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PDF XR76121 Data sheet ( Hoja de datos )
| Número de pieza | XR76121 | |
| Descripción | 20A Synchronous Step-Down COT Regulators | |
| Fabricantes | Exar | |
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XR76121
PowerBloxTM 20A Synchronous
Step-Down COT Regulators
Description
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.
The XR76121 is available in a RoHS compliant, green/halogen-free
space-saving 5mm x 6mm QFN package.
Typical Application
ENABLE
VIN
POWER GOOD
CIN R
CBST
EN BST
VIN SW
RLIM
PVIN ILIM
PGOOD
VCC
XR76121
FB
SS FCCM
CVCC CSS
TON
RON
AGND
VSNS
PGND
L1
CFF
RFF
VOUT
R1
R2
VOUT
R1
COUT
R2
Figure 1. Typical Application
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
APPLICATIONS
■■ Servers
■■ Distributed power architecture
■■ Point-of-load converters
■■ FPGA, DSP and processor supplies
■■ Base stations, switches/routers
100
98
96
94
92
90
88
86
84
82
80
78
76
74
72
70
0.1
600kHz
800kHz
5.0V
3.3V
2.5V
1.8V
1.5V
1.2V
1.0V
5.1 10.1 15.1 20.1
IOUT (A)
Figure 2. Efficiency
REV1A
1/18
1 page  
Pin Configuration
TOP VIEW
SW
PVIN 13
12
XR76121
BOTTOM VIEW
11 PGND
1234567
BST 14
EN 15
SS 16
17
AGND
8 VS
9 VIN
10 VC
BST 14
EN 15
SS 16
17
AGND
10 VCC
9 VIN
8 VSNS
1234567
PVIN 13
11 PG
12
SW
Pin Functions
Pin Number
Pin Name
Type
Description
1 FB A Feedback input to feedback comparator.
2 FCCM I Forcing this pin logic level high forces CCM operation.
3
AGND
A Signal ground for control circuitry. Connect to AGND pad with a short trace.
4
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 Power-good output. Open drain to AGND. Low Z when IC unpowered.
8 VSNS A Sense pin for output OVP and open FB.
9 VIN
10 VCC
A Supply input for the regulator’s LDO. Normally connected to PVIN.
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
16 SS
17 AGND PAD
I Precision enable pin. Pulling this pin above 2V will enable the regulator.
A
Soft-start pin. Connect an external capacitor between SS and AGND to program the soft-
start rate based on the 10µA internal source current.
A Signal ground for control circuitry.
NOTE:
A = Analog, I = Input, O = Output, OD = Open Drain, PWR = Power.
REV1A
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5 Page 
Functional Block Diagram
XR76121
VIN
VCC
10µA
SS
0.6V
FB
0.555V
VSNS
VH = 1.2 x VREF
VL = 1.15 x VREF
FCCM
VCC PGOOD
VCC UVLO
4.25V
LDO
POWER GOOD
THERMAL
SHUTDOWN
ENABLING SWITCHING
COT CONTROL LOOP
XR76121
VCC
LEVEL
SHIFT
AND
NON
OVERLAP
CONTROL
HS
DRV
LS VCC
DRV
DELAY OVP
SW
PGND
1.9V
ZC
EN
FB
0.36V
VCC
SCCOMP
HICCUP
ILIM
PGND
BST
PVIN
SW
PGND
TON EN
ILIM
Figure 26. Functional Block Diagram
AGND
REV1A
11/18
11 Page | ||
| Páginas | Total 18 Páginas | |
| PDF Descargar | [ Datasheet XR76121.PDF ] | |
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