LTC1700 Datasheet, PDF (1/16 Pages) Linear Technology – No RSENSE Synchronous Step-Up DC/DC Controller

LTC1700
No R_SENSE Synchronous
Step-Up DC/DC Controller
FEATURES
DESCRIPTIO
s _{High Efficiency: Up to 95%}
s _{No Current Sense Resistor Required}
s _{Constant Frequency 530kHz Operation Allows}
Small Size, Surface Mount Inductors
s _OPTI-LOOP^TM _{Compensation Minimizes COUT}
s _{Selectable Burst Mode}^TM _Operation
s _{Minimum Start-Up Voltage as low as 0.9V}
s _{Synchronizable Between 400kHz and 750kHz}
s _{Micropower Shutdown: 10µA}
s _{Current Mode Operation for Excellent Line and Load}
Transient Response
s _{Soft-Start Reduces Supply Current Transients}
s _{1.5% Output Voltage Accuracy}
s _{Uses Low Value, Small Size, Surface Mount Inductors}
s _{Available in 10-Lead MSOP Package}
U
APPLICATIO S
s _{Cellular Telephones}
s _{Wireless Modems}
s _{RF Communications}
s _{2.5V to 3.3V, 2.5V to 5V Converters}
s _{Battery-Powered Equipment}
s _{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.
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.
TYPICAL APPLICATIO
C5
220pF
R3
2200Ω
C3
220pF
R2
100k
R1
316k
2
I_TH
4
RUN/SS
10
SW
8
BG
C4
0.1µF
LTC1700
1
SGND
9
PGND
3
V_FB
6
TG
5
7
SYNC/MODE V_OUT
L1
1.8µH
C1 ⁺
22µF
M2
M1
V_IN
C2 ^{3.3V to 4.2V}
68µF
6.3V
C6
10µF
+
5V
2A
C7
330µF
6V
C1: CERAMIC TAIYO YUDEN LMK432BJ226MM
C2: AVX TAJB686K006R
L1: TOKO 919AS-IR8N (D104C TYPE)
C6: CERAMIC TAIYO YUDEN JMK316BJ106ML
C7: SANYO POSCAP 6TPB330M
1700 • F01a
M1: SILICONIX Si9804
M2: SILICONIX Si9803
Figure 1. High Efficiency Step-Up Converter
Efficiency vs Load Current
100
V_IN = 4.2V
90
80
V_IN = 3.3V
70
60
50
40
0.001
0.01
0.1
LOAD CURRENT (A)
1.0
1700 F01b
1