XR76108 and XR76112
8A and 12A Synchronous Step Down COT Regulators
September 10, 2021
218DSR00
General Description
FEATURES
The XR76108 and XR76112 are synchronous step-down
regulators combining the controller, drivers, bootstrap
diode and MOSFETs in a single package for Point-of-Load
supplies. The XR76108 has a load current rating of 8A and
the XR76112 has a load current rating of 12A. A wide 4.5V
to 22V input voltage range allows for single supply
operation from industry standard 5V, 12V and 19.6V rails.
• 8A and 12A capable step down
regulators
− 4.5V to 5.5V low VIN operation
− 4.5V to 22V wide single input voltage
− ≥0.6V adjustable output voltage
• Controller, drivers, bootstrap diode and
MOSFETs integrated in one package
With a proprietary emulated current mode Constant OnTime (COT) control scheme, the XR76108 and XR76112
provide 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 0.25% 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.
• Proprietary Constant On-Time control
− No loop compensation required
− Ceramic output capacitor stable
operation
− Programmable 200ns - 2µs on-time
− Constant 200kHz - 800kHz frequency
− Selectable CCM or CCM / DCM
operation
• Precision enable and Power-Good flag
• Programmable soft-start
• 5x5mm 30-pin QFN package
A host of protection features, including over-current,
over-temperature, short-circuit and UVLO, help achieve
safe operation under abnormal operating conditions.
APPLICATIONS
The XR76108 and XR76112 are available in a RoHScompliant, green / halogen-free, space-saving QFN
5x5mm package.
• Distributed power architecture
• Point-of-Load converters
• Power supply modules
• FPGA, DSP, and processor supplies
• Base stations, switches / routers, and
servers
Typical Application
1.220
VIN
1.215
Power Good
CIN
R3
PVIN
EN/MODE
BST
PGOOD
SW
VCC
SS
TON
CVCC
CSS
RON
AGND
XR76108
XR76112
CBST
L1
RLIM
ILIM
1.210
VOUT
CFF
VOUT (V)
Enable/Mode
VIN
R1
COUT
FB
PGND
R2
1.205
1.200
1.195
1.190
1.185
1.180
5
10
15
20
VIN (V)
Figure 2: XR76112 Line Regulation
Figure 1: XR76108 and XR76112 Application Diagram
1
XR76108 / XR76112
Absolute Maximum Ratings
Operating Ratings
PVIN .............................................................. 3V to 22V
VIN ............................................................. 4.5V to 22V
VCC ............................................................ 4.5V to 5.5V
SW, ILIM ................................................... -1V to 22V(2)
PGOOD, VCC, TON, SS, EN............................ -0.3V to 5.5V
Switching frequency ............................ 200kHz-800kHz(3)
Junction temperature range (TJ) ...............-40°C to 125°C
XR76108 package power dissipation max at 25°C ..... 3.8W
XR76112 package power dissipation max at 25°C ..... 4.1W
XR76108 JEDEC51 package thermal resistance θJA .... 26°C/W
XR76112 JEDEC51 package thermal resistance θJA .... 24°C/W
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, VIN .................................................... -0.3V to 25V
VCC .......................................................... -0.3V to 6.0V
BST ....................................................... -0.3V to 31V(1)
BST-SW ...................................................... -0.3V to 6V
SW, ILIM .................................................. -1V to 25V(1,2)
All other pins ..................................... -0.3V to VCC+0.3V
Storage temperature .............................. -65°C to 150°C
Junction temperature ........................................... 150°C
Power dissipation ................................ Internally Limited
Lead temperature (soldering, 10 sec)..................... 300°C
ESD Rating (HBM – Human Body Model) ................... 2kV
ESD Rating (CDM – Charged Device Model) ............. 1.5kV
Note 1: No external voltage applied
Note 2: SW pin’s DC range is -1V, transient is -5V for less
than 50ns
Note 3: Recommended
Ordering Information
Part Number
Operating Temperature Range
Package
Packing Method
Lead-Free
XR76108ELTR-F
-40°C≤TJ≤+125°C
5x5mm QFN
Tape & Reel
Yes
XR76112EL-F
-40°C≤TJ≤+125°C
5x5mm QFN
Bulk
Yes
XR76112ELTR-F
-40°C≤TJ≤+125°C
XR76108 Evaluation Board
XR76112 Evaluation Board
5x5mm QFN
Tape & Reel
Yes
XR76108EVB
XR76112EVB
Note: For most up-to-date ordering information and additional information on environmental rating, go to
www.maxlinear.com/XR76108 and www.maxlinear.com/XR76112
Electrical Characteristics
Specifications are for the 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.
