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42V Input Standoff Voltage, 0.7A Step-Down Converter
BL9641
1
2
3
6
4
SOT23-6
SW
BST
FB
EN
GND
5
IN
GND
FB
IN
SW
V
OUT
3.3V/0.5A
10μH
49.9K
16.2K
EN
50V
10μF
6.3V
22μF
5
4
6
3
2
BST
10nF
1
D1
VIN Standoff up to 42V
DESCRIPTION
The BL9641 is a wide input range, high-efficiency,
and high frequency DC-to-DC step-down
switching regulator, capable of delivering up to
0.7A of output current. With a fixed switching
frequency of 660KHz, this current mode PWM
controlled converter allows the use of small
external components, such as ceramic input and
output caps, as well as small inductors.BL9641
also employs a proprietary control scheme that
switches the device into a power save mode
during light load, thereby extending the range of
high efficiency operation. An OVP function
protects the IC itself and its downstream system
against input voltage surges. With this OVP
function, the IC can stand off input voltage as
high as 42V, making it an ideal solution for
industrial applications such as smart meters as
well as automotive applications.
In automotive systems, power comes from the
battery, with its voltage typically between 9V and
24V. Including cold crank and double battery
jump-starts, the minimum input voltage may be
as low as 4V and the maximum up to 36V, with
even higher transient voltages. With these high
input voltages, linear regulators cannot be used
for high supply currents without overheating the
regulator. Instead, high efficiency switching
regulators such as BL9641 must be used to
minimize thermal dissipation.
BL9641 is available SOT23-6 Packages.
TYPICAL APPLICATION
FEATURES
Wide Input Operating Range from 4V to 38V
Standoff Input Voltage: 42V
High Efficiency at 12V In 5V Out: Up to 92%:
High Efficiency PFM mode at light load
Capable of Delivering 0.7A
No External Compensation Needed
Current Mode control
Logic Control Shutdown
Thermal shutdown and UVLO
Available in SOT23-6 Package
APPLICATIONS
Smart Meters
Industrial Applications
Automotive Applications
PIN OUT
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BL9641
Mark Explanation
aa: Type
b: Year
c: Week
PIN #
NAME
DESCRIPTION
1
BST
Bootstrap pin. Connect a 10nF capacitor from this pin to SW
2
GND
Ground
3
FB
Feedback Input. Connect an external resistor divider from the output to FB and GND to set VOUT
4
EN
Enable pin for the IC. Drive this pin high to enable the part, low to disable.
5
IN
Supply Voltage. Bypass with a 10μF ceramic capacitor to GND
6
SW
Inductor Connection. Connect an inductor Between SW and the regulator output.
REG
&REF
PWM
Logic
DRIVER
FB
+
+
-
Slope Comp
OSC
Σ
IN
BST
SW
GND
UVLO &
Thermal
shutdown
Current
Sense
EA
+
-
-
EN
COMP
network
MARK and ORDERING INFORMATION
PINOUT DESCRIPTION
BLOCK DIAGRAM
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BL9641
Parameter
Value
Input Voltage Range
-0.3V-42V
SW, EN Voltage
–0.3V to VIN+0.3V
BST Voltage
–0.3V to SW+6V
FB Voltage
–0.3V to 6V
SW to ground curren
Internally limited
Operating Junction Temperature(Tj)
-40C –85C
Package Thermal Resistance (jc)
SOT23-6
110C / W
Storage Temperature(Ts)
-55C - 150C
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Input Standoff Voltage
42
V
Input Voltage Range
4 38
V
Input UVLO
Rising, Hysteresis=140mV
3.80 V
Input OVP
Rising, Hysteresis=1.3V
38 V
Input Supply Current
VFB =0.85V
0.6 mA
Input Shutdown Current
6
μA
FB Feedback Voltage
0.800 V
FB Input Current
0.01 μA
Switching Frequency
660 KHz
Maximum Duty Cycle
90
%
FoldBack Frequency
VFB = 0V
60 KHz
High side Switch On Resistance
ISW =200mA
400 mΩ
High side Switch Current Limit
1.2 A
SW Leakage Current
VIN=12V,VSW=0, EN= GND
10
μA
EN Input Current
VIN=12V ,VEN =5V
1 5
μA
EN Input Low Voltage
Rising, Hysteresis=100mV
0.8
1.1
1.4
V
Thermal Shutdown
Hysteresis=40°C
150 °C
ABSOLUTE MAXIMUM RATING
Note: Exceed these limits to damage to the device. Exposure to absolute maximum
rating conditions may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VIN = 12V, unless otherwise specified. Typical values are at TA = 25C .)
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BL9641
TYPICAL PERFORMANCE CHARACTERISTICS
(Typical values are at TA = 25C unless otherwise specified.)
