XR76203 / XR76205 / XR76208
40V 3A/5A/8A Synchronous
Step Down COT Regulator
exar.com/XR76203/5/8
Rev 1B
1 / 20
General Description
The XR76203, XR76205 and XR76208 are synchronous step-down
regulators combining the controller, drivers, bootstrap diode and
MOSFETs in a single package for point-of-load supplies. The XR76203,
XR76205 and XR76208 have load current ratings of 3A, 5A and 8A
respectively. A wide 5V to 40V input voltage range allows for single
supply operation from industry standard 24V ±10%, 18V-36V, and
rectified 18VAC and 24VAC rails.
With a proprietary emulated current mode Constant On-Time (COT)
control scheme, the XR76203, XR76205 and XR76208 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
0.07% load and 0.15% line regulation and maintains constant operating
frequency. A selectable power saving mode allows the user to operate in
discontinuous conduction mode (DCM) at light current loads thereby
significantly increasing the converter efficiency.
A host of protection features, including over-current, over-temperature,
short-circuit and UVLO, helps achieve safe operation under abnormal
operating conditions.
The XR76203/5/8 are available in a RoHS-compliant, green/halogen-free
space-saving QFN 5x5mm package.
FEATURES
Controller, drivers, bootstrap diode and
MOSFETs integrated in one package
3A, 5A and 8A Step Down Regulators
Wide 5V to 40V Input Voltage Range
≥0.6V Adjustable Output Voltage
Proprietary Constant On-Time Control
No Loop Compensation Required
Stable Ceramic Output Capacitor Operation
Programmable 200ns to 2μs On-Time
Constant 100kHz to 800kHz Frequency
Selectable CCM or CCM/DCM
CCM/DCM for high efficiency at light-load
CCM for constant frequency at light-load
Programmable Hiccup Current Limit with
Thermal Compensation
Precision Enable and Power Good flag
Programmable Soft-start
30-pin 5x5mm QFN package
APPLICATIONS
Distributed Power Architecture
Point-of-Load Converters
Power Supply Modules
FPGA, DSP, and Processor Supplies
Base Stations, Switches/Routers, and Servers
Ordering Information – back page
Typical Application
3.260
3.270
3.280
3.290
3.300
3.310
3.320
3.330
3.340
5 10152025303540
V
OUT
(V)
V
IN
(V)
PGND
FB
ILIM
SW
BST
XR76208
VIN
EN/MODE
PGOOD
VCC
SS
TON
AGND
CSS RON
CVCC
Enable/Mode
Power Good
R
VIN
VOUT
RLIM
CBST
L1
CFF R1
R2
COUT
CIN
XR76205
PVIN
XR76203
Line Regulation
XR76203/5/8
2 / 20 exar.com/XR76203/5/8
Rev 1B
Absolute Maximum Ratings
Stresses beyond the limits listed below 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 43V
VCC...........................................................................-0.3V to 6.0V
BST..........................................................................-0.3V to 48V(1)
BST-SW.......................................................................-0.3V to 6V
SW, ILIM..................................................................-1V to 43V(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
Operating Conditions
PVIN...............................................................................5V to 40V
VIN.................................................................................5V to 40V
SW, ILIM.....................................................................-1V to 40V(1)
PGOOD, VCC, TON, SS, EN, FB...............................-0.3V to 5.5V
Switching Frequency......................................100kHz to 800kHz(3)
Junction Temperature Range..............................-40°C to +125°C
XR76203 JEDEC51 Package Thermal Resistance, JA...............28°C/W
XR76205 JEDEC51 Package Thermal Resistance, JA...............26°C/W
XR76208 JEDEC51 Package Thermal Resistance, JA...............25°C/W
XR76203 Package Power Dissipation at 25°C......................3.6W
XR76205 Package Power Dissipation at 25°C......................3.8W
XR76208 Package Power Dissipation at 25°C......................4.0W
Note 1: No external voltage applied.
Note 2: SW pin’s minimum DC range is -1V, transient is -5V for less than
50ns.
