LTC1700
No R
SENSE
Synchronous
Step-Up DC/DC Controller
FEATURES
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DESCRIPTIO
High Efficiency: Up to 95%
No Current Sense Resistor Required
Constant Frequency 530kHz Operation Allows
Small Size, Surface Mount Inductors
OPTI-LOOP
®
Compensation Minimizes C
OUT
Selectable Burst Mode
®
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 are registered trademarks of Linear Technology Corporation.
No R
SENSE
is a trademark 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
LTC1700
SGND
V
FB
L1
1.8µH
SW
BG
10
8
M1
C1
22µF
M2
+
V
IN
3.3V to 4.2V
C2
68µF
6.3V
5V
2A
C6
10µF
C7
330µF
6V
Efficiency, Power Loss vs Load Current
100
90
80
EFFICIENCY (%)
C5
220pF
+
9
6
7
PGND
TG
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
1700fa
U
1.0
4.2V EFFICIENCY
70
60
50
40
30
20
10
0
0.001
0.001
0.01
0.1
LOAD CURRENT
1
2
3.3V POWER
4.2V POWER
0.01
3.3V EFFICIENCY
POWER LOSS (W)
U
U
0.1
1700 F01b
1
LTC1700
ABSOLUTE
(Note 1)
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
ORDER PART
NUMBER
TOP VIEW
SGND
I
TH
V
FB
RUN/SS
SYNC/MODE
1
2
3
4
5
10
9
8
7
6
SW
PGND
BG
V
OUT
TG
Output Supply Voltage (V
OUT
) .....................– 0.3V to 6V
RUN/SS, V
FB
Voltages ..............................– 0.3V to 2.4V
SYNC/MODE, I
TH
Voltages ...........................– 0.3V to 6V
SWITCH Voltage (SW) ..............................– 0.3V to 6.5V
TG, BG Peak Output Current (<10µs) ......................... 1A
Operating Temperature Range (Note 2) ...–40°C to 85°C
Junction Temperature (Note 3) ............................. 125°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
LTC1700EMS
MS PART
MARKING
LTLC
MS PACKAGE
10-LEAD PLASTIC MSOP
T
JMAX
= 125°C,
θ
JA
= 150°C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25
°
C. V
OUT
= 3V unless otherwise specified.
SYMBOL
V
SOP
V
OP
I
S
PARAMETER
Start-Up Minimum Operating Voltage
Minimum Operating Voltage
Hysteresis
Input DC Supply Current
Normal Mode
Sleep Mode
Start-Up Mode
Shutdown
Feedback Current
Regulated Output Voltage
Reference Voltage Line Regulation
Output Voltage Load Regulation
Output Overvoltage Lockout
Shutdown Threshold
Soft-Start Current Source
Oscillator Frequency
Start-Up Oscillator Frequency
SYNC/MODE Threshold
Maximum Duty Cycle
Maximum Current Sense Voltage
Current Limit At Start-Up
Transconductance of Error Amplifier
V
OUT
= 1.8V
V
FB
= V
REF
±
10mV
CONDITIONS
(Note 4)
(Note 5) V
OUT
Ramping Up
(Note 6)
V
FB
= 1.6V, V
MODE
= 0V, V
RUN/SS
= 3V
V
FB
= 1.6V, V
MODE
= 3V, V
RUN/SS
= 3V
V
FB
= 0V, V
MODE
, V
RUN/SS,
V
OUT
= 1.8V
V
FB
= 0V, V
MODE
= 3V, V
RUN/SS
= 0V
V
FB
= 1.20V
(Note 7)
V
IN
= 2.7V to 5V (Note 7)
Measured in Servo Loop; V
ITH
= 0.3V to 0.9V
Reference to Nominal V
FB
V
RUN/SS
Ramping Up
V
RUN/SS
= 0V
V
OUT
= 4.2V
V
OUT
= 1.8V, V
RUN/SS
= 1.8V, V
SW
= 1.1V
V
SYNC/MODE
Ramping Down from 1.2V
f
OSC
= 550kHz
●
●
●
●
ELECTRICAL CHARACTERISTICS
MIN
TYP
0.9
2.34
90
536
179
35
10
1
MAX
1.8
2.6
UNITS
V
V
mV
µA
µA
µA
µA
nA
V
%/V
%
%
V
µA
kHz
kHz
V
%
mV
mV
mA
m
620
210
45
14
50
1.223
0.080
0.065
9
1.2
6
680
1.25
92
100
I
VFB
V
FB
∆V
OSENS
V
LOADREG
V
OVL
V
RUN/SS
I
RUN/SS
f
OSC
V
SYNC/MODE
DC MAX
∆V
SENSE(MAX)
I
LIMIT
g
m
1.187
1.205
0.0106
0.036
2.5
0.7
2
460
150
1.03
84
55
63
40
0.65
4.8
1.09
3.79
530
225
1.13
88
78
60
0.9
1.30
1700fa
2
Ω
U
W
U
U
W W
W
LTC1700
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
OUT
= 3V unless otherwise specified.