Parameter
Min.
Typ.
Max. Units
Conditions
Power Supply Characteristics
4.5
12
22
4.5
5.0
5.5
IVIN, VIN supply current
0.7
1.3
mA
IVCC, VCC quiescent current
0.7
1.3
mA
VIN, input voltage range
V
•
VCC regulating or in dropout
VCC tied to VIN
• Not switching, VIN = 12V, VFB = 0.7V
• Not switching, VCC = VIN = 5V, VFB = 0.7V
IVIN, VIN supply current (XR76112)
8
mA
f = 300kHz, RON = 107k, VFB = 0.58V
IVIN, VIN supply current (XR76108)
6
mA
f = 300kHz, RON = 107k, VFB = 0.58V
0.5
μA
Enable = 0V, VIN = 12V, VIN = PVIN
IOFF, shutdown current
Enable and Under-Voltage Lock-Out UVLO
VIH_EN, EN pin rising threshold
VEN_HYS, EN pin hysteresis
VIH_EN, EN pin rising threshold for
DCM/CCM operation
1.8
218DSR00
2.0
V
50
2.8
3.0
4.00
4.25
VEN_HYS, EN pin hysteresis
VCC UVLO start threshold, rising edge
1.9
•
mV
3.1
V
100
•
mV
4.40
V
2
•
Rev. 2D
XR76108 / XR76112
Parameter
VCC UVLO hysteresis
Min.
Typ.
150
230
Max. Units
0.597
0.600
0.603
V
0.596
0.600
0.604
V
mV
Conditions
•
Reference Voltage
VREF, reference voltage
0.594
0.600
0.606
V
DC load regulation
±0.25
%
DC Line regulation
±0.1
%
Parameter
VIN = 4.5V - 22V VCC regulating or in dropout
VIN = 4.5V - 5.5V VCC tied to VIN
• VIN = 4.5V - 22V VCC regulating or in dropout,
VIN = 4.5V - 5.5V VCC tied to VIN
CCM operation, closed loop, applies to any COUT
Min.
Typ.
Max. Units
Conditions
On-time 1
1.66
1.95
2.24
µs
• RON = 140kΩ, VIN = 22V
f corresponding to on-time 1
243
280
329
kHz
VIN = 22V, VOUT = 12V
ns
RON = 6.98kΩ, VIN = 22V
• RON = 6.98kΩ, VIN = 12V
Programmable Constant On-Time
109
Minimum Programmable on-time
On-time 2
162
202
226
f corresponding to on-time 2
1217
1361
1698
kHz
f corresponding to on-time 2
369
413
514
kHz
On-time 3
352
422
492
ns
250
350
ns
Minimum off-time
ns
VOUT = 3.3V
VOUT = 1.0V
• RON = 16.2kΩ, VIN = 12V
•
Diode Emulation Mode
-2
Zero crossing threshold
mV
DC value measured during test
Soft-Start
SS charge current
SS discharge current
-14
-10
1
3
-6
µA
•
mA
• Fault present
VCC Linear Regulator
VCC output voltage
4.8
5.0
4.3
4.37
5.2
-10
-7.5
-5
2
4
V
• VIN = 6V to 22V, Iload = 0 to 30mA
• VIN = 4.5V, RON = 16.2kΩ, fsw = 678kHz, XR76112
Power Good Output
Power Good threshold
Power Good hysteresis
Power Good sink current
1
%
%
15
mA
Protection: OCP, OTP, Short-Circuit
110
Hiccup timeout
ILIM pin source current
45
ms
55
0.4
ILIM current temperature coefficient
ILIM comparator offset
50
-8
0
µA
%/°C
+8
mV
Current limit blanking
100
ns
Thermal shutdown threshold
150
°C
15
°C
Thermal hysteresis
Feedback pin short-circuit threshold
60
70
%
High-side MOSFET RDSON
21
28
mΩ
Low-side MOSFET RDSON
7
10
mΩ
50
•
Rising temperature
•
Percent of VREF, short circuit is active
