LT1308 Просмотр технического описания (PDF) - Linear Technology
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LT1308 Datasheet PDF : 8 Pages
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APPLICATIONS INFORMATION
DECT PHONES
The DECT standard specifies a transmit pulse 416µs in
duration. The LT1308 is capable of delivering a 400mA
pulse load from a 1.2V input with output capacitance of
100µF. Figure 11 depicts VOUT transient response of
Figure 6’s circuit, configured for a 3.3V output by chang-
ing resistor R1 to 169k. Figure 12 shows detail of one
transmit pulse at a higher sweep speed.
NiCd
OR
Li-Ion
CELL
SHDN
VIN
LBI
SW
LT1308
LBO
FB
C1
VC
GND
10µF
CERAMIC
47k
33nF
L1
4.7µH
D1
MBRS120
R1
5V/1A OR
3.3V/300mA
+
100k
C2
100µF
L1: TOKO 636CY4R7M
COILTRONICS CTX5-1
FOR VOUT = 5V: R1 = 309k
FOR VOUT = 3.3V: R1 = 169k
1308F06
Figure 6. DC/DC Converter for GSM/DECT Application
VOUT
200mV/DIV
AC COUPLED
VIN = 3.6V
IL, 1A/DIV
ILOAD 1A
100mA
100µs/DIV
1308 F07
Figure 7. GSM Load Transient Response.
100mA to 1A Transient Response for Figure 6’s Circuit.
Pulse Width = 577µs
VIN = 3.6V
VOUT
200mV/ DIV
AC COUPLED
1A
ILOAD
100mA
1ms/DIV
1308 F08
Figure 8. GSM Load Transient Response. Slower
Sweep Speed (1ms/DIV) Shows VOUT over Several
Transmit Pulses
LT1308
VIN = 2.7V
VOUT
200mV/ DIV
AC COUPLED
1A
ILOAD
100mA
1ms/DIV
1308 F09
Figure 9. GSM Load Transient Response.
At Low VIN, Large Output Capacitor (2200µF)
Serves to Hold up VOUT
VOUT
200mV/ DIV
AC COUPLED
VIN = 2.7V
IL, 1A/DIV
ILOAD 1A
100mA
500µs/DIV
1308 F10
Figure 10. GSM Load Transient Response.
Faster Sweep Speed (500µs/DIV) Details VOUT
and Inductor Current of One Transmit Pulse
VOUT
200mV/ DIV
AC COUPLED
VIN = 1.2V
ILOAD 400mA
50mA
2ms/DIV
1308 F11
Figure 11. DECT Load Transient Response.
With a Single NiCd Cell the LT1308 Provides 3.3V
with 400mA Pulsed Load. Pulse Width = 416µs
VOUT
200mV/ DIV
AC COUPLED
VIN = 1.2V
IL, 1A/DIV
400mA
ILOAD 50mA
100µs/DIV
1308 F09
Figure 12. DECT Load Transient Response.
Faster Sweep Speed (100µs/DIV) Details VOUT and
Inductor Current of Single DECT Transmit Pulse
7
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