XR76203EL-F [EXAR]
3A/5A/8A Synchronous Step Down COT Regulator;
| 型号： | XR76203EL-F |
| 厂家： | 
EXAR CORPORATION |
| 描述： | 3A/5A/8A Synchronous Step Down COT Regulator 开关 |
| 文件： | 总20页 (文件大小：1126K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
XR76203/5/8
TM
40V PowerBlox
3A/5A/8A Synchronous Step Down COT Regulator
FEATURES
General Description
Controller, drivers, bootstrap diode and
MOSFETs integrated in one package
The XR76203, XR76205 and XR76208 are synchronous step-down regu-
lators 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.
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
With a proprietary emulated current mode Constant On-Time (COT) con-
trol 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 sig-
nificantly increasing the converter efficiency.
Programmable Hiccup Current Limit with
Thermal Compensation
Precision Enable and Power Good flag
Programmable Soft-start
30-pin 5x5mm QFN package
A host of protection features, including over-current, over-temperature,
short-circuit and UVLO, helps achieve safe operation under abnormal
operating conditions.
APPLICATIONS
Distributed Power Architecture
Point-of-Load Converters
Power Supply Modules
The XR76203/5/8 are available in a RoHS-compliant, green/halogen-free
space-saving QFN 5x5mm package.
FPGA, DSP, and Processor Supplies
Base Stations, Switches/Routers, and Servers
Ordering Information – back page
Typical Application
Line Regulation
3.340
3.330
3.320
VIN
VIN
PVIN
BST
SW
CBST
Enable/Mode
EN/MODE
PGOOD
VOUT
L1
Power Good
R
3.310
3.300
3.290
3.280
3.270
3.260
CIN
XR76208
VCC
SS
XR76205
XR76203
RLIM
CFF
R1
R2
ILIM
FB
COUT
TON
AGND
CVCC
CSS
RON
PGND
5
10 15 20 25 30 35 40
VIN (V)
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Absolute Maximum Ratings
Operating Conditions
PVIN...............................................................................5V to 40V
Stresses beyond the limits listed below may cause perma-
nent damage to the device. Exposure to any Absolute Max-
imum Rating condition for extended periods may affect
device reliability and lifetime.
VIN.................................................................................5V to 40V
SW, ILIM.....................................................................-1V to 40V1
PGOOD, VCC, TON, SS, EN, FB...............................-0.3V to 5.5V
PVIN, VIN...................................................................-0.3V to 43V
V
CC...........................................................................-0.3V to 6.0V
Switching Frequency......................................100kHz to 800kHz3
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
BST..........................................................................-0.3V to 48V1
BST-SW.......................................................................-0.3V to 6V
SW, ILIM..................................................................-1V to 43V1, 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
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: T = 25°C, V =24V, BST=V , SW=AGND=PGND=0V, C =4.7uF. Limits applying over the full
VCC
J
IN
CC
operating temperature range are denoted by a “•”
Symbol
Parameter
Conditions
Min
Typ
Max
Units
Power Supply Characteristics
VIN
VCC regulating
5.5
40
2