After PGOOD is up
XR76108 Output Power Stage
Maximum output current
A
8
VGS = 4.5V, IDS = 2A
VGS = 4.5V, IDS = 2A
•
XR76112 Output Power Stage
High-side MOSFET RDSON
11
15.5
mΩ
Low-side MOSFET RDSON
5
9
mΩ
Maximum output current
218DSR00
A
12
3
VGS = 4.5V, IDS = 2A
VGS = 4.5V, IDS = 2A
•
Rev. 2D
XR76108 / XR76112
Block Diagram
Figure 3: XR76108 / XR76112 Block Diagram
218DSR00
4
Rev. 2D
XR76108 / XR76112
Pin Assignment
BST
SW
PVIN
PVIN
PVIN
PVIN
PVIN
PVIN
30
29
28
27
26
25
24
23
PVIN PAD
1
EN
2
21 PVIN
TON
3
20
SW
SS
4
19
PGND
PGOOD
5
18
PGND
17
PGND
16
PGND
15
PGND
FB
6
AGND
7
22 PVIN
PGND PAD
ILIM
SW PAD
AGND PAD
8
9
10
11
12
13
14
VIN
VCC
AGND
SW
SW
SW
SW
Figure 4: XR76108 / XR76112 Pin Assignment
218DSR00
5
Rev. 2D
XR76108 / XR76112
Pin Description
Name
Pin Number
ILIM
1
Over-current protection programming. Connect with a resistor to SW.
EN/MODE
2
Precision enable pin. Pulling this pin above 1.9V will turn the regulator on and it will
operate in CCM. If the voltage is raised above 3.0V, then the regulator will operate in
DCM / CCM, depending on load.
TON
3
Constant On-Time programming pin. Connect with a resistor to AGND.
SS
4
Soft-start pin. Connect an external capacitor between SS and AGND to program the
soft-start rate based on the 10µA internal source current.
PGOOD
5
Power-good output. This open-drain output is pulled low when VOUT is outside the
regulation.
FB
6
Feedback input to feedback comparator. Connect with a set of resistors to VOUT and
AGND in order to program VOUT.
AGND
7, 10,
AGND Pad
Signal ground for control circuitry. Connect AGND Pad with a short trace to pins 7 and
10.
VIN
8
VCC
9
Supply input for the regulator’s LDO. Normally it is connected to PVIN.
The output of regulator’s LDO. For operation using a 5V rail, VCC should be shorted to
VIN.
SW
PGND
PVIN
BST
218DSR00
Description
Switch node. The drain of the low-side N-channel MOSFET. The source of the high-side
11-14, 20, 29,
MOSFET is wire-bonded to the SW Pad. Pins 20 and 29 are internally connected to the
SW Pad
SW pad.
15-19,
Ground of the power stage. Should be connected to the system’s power ground plane.
PGND Pad
The source of the low-side MOSFET is wire-bonded to PGND Pad.
21-28,
Input voltage for power stage. The drain of the high-side N-channel MOSFET.
PVIN Pad
30
High-side driver supply pin. Connect a bootstrap capacitor between BST and pin 29.
6
Rev. 2D
XR76108 / XR76112
Typical Performance Characteristics
All data taken at VIN = 12V, VOUT = 1.2V, f = 600kHz, TA = 25°C, no Air flow, Forced CCM, unless otherwise specified. The
schematic and BOM are from the Applications Circuit section of this datasheet.
