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PDF XR75100 Data sheet ( Hoja de datos )
| Número de pieza | XR75100 | |
| Descripción | 40V Synchronous Step Down COT Controller | |
| Fabricantes | Exar | |
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XR75100
40V Synchronous Step Down COT Controller
General Description
The XR75100 is a synchronous step-down controller for point-of load sup-
plies up to 20A. A wide 5.5V to 40V input voltage range allows for single
supply operation from industry standard 12V, 18V, and 24V DC and AC
rails.
With a proprietary emulated current mode Constant On-Time (COT) con-
trol scheme, the XR75100 provides extremely fast line and load transient
response using ceramic output capacitors. It requires no loop compensa-
tion hence simplifying circuit implementation and reducing overall compo-
nent count. The control loop also provides exceptional load and 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 over-current, over-temperature,
short-circuit and UVLO, help achieve safe operation under abnormal
operating conditions.
The XR75100 is available in RoHS compliant, green/halogen free space-
saving 16-pin 3x3 QFN package.
FEATURES
20A Capable Step Down Controller
Wide 5.5V to 40V Input Voltage Range
Integrated High Current 2A/3A Drivers
0.6 to 30V 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 Operation
Programmable Hiccup Current Limit with Ther-
mal Compensation
Precision Enable and Power Good flag
Programmable Soft-start
Integrated Bootstrap diode
16-pin QFN package
APPLICATIONS
Networking and Communications
Fast Transient Point-of-Loads
Industrial and Medical Equipment
Embedded High Power FPGA
Ordering Information – back page
Typical Application
VIN
Enable/Mode
Power Good
CIN
R3
CBST
VIN BST
EN/MODE
GH
PGOOD
SW
VCC XR75100 ILIM
RLIM
SS GL
CVCC CSS
RON
TON
AGND
FB
PGND
Q1
L1
VOUT
Q2 CFF R1
R2
COUT
3.340
3.330
3.320
3.310
3.300
3.290
3.280
3.270
3.260
5
+0.5%
Typical
-0.5%
10 15 20 25 30
VIN (V)
© 2016 Exar Corporation
1 / 15
exar.com/XR75100
Rev 1C
1 page  
XR75100
Pin Configuration
Pin Assignments
PGND VCC
16 15
VIN AGND
14 13
GL 1
12 AGND
NC 2
SW 3
EXPOSED PAD
11 FB
10 PGOOD
GH 4
9 SS
5678
BST ILIM EN TON
Pin No.
Pin Name
1 GL
2 NC
3 SW
4 GH
5 BST
6 ILIM
7 EN/MODE
8 TON
9 SS
10 PGOOD
11 FB
12, 13
14
15
16
AGND
VIN
VCC
PGND
Exposed Pad
Type
O
A
O
A
A
I
A
A
OD
A
A
PWR
PWR
PWR
A
Description
Driver output for Low-side N-channel synchronous MOSFET.
Internally not connected. Leave this pin floating.
Lower supply rail for high-side gate driver GH. Connect this pin to the junction between the two
external N-channel MOSFETs.
Driver output for high-side N-channel switching MOSFET.
High-side driver supply pin. Connect a 0.1uF bootstrap capacitor between BST and SW.
Over-current protection programming. Connect with a resistor to the drain of the low-side MOS-
FET.
Precision enable pin. Pulling this pin above 1.9V will turn the IC on and it will operate in Forced
CCM. If the voltage is raised above 3.0V, then the IC will operate in DCM or CCM depending
on load.
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.
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 GND in
order to program VOUT.
Analog ground. Control circuitry of the IC is referenced to this pin.
IC supply input. Provides power to internal LDO.
The output of LDO. For operation using a 5V rail, VCC should be shorted to VIN.
Low side driver ground
Thermal pad for heat dissipation. Connect to AGND with a short trace.
Type: A = Analog, I = Input, O = Output, I/O = Input/Output, PWR = Power, OD = Open-Drain
© 2016 Exar Corporation
5 / 15
exar.com/XR75100
Rev 1C
5 Page 
XR75100
correct time to turn it off. Ideally, this threshold is -1mV,
meaning there is still positive current in the inductor (posi-
tive inductor current refers to current from SW to VOUT).
However, there is a range to the sensed voltage from -4mV
to +2mV. In the case where a very low RDSON low side
MOSFET is used a higher negative inductor current is
required to reach the +2mV. For instance, a 2mohm MOS-
FET would require a negative 1A inductor valley current
before the XR75100 recognizes the signal to turn off the low
side MOSFET. As a result, the XR75100 will not enter PFM
until the load reduces further. It should be noted that the net
power saving between ideal zero cross detection and the
-4mV to +2mV range of the XR75100 is minor. The operat-
ing frequency will have changed little from what one would
have in the ideal case.
One important feature added to the DCM detection is a
counter which allows 8 switching cycles to trigger in the
zero cross comparator before enabling DCM operation.
This ensures that during large unloading events, the
XR75100 will respond quickly. This operation can be seen
during the unloading event in Figure 4 in the Typical Perfor-
mance Characteristics section above.
Programming the On-Time
The On-Time TON is programmed via resistor RON accord-
ing to following equation:
RON = 3-V---.-I4--N--------1-T--0--O--–--1-N--0-
is reduced below the programmed IOCP. In order to program
over-current protection use the following equation:
RLIM
=
---I--O---C----P---------R----D-----S--------+----8----m-----V--
ILIM
Where:
RLIM is resistor value for programming IOCP
IOCP is the over-current threshold to be programmed
RDS is the MOSFET rated on resistance
8mV is the OCP comparator offset
ILIM is the internal current that generates the necessary
OCP comparator threshold (use 45μA).
Note that ILIM has a positive temperature coefficient of
0.4%/°C. This is meant to roughly match and compensate
for positive temperature coefficient of the synchronous FET
RDS. In order for this feature to be effective the temperature
rise of the IC should approximately match the temperature
rise of the FET. A graph of typical IOCP versus RLIM is
shown in figure 11.
Short-Circuit Protection (SCP)
If the output voltage drops below 60% of its programmed
value, the IC will enter hiccup mode. Hiccup will persist until
short-circuit is removed. SCP circuit becomes active after
PGOOD asserts high.
where TON is calculated from:
TON
=
--V----O----U---T---
VIN f
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 ini-
tiated and operation resumes.
As an example the calculated TON for the application circuit
is 275ns. An RON of 19.4k is required in order to set TON to
275ns. A graph of typical TON versus RON is shown in fig-
ure 7.
Over-Current Protection (OCP)
If load current exceeds the programmed over-current IOCP
for four consecutive switching cycles, then IC 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 IC will remain in hiccup mode until load current
Programming the Output Voltage
Use an external voltage divider as shown in the application
circuit to program the output voltage VOUT.
R1
=
R2
V---0--O--.-6U----T-
–
1
where R2 has a nominal value of 2kΩ.
© 2016 Exar Corporation
11 / 15
exar.com/XR75100
Rev 1C
11 Page | ||
| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet XR75100.PDF ] | |
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