English

BL9370
18V/2A
Sync. Step-Down Converter
DESCRIPTION
FEATURES
The BL9370 is a current mode monolithic buck
switching regulator. Operating with an input range
of 4.7V~18V, the BL9370 delivers 2A of
continuous output current with two integrated
N-Channel MOSFETs. The internal synchronous
power switches provide high efficiency without
the use of an external Schottky diode. At light
loads, the regulator operates in low frequency to
maintain high efficiency and low output ripples.
Current mode control provides tight load transient
response and cycle-by-cycle current limit.
The BL9370 guarantees robustness with
short-circuit protection, thermal protection,
current run-away protection, input under voltage
lockout.
The BL9370 is available in 6-pin TSOT23-6
package, which provides a compact solution with
minimal external components.
4.7V to 18V operating input range
2A output current
Up to 95% efficiency
High efficiency (>85%) at light load
Fixed 500kHz Switching frequency
Input under voltage lockout
Feedback short protection
SW pin short protection
Current run-away protection
Short circuit protection
Thermal protection
Available in TSOT23-6 package
APPLICATIONS
Distributed Power Systems
Networking Systems
FPGA, DSP, ASIC Power Supplies
Green Electronics/ Appliances
Notebook Computers
TYPICAL APPLICATION
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V1.1
BL9370
ORDER INFORMATION
Part Number
BL9370
Package
TSOT23-6
Top Marking
Packing
BL9370
3000pcs/Tape & Reel
PIN CONFIGURATION
TOP VIEW
6 B ST
GND 1
SW 2
5 EN
VIN 3
4 FB
TSO T23-6
ABSOLUTE MAXIMUM RATING1)
VIN, EN, SW Pin …................................................................................................................ -0.3V to 20V
BST Pin ...................................................................................................................... SW-0.3V to SW+5V
All other Pins ............................................................................................................................ -0.3V to 6V
Junction Temp. 2) 3) ............................................................................................................................150ºC
Lead Temperature ............................................................................................................................260 ºC
RECOMMENDED OPERATING CONDITIONS
Input Voltage VIN .................................................................................................................... 4.7V to 18V
Output Voltage Vout ............................................................................................................0.8V to VIN-3V
THERMAL PERFORMANCE4)
Absolute Temp.
(storage temp) (+/- ºC)
Maximum Operating
Junction Temp. (+/- ºC)
TC
Tj
[email protected]ºC
RθJC
PSiJT
(ºC)
(ºC)
(W)
(ºC/W )
(ºC/W )
-65ºC to 150ºC
-40ºC to 125ºC
87
150
1.14
55
110
Note:
:
1)
2)
3)
4)
Exceeding these ratings may damage the device.
The BL9370 guarantees robust performance from -40°C to 150°C junction temperature. The junction tempera ture
range specification is assured by design, characterization and correlation with statistical process controls.
The BL9370 includes thermal protection that is intended to protect the device in overload conditions. Thermal
protection is active when junction temperature exceeds the maximum operating junction temperature. Continuous
operation over the specified absolute maximum operating junction temperature may damage the device.
Measured on JESD51-7, 4-layer PCB.
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V1.1
BL9370
ELECTRICAL CHARACTERISTICS
VIN=12V, TA=25℃,Unless otherwise stated。
Item
Symbol
Conditions
VIN Under Voltage Lock-out Threshold
VIN_MIN
VIN Undervoltage Lockout Hysteresis
VIN_MIN_HYST
Shutdown Supply Current
ISD
VEN=0V
Supply Current
IQ
VEN=5V, VFB=1.2V
VFB
4.7V<VVIN<20V
Feedback Voltage
Top Switch Resistance
5)
Min.
VIN rising
Typ.
Max.
Unit
4.0
V
350
mV
µA
10
µA
55
776
800
824
mV
RDS(ON)T
170
mΩ
Bottom Switch Resistance5)
RDS(ON)B
108
mΩ
Top Switch Leakage Current
ILEAK_TOP
0.5
µA
Bottom Switch Leakage Current
ILEAK_BOT
0.5
µA
Top Switch Current Limit
ILIM_TOP
3.5
A
Switch Frequency
FSW
500
kHz
Minimum On Time
TON_MIN
120
ns
Minimum Off Time
TOFF_MIN
VFB=0.4V
120
ns
EN shut down threshold voltage
VEN_TH
VEN rising
EN shut down hysteresis
VEN_HYST
100
mV
Soft-Start Period
tSS
0.8
ms
TTSD
140
°C
TTSD_HYST
15
°C
Thermal Shutdown
5)
Thermal Shutdown hysteresis5)
VIN=18V, VEN=0V,
VSW=0V
VIN=18, VEN=0V,
VSW=0V
Minimum
Cycle
Duty
3
1.08
1.18
1.28
V
Note:
:
5)
Guaranteed by design.
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V1.1
BL9370
PIN DESCRIPTION
TSOT23-6
Pin
Name
1
GND
2
SW
3
VIN
4
FB
5
EN
6
BST
Description
Ground.
SW is the switching node that supplies power to the output. Connect the output LC filter from
SW to the output load.
Input voltage pin. VIN supplies power to the IC. Connect a 4.7V to 18V supply to VIN and
bypass VIN to GND with a suitably large capacitor to eliminate noise on the input to the IC.
Output feedback pin. FB senses the output voltage and is regulated by the control loop to
0.8V. Connect a resistive divider at FB.
Drive EN pin high to turn on the regulator and low to turn off the regulator.