1.220
1.220
1.215
1.215
1.210
1.210
1.205
1.205
VOUT (V)
VOUT (V)
REGULATION
1.200
1.195
1.200
1.195
1.190
1.190
1.185
1.185
1.180
0
2
4
6
8
10
1.180
12
5
10
15
20
VIN (V)
IOUT (A)
Figure 5: XR76112 Load Regulation, VIN=12V
Figure 6: XR76112 Line Regulation, IOUT=12A
SW
SW
VOUT
AC coupled
20MHz Filter
VOUT
AC coupled
20MHz Filter
IL
IL
1us/d
2ms/d
Figure 8: XR76112 VOUT Ripple is 22mV at 0A, DCM
Figure 7: XR76112 VOUT Ripple is 14mV at 12A
610
700
600
605
VREF (mV)
f (kHz)
500
400
VOUT=5V, RON=29.4k
300
VOUT=1.2V, RON=6.8k
200
600
595
100
0
0
2
4
6
8
10
590
12
IOUT(A)
-20
0
20
40
60
80
100
120
Tj (°C)
Figure 9: XR76112 Frequency vs. IOUT, Forced CCM
218DSR00
-40
Figure 10: VREF vs. Temperature
7
Rev. 2D
XR76108 / XR76112
Typical Performance Characteristics
All data taken at VIN = 12V, VOUT = 1.2V, f =600kHz, T A= 25°C, no Air flow, Forced CCM, unless otherwise specified. The
schematic and BOM are from the Applications Circuit section of this datasheet.
70
500
490
480
60
460
ILIM (uA)
TON (ns)
470
450
440
430
50
40
420
410
400
-40
-20
0
20
40
60
80
30
100 120
-40
Tj (°C)
0
20
40
60
80
100 120
Tj (°C)
Figure 11: On-Time vs. Temperature
Figure 12: ILIM vs. Temperature
SW
VOUT
AC coupled
20MHz Filter
-20
SW
VOUT
AC coupled
20MHz Filter
36mV
47mV
-35mV
-73mV
∆IOUT/∆t
=2.5A/us
IL
IL
40us/d
40us/d
Figure 13: XR76108 Load Step, DCM/CCM, 0A - 4A - 0A
Figure 14: XR76108 Load Step, Forced CCM, 4A – 8 - 4A
SW
VOUT
AC coupled
20MHz Filter
∆IOUT/∆t
=2.5A/us
SW
60mV
VOUT
AC coupled
20MHz Filter
50mV
-50mV
-80mV
∆IOUT/∆t
=2.5A/us
IL
IL
∆IOUT/∆t
=2.5A/us
20us/d
20us/d
Figure 15: XR76112 Load Step, DCM / CCM, 0A - 6A - 0A
Figure 16: XR76112 Load Step, Forced CCM, 6A - 12A - 6A
218DSR00
8
Rev. 2D
XR76108 / XR76112
Power-Up
VIN
VIN
EN/MODE
EN/MODE
VOUT
VOUT
IOUT
IOUT
4ms/d
4ms/d
Figure 18: XR76112 Power-up, Forced CCM, IOUT =12A
Figure 17: XR76112 Power-up, Forced CCM, IOUT = 0A
VIN
VIN
EN/MODE
EN/MODE
VOUT
VOUT
IOUT
IOUT
4ms/d
4ms/d
Figure 20: XR76112 Power-up, DCM / CCM, IOUT = 12A
Figure 19: XR76112 Power-up, DCM / CCM, IOUT = 0A
20
EN
18
XR76112
XR76108
IOCP (A)
16
VOUT
14
12
SW
IL
10
8
20ms/d
1.2
1.4
1.6
1.8
2
2.2
2.4
2.6
RLIM (k)
Figure 22: Typical IOCP versus RLIM
Figure 21: XR76112 Enable Turn On / Turn Off, 1.2VOUT, 12A
218DSR00
9
Rev. 2D
XR76108 / XR76112
Efficiency – XR76108/ XR76112
100
100
95
95
90
90
85
85
Efficiency (%)
Efficiency (%)
TAMBIENT = 25°C, no Air flow, inductor losses are included.
