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PDF LTC1262 Data sheet ( Hoja de datos )
| Número de pieza | LTC1262 | |
| Descripción | 12V/ 30mA Flash Memory Programming Supply | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC1262
12V, 30mA Flash Memory
Programming Supply
FEATURES
s Regulated 12V ±5% Output Voltage
s No Inductors
s Supply Voltage Range: 4.75V to 5.5V
s Guaranteed 30mA Output
s Low Power: ICC = 500µA
s ICC in Shutdown: 0.5µA
s 8-Pin PDIP or SO-8 Package
APPLICATI S
s 12V Flash Memory Programming Supplies
s Compact 12V Op Amp Supplies
s Battery-Powered Systems
DESCRIPTIO
The LTC®1262 is a regulated 12V, 30mA output DC/DC
converter. It is designed to provide the 12V ±5% output
necessary to program byte-wide flash memories. The
output will provide up to 30mA from input voltages as low
as 4.75V without using any inductors. Only four external
capacitors are required to complete an extremely small
surface mountable circuit.
The TTL compatible shutdown pin can be directly con-
nected to a microprocessor and reduces the supply cur-
rent to less than 0.5µA. The LTC1262 offers improved
shutdown current performance and requires fewer exter-
nal components than competing solutions.
The LTC1262 is available in an 8-pin PDIP or SO-8
package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATI
0.22µF
0.22µF
1 C1–
SHDN 8 FROM MPU
2 C1+
GND 7
LTC1262
3 C2–
VOUT 6
+
4 C2+
VCC 5
4.7µF
+ 4.7µF
VCC
4.75V TO 5.5V
FLASH
MEMORY
VPP
VCC
LTC1262 • TA01
In/Out of Shutdown
SHDN 5V
5V/DIV 0V
12V
VOUT
5V/DIV 5V
0V
1ms/DIV
1262 TA01a
1
1 page  
LTC1262
APPLICATIONS INFORMATION
Operation
The LTC1262 uses a charge pump tripler to generate 12V
from a VCC of 5V. The charge pump operates when clocked
by a 300kHz oscillator. When the oscillator output is low,
C1 and C2 are connected between VCC and GND, charging
them to VCC. When the oscillator output goes high, C1 and
C2 are stacked in series with the bottom plate of C1 pulled
to VCC. The top plate of C2 is switched to charge COUT and
VOUT rises. VOUT is regulated to within 5% of 12V by an
oscillator pulse gating scheme. A resistor divider senses
VOUT. When the output of the divider (VDIV) is less than the
output of a bandgap (VBGAP) by the hysteresis voltage
(VHYST) of the comparator, oscillator pulses are applied to
the charge pump to raise VOUT. When VDIV is above VBGAP
by VHYST, the oscillator pulses are prevented from clock-
ing the charge pump. VOUT drops until VDIV is below VBGAP
by VHYST again. The gates of all internal switches are
driven between VOUT and GND. An internal diode ensures
that the LTC1262 will start up under load by charging COUT
to one diode drop below VCC.
To reduce supply current the LTC1262 may be put into
shutdown mode by floating the SHDN pin or taking it to
VCC. In this mode the bandgap, comparator, oscillator and
resistor divider are switched off to reduce supply current
to typically 0.5µA. At the same time an internal switch
shorts VOUT to VCC; VOUT takes 3.3ms to reach 5.1V (see
tOFF in Figure 1). When the SHDN pin is low, the LTC1262
exits shutdown and the charge pump operates to raise
VOUT to 12V. VOUT takes 500µs to reach the lower regula-
tion limit of 11.4V (see tON in Figure 1).
Choice of Capacitors
The LTC1262 is tested with the capacitors shown in
Figure 2. C1 and C2 are 0.22µF ceramic capacitors and
CIN and COUT are 4.7µF tantalum capacitors. Refer to
Table 1 if other choices are desired.
Table 1. Recommended Capacitor Types and Values
CAPACITOR
CERAMIC
TANTALUM
ALUMINUM
C1, C2
0.22µF to 1µF
Not
Not
Recommended Recommended
COUT
2µF (Min)
4.7µF (Min)
10µF (Min)
CIN
1µF (Min)
4.7µF (Min)
10µF (Min)
C1 and C2 should be ceramic capacitors with values in the
range of 0.22µF to 1µF. Higher values provide better load
regulation. Tantalum capacitors are not recommended as
the higher ESR of these capacitors degrades performance
when the load current is above 25mA with VCC = 4.75V.
CIN and COUT can be ceramic, tantalum or electrolytic
capacitors. The ESR of COUT introduces steps in the VOUT
waveform whenever the charge pump charges COUT. This
tends to increase VOUT ripple. Ceramic or tantalum capaci-
tors are recommended for COUT if minimum ripple is
desired. The LTC1262 does not require a 0.1µF capacitor
between VCC and VOUT for stability.
Maximum Load Current
The LTC1262 will source up to 50mA continuously without
any damage to itself. Do not short the VOUT pin to ground.
If the VOUT pin is shorted to ground, irreversible damage
to the device will result.
5
5 Page | ||
| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet LTC1262.PDF ] | |
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