Note 3: Recommended frequency
Electrical Characteristics
Unless otherwise noted: TJ= 25°C, VIN=24V, BST=VCC, SW=AGND=PGND=0V, CVCC=4.7uF. Limits applying over the full
operating temperature range are denoted by a “•”
Symbol Parameter Conditions Min Typ Max Units
Power Supply Characteristics
VIN Input Voltage Range VCC regulating 5.5 40 V
IVIN VIN Input Supply Current Not switching, VIN = 24V, VFB = 0.7V 0.7 2 mA
IVIN VIN Input Supply Current (XR76203) f=300kHz, RON=215k, VFB=0.58V 12 mA
IVIN VIN Input Supply Current (XR76205) f=300kHz, RON=215k, VFB=0.58V 15 mA
IVIN VIN Input Supply Current (XR76208) f=300kHz, RON=215k, VFB=0.58V 19 mA
IOFF Shutdown Current Enable = 0V, VIN = 12V 1 µA
Enable and Under-Voltage Lock-Out UVLO
VIH_EN_1 EN Pin Rising Threshold 1. 8 1. 9 2 . 0 V
VEN_H_1 EN Pin Hysteresis 70 mV
VIH_EN_2 EN Pin Rising Threshold for DCM/
CCM operation
2.8 3.0 3.1 V
VEN_H_2 EN Pin Hysteresis 100 mV
XR76203/5/8
3 / 20 exar.com/XR76203/5/8
Rev 1B
VCC UVLO Start Threshold, Rising
Edge
4.00 4.25 4.40 V
VCC UVLO Hysteresis 230 mV
Reference Voltage
VREF Reference Voltage
VIN = 5.5V to 40V, VCC regulating 0.596 0.600 0.604 V
VIN = 5.5V to 40V, VCC regulating 0.594 0.600 0.606 V
DC Line Regulation CCM, closed loop, VIN=5.5V-40V, applies
to any COUT
±0.33 %
DC Load Regulation CCM, closed loop, applies to any COUT ±0.39 %
Programmable Constant On-Time
TON1 On-Time 1 RON = 237k, VIN = 40V 1570 1840 2120 ns
f Corresponding to On-Time 1 VOUT= 24V, VIN = 40V, RON = 237k 283 326 382 kHz
TON(MIN) Minimum Programmable On-Time RON = 14k, VIN = 40V 120 ns
TON2 On-Time 2 RON = 14k, VIN = 24V 174 205 236 ns
TON3 On-Time 3 RON = 35.7k, VIN = 24V 407 479 550 ns
f Corresponding to On-Time 3 VOUT = 3.3V, VIN = 24V, RON = 35.7k 250 287 338 kHz
f Corresponding to On-Time 3 VOUT = 5.0V, VIN = 24V, RON = 35.7k 379 435 512 kHz
Minimum Off-Time 250 350 ns
Diode Emulation Mode
Zero Crossing Threshold DC value measured during test -2 mV
Soft-start
SS Charge Current -14 -10 -6 µA
SS Discharge Current Fault present 1mA
VCC Linear Regulator
VCC Output Voltage
VIN = 6V to 40V, ILOAD = 0 to 30mA 4.8 5.0 5.2 V
VIN = 5V, ILOAD = 0 to 20mA 4.51 4.7 V
Power Good Output
Power Good Threshold -10 -6.9 -5 %
Power Good Hysteresis 1. 6 4 %
Power Good Sink Current 1 mA
Protection: OCP, OTP, Short-Circuit
Hiccup Timeout 110 m s
ILIM Pin Source Current 45 50 55 µA
ILIM Current Temperature Coefficient 0.4 %/°C
OCP Comparator Offset -8 0 +8 mV
Symbol Parameter Conditions Min Typ Max Units
XR76203/5/8
4 / 20 exar.com/XR76203/5/8
Rev 1B
Note 1: Guaranteed by design
Current Limit Blanking GL rising>1V 100 ns
Thermal Shutdown Threshold1Rising temperature 150 °C
Thermal Hysteresis115 °C
VSCTH Feedback Pin Short-Circuit
Threshold
Percent of VREF
, short circuit is active after
PGOOD is asserted
50 60 70 %
XRP76203 Output Power Stage
RDSON
High-Side MOSFET RDSON
IDS = 1A
115 16 0 m
Low-Side MOSFET RDSON 40 59 m
IOUT Maximum Output Current 3A A
XRP76205 Output Power Stage
RDSON
High-Side MOSFET RDSON
IDS = 2A
42 59 m
Low-Side MOSFET RDSON 40 59 m