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BL9641
Start-up Waveform with EN
VIN=12V,VOUT=5V,IOUT=0A
5ms/div
VEN
V
OUT
ISW
Start-up Waveform with EN=VIN
VIN=12V,VOUT=5V,IOUT=0A
5ms/div
Shutdown Waveform with EN
VIN=30V,VOUT=5V,IOUT=0.5A
5ms/div
V
OUT
ISW
I
SW
VIN
V
OUT
VSW
VSW
VEN
VSW
Switching Waveform
VIN=12V,VOUT=5V,IOUT=0.1A
5ms/div
V
OUT
Switching Waveform
VIN=12V,VOUT=5V,IOUT=0.3A
5ms/div
Load Transient Response
VIN=12V,VOUT=3.3V,IOUT=0 to 0.5A
5ms/div
V
OUT
ISW
V
OUT
VSW
VSW
Load Transient Response
VIN=12V,VOUT=5V,IOUT=0 to 0.5A
5ms/div
V
OUT
ISW
Short-Circuit Response
VIN=24V,VOUT=5V,IOUT=0A to
5ms/div
Short-Circuit Recovery
VIN=24V,VOUT=5V,IOUT= Short to 0A
5ms/div
V
OUT
ISW
I
SW
V
OUT
TYPICAL CHARACTERISTICS
(Typical values are at TA = 25C unless otherwise specified.)
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BL9641
VOUT (V)
COUT (μF)
L (μH) 8 22
15 to 22
5
22
10 to 15
3.3
22
6.8 to 10
FUNCTIONAL DECRIPTIONS
Loop Operation
The BL9641 is a wide input range, high-efficiency, DC-to-DC step-down switching regulator, capable of delivering up to
0.7A of output current, integrated with a 400mΩ high side MOSFET. It uses a PWM current-mode control scheme. An
error amplifier integrates error between the FB signal and the internal reference voltage. The output of the integrator is
then compared to the sum of a current-sense signal and the slope compensation ramp. This operation generates a PWM
signal that modulates the duty cycle of the power MOSFETs to achieve regulation for output voltage.
Light Load Operation
Traditionally, a fixed constant frequency PWM DC-DC regulator always switches even when the output load is small.
When energy is shuffling back and forth through the power MOSFETs, power is lost due to the finite RDSONs of the
MOSFETs and parasitic capacitances. At light load, this loss is prominent and efficiency is therefore very low. BL9641
employs a proprietary control scheme that improves efficiency in this situation by enabling the device into a power save
mode during light load, thereby extending the range of high efficiency operation.
APPLICATION INFORMATION
Setting Output Voltages
Output voltages are set by external resistors. The FB threshold is 0.8V.
RTOP = RBOTTOM x [(VOUT / 0.8) - 1]
Inductor Selection
The peak-to-peak ripple is limited to 30% of the maximum output current. This places the peak current far enough from
the minimum overcurrent trip level to ensure reliable operation while providing enough current ripples for the current
mode converter to operate stably. In this case, for 0.7A maximum output current, the maximum inductor ripple current
is 300 mA. The inductor size is estimated as following equation:
LIDEAL=(VIN(MAX)-VOUT)/IRIPPLE*DMIN*(1/FOSC)
Therefore, for VOUT=5V, The inductor values is calculated to be L = 13μH. Chose 10μH or 15Μh
For VOUT =3.3V,The inductor values is calculated to be L = 9.2μH. Chose 10μH
Output Capacitor Selection
For most applications a nominal 22μF or larger capacitor is suitable. The ETA2841 internal compensation is designed for
a fixed corner frequency that is equal to FC= 8.7Khz
For example, for VOUT=5V, L=15μH, COUT=22μF.
The output capacitor keeps output ripple small and ensures control-loop stability. The output capacitor must also have
low impedance at the switching frequency. Ceramic, polymer, and tantalum capacitors are suitable, with ceramic
exhibiting the lowest ESR and high-frequency impedance. Output ripple with a ceramic output capacitor is approximately
as follows:VRIPPLE = IL(PEAK)[1 / (2π x fOSC x COUT)]
If the capacitor has significant ESR, the output ripple component due to capacitor ESR is as follows:
VRIPPLE(ESR) = IL(PEAK) x ESR
Input Capacitor Selection
The input capacitor in a DC-to-DC converter reduces current peaks drawn from the battery or other input power source
and reduces switching noise in the controller. The impedance of the input capacitor at the switching frequency should be
less than that of the input source so high-frequency switching currents do not pass through the input source. The output
capacitor keeps output ripple small and ensures control-loop stability.
Components Selection
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BL9641
PACKAGE OUTLINE
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