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PDF L5970AD Data sheet ( Hoja de datos )
| Número de pieza | L5970AD | |
| Descripción | 1.5A SWITCH STEP DOWN SWITCHING REGULATOR | |
| Fabricantes | STMicroelectronics | |
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L5970ADwww.DataSheet4U.com
1.5A SWITCH STEP DOWN SWITCHING REGULATOR
1 General Features
■ 1.5A INTERNAL SWITCH
■ OPERATING INPUT VOLTAGE FROM 4.4V TO 36V
■ 3.3V / (±2%) REFERENCE VOLTAGE
■ OUTPUT VOLTAGE ADJUSTABLE FROM
1.235V TO 35V
■ LOW DROPOUT OPERATION: 100% DUTY
CYCLE
■ 500KHz INTERNALLY FIXED FREQUENCY
■ VOLTAGE FEEDFORWARD
■ ZERO LOAD CURRENT OPERATION
■ INTERNAL CURRENT LIMITING
■ INHIBIT FOR ZERO CURRENT
CONSUMPTION
■ SYNCHRONIZATION
■ PROTECTION AGAINST FEEDBACK
DISCONNECTION
■ THERMAL SHUTDOWN
1.1 APPLICATIONS:
■ CONSUMER: STB, DVD, TV, VCR,CAR
RADIO, LCD MONITORS
■ NETWORKING: XDSL, MODEMS,DC-DC
MODULES
■ COMPUTER: PRINTERS, AUDIO/GRAPHIC
CARDS, OPTICAL STORAGE, HARD DISK
DRIVE
■ INDUSTRIAL: CHARGERS, CAR BATTERY
DC-DC CONVERTERS
Figure 1. Package
SO-8
Table 1. Order Codes
Part Number
L5970AD
L5970ADTR
Package
SO-8
SO-8 in Tape & Reel
2 Description
The L5970AD is a step down monolithic power
switching regulator with a switch current limit of 1.5A
so it is able to deliver more than 1A DC current to the
load depending on the application conditions.
The output voltage can be set from 1.235V to 35V.
The device uses an internal P-Channel D-MOS tran-
sistor (with a typical RDSON of 200mΩ) as switching
element to avoid the use of bootstrap capacitor and
guarantee high efficiency.
An internal oscillator fixes the switching frequency at
500KHz to minimize the size of external components.
Having a minimum input voltage of 4.4V only, it is
particularly suitable for 5V bus, available in all com-
puter related applications.
Pulse by pulse current limit with the internal frequen-
cy modulation offers an effective constant current
short circuit protection.
Figure 2. Test and Application Circuit
VREF
3.3V
6
1
VIN = 4.4V to 35V
VCC
8 L5970AD
SYNC. 2
C1
10µF
35V
CERAMIC
COMP
C4
22nF
43
INH
C3
220pF
R3
4.7K
5
7
GND
OUT L1 15µH
VOUT=3.3V
D1
STPS2L25U R1
5.6K
FB
R2
3.3K
C2
330µF
10V
March 2005
D05IN1530
Rev. 1
1/11
1 page  
Figure 5. Internal Regulator Circuit
VCC
L5970AD
www.DataSheet4U.com
STARTER
PREREGULATOR
VREG
BANDGAP
IC BIAS
D00IN1126
VREF
3.3 OSCILLATOR & SYNCHRONIZATOR
Figure 6 shows the block diagram of the oscillator circuit.
The Clock Generator provides the switching frequency of the device that is internally fixed at 500KHz. The frequency
shifter block acts reducing the switching frequency in case of strong overcurrent or short circuit. The clock signal is
then used in the internal logic circuitry and is the input of the Ramp Generator and Synchronizator blocks.
The Ramp Generator circuit provides the sawtooth signal, used to realize the PWM control and the internal volt-
age feed forward, while the Synchronizator circuit generates the synchronization signal. Infact the device has a
synchronization pin that can works both as Master and Slave.
As Master to synchronize external devices to the internal switching frequency.
As Slave to synchronize itself by external signal.
In particular, connecting together two devices, the one with the lower switching frequency works as Slave and
the other one works as Master.
To synchronize the device, the SYNC pin has to pass from a low level to a level higher than the synchronization
threshold with a duty cycle that can vary approximately from 10% to 90%, depending also on the signal frequen-
cy and amplitude.
The frequency of the synchronization signal must be at least higher than the internal switching frequency of the
device (500KHz).
Figure 6. Oscillator Circuit
FREQUENCY
SHIFTER
Ibias_osc
CLOCK
GENERATOR
CLOCK
t
RAMP
GENERATOR
RAMP
D00IN1131
SYNCHRONIZATOR
SYNC
5/11
5 Page 
L5970AD
www.DataSheet4U.com
Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences
of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted
by implication or otherwise under any patent or patent rights of STMicroelectronics. Specifications mentioned in this publication are subject
to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are not
authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics.
The ST logo is a registered trademark of STMicroelectronics.
All other names are the property of their respective owners
© 2005 STMicroelectronics - All rights reserved
STMicroelectronics group of companies
Australia - Belgium - Brazil - Canada - China - Czech Republic - Finland - France - Germany - Hong Kong - India - Israel - Italy - Japan -
Malaysia - Malta - Morocco - Singapore - Spain - Sweden - Switzerland - United Kingdom - United States of America
www.st.com
11/11
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