Input Voltage Range
V
IVIN
IVIN
IVIN
IVIN
IOFF
VIN Input Supply Current
Not switching, VIN = 24V, VFB = 0.7V
f=300kHz, RON=215k, VFB=0.58V
f=300kHz, RON=215k, VFB=0.58V
f=300kHz, RON=215k, VFB=0.58V
Enable = 0V, VIN = 12V
0.7
12
15
19
1
mA
mA
mA
mA
μA
VIN Input Supply Current (XR76203)
VIN Input Supply Current (XR76205)
VIN Input Supply Current (XR76208)
Shutdown Current
Enable and Under-Voltage Lock-Out UVLO
VIH_EN_1
VEN_H_1
VIH_EN_2
EN Pin Rising Threshold
EN Pin Hysteresis
1. 8
1. 9
70
2.0
3.1
V
mV
V
EN Pin Rising Threshold for DCM/
CCM operation
2.8
3.0
VEN_H_2
EN Pin Hysteresis
100
mV
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Symbol
Parameter
Conditions
Min
Typ
Max
Units
VCC UVLO Start Threshold, Rising
Edge
4.00
4.25
4.40
V
VCC UVLO Hysteresis
230
mV
Reference Voltage
V
IN = 5.5V to 40V, VCC regulating
0.596
0.594
0.600
0.604
0.606
V
VREF
Reference Voltage
DC Line Regulation
VIN = 5.5V to 40V, VCC regulating
0.600
0.33
V
CCM, closed loop, VIN=5.5V-40V, applies
to any COUT
%
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
283
1840
326
120
205
479
287
435
250
2120
382
ns
kHz
ns
f Corresponding to On-Time 1
Minimum Programmable On-Time
On-Time 2
VOUT= 24V, VIN = 40V, RON = 237k
RON = 14k, VIN = 40V
TON(MIN)
TON2
RON = 14k, VIN = 24V
174
407
250
379
236
550
338
512
350
ns
TON3
On-Time 3
RON = 35.7k, VIN = 24V
ns
f Corresponding to On-Time 3
f Corresponding to On-Time 3
Minimum Off-Time
VOUT = 3.3V, VIN = 24V, RON = 35.7k
kHz
kHz
ns
VOUT = 5.0V, VIN = 24V, RON = 35.7k
Diode Emulation Mode
Zero Crossing Threshold
DC value measured during test
-2
mV
Soft-start
SS Charge Current
-14
1
-10
-6
μA
SS Discharge Current
Fault present
mA
VCC Linear Regulator
V
V
IN = 6V to 40V, ILOAD = 0 to 30mA
IN = 5V, ILOAD = 0 to 20mA
4.8
5.0
4.7
5.2
V
V
VCC Output Voltage
4.51
Power Good Output
Power Good Threshold
-10
1
-6.9
1.6
-5
4
%
%
Power Good Hysteresis
Power Good Sink Current
Protection: OCP, OTP, Short-Circuit
Hiccup Timeout
mA
110
50
0.4
0
ms
μA
ILIM Pin Source Current
45
-8
55
+8
ILIM Current Temperature Coefficient
OCP Comparator Offset
%/°C
mV
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Symbol
Parameter
Current Limit Blanking
Thermal Shutdown Threshold1
Thermal Hysteresis1
Conditions
Min
Typ
Max
Units
GL rising>1V
100
150
ns
°C
Rising temperature
15
60
°C
%
VSCTH Feedback Pin Short-Circuit
Threshold
Percent of VREF, short circuit is active after
PGOOD is asserted
50
70
XRP76203 Output Power Stage
High-Side MOSFET RDSON
115
40
160
59
mΩ
mΩ
A
RDSON
IDS = 1A
IDS = 2A
IDS = 2A
Low-Side MOSFET RDSON
Maximum Output Current
IOUT
3A
5A
8A
XRP76205 Output Power Stage
High-Side MOSFET RDSON
42
40
59
59
mΩ
mΩ
A
RDSON
Low-Side MOSFET RDSON
Maximum Output Current
IOUT
XRP76208 Output Power Stage
High-Side MOSFET RDSON
42
59
mΩ
mΩ
A
RDSON
Low-Side MOSFET RDSON
Maximum Output Current
16.2
21.5
IOUT
Note 1: Guaranteed by design
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Pin Configuration, Top View
BST
30
SW PVIN PVIN PVIN PVIN PVIN PVIN
29
28
27
26
25
24
23
ILIM
EN
1
2
3
4
5
6
7
22 PVIN
PVIN PAD
21 PVIN
20 SW
TON
SS
19 PGND
18 PGND
PGOOD
FB
SW PAD
AGND PAD
PGND
PAD
17
PGND
AGND
16 PGND
15 PGND
8
9
10
11
12
13
14
VIN
VCC AGND SW
SW
SW
SW
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Pin Assignments
Pin No.