IOUT Maximum Output Current 5A A
XRP76208 Output Power Stage
RDSON
High-Side MOSFET RDSON
IDS = 2A
42 59 m
Low-Side MOSFET RDSON 16.2 21.5 m
IOUT Maximum Output Current 8A A
Symbol Parameter Conditions Min Typ Max Units
XR76203/5/8
5 / 20 exar.com/XR76203/5/8
Rev 1B
Pin Configuration, Top View
1
2
3
4
5
6
7
8 9 11 12 13 14
15
16
17
18
19
20
21
22
23242526272830
PVIN PAD
SW PAD
AGND PAD PGND
PAD
PVIN PVIN PVIN PVIN PVIN PVIN
PVIN
PVIN
PGND
PGND
PGND
PGND
PGND
SW
SWSWSWSW
SWBST
ILIM
EN
TON
SS
PGOOD
FB
AGND
VIN VCC AGND
10
29
XR76203/5/8
6 / 20 exar.com/XR76203/5/8
Rev 1B
Pin Assignments
Type: A = Analog, I = Input, O = Output, I/O = Input/Output, PWR = Power, OD = Open-Drain
Pin No. Pin Name Type Description
1 ILIM A Over-current protection programming. Connect with a resistor to SW.
2 EN/MODE I 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 depend-
ing on load
3 TON A Constant on-time programming pin. Connect with a resistor to AGND.
4 SS A Soft-Start pin. Connect an external capacitor between SS and AGND to program the soft-start
rate based on the 10uA internal source current.
5 PGOOD O, OD Power-good output. This open-drain output is pulled low when VOUT is outside the regulation.
6 FB A Feedback input to feedback comparator. Connect with a set of resistors to VOUT and AGND
in order to program VOUT.
7, 1 0 , A G N D
Pad
AGND A Signal ground for control circuitry. Connect AGND Pad with a short trace to pins 7 and 10.
8 VIN A Supply input for the regulator’s LDO. Normally it is connected to PVIN.
9 VCC A The output of regulator’s LDO. For operation using a 5V rail, VCC should be shorted to VIN.
11-14, 20,
29, SW Pad
SW PWR Switch node. Drain of the low-side N-channel MOSFET. Source of the high-side MOSFET is
wire-bonded to the SW Pad. Pins 20 and 29 are internally connected to SW pad.
15-19,
PGND Pad
PGND PWR Ground of the power stage. Should be connected to the system’s power ground plane. Source
of the low-side MOSFET is wire-bonded to PGND Pad.
21-28, PVIN
Pad
PVIN PWR Input voltage for power stage. Drain of the high-side N-channel MOSFET.
30 BST A High-side driver supply pin. Connect a bootstrap capacitor between BST and pin 29.
XR76203/5/8
7 / 20 exar.com/XR76203/5/8
Rev 1B
Functional Block Diagram
Q
Q
R
S
Dead
Time
Control
On-Time
1.9 V
Hiccup
Mode
+-
PGND
FB
VIN
GH
Minimum
On Time
Enable
Hiccup
OCP
comparator
Feedback
comparator
current
emulation &
DC correction
PGOOD
LDO
VCC
VCC
GL
SW
BST
VCC
50uA
+
-
+
-
+
-
3 V
-2 mV
SW
Enable LDO
CCM or CCM/DCM
Zero Cross Detect
If 8 consecutive ZCD
Then DCM
If 1 non-ZCD
Then exit DCM
Q
Q
R
S
AGND ILIM
If four
consecutive OCP
VIN
TON
+
-
+
-
+
-
PGOOD comparator
Short-circuit detection
0.555 V
0.36 V
Switching
Enabled
10uA
+
-
Switching
Enabled
SS
0.6 V
+
-
+
-
Switching
Enabled
Enable LDO VCC UVLO
4.25 V
OTP
150 C
TJ
VCC
TON
Enable LDO
PVIN
EN/MODE
FB 0.6V
XR76203/5/8
8 / 20 exar.com/XR76203/5/8
Rev 1B
Typical Performance Characteristics
Unless otherwise noted: VIN = 24V, VOUT=3.3V, IOUT=8A, f=400kHz, TA = 25°C. Schematic from the application information
section.