SYMBOL
TG t
r
TG t
f
BG t
r
BG t
f
t
dll
t
dhh
PARAMETER
TG Transition Time
TG Gate Drive Rise Time
TG Gate Drive Fall Time
BG Transition Time
BG Gate Drive Rise Time
BG Gate Drive Fall Time
Dead Time
BG and TG Gates Go Low
BG and TG Gates Go High
CONDITIONS
C
LOAD
= 3000pF, 10% to 90%
C
LOAD
= 3000pF, 90% to 10%
C
LOAD
= 3000pF, 10% to 90%
C
LOAD
= 3000pF, 90% to 10%
C
LOAD
= 3000pF on BG and TG
C
LOAD
= 3000pF on TG and BG
MIN
TYP
60
60
80
50
88
66
MAX
100
100
100
70
110
90
UNITS
ns
ns
ns
ns
ns
ns
ELECTRICAL CHARACTERISTICS
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LTC1700E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 3:
T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formula:
T
J
= T
A
+ (P
D
• 150°C/W)
Note 4:
At an input supply less than 2.3V, only the start-up circuitry of the
LTC1700 is active. This test ensures the start-up circuitry is working.
Note 5:
An input supply at or above this minimum operating voltage
activates the main control loop. Start-up circuitry of the LTC1700 is
shut off.
Note 6:
Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency.
Note 7:
The LTC1700 is tested in a feedback loop that servos V
FB
to the
feedback point for the error amplifier (V
ITH
= 0.6V)
TYPICAL PERFORMANCE CHARACTERISTICS
Reference Voltage vs
Temperature
1.210
1.208
SHUTDOWN CURRENT (µA)
1.204
1.202
1.200
1.198
1.196
1.194
1.192
1.190
– 55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
1700 G01
14
12
10
8
6
4
2
0
1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
SUPPLY VOLTAGE (V)
1700 G02
QUIESCENT CURRENT (µA)
REFERENCE VOLTAGE (V)
1.206
U W
Shutdown Current vs Supply
Voltage
20
18
16
200
250
Quiescent Current vs Supply
Voltage
150
100
50
0
1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
SUPPLY VOLTAGE (V)
1700 G03
1700fa
3
LTC1700
TYPICAL PERFORMANCE CHARACTERISTICS
RUN/SS Current vs Temperature
6
5
1.08
1.06
NORMALIZED FREQUENCY
START-UP VOLTAGE (V)
RUN/SS CURRENT (µA)
4
3
2
1
0
– 55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
1700 G04
Maximum Current Sense Voltage
vs Temperature
90
0.16
0.14
START-UP CURRENT LIMIT (A)
SENSE VOLTAGE (mV)
0.10
0.08
0.06
0.04
0.02
EFFICIENCY (%)
80
70
60
– 55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
1700 G7
3.3V Output Efficiency, Circuit of
Figure 1 with Burst Mode
Operation
100
90
80
V
IN
= 2.7V
100
90
80
EFFICIENCY (%)
70
60
50
40
EFFICIENCY (%)
V
IN
= 2V
70
60
50
40
30
0.001
0.01
0.1
LOAD CURRENT (A)
4
U W
1.0
1700 G10
Normalized Oscillator Frequency
vs Temperature
1.4
1.2
1.0
0.8
0.6
0.4
0.2
Minimum Operating Voltage
vs Temperature
2.28
2.26
START-UP
CIRCUIT
2.24
2.22
2.20
MAIN
CONTROLLER
2.18
2.16
2.14
85 105 125
1700 G6
1.04
1.02
1.00
0.98
0.96
0.94
– 55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
1700 G5
0
– 55 –35 –15
5 25 45 65
TEMPERATURE (°C)
Start-Up Current Limit vs
Temperature
100
90
80
70
60
50
Efficiency vs Load Current
(Burst Mode Operation Disabled)
V
IN
= 4.2V
0.12
V
IN
= 3.3V
0
– 55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
1700 G8