Pin Name
Type
Description
1
2
ILIM
A
I
Over-current protection programming. Connect with a resistor to SW.
EN/MODE
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
4
TON
SS
A
A
Constant on-time programming pin. Connect with a resistor to AGND.
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
6
PGOOD
FB
O, OD
A
Power-good output. This open-drain output is pulled low when VOUT is outside the regulation.
Feedback input to feedback comparator. Connect with a set of resistors to VOUT and AGND
in order to program VOUT
.
7, 10 , AG N D
Pad
AGND
A
Signal ground for control circuitry. Connect AGND Pad with a short trace to pins 7 and 10.
8
9
VIN
VCC
SW
A
A
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.
11-14, 20,
29, SW Pad
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
PVIN
BST
PWR
PWR
A
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
Input voltage for power stage. Drain of the high-side N-channel MOSFET.
30
High-side driver supply pin. Connect a bootstrap capacitor between BST and pin 29.
Type: A = Analog, I = Input, O = Output, I/O = Input/Output, PWR = Power, OD = Open-Drain
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Functional Block Diagram
VCC
TON
BST
PVIN
VCC UVLO
Enable LDO
Switching
Enabled
+
-
4.25 V
LDO
VIN
VCC
VCC
OTP
FB
0.6V
+
-
TJ
150 C
PGOOD
SS
current
emulation &
DC correction
VIN
10uA
0.6 V
On-Time
+
-
Switching
Enabled
Feedback
comparator
TON
GH
R
Q
Q
+
-
S
FB
SW
PGOOD comparator
Dead
Time
Control
VCC
+
-
Minimum
On Time
0.555 V
Switching
Enabled
Short-circuit detection
GL
+
R
S
Q
Q
0.36 V
Enable
Hiccup
-
Hiccup
Mode
Enable LDO
Enable LDO
+
-
EN/MODE
1.9 V
If four
consecutive OCP
CCM or CCM/DCM
If 8 consecutive ZCD
Then DCM
OCP
comparator
+
-
50uA
3 V
-
+
If 1 non-ZCD
Then exit DCM
Zero Cross Detect
+
-
SW
-2 mV
AGND
ILIM
PGND
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Typical Performance Characteristics
Unless otherwise noted: V = 24V, V
=3.3V, I
=8A, f=400kHz, T = 25°C. Schematic from the application information
IN
OUT
OUT
A
section.
3.340
3.330
3.320
3.310
3.300
3.290
3.280
3.270
3.260
3.340
3.330
3.320
3.310
3.300
3.290
3.280
3.270
3.260
5
10 15 20 25 30 35 40
0
2
4
6
8
VIN (V)
Figure 2: Line regulation
IOUT (A)
Figure 1: Load Regulation
1,000
1,500
1,300
1,100
900
Calculated
Typical
Typical
Calculated
100
700
500
300
100
10
1
10
100
5
10 15 20 25 30 35 40
VIN (V)
RON (kΩ)
Figure 3: TON versus RON
Figure 4: TON versus VIN, RON=27.4k
600
600
500
400
300
200
100
0
500
400
300
200
100
0
5
10 15 20 25 30 35 40
0
2
4
6
8
IOUT (A)
VIN (V)
Figure 5: frequency versus IOUT
Figure 6: frequency versus VIN
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Typical Performance Characteristics
Unless otherwise noted: V = 24V, V
=3.3V, I
=8A, f=400kHz, T = 25°C. Schematic from the application information
IN
OUT
OUT
A
section.
