µA
CSS = tSS x
0.6V
1
CFF =
2 x π x R1 x 5 x fLC
(IOCP + (0.5 × ∆IL))
1 I
R
=
+ 0.16kΩ
CFFLIM
=
LIM
Where fLC, the
output
frequency is
2 x π x filter
R1 x 5Rdouble-pole
x fLC
1 DS
calculated from: f =
LC
2 x π x √ L x COUT
1
fLC =
2 x π x √ L x COUT
1
=
VOUT
You must use RFF
manufacturer’s
π
x
f x CFF–DC
2
x
1 derating curves to
R1 = R2 x
0.6
determine the effective capacitance
corresponding to VOUT.
A load step test
a1 loop frequency response test)
RFF(and/or
=
x π xiff necessary
x CFF
should be performed2and
CFF can be adjusted
10µAtransient load response.
in order to get a critically damped
CSS = tSS x
0.6V
In applications where output voltage ripple is less than
about 3mV, such as when a large number of ceramic
COUT are paralleled, it is necessary
to use ripple injection
1
CFF =
from across the inductor.
x R1 xcircuit
5 x fLCand corresponding
2 x πThe
calculations are explained in the MaxLinear design note.
Thermal Design
Proper thermal design is critical in controlling device
temperatures and in achieving robust designs. There are
a number of factors that affect the thermal performance.
One key factor is the temperature rise of the devices in
the package, which is a function of the thermal resistances
of the devices inside the package and the power
being dissipated.
The thermal resistance of the XR76121 is specified in
the Operating Ratings section of this datasheet. The θJA
thermal resistance specification is based on the XR76121
evaluation board operating without forced airflow. Since the
actual board design in the final application will be different,
the thermal resistances in the final design may be different
from those specified.
The package thermal derating curves for the XR76121 are
shown in Figures 5 and 6. These correspond to input voltage
of 12V and 5V, respectively. The package thermal derating
curves for the XR76121 are shown in Figures 9 and 10.
Feed-Forward Resistor (RFF)
1
fLC =CFF is used. RFF, in conjunction with
RFF is required when
π x √ Lfrequency
x COUT pole and adds
CFF, functions similar to 2ax high
gain margin to the frequency response. Calculate RFF from:
RFF =
1
2 x π x f x CFF
Where f is the switching frequency.
If RFF is greater than 0.1 x R1, then instead of CFF/RFF, use
ripple injection circuit as described in MaxLinear’s design
note.
REV1D
14/18
XR76121
Applications Information
REN2 3.83k
REN1 10k
VIN = 12V
VIN
2 x 0.1µF
13
14
BST
16
15
EN
PVIN
12 SW
4 x 0.1µF
XR76121
ILIM
PGOOD
VOUT
CFF
470pF
PGND
7
RPGOOD 10k
800kHz, 1.8V, 0-20A
L1, IHLP-5050FD-01
0.4µH at 44A, 0.9m Ohm V
OUT
11
6
RLIM 1.82k
TON
RFF
0.4k
VCC
RSENS1
4.02k
4 x 22µF/25V/X6T/1206
0.1µF
SW
AGND
VCC
VCC
5
8
SW
4
AGND
VIN
RON 6.19k
FCCM
10
3
FB
VSENSE
2
9
1
VCC
EPAD_AGND
FB
CBST
SS
17
CSS
47nF
5 x 100µF/6.3V/X6T/1206
R1
4.02k
FB
VIN
RSENS2
2k
CIN
CVCC
0.1µF
4.7µF
R2
2k
Figure 27. Application Circuit Schematic
REV1D
15/18
XR76121
Mechanical Dimensions
TOP VIEW
BOTTOM VIEW
SIDE VIEW
TERMINAL DETAILS
Drawing No.: POD-00000071
Revision: D
Figure 28. Mechanical Dimensions
REV1D
16/18
XR76121
Recommended Land Pattern and Stencil
TYPICAL RECOMMENDED LAND PATTERN
TYPICAL RECOMMENDED STENCIL
Drawing No.: POD-00000071
Revision: D
Figure 29. Recommended Land Pattern and Stencil
REV1D
17/18
XR76121
Ordering Information(1)
Part Number
Operating Temperature Range
Lead-Free
Package
-40°C ≤ TJ ≤ 125°C
Yes(2)
5mm x 6mm QFN
XR76121EL-F
XR76121ELTR-F
XR76121EVB
Packaging
Method
Bulk
Tape and Reel
XR76121 evaluation board
NOTE:
1. Refer to www.exar.com/XR76121 for most up-to-date Ordering Information.
2. Visit www.exar.com for additional information on Environmental Rating.
Revision History
Revision
Date
1A
July 2016
1B
November 2017
1C
May 2018
1D
February 2019
Description
Initial Release
Added MaxLinear logo. Updated format and Ordering Information table. Changed name of
Package Description section to Mechanical Dimensions and Recommended Land Pattern and
Stencil per updated format. Corrected typo in Package Description / Mechanical Dimensions.
Updated Land Pattern and Stencil.
Package dimension A updated to align with JEDEC. Update Ordering Information.
Corporate Headquarters:
5966 La Place Court
Suite 100
Carlsbad, CA 92008
Tel.:+1 (760) 692-0711
Fax: +1 (760) 444-8598
www.maxlinear.com
The content of this document is furnished for informational use only, is subject to change without notice, and should not be construed as a commitment by MaxLinear, Inc.. MaxLinear, Inc. assumes
no responsibility or liability for any errors or inaccuracies that may appear in the informational content contained in this guide. Complying with all applicable copyright laws is the responsibility of the
user. Without limiting the rights under copyright, no part of this document may be reproduced into, stored in, or introduced into a retrieval system, or transmitted in any form or by any means (electronic,
mechanical, photocopying, recording, or otherwise), or for any purpose, without the express written permission of MaxLinear, Inc.
Maxlinear, Inc. does not recommend the use of any of its products in life support applications where the failure or malfunction of the product can reasonably be expected to cause failure of the life support
system or to significantly affect its safety or effectiveness. Products are not authorized for use in such applications unless MaxLinear, Inc. receives, in writing, assurances to its satisfaction that: (a) the
risk of injury or damage has been minimized; (b) the user assumes all such risks; (c) potential liability of MaxLinear, Inc. is adequately protected under the circumstances.
MaxLinear, Inc. may have patents, patent applications, trademarks, copyrights, or other intellectual property rights covering subject matter in this document. Except as expressly provided in any written
license agreement from MaxLinear, Inc., the furnishing of this document does not give you any license to these patents, trademarks, copyrights, or other intellectual property.
MaxLinear, the MaxLinear logo, and any MaxLinear trademarks, MxL, Full-Spectrum Capture, FSC, G.now, AirPHY and the MaxLinear logo are all on the products sold, are all trademarks of MaxLinear,
Inc. or one of MaxLinear’s subsidiaries in the U.S.A. and other countries. All rights reserved. Other company trademarks and product names appearing herein are the property of their respective owners.
© 2016 - 2019 MaxLinear, Inc. All rights reserved
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REV1D
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