40
0.001
0.01
0.1
LOAD CURRENT (A)
1.0
1700 G09
3.3V Output Efficiency, Circuit of
Figure 1 with Burst Mode
Operation Inhibited
A/C COUPLED
OUTPUT
VOLTAGE
(0.2V/DIV)
INDUCTOR
CURRENT
(2A/DIV)
Load Step Transient Response
Burst Mode Operation Enabled
V
IN
= 2.7V
V
IN
= 2V
30
0.001
V
IN
= 3.3V
V
OUT
= 5V
0.1
0.01
LOAD CURRENT (A)
1.0
1700 F16
2A/DIV
V
SYNC
= V
IN
LOAD STEP = 100mA TO 1.7A
1700 G12
1700fa
LTC1700
TYPICAL PERFORMANCE CHARACTERISTICS
Load Step Transient Response
Burst Mode Operation Inhibited
A/C COUPLED
OUTPUT
VOLTAGE
(0.2V/DIV)
INDUCTOR
CURRENT
(2A/DIV)
A/C COUPLED
OUTPUT
VOLTAGE
(0.2V/DIV)
INDUCTOR
CURRENT
(2A/DIV)
1700 G14
V
IN
= 3.3V
V
OUT
= 5V
2A/DIV
V
SYNC
= 0V
LOAD STEP = 100mA TO 1.7A
PIN FUNCTIONS
SGND (Pin 1):
Small-Signal Ground. Must be routed
separately from other grounds to the (–) terminal of C
OUT
.
I
TH
(Pin 2):
Error Amplifier Compensation Point. The
current comparator threshold increases with this control
voltage. Nominal voltage range for this pin is 0V to 1.18V.
V
FB
(Pin 3):
Receives the feedback voltage from an exter-
nal resistive divider across the output capacitor.
RUN/SS (Pin 4):
Combination of Soft-Start and Run
Control Inputs. A capacitor to ground at this pin sets the
ramp time to full output current. The time is approximately
0.45s/µF. Forcing this pin below 1.08V causes all circuitry
to be shut down.
SYNC/MODE (Pin 5):
This pin performs three functions. A
voltage greater than 1.2V on this pin allows Burst Mode
operation at low load currents, while grounding or apply-
ing a clock signal on this pin defeats Burst Mode operation.
An external clock between 400kHz and 750kHz applied to
this pin forces the LTC1700 to operate at the external clock
frequency.
Do not attempt to synchronize below 400kHz
or above 750kHz.
TG (Pin 6):
Top Gate Drive. Drives the external synchro-
nous P-channel MOSFET with a voltage swing between 0V
to V
OUT
.
V
OUT
(Pin 7):
This pin performs two functions. It serves as
the supply pin and also as one of the inputs to the current
reversal comparator.
BG (Pin 8):
Bottom Gate Drive. Drives the external main
N-channel MOSFET with a voltage swing between 0V to
V
OUT
.
PGND (Pin 9):
Top and Bottom Gate Drivers Ground.
Connects to the (–) terminal of C
OUT
. Source of the main
N-channel MOSFET must be connected close to this pin
since this pin is also one of the inputs to the V
DS
sense
amplifier.
SW (Pin 10):
This pin connects to the inputs of two
comparators: The V
DS
sense amplifier and the current
reversal comparator. The drain of an internal N-channel
start-up MOSFET (M1) is also connected to this pin.
U W
Load Step Transient Response
Burst Mode Operation Enabled
A/C COUPLED
OUTPUT
VOLTAGE
(0.2V/DIV)
INDUCTOR
CURRENT
(2A/DIV)
Load Step Transient Response
Burst Mode Operation Inhibited
1700 G13
1700 G15
V
IN
= 4.2V
V
OUT
= 5V
2A/DIV
V
SYNC
= V
IN
LOAD STEP = 100mA TO 1.7A
V
IN
= 4.2V
V
OUT
= 5V
2A/DIV
V
SYNC
= 0V
LOAD STEP = 100mA TO 1.7A
U
U
U
1700fa
5
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