Figure 1: Load Regulation Figure 2: Line regulation
Figure 3: TON versus RON Figure 4: TON versus VIN, RON=27.4k
Figure 5: frequency versus IOUT Figure 6: frequency versus VIN
3.260
3.270
3.280
3.290
3.300
3.310
3.320
3.330
3.340
5 10152025303540
VOUT (V)
V
IN
(V)
3.260
3.270
3.280
3.290
3.300
3.310
3.320
3.330
3.340
02468
V
OUT
(V)
I
OUT
(A)
10
100
1,000
1 10 100
TON (ns)
RON (kΩ)
Typical
Calculated
100
300
500
700
900
1,100
1,300
1,500
5 10152025303540
T
ON
(ns)
V
IN
(V)
Calculated
Typical
600
OUT
0
100
200
300
400
500
600
5 10152025303540
f (kHz)
V
IN
(V)
XR76203/5/8
9 / 20 exar.com/XR76203/5/8
Rev 1B
Typical Performance Characteristics
Unless otherwise noted: VIN = 24V, VOUT=3.3V, IOUT=8A, f=400kHz, TA = 25°C. Schematic from the application information
section.
Figure 7: XR76208 IOCP versus RLIM Figure 8: XR76205 IOCP versus RLIM
Figure 9: XR76203 IOCP versus RLIM Figure 10: ILIM versus temperature
Figure 11: VREF versus temperature Figure 12: TON versus temperature, RON=35.7k
2
4
6
8
10
12
14
23456
I
OCP
(A)
R
LIM
(kΩ)
0
2
4
6
8
45678
I
OCP
(A)
R
LIM
(kΩ)
590
595
600
605
610
-40 -20 0 20 40 60 80 100 120
V
REF
(mV)
T
J
(°C)
430
440
450
460
470
480
490
500
510
520
530
-40-200 20406080100120
TON (ns)
T
J
(°C)
30
40
50
60
70
-40 -20 0 20 40 60 80 100 120
ILIM (uA)
T
J
(°C)
0
1
2
3
4
5
2.5 3.0 3.5 4.0 4.5
I
OCP
(A)
R
LIM
(kΩ)
XR76203/5/8
10 / 20 exar.com/XR76203/5/8
Rev 1B
Typical Performance Characteristics
Unless otherwise noted: VIN = 24V, VOUT=3.3V, IOUT=8A, f=400kHz, TA = 25°C. Schematic from the application information
section.
Figure 13: Steady state, IOUT=8A Figure 14: Steady state, DCM, IOUT=0A
Figure 15: Power up, Forced CCM Figure 16: Power up, DCM/CCM
Figure 17: Load step, Forced CCM, 0A-4A-0A Figure 18: Load step, DCM/CCM, 0A-4A-0A
XR76203/5/8
11 / 20 exar.com/XR76203/5/8
Rev 1B
Efficiency
Unless otherwise noted: TAMBIENT = 25°C, No Air flow, f=400kHz, Inductor losses are included, Schematic from the applica-
tion information section.
