Document
BL8542B REV1.2, DEC 2010
0.85V startup, 1MHz, 300mA Iout, Synchronous Boost Converter
DESCRIPTION
The BL8542B is a step-up converter that provides a boosted output voltage from a low voltage source. Because of its proprietary design, it starts up at a very low input voltage down to 850mV, making it an ideal choice for single cell alkaline/NiMH battery operations.
A switching frequency of 1MHz minimizes solution footprint by allowing the use of tiny, low profile inductors and ceramic capacitors. The current mode PWM design is internally compensated, reducing external parts count.
BL8542B is housed in a tiny SOT23-5 and SOT89-3 Package.
TYPICAL APPLICATION CIRCUIT
BL8542B
BL8542B
FEATURES
•• Up to 95% Efficiency •• Output voltage accuracy 3% •• 1MHz Switching Frequency allows small inductor
and output cap •• Input boost-strapping allows using small or no
input cap •• Low Vin Start-up Voltage down to 850mV Ideal
for Single Alkaline Cell operations •• Maximum Output Current up to 300mA •• Low Noise PWM control •• Internally Compensated Current Mode Control •• Internal Synchronous Rectifier •• Logic Control Shutdown (IQ<1uA)
APPLICATIONS
•• One to Three Cell Battery Operated Devices •• Medical Instruments •• Bluetooth Headsets •• Flash-Based MP3 Players •• Noise Canceling Headphones
PIN CONFIGURATION
NOTE: Input capacitor (Cin=0.47uF) and Output capacitor (Cout≥4.7uF) are recommended in all application circuit.
ORDERING INFORMATION
Product BL8542B-ADJ BL8542B-3.3V
BL8542B-5.0V
Product Code BL8542BCB5TR BL8542BCB5TR33
BL8542BCB5TR50
BL8542B-3.3V
BL8542BCC3TR33
BL8542B-5.0V
BL8542BCC3TR50
Package SOT23-5 SOT23-5 SOT23-5
SOT89-3
SOT89-3
BL8542B
SOT23-5
Devices per Reel 3000 3000 3000 1000 1000
BL8542B
3 SW 2 OUT
1G
SOT89-3
Top Marking AAXZ AAWZ AAVZ
AAWZ XXXX AAVZ XXXX
XXXX:The last 4 characters of the LOT NO.
www.belling.com.cn
1
BLOCK DIAGRAM
BL8542B
EN
Low Input startup
osc
Reference
+
GM
FB -
+
Comparator
-
Logic
Driver
+ -
OUT SW G
DETAIL DESCRIPTION
BL8542B is a low input voltage start up, current mode dc-dc step up converter. It’s operation can be best understood by referring to the block diagram. Upon starting up, the low voltage startup circuitry drives SW with on-off cycles, transferring energy from input to OUT by storing energy in the inductor during on-time and releasing it to the output during off-time. When OUT reaches 2V, the startup circuit turns off and the main controller takes over. The main control loop consists of a reference, a GM error amplifier, a PWM controller, a current sense amplifier, an oscillator, a PWM logic control, and it is power stage including its driver. The main control loop is a classic current mode control loop. The GM stage integrates the error between FB and REF, and its output is used to compare with a triangular wave which the summing result of the current sense amplifier output and a slope compensation voltage. The output of the comparator is used to drive the power stage to.