LTC1522 Linear Technology, LTC1522 Datasheet - Page 4

• Manufacturer Part Number: LTC1522
• Description: Micropower/ Regulated 5V Charge Pump DC/DC Converter
• Manufacturer: Linear Technology

APPLICATIONS
LTC1522
Operation
The LTC1522 uses a switched capacitor charge pump to
boost V
tion is achieved by sensing the output voltage through an
internal resistor divider and enabling the charge pump
when the output voltage droops below the lower trip point
of COMP1. When the charge pump is enabled, a 2-phase,
nonoverlapping clock controls the charge pump switches.
Clock 1 closes the S1 switches which enables the flying
capacitor to charge up to the V
the S2 switches that stack C
connect the top plate of C
V
ues at a free-running frequency of 700kHz (typ) until the
output has risen to the upper trip point of COMP1 and the
charge pump is disabled. When the charge pump is
disabled, the LTC1522 draws only 4 A (typ) from V
which provides high efficiency at low load conditions.
In shutdown mode, all circuitry is turned off and the part
draws only leakage current from the V
also disconnected from V
input with a threshold of approximately V
the SHDN pin can be driven by logic levels that exceed the
V
4
BLOCK
OUT
IN
voltage. The part enters shutdown mode when a logic
. This sequence of charging and discharging contin-
IN
V
to a regulated 5V 4% output voltage. Regula-
IN
0.22 F
10 F
C
DIAGRAM
C
FLY
IN
+
C
C
U
+
–
CHARGE PUMP SHOWN IN DISCHARGE CYCLE
INFORMATION
U
IN
W
FLY
. The SHDN pin is a CMOS
FLY
to the output capacitor at
IN
CHARGE PUMP
S1A
S1B
voltage. Clock 2 closes
in series with V
W
S2A
S2B
IN
supply. V
IN
/2; however,
U
CLOCK 1
CLOCK 2
IN
OUT
and
IN
is
CONTROL
LOGIC
high is applied to the SHDN pin. The SHDN pin should not
be floated; it must be driven with a logic high or low.
Short-Circuit/Thermal Protection
During short-circuit conditions, the LTC1522 will draw
between 100mA and 200mA from V
the junction temperature. On-chip thermal shutdown
circuitry disables the charge pump once the junction
temperature exceeds 160 C, and reenables the charge
pump once the junction temperature falls back to 145 C.
The LTC1522 will cycle in and out of thermal shutdown
indefinitely without latchup or damage until the V
short is removed.
Capacitor Selection
For best performance, it is recommended that low ESR
(< 0.5 ) capacitors be used for both C
reduce noise and ripple. The C
should be either ceramic or tantalum and should be 3.3 F
or greater (aluminum capacitors are not recommended
because of their high ESR). If the input source impedance
is very low, C
C
OUT
to 10 F or greater will reduce output voltage ripple.
V
REF
IN
may not be needed. Increasing the size of
COMP1
+
–
1 A
IN
LTC1522 BD
and C
IN
+
causing a rise in
IN
OUT
V
C
10 F
SHDN
OUT
OUT
and C
capacitors
OUT
OUT
to