LT1054_06 Datasheet, PDF (11/27 Pages) Texas Instruments – SWITCHED-CAPACITOR VOLTAGE CONVERTERS WITH REGULATORS

LT1054
SWITCHEDĆCAPACITOR VOLTAGE CONVERTERS
WITH REGULATORS
SLVS033F − FEBRUARY 1990 − REVISED NOVEMBER 2004
APPLICATION INFORMATION
regulation
The feedback/shutdown (FB/SD) terminal has two functions. Pulling FB/SD below the shutdown threshold
(≈ 0.45 V) puts the device into shutdown. In shutdown, the reference/regulator is turned off and switching stops.
The switches are set such that both C_IN and C_OUT are discharged through the output load. Quiescent current
in shutdown drops to approximately 100 µA. Any open-collector gate can be used to put the LT1054 into
shutdown. For normal (unregulated) operation, the device will restart when the external gate is shut off. In
LT1054 circuits that use the regulation feature, the external resistor divider can provide enough pulldown to keep
the device in shutdown until the output capacitor (C_OUT) has fully discharged. For most applications, where the
LT1054 is run intermittently, this does not present a problem because the discharge time of the output capacitor
is short compared to the off time of the device. In applications where the device has to start up before the output
capacitor (C_OUT) has fully discharged, a restart pulse must be applied to FB/SD of the LT1054. Using the circuit
shown in Figure 16, the restart signal can be either a pulse (t_p > 100 µs) or a logic high. Diode coupling the restart
signal into FB/SD allows the output voltage to rise and regulate without overshoot. The resistor divider R3/R4
shown in Figure 16 should be chosen to provide a signal level at FB/SD of 0.7−1.1 V.
FB/SD also is the inverting input of the LT1054 error amplifier and, as such, can be used to obtain a regulated
output voltage.
R3
VIN
1
FB/SD
8
VCC
2.2 µF
+
2
CAP+
7
OSC
R4
CIN
10-µF
+
Tantalum
LT1054
3
6
GND
VREF
R1
4
CAP−
5
R2
VOUT
Restart
Shutdown
For example: To get VO = −5 V, referenced to the ground terminal of the LT1054
ǒ Ǔ ǒ Ǔ R2 + R1
Ť
VREF
2
V
Ť
OUT
* 40
mV
)
1
+ 20 kW
2.5
2
|–5
V_*
V|
40
mV
)
1
+ 102.6 kW ^†
Where: R1 = 20 kΩ
VREF = 2.5 V Nominal
† _{Choose the closest 1% value.}
Pin numbers shown are for the P package.
VOUT
C1
COUT
100-µF
+ _Tantalum
Figure 16. Basic Regulation Configuration
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