8
6
4
2
0
14
12
10
8
6
4
2
4
5
6
7
8
2
3
4
5
6
RLIM (kΩ)
RLIM (kΩ)
Figure 7: XR76208 IOCP versus RLIM
Figure 8: XR76205 IOCP versus RLIM
5
70
4
3
2
1
0
60
50
40
30
-40 -20
0
20 40 60 80 100 120
2.5
3.0
3.5
4.0
4.5
RLIM (kΩ)
T (°C)
J
Figure 9: XR76203 IOCP versus RLIM
Figure 10: ILIM versus temperature
530
520
510
500
490
480
470
460
450
440
430
610
605
600
595
590
-40 -20
0
20 40 60 80 100 120
-40 -20
0
20 40 60 80 100 120
T (°C)
T (°C)
J
J
Figure 11: VREF versus temperature
Figure 12: TON versus temperature, RON=35.7kꢀ
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Typical Performance Characteristics
Unless otherwise noted: V = 24V, V
=3.3V, I
=8A, f=400kHz, T = 25°C. Schematic from the application information
IN
OUT
OUT
A
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
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Efficiency
Unless otherwise noted: T
tion information section.
= 25°C, No Air flow, f=400kHz, Inductor losses are included, Schematic from the applica-
AMBIENT
100
100
98
96
94
92
90
88
86
84
82
80
78
76
74
72
98
96
94
92
90
88
86
84
82
80
78
76
74
72
70
200kHz, 8.2uH
3.3uH
3.3uH
2.2uH
1.5uH
2.2uH
1.5uH
12V DCM
12V CCM
5.0V CCM
3.3V CCM
1.8V CCM
5.0V DCM
3.3V DCM
1.8V DCM
5.0V DCM
5.0V CCM
3.3V CCM
1.8V CCM
3.3V DCM
1.8V DCM
70
0.1
1.0
10.0
0.1
1.0
10.0
IOUT (A)
IOUT (A)
Figure 19: XR76208 efficiency, VIN=12V
Figure 20: XR76208 efficiency, VIN=24V
100
98
100
98
200kHz
6.8uH
4.7uH
96
96
94
92
90
88
86
84
82
80
78
76
74
72
70
4.7uH
3.3uH
94
92
90
88
3.3uH
2.2uH
86
2.2uH
84
82
80
78
76
12V DCM
5.0V DCM
3.3V DCM
1.8V DCM
12V CCM
5.0V DCM
3.3V DCM
1.8V DCM
5.0V CCM
3.3V CCM
1.8V CCM
5.0V CCM
3.3V CCM
1.8V CCM
74
72
70
0.1
1.0
10.0
0.1
1.0
10.0
IOUT (A)
IOUT (A)
Figure 21: XR76205 efficiency, VIN=12V
Figure 22: XR76205 efficiency, VIN=24V
100
98
100
98
200kHz
96
94
96
10uH
94
92
90
88
86
84
82
80
78
76
74
72
70
6.8uH
4.7uH
92
6.8uH
90
4.7uH
88
86
3.3uH
84
3.3uH
82
80
78
76
12V DCM
5.0V DCM
3.3V DCM
1.8V DCM
12V CCM
5.0V CCM
3.3V CCM
1.8V CCM
5.0V DCM
3.3V DCM
1.8V DCM
5.0V CCM
3.3V CCM
1.8V CCM
74
72
70
0.1
1.0
10.0
0.1
1.0
10.0
IOUT (A)
IOUT (A)
Figure 23: XR76203 efficiency, VIN=12V
Figure 24: XR76203 efficiency, VIN=24V
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Thermal Derating
Unless otherwise noted: No Air flow, f=400kHz, Schematic from the application information section.