Figure 19: XR76208 efficiency, VIN=12V Figure 20: XR76208 efficiency, VIN=24V
Figure 21: XR76205 efficiency, VIN=12V Figure 22: XR76205 efficiency, VIN=24V
Figure 23: XR76203 efficiency, VIN=12V Figure 24: XR76203 efficiency, VIN=24V
70
72
74
76
78
80
82
84
86
88
90
92
94
96
98
100
0.1 1.0 10.0
Efficiency %
I
OUT
(A)
5.0V DCM 5.0V CCM
3.3V DCM 3.3V CCM
1.8V DCM 1.8V CCM
3.3uH
4.7uH
6.8uH
70
72
74
76
78
80
82
84
86
88
90
92
94
96
98
100
0.1 1.0 10.0
Efficiency %
I
OUT
(A)
12V DCM 12V CCM
5.0V DCM 5.0V CCM
3.3V DCM 3.3V CCM
1.8V DCM 1.8V CCM
3.3uH
4.7uH
6.8uH
10uH
200kHz
70
72
74
76
78
80
82
84
86
88
90
92
94
96
98
100
0.1 1.0 10.0
Efficiency %
I
OUT
(A)
12V DCM 12V CCM
5.0V DCM 5.0V CCM
3.3V DCM 3.3V CCM
1.8V DCM 1.8V CCM
6.8uH
4.7uH
3.3uH
2.2uH
200kHz
70
72
74
76
78
80
82
84
86
88
90
92
94
96
98
100
0.1 1.0 10.0
Efficiency %
I
OUT
(A)
5.0V DCM 5.0V CCM
3.3V DCM 3.3V CCM
1.8V DCM 1.8V CCM
2.2uH
3.3uH
4.7uH
70
72
74
76
78
80
82
84
86
88
90
92
94
96
98
100
0.1 1.0 10.0
Efficiency %
I
OUT
(A)
5.0V DCM 5.0V CCM
3.3V DCM 3.3V CCM
1.8V DCM 1.8V CCM
3.3uH
2.2uH
1.5uH
70
72
74
76
78
80
82
84
86
88
90
92
94
96
98
100
0.1 1.0 10.0
Efficiency %
I
OUT
(A)
12V DCM 12V CCM
5.0V DCM 5.0V CCM
3.3V DCM 3.3V CCM
1.8V DCM 1.8V CCM
200kHz, 8.2uH
3.3uH
2.2uH
1.5uH
XR76203/5/8
12 / 20 exar.com/XR76203/5/8
Rev 1B
Thermal Derating
Unless otherwise noted: No Air flow, f=400kHz, Schematic from the application information section.
Figure 25: XR76208, VIN=12V Figure 26: XR76208, VIN=24V
Figure 27: XR76205, VIN=12V Figure 28: XR76205, VIN=24V
Figure 29: XR76203, VIN=12V Figure 30: XR76203, VIN=24V
50
60
70
80
90
100
110
120
130
12345678
T
AMBIENT
(°C)
I
OUT
(A)
1.8 VOUT
3.3 VOUT
5.0 VOUT
50
60
70
80
90
100
110
120
130
12345678
T
AMBIENT
(°C)
I
OUT
(A)
1.8 VOUT
3.3 VOUT
5.0 VOUT
12 VOUT
200kHz
50
60
70
80
90
100
110
120
130
12345
T
AMBIENT
(°C)
I
OUT
(A)
1.8 VOUT
3.3 VOUT
5.0 VOUT
50
60
70
80
90
100
110
120
130
12345
T
AMBIENT
(°C)
I
OUT
(A)
1.8 VOUT
3.3 VOUT
5.0 VOUT
12 VOUT
200kHz
50
60
70
80
90
100
110
120
130
1.0 1.5 2.0 2.5 3.0
T
AMBIENT
(°C)
I
OUT
(A)
1.8 VOUT
3.3 VOUT
5.0 VOUT
50
60
70
80
90
100
110
120
130
1.0 1.5 2.0 2.5 3.0
T
AMBIENT
(°C)
I
OUT
(A)
1.8 VOUT
3.3 VOUT
5.0 VOUT
12 VOUT
200kHz
XR76203/5/8
13 / 20 exar.com/XR76203/5/8
Rev 1B
Functional Description
XR76203, XR76205 and XR76208 are synchronous step-
down proprietary emulated current-mode Constant On-
Time (COT) regulators. The on-time, which is programmed
via RON, is inversely proportional to VIN and maintains a
nearly constant frequency. The emulated current-mode
control is stable with ceramic output capacitors.