80
75
70
3.3V_DCM
2.5V_CCM
2.5V_DCM
1.8V_CCM
65
60
3.3V_CCM
0.1
1.8V_DCM
1.5V_CCM
1.5V_DCM
1.2V_CCM
1.2V_DCM
1.0V_CCM
1.0V_DCM
1
80
75
70
65
60
10
0.1
3.3V_ CCM
3.3V_DCM
2.5V_ CCM
2.5V_DCM
1.8V_ CCM
1.8V_DCM
1.5V_ CCM
1.5V_DCM
1.2V_ CCM
1.2V_DCM
1.0V_ CCM
1.0V_DCM
1
10
IOUT (A)
IOUT (A)
Figure 24: XR76112, 5VIN, 600kHz, 0.56µH
Figure 23: XR76108, 5VIN, 600kHz, 1µH
100
100
1uH
95
95
90
90
85
85
1uH
80
75
70
65
60
Efficiency (%)
Efficiency (%)
2.2uH
0.1
5.0V_CCM
5.0V_DCM
3.3V_CCM
3.3V_DCM
2.5V_CCM
2.5V_DCM
1.8V_CCM
1.8V_DCM
1.5V_CCM
1.5V_DCM
1.2V_CCM
1.2V_DCM
1.0V_CCM
1.0V_DCM
1
80
0.56uH
75
70
65
60
10
0.1
95
95
90
90
85
85
Efficiency (%)
Efficiency (%)
100
80
75
0.1
5.0V_CCM
5.0V_DCM
3.3V_CCM
3.3V_DCM
2.5V_CCM
2.5V_DCM
1
2.5V_DCM
1.8V_CCM
1.8V_DCM
1.5V_CCM
1.5V_DCM
1.2V_CCM
1.2V_DCM
1.0V_CCM
1.0V_DCM
10
80
75
70
65
60
10
IOUT (A)
0.1
5.0V_CCM
5.0V_DCM
3.3V_CCM
3.3V_DCM
2.5V_CCM
2.5V_DCM
1
10
IOUT (A)
Figure 27: XR76108, 22VIN, 400kHz, 3.3µH
218DSR00
3.3V_DCM
2.5V_CCM
Figure 26: XR76112, 12VIN, 600kHz
100
60
3.3V_CCM
IOUT (A)
Figure 25: XR76108, 12VIN, 600kHz
65
5.0V_DCM
1
IOUT (A)
70
5.0V_CCM
Figure 28: XR76112, 22VIN, 400kHz, 2.2µH
10
Rev. 2D
XR76108 / XR76112
Thermal Characteristics
No Air flow, f = 600kHz
TAMBIENT vs IOUT
130
120
120
110
110
TAMBIENT (°C)
TAMBIENT (°C)
TAMBIENT vs IOUT
130
100
90
1.2
80
50
90
70
3.3
60
3.3
50
1
1.2
80
1.8
1.8
70
60
100
2
3
4
5
6
7
8
1
2
3
4
120
120
110
110
100
100
1.2
80
1.8
70
3.3
2
3
4
5
6
7
8
1.2
80
1.8
60
50
8
9
10
11
50
12
IOUT (A)
3.3
1
2
3
4
5
6
7
8
9
10
11
12
IOUT (A)
Figure 31: XR76112 Package Thermal Derating, 12VIN
218DSR00
90
70
1
7
TAMBIENT vs IOUT
130
TAMBIENT (°C)
TAMBIENT (°C)
TAMBIENT vs IOUT
130
60
6
Figure 30: XR76108 Package Thermal Derating, 5VIN
Figure 29: XR76108 Package Thermal Derating, 12VIN
90
5
IOUT (A)
IOUT (A)
Figure 32: XR76112 Package Thermal Derating, 5VIN
11
Rev. 2D
XR76108 / XR76112
Detailed Operation
The XR76108 / XR76112 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.
Each switching cycle begins with the high-side (switching)
FET turning on for a pre-programmed time. At the end of
the on-time, the high-side FET is turned off and the lowside (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.
Figure 33: Selecting Forced CCM by Deriving EN/MODE
from VIN
Enable / Mode
The EN/MODE pin accepts a tri-level signal that is used to
control channel turn-on and turn-off. It also selects
between two modes of operation: ‘Forced CCM’ and
‘DCM / CCM’. If EN is pulled below 1.9V, the regulator
shuts down. A voltage between 1.9V and 3V selects the
Forced CCM mode, which will run the converter in
continuous conduction for all load currents. A voltage
higher than 3V selects the DCM / CCM mode, which will
run the converter in discontinuous conduction mode at
light loads.