130
120
110
100
90
130
120
110
100
90
200kHz
1.8 VOUT
3.3 VOUT
5.0 VOUT
1.8 VOUT
3.3 VOUT
5.0 VOUT
12 VOUT
80
80
70
70
60
60
50
50
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
IOUT (A)
Figure 26: XR76208, VIN=24V
IOUT (A)
Figure 25: XR76208, VIN=12V
130
130
120
110
100
90
120
110
100
90
200kHz
80
1.8 VOUT
3.3 VOUT
5.0 VOUT
80
1.8 VOUT
3.3 VOUT
5.0 VOUT
12 VOUT
70
70
60
60
50
50
1
2
3
4
5
1
2
3
4
5
IOUT (A)
Figure 27: XR76205, VIN=12V
IOUT (A)
Figure 28: XR76205, VIN=24V
130
130
120
110
100
90
120
110
100
90
200kHz
1.8 VOUT
3.3 VOUT
5.0 VOUT
12 VOUT
80
80
1.8 VOUT
3.3 VOUT
5.0 VOUT
70
70
60
60
50
50
1.0
1.5
2.0
2.5
3.0
1.0
1.5
2.0
2.5
3.0
IOUT (A)
IOUT (A)
Figure 29: XR76203, VIN=12V
Figure 30: XR76203, VIN=24V
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derived from V . If V is well regulated, use a resistor
Functional Description
IN
IN
divider and set the voltage to 4V. If V varies over a wide
IN
XR76203, XR76205 and XR76208 are synchronous step-
down proprietary emulated current-mode Constant On-
Time (COT) regulators. The on-time, which is programmed
via R , is inversely proportional to V and maintains a
range, the circuit shown in figure 32 can be used to gener-
ate the required voltage.
ON
IN
V IN
nearly constant frequency. The emulated current-mode
control is stable with ceramic output capacitors.
RZ
10k
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 mini-
mum time (250ns nominal). This parameter is termed Mini-
mum Off-Time. After the minimum off-time, the voltage at
the feedback pin FB is compared to an internal voltage
R1
Zener
30.1k, 1%
EN/MODE
MMSZ4685T1G or Equivalent
R2
35.7k, 1%
ramp at the feedback comparator. When V drops below
FB
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 fil-
tering.
Figure 31: Selecting Forced CCM by deriving EN/MODE from
VIN
Enable/Mode Input (EN/MODE)
EN/MODE pin accepts a tri-level signal that is used to con-
trol turn on/off. It also selects between two modes of opera-
tion: ‘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
V IN
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 exter-
nal control is not available, the EN/MODE can be derived
RZ
10k
V EN
EN/MODE
from V . If V is well regulated, use a resistor divider and
IN
IN
set the voltage to 2.5V. If V varies over a wide range, the
circuit shown in figure 31 can be used to generate the
Zener
IN
MMSZ4685T1G or Equivalent
required voltage. Note that at V of 5.5V and 40V the nom-
IN
inal Zever voltage is 4.0V and 5.0V respectively. Therefore
for V in the range of 5.5V to 40V, the circuit shown in fig-
IN
ure 31 will generate V required for Forced CCM.
EN
Selecting the DCM/CCM Mode
In order to set the Regulator operation to DCM/CCM, a volt-
age 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
Figure 32: Selecting DCM/CCM by deriving EN/MODE from
VIN
13 / 20
exar.com/XR76203/5/8
Rev 1A
© 2015 Exar Corporation
XR76203/5/8
Programming the On-Time
The On-Time T is programmed via resistor R
I
is the over-current threshold to be programmed
OCP
accord-
RDS is
the
MOSFET rated On
Resistance;
ON
ON
ing to following equation:
XR76208=21.5mΩ, XR76205=59mΩ, XR76203=59mΩ
8mV is the OCP comparator maximum offset
TON–2510–9
ILIM is the internal current that generates the necessary
OCP comparator threshold (use 45ꢀA).
VIN
-----------------------------------------------------------
=
RON
3.0510–10
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 syn-
where T is calculated from:
ON
chronous FET. Graph of typical I
versus RLIM is shown
OCP
in figure 7-9. Maximum allowable RLIM for XR76205 is
8.06kΩ.
VOUT
------------------------------
=
TON
VIN f Eff
Short-Circuit Protection (SCP)
If the output voltage drops below 60% of its programmed
value, the Module will enter hiccup mode. Hiccup will per-
sist until short-circuit is removed. SCP circuit becomes
active after PGOOD asserts high.
where:
f is the desired switching frequency at nominal I
OUT
Eff is the Regulator efficiency corresponding to nominal
shown in figures 19-24
Over-Temperature (OTP)
I
OUT
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 ini-
tiated and operation resumes.