Each switching cycle begins with GH signal turning on the
high-side (control) FET 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
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 makes possible the use of ceramic
capacitors, in addition to other capacitor types, for output
filtering.
Enable/Mode Input (EN/MODE)
EN/MODE pin accepts a tri-level signal that is used to
control turn on/off. It also selects between two modes of
operation: ‘Forced CCM’ and ‘DCM/CCM’. If EN is pulled
below 1.8V, the Regulator shuts down. A voltage between
2.0V and 2.8V selects the Forced CCM mode which will run
the Regulator in continuous conduction at all times. A
voltage higher than 3.1V selects the DCM/CCM mode
which will run the Regulator in discontinuous conduction at
light loads.
Selecting the Forced CCM Mode
In order to set the Regulator to operate in Forced CCM, a
voltage between 2.0V and 2.8V must be applied to EN/
MODE. 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 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 31 can be used to
generate the required voltage. Note that at VIN of 5.5V and
40V the nominal Zener voltage is 4.0V and 5.0V
respectively. Therefore for VIN in the range of 5.5V to 40V,
the circuit shown in Figure 31 will generate VEN required for
Forced CCM.
Selecting the DCM/CCM Mode
In order to set the Regulator operation to DCM/CCM, a
voltage between 3.1V and 5.5V must be applied to
EN/MODE pin. If an external control signal is available, it
can be directly connected to EN/MODE. In applications
where an external control is not available, EN/MODE input
can be derived from VIN. If VIN is well regulated, use a
resistor divider and set the voltage to 4V. If VIN varies over a
wide range, the circuit shown in Figure 32 can be used to
generate the required voltage.
Figure 31: Selecting Forced CCM
by deriving EN/MODE from VIN
Figure 32: Selecting DCM/CCM
by deriving EN/MODE from VIN
R1
30.1k, 1%
RZ
10k
EN/MODE
R2
35.7k, 1%
Zener
MMSZ4685T1G or Equivalent
IN
V
Zener
MM SZ4685T1G or Equivalent
RZ
10k
EN/MODE
VIN
VEN
XR76203/5/8
14 / 20 exar.com/XR76203/5/8
Rev 1B
Programming the On-Time
The On-Time TON is programmed via resistor RON
according to following equation:
where TON is calculated from:
where:
f is the desired switching frequency at nominal IOUT
Eff is the Regulator efficiency corresponding to nominal
IOUT shown in Figures 19-24
Substituting for TON in the first equation we get:
Over-Current Protection (OCP)
If load current exceeds the programmed over-current, IOCP
,
for four consecutive switching cycles, the Module enters
hiccup mode of operation. In hiccup, 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 Module will remain in hiccup
mode until load current is reduced below the programmed
IOCP . In order to program the over-current protection, use
the following equation:
Where:
RLIM is resistor value for programming IOCP
IOCP is the over-current threshold to be programmed
RDS is the MOSFET rated On Resistance;
XR76208=21.5m, XR76205=59m, XR76203=59m
8mV is the OCP comparator maximum offset
ILIM is the internal current that generates the necessary
OCP comparator threshold (use 45A).
Note that ILIM has a positive temperature coefficient of
0.4%/°C (Figure 10). This is meant to roughly match and
compensate for positive temperature coefficient of the
synchronous FET. Graph of typical IOCP versus RLIM is
shown in Figure 7-9. Maximum allowable RLIM for
XR76205 is 8.06k.
Short-Circuit Protection (SCP)
If the output voltage drops below 60% of its programmed
value, the Module will enter hiccup mode. Hiccup will
persist until short-circuit is removed. SCP circuit becomes
active after PGOOD asserts high.
Over-Temperature (OTP)
OTP triggers at a nominal die temperature of 150°C. The
gate of switching FET and synchronous FET are turned off.