Selecting the Forced CCM Mode
In order to set the controller to operate in Forced CCM, a
voltage between 1.9V and 3.0V must be applied to the
EN/MODE pin. This can be achieved with an external
control signal that meets the above voltage requirement.
Where an external control is not available, the EN/MODE
signal can be derived from VIN. If VIN is well regulated, use
a resistor divider and set the voltage to 2.5V. If VIN varies
over a wide range, the circuit shown in Figure 33 can be
used to generate the required voltage. Note that at VIN of
5.5V to 22V, the nominal Zener voltage is respectively
4.0V to 5.0V. Therefore, for VIN in the range of 5.5V to
22V, the circuit shown in Figure 33 will generate voltage
at the EN/MODE pin required for Forced CCM.
Figure 34: Selecting DCM/CCM by Deriving EN/MODE
from VIN
Selecting the DCM / CCM Mode
In order to set the controller operation to DCM / CCM, a
voltage between 3.1V and 5.5V must be applied to the
EN/MODE pin. If an external control signal is available, it
can be directly connected to the EN/MODE pin. In
applications where an external control signal is not
available, the EN/MODE input can be derived from VIN. If
VIN is well regulated, use a resistor divider and set the
voltage to 4.0V. If VIN varies over a wide range, the circuit
shown in Figure 34 can be used to generate the required
voltage.
218DSR00
12
Rev. 2D
XR76108 / XR76112
Programming the On-Time
ILIM is the internal current that generates the
necessary OCP comparator threshold (45µA)
The on-time TON is programmed via resistor RON according
to following equation:
𝑅𝑅𝑂𝑂𝑂𝑂 =
Note that ILIM has a positive temperature coefficient of
0.4%/°C. This is meant to approximately match and
compensate for the positive temperature coefficient of the
synchronous FET’s RDSON.
𝑉𝑉𝐼𝐼𝐼𝐼 × [𝑇𝑇𝑂𝑂𝑂𝑂 − (3 × 10−8 )]
2.9 × 10−10
The above equation is for worst-case analysis and
safeguards against premature OCP. Actual value of IOCP,
for a given RLIM, will be higher than that predicted by the
above equation. Typical IOCP versus RLIM is shown in Figure
22.
where TON is calculated from:
𝑇𝑇𝑂𝑂𝑂𝑂 =
where:
𝑉𝑉𝑂𝑂𝑂𝑂𝑂𝑂
𝑉𝑉𝐼𝐼𝐼𝐼 × 𝑓𝑓 × 𝐸𝐸𝐸𝐸𝐸𝐸.
f is the desired switching frequency at nominal IOUT
Short-Circuit Protection (SCP)
Eff. is the converter efficiency corresponding to nominal
IOUT
If the output voltage drops below 60% of its programmed
value, the regulator will enter hiccup mode. Hiccup mode
will persist until the short-circuit is removed. The SCP
circuit becomes active after PGOOD asserts high.
Substituting for TON in the first equation we get:
𝑅𝑅𝑂𝑂𝑂𝑂 =
𝑉𝑉
� 𝑂𝑂𝑂𝑂𝑂𝑂 � − [(3 × 10−8 ) × 𝑉𝑉𝐼𝐼𝐼𝐼 ]
𝑓𝑓 × 𝐸𝐸𝐸𝐸𝐸𝐸.
(2.9 × 10−10 )
Over-Temperature Protection (OTP)
OTP triggers at a nominal controller temperature of 150°C.
The gates of the switching FET and the synchronous FET
are turned off. When controller temperature cools down to
135°C, soft-start is initiated and operation resumes.
At VIN = 12V, f = 600kHz, IOUT = 8A and using the efficiency
numbers from Figure 25, we get the following RON for
XR76108:
VOUT (V)
5.0
3.3
2.5
1.8
1.5
1.2
1.0
RON (kΩ)
29.3
19.4
14.5
10.4
8.67
6.87
5.68
Programming the Output Voltage
Use an external voltage divider as shown in Figure 1 to
program the output voltage VOUT.
