LTC1263 Linear Technology, LTC1263 Datasheet - Page 5

• Manufacturer Part Number: LTC1263
• Description: 12V/ 60mA Flash Memory Programming Supply
• Manufacturer: Linear Technology

OPERATION
APPLICATIONS
Choice of Capacitors
The LTC1263 is tested with the capacitors shown in Figure
2. C1 and C2 are 0.47 F ceramic capacitors and C
C
other choices are desired.
Table 1. Recommended Capacitor Types and Values
The LTC1263 uses a charge pump tripler to generate 12V
from a V
internal oscillator. The oscillator frequency is not critical
and may vary from the typical value of 300kHz. When the
oscillator output is low, C1 and C2 are each connected
between V
3). When the oscillator output goes high, C1 and C2 are
stacked in series with the bottom plate of C1 pulled to V
(see Figure 4). The top plate of C2 is switched to charge
C
V
gating scheme that turns the charge pump on and off
based on the comparator results of V
voltage. First, a resistor divider senses V
of the divider (V
(V
tor, then oscillator pulses are applied to the charge pump
to raise V
CAPACITOR
OUT
OUT
OUT
C1, C2
BGAP
C
C
OUT
IN
, which enables V
is regulated to within 5% of 12V by an oscillator pulse
are 10 F tantalum capacitors. Refer to Table 1 if
) by the hysteresis voltage (V
CC
OUT
CC
0.47 F to 1 F
of 5V. The charge pump is clocked by an
10 F (Min)
10 F (Min)
CERAMIC
and GND, charging them to V
. When V
Figure 3. C1 and C2 Charge to V
DIV
U
) is less than the output of a bandgap
U
OUT
+
DIV
C1
INFORMATION
Not Recommended Not Recommended
V
U
is above V
to rise.
CC
TANTALUM
10 F (Min)
10 F (Min)
+
LTC1263 • F03
C2
HYST
W
OUT
BGAP
) of the compara-
OUT
CC
and a reference
CC
by V
; if the output
ALUMINUM
10 F (Min)
10 F (Min)
(see Figure
U
HYST
IN
, the
and
CC
C1 and C2 should be ceramic capacitors with values in the
range of 0.47 F to 1 F. Higher values provide better load
regulation. Tantalum capacitors are not recommended as
the higher ESR of these capacitors degrades performance
at high load currents and V
C
capacitors. The ESR of C
waveform whenever the charge pump charges C
tends to increase V
tors are recommended for C
oscillator pulses are prevented from clocking the charge
pump. As a result, V
V
To ensure proper start-up when V
and maintain proper operation when V
V
GND and the higher of either V
To reduce supply current, the LTC1263 may be put into
shutdown mode by “floating” the SHDN pin or connecting
it to V
tor and resistor divider are switched off to reduce the
supply current to typically 0.5 A. At the same time an
internal switch shorts V
to reach 5.1V (see t
is low, the LTC1263 exits shutdown and the charge pump
operates to raise V
reach the lower regulation limit of 11.4V (see t
HYST
CC
IN
Figure 4. C1 and C2 Stacked in Series with C1
, the gates of all internal switches are driven between
and C
CC
again.
. In this mode, the bandgap, comparator, oscilla-
OUT
V
CC
can be ceramic, tantalum or electrolytic
+
OUT
OUT
OUT
OFF
C1
ripple. Ceramic or tantalum capaci-
to 12V. V
OUT
drops until V
in Figure 1). When the SHDN pin
OUT
CC
to V
+
introduces steps in the V
= 4.75V.
OUT
OUT
CC
C2
OUT
; V
LTC1263 • F04
OUT
if minimum ripple is
or V
DIV
OUT
takes 600 s (typ) to
C
OUT
V
OUT
is lower than V
OUT
is below V
CC
takes 10ms (typ)
LTC1263
.
ON
–
is higher than
Tied to V
in Figure 1).
OUT
BGAP
. This
CC
5
OUT
by
CC