LTC1700
No R
SENSE
Synchronous
Step-Up DC/DC Controller
FEATURES
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DESCRIPTIO
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High Efficiency: Up to 95%
No Current Sense Resistor Required
Constant Frequency 530kHz Operation Allows
Small Size, Surface Mount Inductors
OPTI-LOOP
TM
Compensation Minimizes C
OUT
Selectable Burst Mode
TM
Operation
Minimum Start-Up Voltage as low as 0.9V
Synchronizable Between 400kHz and 750kHz
Micropower Shutdown: 10µA
Current Mode Operation for Excellent Line and Load
Transient Response
Soft-Start Reduces Supply Current Transients
1.5% Output Voltage Accuracy
Uses Low Value, Small Size, Surface Mount Inductors
Available in 10-Lead MSOP Package
The LTC
®
1700 is a current mode synchronous step-up
DC/DC controller that drives external N-channel and
P-channel power MOSFETs using a constant frequency
PWM architecture. Current limiting is provided by sensing
the voltage drop across the main MOSFET, eliminating the
need of a sense resistor. This No R
SENSE
TM
technique helps
the LTC1700 maintain high efficiency at heavy loads while
Burst Mode operation ensures high efficiency at light loads,
thus providing high efficiencies over a wide range of load
currents.
The LTC1700 operates at a minimum input voltage as low as
0.9V. The device boasts a
±1.5%
output voltage accuracy and
consumes only 200µA of quiescent current. In shutdown, it
only draws 10µA.
To prevent inductor current runaway, the duty cycle is limited
to 90%. Overvoltage protection is also provided which shuts
both the external MOSFETs off when tripped.
High constant operating frequency of 530kHz allows the use
of small inductors and output capacitors. The LTC1700 can
also be synchronized between 400kHz to 750kHz. Burst
Mode operation is inhibited when the device is externally
clocked or when the SYNC/MODE pin is pulled low to reduce
noise and RF interference.
APPLICATIO S
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Cellular Telephones
Wireless Modems
RF Communications
2.5V to 3.3V, 2.5V to 5V Converters
Battery-Powered Equipment
Telecom/Network Systems
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode, OPTI-LOOP and No R
SENSE
are trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
2
R3
2200Ω
C3
220pF
4
C4
0.1µF
1
3
R2
100k
5
R1
316k
I
TH
RUN/SS
L1
1.8µH
SW
BG
10
8
M1
C1
22µF
M2
+
C2
68µF
6.3V
V
IN
3.3V to 4.2V
5V
2A
C6
10µF
LTC1700
SGND
V
FB
PGND
TG
9
6
7
+
C7
330µF
6V
EFFICIENCY (%)
C5
220pF
SYNC/MODE V
OUT
1700 • F01a
C1: CERAMIC TAIYO YUDEN LMK432BJ226MM
C2: AVX TAJB686K006R
L1: TOKO 919AS-IR8N (D104C TYPE)
C6: CERAMIC TAIYO YUDEN JMK316BJ106ML
C7: SANYO POSCAP 6TPB330M
M1: SILICONIX Si9804
M2: SILICONIX Si9803
Figure 1. High Efficiency Step-Up Converter
U
Efficiency vs Load Current
100
90
80
70
60
50
40
0.001
V
IN
= 4.2V
V
IN
= 3.3V
0.01
0.1
LOAD CURRENT (A)
1.0
1700 F01b
U
U
1
LINER [ LINEAR TECHNOLOGY ]