𝑉𝑉𝑂𝑂𝑂𝑂𝑂𝑂
𝑅𝑅1 = 𝑅𝑅2 × �
− 1�
0.6
The recommended value for R2 is 2kΩ.
Figure 35: XR76108 RON for Common Output Voltages,
VIN = 12V, IOUT = 8A, f = 600kHz
Programming the Soft-Start
Place a capacitor CSS between the SS and GND pins to
program the soft-start. In order to program a soft-start
time of TSS, calculate the required capacitance CSS from the
following equation:
Over-Current Protection (OCP)
If the load current exceeds the programmed over-current
IOCP for four consecutive switching cycles, then the
regulator enters the hiccup mode of operation. In hiccup
mode, the MOSFET gates are turned off for 110ms (hiccup
timeout). Following the hiccup timeout, a soft-start is
attempted. If OCP persists, hiccup timeout will repeat. The
regulator will remain in hiccup mode until load current is
reduced below the programmed IOCP. In order to program
over-current protection, use the following equation:
where:
𝑅𝑅𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼 =
𝐶𝐶𝑆𝑆𝑆𝑆 = 𝑇𝑇𝑆𝑆𝑆𝑆 ×
Feed-Forward Capacitor CFF
The voltage divider R1-R2 attenuates the output voltage
ripple (VOUT,RIPPLE) that is fed back to the controller’s FB pin.
The steady-state voltage ripple at FB (VFB,RIPPLE) must not
exceed 50mV in order for the controller to function
correctly. If VFB,RIPPLE is larger than 50mV, a CFF should not
be used. COUT should be increased as necessary in order to
keep the VFB,RIPPLE below 50mV.
(𝐼𝐼𝑂𝑂𝑂𝑂𝑂𝑂 × 𝑅𝑅𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷 ) + 8𝑚𝑚𝑚𝑚
𝐼𝐼𝐿𝐿𝐿𝐿𝐿𝐿
It is recommended to use a feed-forward capacitor (CFF) if
output voltage ripple (VOUT,RIPPLE) is less than 50mV. CFF
provides a low-impedance / high-frequency path for the
VOUT,RIPPLE to be transmitted to FB. It also helps achieve an
optimum transient load response. Calculate CFF from:
RLIM is resistor value for programming IOCP
IOCP is the over-current value to be programmed
RDSON = 10mΩ (XR76108)
RDSON = 9mΩ (XR76112)
𝐶𝐶𝐹𝐹𝐹𝐹 =
8mV is the OCP comparator offset
218DSR00
10𝑢𝑢𝑢𝑢
0.6𝑉𝑉
13
1
2 × 𝜋𝜋 × 𝑓𝑓 × 0.1 × 𝑅𝑅1
Rev. 2D
XR76108 / XR76112
A load step test should be performed and if necessary CFF
can be adjusted in order to get a critically damped
transient load response.
board design in the final application will be different from
the board defined in the standard, the thermal resistances
in the final design may be different from those shown.
Feed-Forward Resistor RFF
The package thermal derating curves for the XR76108 are
shown in Figures 29 and 30. These correspond to input
voltages of 12V and 5V respectively. The package thermal
derating curves for the XR76112 are shown in Figures 31
and 32.
Fast turn on and turn off of power FETs gives rise to
switching noise that may be coupled to the feedback pin.
Excessive switching noise at FB will result in poor load
regulation. A resistor RFF, in series with CFF, helps decouple
noise and restore good load regulation. Maximum value of
RFF should not exceed 0.02×R1.
Operation at VIN < 6V
As VIN falls below approximately 5V, the VCC regulator will
start to operate in dropout. This means it is no longer
regulating the output of VCC. VCC is designed with a UVLO
function to ensure all internal circuitry has sufficient
voltage to operate to meet datasheet specifications and
properly drive the internal MOSFETs. The UVLO is set to
allow the chip to start operating once VCC reaches 4.25V
and will disable the chip if the voltage falls below 4.00V.
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.
