參數(shù)資料
型號: L6920DB
廠商: STMICROELECTRONICS
元件分類: 穩(wěn)壓器
英文描述: 0.9 A SWITCHING REGULATOR, 1000 kHz SWITCHING FREQ-MAX, PDSO8
封裝: LEAD FREE, MSOP-8
文件頁數(shù): 14/16頁
文件大?。?/td> 402K
代理商: L6920DB
L6920DB
Detailed description
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5
Detailed description
The L6920DB is a high efficiency, low voltage step-up DC/DC converter particularly suitable
for 1 to 3 cells (Li-Ion/ polymer, NiMH respectively) battery up conversion.
These performances are achieved via a strong reduction of quiescent current (10
A only)
and adopting a synchronous rectification that implies also a reduced cost in the application
(no external diode required).
Operation is based on maximum ON time - minimum OFF time control, tailored by a current
limit set to 800mA. A simplified block diagram is shown here below.
Figure 5.
Simplified block diagram
5.1
Principle of operation
In L6920DB the control is based on a comparator that continuously checks the status of
output voltage.
If the output voltage is lower than the expected value, the control function of the L6920DB
directs the energy stored in the inductor to be transferred to the load. This is accomplished
by alternating between two basic steps:
TON phase: the energy is transferred from the battery to the inductor by shorting LX
node to ground via the N-channel power switch. The switch is turned off if the current
flowing in the inductor reaches 750mA or after a maximum on time set to 5
s.
TOFF phase: the energy stored in the inductor is transferred to the load through the
synchronous switch for at least a minimum off time equal to 1
s. After this, the
synchronous switch is turned off as soon as the output voltage goes lower than the
regulated voltage or the current flowing in the inductor goes down to zero.
R
Q
S
Ton max
5
sec
Toff min
1
sec
VBG
A
B
C
-
+
-
+
-
+
-
+
-
+
VOUT
ZERO CROSSING
OPAMP
(CR)
CURRENT LIMIT
OUT
FB
GND
VREF
LBI
LBO
D99IN1041
SHDN
LX
VIN
VOUT
GND
R1,R2
FB
Y
A
B
C
- +
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