TC1268 Datasheet, PDF (4/12 Pages) Microchip Technology – 500mA Fixed Output, Fast Response CMOS LDO with Shutdown

TC1268
2.0 PIN DESCRIPTIONS
The descriptions of the pins are listed in Table 2-1.
TABLE 2-1: PIN FUNCTION TABLE
Pin No.
(8-Pin SOIC)
1
2
3
4
5
6
7
8
Symbol
Description
V_OUT
GND
NC
BYPASS
ERROR
SHDN
NC
V_IN
Regulated voltage output.
Ground terminal.
No connect.
Reference bypass input. Connecting a 470pF to this input further reduces output noise.
Out-of-Regulation Flag. (Open drain output). This output goes low when V_OUT is out-of-tolerance
by approximately -5%.
Shutdown control input. The regulator is fully enabled when a logic high is applied to this input.
The regulator enters shutdown when a logic low is applied to this input. During shutdown, output
voltage falls to zero and supply current is reduced to 5µA (typical).
No connect.
Unregulated supply input.
3.0 DETAILED DESCRIPTION
The TC1268 is a precision, fixed output LDO. Unlike
bipolar regulators, the TC1268 supply current does
not increase with load current. In addition, V_OUT
remains stable and within regulation over the entire
0mA to I_LOADMAX load current range, (an important
consideration in RTC and CMOS RAM battery back-up
applications). Figure 3-1 shows a typical application
circuit.
FIGURE 3-1:
TYPICAL APPLICATION
CIRCUIT
+ _CIN ^VIN
+
1µF
V_OUT
+
V_OUT
C_OUT
1µF
Battery
TC1268
ON
–
SHDN
SHDN ^OFF
V⁺
C_BYP
10nF
BYP
R1
1M
GND ERROR
+
C1 0.2µF
C1 required only if ERROR is used
as a processor RESET signal (See Text)
3.1 Turn On Response
The turn on response is defined as two separate
response categories, Wake-up Time (T_WK) and Settling
Time (T_S).
The TC1268 has a fast Wake-up Time (5µsec typical)
when released from shutdown. See Figure 3-2 for the
Wake-up Time designated as T_WK. The Wake-up Time
is defined as the time it takes for the output to rise to 2%
of the V_OUT value after being released from shutdown.
The total turn on response is defined as the Settling
Time (T_S), see Figure 3-2. Settling Time (inclusive with
T_WK) is defined as the condition when the output is
within 2% of its fully enabled value (15µsec typical)
when released from shutdown. The settling time of the
output voltage is dependent on load conditions and
output capacitance on V_OUT (RC response).
The Wake-up Time (T_WK) is an important parameter
to consider when using the TC1268 in RAMBUS
applications. In this application, the bus voltage is held
at 2.5V by a switching regulator during normal power
conditions and can be switched to low power mode,
where the TC1268 takes over and supplies the same
2.5V, but at a much lower current (300mA). In order to
not see the bus voltage drop during the transition from
high power to low power, the TC1268 has a very fast
wake-up time of 5µsec to support the 2.5V rail. This
makes the TC1268 ideal for applications involving
RAMBUS.
FIGURE 3-2:
SHDN
V_IL
V_OUT
WAKE-UP RESPONSE
TIME
V_IH
T_S
98%
2%
T_WK
DS21379B-page 4
© 2002 Microchip Technology Inc.