When VIN is 4.5V and the part is not switching, the output
of the VCC regulator will be close to VIN and be high enough
to ensure it is above the VCC UVLO. Although once
switching starts, the output of VCC may fall as low as 4.3V,
the UVLO shutdown threshold is guaranteed to be less than
4.25V.
The thermal resistances of the XR76108 / XR76112 are
specified in the “Operating Ratings” section of this
datasheet. The JEDEC θJA thermal resistance provided is
based on tests that comply with the JESD51-2A
“Integrated Circuit Thermal Test Method Environmental
Conditions – Natural Convection” standard. JESD51-xx are
a group of standards whose intent is to provide
comparative data based on a standard test condition which
includes a defined board construction. Since the actual
218DSR00
14
Rev. 2D
XR76108 / XR76112
Applications Circuit
Circuit to derive EN / MODE from VIN
R3 60.4k
12VIN
CBST
0.1uF
RON
CSS
PGOOD
3
6.8k
4
47nF
5
VCC
6
R5
7
10k
ILIM
23
24
25
26
27
EN
PVIN PAD
2
PVIN
1
2.5k
PVIN
RLIM
PVIN
SW
EN/MODE
BST
1-2 --> CCM
PVIN
R4 71.5k
PVIN
PVIN
0.22uF
28
C
29
3
2
1
3
2
1
10k
30
J1
RZ
PVIN
2-3 --> DCM / CCM
MMSZ4685
SW
DZ
TON
22
PVIN
PVIN
20
SW
SS
19
PGND
XR76112
PGOOD
18
PGND
FB
17
PGND
AGND
SW PAD
SW
PGND PAD
RSNB
1 Ohm
CFF
2.2nF
470uF
VCC
3x22uF
R1
2k
RFF
5 Ohm
CSNB 1.5nF
PVIN
4.7uF
600kHz, 12A@1.2VOUT
L1 IHLP-4040DZ-01
0.56uH @ 27A, 1.7mOhm
14
13
SW
SW
12
11
SW
AGND
10
VCC
VIN
9
8
0.1uF
CVCC
15
PGND
AGND PAD
CIN
16
PGND
FB
3x10uF
21
FB
R2
2k
Figure 36: XR76112 Application Circuit Schematic
Circuit to derive EN / MODE from VIN
12VIN
CBST
0.1uF
CSS
47nF
6.8k
3
4
5
VCC
6
R5
10k
7
23
24
EN
PVIN PAD
ILIM
PVIN
1
2
RON
PGOOD
2.2k
PVIN
RLIM
PVIN
SW
EN/MODE
BST
1-2 --> CCM
25
PVIN
26
R4 71.5k
PVIN
R3 60.4k
27
0.22uF
PVIN
C
28
3
2
1
PVIN
3
2
1
10k
30
J1
RZ
29
2-3 --> DCM / CCM
MMSZ4685
SW
DZ
PVIN
PVIN
SW
TON
PGND
SS
XR76108
PGOOD
PGND
FB
PGND
AGND
PGND
FB
PGND
4.7uF
SW PAD
SW
SW
SW
2x10uF
21
20
19
18
17
16
15
PGND PAD
RSNB
1 Ohm
CSNB 1nF
PVIN
600kHz, 8A@1.2VOUT
L1 IHLP-4040DZ-01
1uH @ 17.5A, 3.7mOhm
CFF
4.7nF
14
13
12
SW
AGND
11
10
VIN
CVCC
0.1uF
9
8
CIN
VCC
AGND PAD
22
RFF
0 Ohm
R1
2k
330uF
3x22uF
FB
R2
2k
VCC
Figure 37: XR76108 Application Circuit Schematic
218DSR00
15
Rev. 2D
XR76108 / XR76112
Mechanical Dimensions
218DSR00
16
Rev. 2D
XR76108 / XR76112
Recommended Land Pattern and Stencil
218DSR00
17
Rev. 2D
XR76108 / XR76112
Revision History
Revision
Date
1A
March 2014
Initial release: ECN 1413-13 03-26-14
2A
August 2014
Changed figure 1, 3, 17-20, 33-38. Extend input operating range down to 4.5V.
Changed VCC dropout conditions. Changed VCC UVLO specification. Added applications
information for operating VIN
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