Bootstrap pin for top switch. A 0.1uF or larger capacitor should be connected between this
pin and the SW pin to supply current to the top switch and top switch driver.
BLOCK DIAGRAM
VIN
+
Current
Ramp
Current
Sensor
+
Oscillator
-
CLK
3.3V
BST
+
Current
Comparator
+
0.8V
Error
+ Amplifier
-
SW
Logic
Control
-
FB
-
3.3V LDO
Current
Sensor
+
1.2V
+
GND
EN
-
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V1.1
BL9370
TYPICAL PERFORMANCE CHARACTERISTICS
Vin =12V, Vout = 3.3V, L = 6.8µH, Cout = 47µF, TA = +25°C, unless otherwise noted
Steady State Test
Startup through Enable
Shutdown through Enable
VIN=12V, Vout=3.3V
Iout=2A
VIN=12V, Vout=3.3V
Iout=2A(Resistive load)
VIN=12V, Vout=3.3V
Iout=2A(Resistive load)
Heavy Load Operation
Medium Load Operation
Light Load Operation
2A LOAD
1A LOAD
0 A LOAD
Short Circuit Protection
Short Circuit Recovery
Load Transient
VIN=12V, Vout=3.3V
Iout=2A- Short
VIN=12V, Vout=3.3V
Iout= Short-2A
1A LOAD → 2A LOAD → 1A LOAD
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V1.1
BL9370
TYPICAL PERFORMANCE CHARACTERISTICS (continued)
FB Voltage Vs. Temperature
Efficiency @ Vout=3.3V
Efficiency
100
Vin=4.7V
Vin=12V
95
Vin=16V
Efficiency(
)
( %)
90
85
80
75
70
65
60
55
50
0
0.5
1
1.5
2
2.5
Io(
( mA)
)
Note: TA = +25°C
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V1.1
BL9370
FUNCTIONAL DESCRIPTION
The BL9370 is a synchronous, current-mode,
step-down regulator. It regulates input voltages
from 4.7V to 18V down to an output voltage as
low as 0.8V, and is capable of supplying up to
2A of load current.
Current-Mode Control
The BL9370 utilizes current-mode control to
regulate the output voltage. The output voltage
is measured at the FB pin through a resistive
voltage divider and the error is amplified by the
internal transconductance error amplifier.
Output of the internal error amplifier is
compared with the switch current measured
internally to control the output current limit.
PFM Mode
The BL9370 operates in PFM mode at light load.
In PFM mode, switch frequency decreases
when load current drops to boost power
efficiency at light load by reducing switch-loss,
while switch frequency increases when load
current rises, minimizing output voltage ripples.
Shut-Down Mode
The BL9370 shuts down when voltage at EN pin
is driven below 0.3V. The entire regulator is off
and the supply current consumed by the
BL9370 drops below 1uA.
Power Switch
N-Channel MOSFET switches are integrated on
the BL9370 to down convert the input voltage to
the regulated output voltage. Since the top
MOSFET needs a gate voltage great than the
input voltage, a boost capacitor connected
between BST and SW pins is required to drive
the gate of the top switch. The boost capacitor is
charged by the internal 3.3V rail when SW is
low.
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Vin Under-Voltage Protection
A resistive divider can be connected between
Vin and ground, with the central tap connected
to EN, so that when Vin drops to the pre-set
value, EN drops below 1.2V to trigger input
under voltage lockout protection.
Output Current Run-Away Protection
At start-up, due to the high voltage at input and
low voltage at output, current inertia of the
output inductor can be easily built up, resulting
in a large start-up output current. A valley
current limit is designed in the BL9370 so that
only when output current drops below the valley
current limit can the top power switch be turned
on. By such control mechanism, the output
current at start-up is well controlled.
Output Short Protection
When output is shorted to ground, output
current rapidly reaches its peak current limit and
the top power switch is turned off. Right after the
top power switch is turned off; the bottom power
switch is turned on and stays on until the output
current falls below the valley current limit. When
output current is below the valley current limit,
the top power switch will be turned on again and
if the output short is still present, the top power
switch is turned off when the peak current limit
is reached and the bottom power switch is
turned on. This cycle goes on until the output
short is removed and the regulator comes into
normal operation again.
SW Short Protection
If the SW pin is detected to be short to ground,
the BL9370 is latched off. The regulator can be
reactivated again through recycling Vin or EN
voltage.
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V1.1
BL9370
FB Short Protection
Thermal Protection
If the FB pin is detected to be short to ground for
more than 15 switch cycles, the BL9370 is
latched off. The regulator can be reactivated
again through recycling Vin or EN voltage.
When the temperature of the BL9370 rises
above 140°C, it is forced into thermal shut-down.
Only when core temperature drops below 125°C
can the regulator becomes active again.
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V1.1
BL9370
APPLICATION INFORMATION
Output Voltage Set
The output voltage is determined by the resistor
divider connected at the FB pin, and the voltage
ratio is:
VOUT ⋅
VFB
R3
R 2 + R3
where VFB is the feedback voltage and VOUT is
the output voltage.
Choose R3 around 10kΩ, and then R2 can be
calculated by:
R32
 V OUT − 1
 0.8 V