When die temperature cools down to 135°C, soft-start is
initiated and operation resumes.
Programming the Output Voltage
Use an external voltage divider as shown in the Application
Circuit to program the output voltage VOUT
.
where R2 has a nominal value of 2kΩ.
Programming the Soft-start
Place a capacitor CSS between the SS and AGND 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:
RON
VIN TON 25 9–
10–
3.05 10–
10
------------------------------------------------------------
=
TON
VOUT
VIN
fEff
-------------------------------
=
RON
VOUT
fEff
----------------


25 9–
10VIN
–
3.05 10–
10
-------------------------------------------------------------------------
=
RLIM IOCP RDS8mV+
ILIM
------------------------------------------------------
=
R1 R2 VOUT
0.6
------------- 1–


=
CSS TSS 10A
0.6V
--------------


=
XR76203/5/8
15 / 20 exar.com/XR76203/5/8
Rev 1B
Feed-Forward Capacitor (CFF)
A feed-forward capacitor (CFF) may be necessary
depending on the Equivalent Series Resistance (ESR) of
COUT
. If only ceramic output capacitors are used for COUT
then a CFF is necessary. Calculate CFF from:
where:
R1 is the resistor that CFF is placed in parallel with
fLC is the frequency of output filter double-pole
fLC frequency must be less than 11kHz when using ceramic
COUT
. If necessary, increase L and/or COUT in order to meet
this constraint.
When using capacitors with higher ESR, such as PANA-
SONIC TPE series, a CFF is not required provided following
conditions are met:
1. The frequency of output filter LC double-pole fLC should
be less than 11kHz.
2. The frequency of ESR Zero fZero,ESR should be at least
five times larger than fLC.
Note that if fZero,ESR is less than 5xfLC, then it is recom-
mended to set the fLC at less than 2kHz. CFF is still not
required.
Maximum Allowable Voltage Ripple at FB pin
Note that the steady-state voltage ripple at 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 should be increased as necessary in
order to keep the VFB,RIPPLE below 50mV.
Feed-Forward Resistor (RFF)
Poor PCB layout can cause FET switching noise at the
output and may couple to the FB pin via CFF. Excessive
noise at FB will cause poor load regulation. To solve this
problem place a resistor RFF in series with CFF
. RFF value
up to 2% of R1 is acceptable.
CFF
1
2
R
17
f
LC
-------------------------------------------------
=
XR76203/5/8
16 / 20 exar.com/XR76203/5/8
Rev 1B
Application Circuit, XR76208
RSNB 1 OhmCSNB 0.56nF
R4 2k
U1
XR76208
ILIM
1
TON
3
EN
2
SS
4
VCC
9
AGND
10
SW
11
SW
12
PGOOD
5
FB
6
AGND
7
VIN
8
SW
13
SW
14
PGND 15
BST 30
PGND 17
PGND 18
PGND 19
SW 20
PVIN 21
PVIN 22
PVIN 23
PVIN 24
PVIN 25
PVIN 26
PVIN 27
PVIN 28
SW 29
PGND 16
AGND PAD 31
PGND PAD 32
SW PAD 33
PVIN PAD 34
400kHz, 3.3V @ 0-8A
24VIN
CIN
2x 10uF/50V
CVCC 4.7uF
IHLP-5050FD-01
2.2uH
R1
9.09k
R2
2k
CSS 47nF
CIN 0.1uF
R5 10k
CFF
0.27nF
PVIN
COUT
3x 47uF/10V
VCC
RON 28k
FB