Substituting for T in the first equation we get:
ON
VOUT
–9
---------------
– 2510 VIN
f Eff
Programming the Output Voltage
------------------------------------------------------------------------
RON
=
3.0510–10
Use an external voltage divider as shown in the Application
Circuit to program the output voltage V
.
OUT
VOUT
0.6
R1 = R2 ------------- – 1
Over-Current Protection (OCP)
If load current exceeds the programmed over-current, I
,
OCP
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 hic-
cup timeout, a soft-start is attempted. If OCP persists, hic-
cup timeout will repeat. The Module will remain in hiccup
mode until load current is reduced below the programmed
where R2 has a nominal value of 2kꢁ.
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:
I
. In order to program the over-current protection, use
OCP
the following equation:
I
OCP RDS + 8mV
-----------------------------------------------------
RLIM =
ILIM
10A
0.6V
--------------
CSS = TSS
Where:
RLIM is resistor value for programming I
OCP
14 / 20
exar.com/XR76203/5/8
Rev 1A
© 2015 Exar Corporation
XR76203/5/8
Feed-Forward Capacitor (C
)
FF
A feed-forward capacitor (C ) may be necessary depend-
FF
ing on the Equivalent Series Resistance (ESR) of C
. If
OUT
only ceramic output capacitors are used for C
then a
OUT
C
is necessary. Calculate C from:
FF
FF
1
-------------------------------------------------
CFF
=
2 R1 7 fLC
where:
R1 is the resistor that C is placed in parallel with
FF
f
is the frequency of output filter double-pole
LC
f
C
frequency must be less than 11kHz when using ceramic
. If necessary, increase L and/or C in order to meet
LC
OUT
OUT
this constraint.
When using capacitors with higher ESR, such as PANA-
SONIC TPE series, a C is not required provided following
FF
conditions are met:
1. The frequency of output filter LC double-pole f should
LC
be less than 11kHz.
2. The frequency of ESR Zero f
should be at least
Zero,ESR
five times larger than f
.
LC
Note that if f
is less than 5xf , then it is recom-
LC
Zero,ESR
mended to set the f at less than 2kHz. CFF is still not
LC
required.
Maximum Allowable Voltage Ripple at FB pin
Note that the steady-state voltage ripple at feedback pin FB
(V
) must not exceed 50mV in order for the Regula-
FB,RIPPLE
tor to function correctly. If V
is larger than 50mV
FB,RIPPLE
then C
should be increased as necessary in order to
OUT
keep the V
below 50mV.
FB,RIPPLE
Feed-Forward Resistor (R
)
FF
Poor PCB layout can cause FET switching noise at the out-
put and may couple to the FB pin via C Excessive noise
FF.
at FB will cause poor load regulation. To solve this problem
place a resistor R in series with C . R value up to 2%
FF
FF FF
of R1 is acceptable.
15 / 20
exar.com/XR76203/5/8
Rev 1A
© 2015 Exar Corporation
XR76203/5/8
Application Circuit, XR76208
OPTIONAL
CSNB 0.56nF RSNB 1 Ohm
CBST 1uF
R4
2k
R3
18.2k
24VIN
CIN
SW
RLIM
5.49k
1
2
3
4
5
6
7
22
21
20
19
18
17
16
15
2x 10uF/50V
ILIM
EN
PVIN
PVIN
RON
28k
TON
SS
SW
CSS 47nF
U1
PGND
PGND
PGND
PGND
PGND
XR76208
PGOOD
FB
VCC
R5
10k
FB
AGND
IHLP-5050FD-01
2.2uH
400kHz, 3.3V @ 0-8A
COUT
CFF
0.27nF
3x 47uF/10V
CIN
0.1uF
R1
9.09k
