參數(shù)資料
型號(hào): LTC1261CS84.5
廠商: LINEAR TECHNOLOGY CORP
元件分類(lèi): 穩(wěn)壓器
英文描述: SWITCHED CAPACITOR REGULATOR, 550 kHz SWITCHING FREQ-MAX, PDSO8
封裝: PLASTIC, SOIC-8
文件頁(yè)數(shù): 14/16頁(yè)
文件大?。?/td> 266K
代理商: LTC1261CS84.5
7
LTC1261
APPLICATIONS INFORMATION
WU
U
+
+
CLK
550kHz
S
R
Q
S2
S3
S7
S1
S5
VCC
OUT
VOUT
LTC1261 F02
60mV
1.18V
VREF = 1.24V
RADJ*
R1*
R0*
*LTC1261CS14 ONLY
COUT
C1
C1+
C1
S4
S6
C2
50k
100k
226k
INTERNALLY
CONNECTED FOR
FIXED OUTPUT
VOLTAGE PARTS
124k
C2+
C2
COMP 1
COMP 2
ADJ/COMP
REG
+
Figure 2. Block Diagram
The output voltage is monitored by COMP1 which com-
pares a divided replica of the output at ADJ (COMP for
fixed output parts) to the internal reference. At the begin-
ning of a cycle the clock is low, forcing the output of the
AND gate low and charging the flying capacitors. The next
rising clock edge sets the RS latch, setting the charge
pump to transfer charge from the flying capacitors to the
output capacitor. As long as the output is below the set
point, COMP1 stays low, the latch stays set and the charge
pump runs at the full 50% duty cycle of the clock gated
through the AND gate. As the output approaches the set
voltage, COMP1 will trip whenever the divided signal
exceeds the internal 1.24V reference relative to OUT. This
resets the RS latch and truncates the clock pulses, reduc-
ing the amount of charge transferred to the output capaci-
tor and regulating the output voltage. If the output exceeds
the set point, COMP1 stays high, inhibiting the RS latch
and disabling the charge pump.
COMP2 also monitors the divided signal at ADJ but it is
connected to a 1.18V reference, 5% below the main
reference voltage. When the divided output exceeds this
lower reference voltage indicating that the output is within
5% of the set value, COMP2 goes high turning on the REG
output transistor. This is an open drain N-channel device
capable of sinking 5mA with a 3.3V VCC and 8mA with a 5V
VCC. When in the “off” state (divided output more than 5%
below VREF) the drain can be pulled above VCC without
damage up to a maximum of 12V above ground. Note that
the REG output only indicates if the magnitude of the
output is
below the magnitude of the set point by 5% (i.e.,
VOUT > –4.75V for a –5V set point). If the magnitude of the
output is forced
higher than the magnitude of the set point
( i.e., to – 6V when the output is set for – 5V) the REG
output will stay low.
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