R23 ⋅ 
The following table lists the recommended
values.
VOUT(V)
R2(kΩ)
R3(kΩ)
2.5
5.1
11
3.3
4.22
13.3
5
2.1
11.2
Input Capacitor
The input capacitor is used to supply the AC
input current to the step-down converter and
maintaining the DC input voltage. The ripple
current through the input capacitor can be
calculated by:
IC1
VOUT

VIN 
ILOAD ⋅
⋅ 1 −
VOUT 
VIN


where ILOAD is the load current, VOUT is the
output voltage, VIN is the input voltage.
Thus the input capacitor can be calculated by
the following equation when the input ripple
voltage is determined.
C1
ILOAD
VOUT

fs ⋅ ∆V IN VIN 
⋅
⋅ 1 −
The input capacitor can be electrolytic, tantalum
or ceramic. To minimizing the potential noise, a
small X5R or X7R ceramic capacitor, i.e. 0.1uF,
should be placed as close to the IC as possible
when using electrolytic capacitors.
A 22uF ceramic capacitor is recommended in
typical application.
Output Capacitor
The output capacitor is required to maintain the
DC output voltage, and the capacitance value
determines the output ripple voltage. The output
voltage ripple can be calculated by:
∆V OUT
VOUT

fs ⋅ L 
⋅ 1 −
VOUT 
1

⋅  RESR +

VIN  
8 ⋅ fs ⋅ C2 
where C2 is the output capacitance value and
RESR is the equivalent series resistance value of
the output capacitor.
The output capacitor can be low ESR
electrolytic, tantalum or ceramic, which lower
ESR capacitors get lower output ripple voltage.
The output capacitors also affect the system
stability and transient response, and a 22uF
ceramic capacitor is recommended in typical
application.
Inductor
The inductor is used to supply constant current
to the output load, and the value determines the
ripple current which affect the efficiency and the
output voltage ripple. The ripple current is
VOUT 
typically allowed to be 30% of the maximum
VIN
switch current limit, thus the inductance value


where C1 is the input capacitance value, fs is the
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switching frequency, △VIN is the input ripple
voltage.
can be calculated by:
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V1.1
BL9370
L
VOUT

fs ⋅ ∆I L 
⋅ 1 −
VOUT 

VIN 
where VIN is the input voltage, VOUT is the
output voltage, fs is the switching frequency,
and △IL is the peak-to-peak inductor ripple
current.
External Boostrap Capacitor
A boostrap capacitor is required to supply
voltage to the top switch driver. A 0.1uF low
ESR ceramic capacitor is recommended to
connected to the BST pin and SW pin.
PCB Layout Note
For minimum noise problem and best operating
performance, the PCB is preferred to following
the guidelines as reference.
1. Place the input decoupling capacitor as
close to BL9370 (VIN pin and PGND) as
possible to eliminate noise at the input pin.
The loop area formed by input capacitor and
GND must be minimized.
2. Put the feedback trace as far away from the
inductor and noisy power traces as possible.
3. The ground plane on the PCB should be as
large as possible for better heat dissipation
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V1.1
BL9370
REFERENCE DESIGN
Reference 1:
:
VIN :
VOUT:
IOUT :
4.7V ~ 18V
3.3V
0~2A
Reference 2:
:
VIN :
VOUT:
IOUT :
6V ~ 18V
5V
0~2A
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V1.1
BL9370
PACKAGE OUTLINE
TSOT23-6
UNIT: mm
2.85±0.10
0~
10°
0.3±0.20
2.65±0.30
1.55±0.10
0.45±0.15
0.25
+0.1
0.15 5
0.05
0.950BSC
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1.1MAX
0.7±0.30
0~0.1
1.90±0.20
V1.1