LTC1522 Linear Technology, LTC1522 Datasheet - Page 6

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

APPLICATIONS
LTC1522
6
The LTC1522 must be out of shutdown for a minimum
duration of 200 s to allow enough time to sense the output
and keep it in regulation. A 2Hz, 98% duty cycle signal will
keep V
V
part is taken out of shutdown must also be increased to
prevent V
phase (see Figure 3b). A 100Hz 98% duty cycle signal on
the SHDN pin ensures proper regulation with load currents
as high as 100 A. When load current greater than 100 A
is needed, the SHDN pin must be forced low as in normal
operation. The typical no-load supply current for this
circuit with V
Figure 3a. No-Load I
OUT
2.7V TO 5V
load current increases, the frequency with which the
OUT
V
IN
OUT
6.0
4.0
2.0
0.0
in regulation under no-load conditions. As the
+
2.0
IN
5V 4%
from drooping below 4.8V during the OFF
V
OUT
10 F
= 3V is only 2.1 A.
+
U
CC
vs Input Voltage for Circuit in Figure 3
INPUT VOLTAGE (V)
10 F
3.0
INFORMATION
U
1
2
3
4
NC
V
V
C
IN
OUT
+
Figure 2. Ultralow Quiescent Current (<2.1 A) Regulated Supply
4.0
LTC1522
0.22 F
W
SHDN
GND
NC
C
1522 F03a
–
5.0
8
7
6
5
U
FROM MPU
SHDN PIN WAVEFORMS:
LOW I
I
OUT
Each time the LTC1522 comes out of shutdown, the part
delivers a minimum of one clock cycle worth of charge to
the output. Under high V
conditions, this behavior may cause a net excess of charge
to be delivered to the output capacitor if a high frequency
signal is used on the SHDN pin (e.g., 50Hz to 100Hz).
Under such conditions, V
may even go out of regulation. To avoid this potential
problem in the low I
part in and out of shutdown at the minimum allowable
frequency (refer to Figure 3b) for a given output load.
Figure 3b. Maximum SHDN OFF Time vs Output Load Current
for Ultralow I
Q
100 A
MODE (2Hz TO 100Hz, 95% TO 98% DUTY CYCLE)
1000
100
10
1
Q
1
Operation
Q
OUTPUT CURRENT ( A)
SHDN ON PULSE WIDTH = 200 s
C
OUT
mode, it is necessary to switch the
10
IN
= 10 F
(> 3.3V) and/or low I
OUT
will slowly drift positive and
100
V
(I
OUT
OUT
LOAD ENABLE MODE
= 100 A TO 20mA)
1522 F03b
1000
OUT
(< 10 A)
1522 F02