PVIN
FB
CVCC
4.7uF
R2
2k
16 / 20
exar.com/XR76203/5/8
Rev 1A
© 2015 Exar Corporation
XR76203/5/8
Application Circuit, XR76205
OPTIONAL
CSNB 0.33nF RSNB 1 Ohm
CBST
1uF
R4
2k
R3
18.2k
24VIN
CIN
SW
RLIM
8.06k
1
2
3
4
5
6
7
22
21
20
19
18
17
16
15
1x 10uF/50V
ILIM
EN
PVIN
PVIN
RON
29.4k
TON
SS
SW
CSS 47nF
U1
PGND
PGND
PGND
PGND
PGND
XR76205
PGOOD
FB
VCC
R5
10k
FB
AGND
Wurth-74437368033
3.3uH
400kHz, 3.3V@ 0-5A
COUT
CFF
0.27nF
2x 47uF/10V
CIN1 0.1uF
R1
9.09k
PVIN
FB
CVCC
4.7uF
R2
2k
17 / 20
exar.com/XR76203/5/8
Rev 1A
© 2015 Exar Corporation
XR76203/5/8
Application Circuit, XR76203
CBST
1uF
R4
2k
R3
18.2k
24VIN
CIN
SW
RLIM
4.02k
1
2
3
4
5
6
7
22
21
20
19
18
17
16
15
10uF/50V
ILIM
EN
PVIN
PVIN
RON
28k
TON
SS
SW
CSS 47nF
U1
PGND
PGND
PGND
PGND
PGND
XR76203
PGOOD
FB
VCC
R5
10k
FB
AGND
Wurth-74437368047
4.7uH
400kHz, 3.3V @ 0-3A
COUT
CFF
47uF/10V
CIN1 0.1uF
0.22nF
R1
9.09k
PVIN
FB
CVCC 4.7uF
R2
2k
18 / 20
exar.com/XR76203/5/8
Rev 1A
© 2015 Exar Corporation
XR76203/5/8
Mechanical Dimensions
19 / 20
exar.com/XR76203/5/8
Rev 1A
© 2015 Exar Corporation
XR76203/5/8
Ordering Information
Part Number
Package
JEDEC
Compliant
OperatingTemperature
Range
Packaging
Marking
XR76208EL-F
Tray
76208E
YYWWF
XXXXXX
XR76208ELTR-F
XR76208ELMTR-F
XR76208EVB
5x5mm QFN
Yes
Yes
Yes
-40°C to +125°C
Tape and Reel
Mini Tape and Reel
XR76208 Evaluation Board
Tray
XR76205EL-F
76205E
YYWWF
XXXXXX
XR76205ELTR-F
XR76205ELMTR-F
XR76205EVB
5x5mm QFN
5x5mm QFN
-40°C to +125°C
Tape and Reel
Mini Tape and Reel
XR76205 Evaluation Board
Tray
XR76203EL-F
76203E
YYWWF
XXXXXX
XR76203ELTR-F
XR76203ELMTR-F
XR76203EVB
-40°C to +125°C
Tape and Reel
Mini Tape and Reel
XR76203 Evaluation Board
“YY” = Year (last two digits)- “WW” = Work Week- “X” = Lot Number; when applicable
Revision History
Revision
Date
Description
1A
February 2015
ECN: 1509-04 Feb 2015
For Further Assistance:
Technical Support: techsupport.exar.com
Technical Documentation: www.exar.com/techdoc
Exar Corporation Headquarters and Sales Offices
48720 Kato Road
Fremont, CA 95438 - USA
Tel.: +1 (510) 668-7000
Fax: +1 (510) 668-7001
NOTICE
EXAR Corporation reserves the right to make changes to the products contained in this publication in order to improve design, performance or reliability. EXAR Corporation
assumes no responsibility for the use of any circuits described herein, conveys no license under any patent or other right, and makes no representation that the circuits are free
of patent infringement. Charts and schedules contained herein are only for illustration purposes and may vary depending upon a user’s specific application. While the information
in this publication has been carefully checked; no responsibility, however, is assumed for inaccuracies.
EXAR Corporation 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 EXAR Corporation
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 EXAR Cor-
poration is adequately protected under the circumstances.
Reproduction, in part or whole, without the prior written consent of EXAR Corporation is prohibited.
20 / 20
exar.com/XR76203/5/8
Rev 1A
© 2015 Exar Corporation
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