R3 18.2k
CBST 1uF
RLIM 5.49k
SW
FB
OPTION AL
XR76203/5/8
17 / 20 exar.com/XR76203/5/8
Rev 1B
Application Circuit, XR76205
RSNB 1 OhmCSNB 0.33nF
R4 2k
U1
XR76205
ILIM
1
TON
3
EN
2
SS
4
VCC
9
AGND
10
SW
11
SW
12
PGOOD
5
FB
6
AGND
7
VIN
8
SW
13
SW
14
PGND 15
BST 30
PGND 17
PGND 18
PGND 19
SW 20
PVIN 21
PVIN 22
PVIN 23
PVIN 24
PVIN 25
PVIN 26
PVIN 27
PVIN 28
SW 29
PGND 16
AGND PAD 31
PGND PAD 32
SW PAD 33
PVIN PAD 34
24VIN
400kHz, 3.3V @ 0-5A
CIN
1x 10uF/50V
CVCC 4.7uF
Wurth-74437368033
3.3uH
R1
9.09k
R2
2k
CSS 47nF
CIN1 0.1uF
R5 10k
CFF
0.27nF
PVIN
COUT
2x 47uF/10V
VCC
RON 29.4k
FB
R3 18.2k
CBST 1uF
RLIM 8.06k
SW
FB
OPTION AL
XR76203/5/8
18 / 20 exar.com/XR76203/5/8
Rev 1B
Application Circuit, XR76203
SW
R4 2k
U1
XR76203
ILIM
1
TON
3
EN
2
SS
4
VCC
9
AGND
10
SW
11
SW
12
PGOOD
5
FB
6
AGND
7
VIN
8
SW
13
SW
14
PGND 15
BST 30
PGND 17
PGND 18
PGND 19
SW 20
PVIN 21
PVIN 22
PVIN 23
PVIN 24
PVIN 25
PVIN 26
PVIN 27
PVIN 28
SW 29
PGND 16
AGND PAD 31
PGND PAD 32
SW PAD 33
PVIN PAD 34
400kHz, 3.3V @ 0-3A
24VIN
CIN
10uF/50V
CVCC 4.7uF
Wurth-74437368047
4.7uH
R1
9.09k
R2
2k
CSS 47nF
CIN1 0.1uF
R5 10k
CFF
0.22nF
PVIN
COUT
47uF/10V
VCC
RON 28k
FB
R3 18.2k
CBST 1uF
SW RLIM 4.02k
FB
XR76203/5/8
19 / 20 exar.com/XR76203/5/8
Rev 1B
Mechanical Dimensions
XR76203/5/8
20 / 20 exar.com/XR76203/5/8
Rev 1B
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copying, recording, or otherwise), or for any purpose, without the express written permission of MaxLinear, Inc.
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Company and product names may be registered trademarks or trademarks of the respective owners with which they are associated.
© 2015 - 2018 MaxLinear, Inc. All rights reserved
Corporate Headquarters:
5966 La Place Court
Suite 100
Carlsbad, CA 92008
Tel.:+1 (760) 692-0711
Fax: +1 (760) 444-8598
www.maxlinear.com
High Performance Analog:
1060 Rincon Circle
San Jose, CA 95131
Tel.: +1 (669) 265-6100
Fax: +1 (669) 265-6101
Email: powertechsupport@exar.com
www.exar.com
Ordering Information(1)
NOTES:
1. R e f e r t o www.exar.com/XR76203, www.exar.com/XR76205, www.exar.com/XR76208 for most up-to-date Ordering Information.
2. Visit www.exar.com for additional information on Environmental Rating.
Revision History
Part Number Operating Temperature Range Lead-Free Package Packaging Method
XR76208EL-F
-40°C to +125°C Ye s (2) 5x5mm QFN
Tray
XR76208ELTR-F Tape and Reel
XR76208ELMTR-F Mini Tape and Reel
XR76208EVB XR76208 Evaluation Board
XR76205EL-F
-40°C to +125°C Ye s (2) 5x5mm QFN
Tray
XR76205ELTR-F Tape and Reel
XR76205ELMTR-F Mini Tape and Reel
XR76205EVB XR76205 Evaluation Board
XR76203EL-F
-40°C to +125°C Ye s (2) 5x5mm QFN
Tray
XR76203ELTR-F Tape and Reel
XR76203ELMTR-F Mini Tape and Reel
XR76203EVB XR76203 Evaluation Board
Revision Date Description
1A February 2015 Initial release
1B June 2018 Update to MaxLinear logo. Update format and Ordering Information table.