LTC1433/LTC1434
450mA, Low Noise
Current Mode Step-Down
DC/DC Converters
DESCRIPTION
The LTC
®
1433/LTC1434 are monolithic pulse width modu-
lated step-down DC/DC converters. By utilizing current
mode switching techniques, they provide excellent AC and
DC load and line regulation. Both devices operate at a fixed
frequency with the LTC1434 phase-lockable to an external
clock signal.
Both devices incorporate two internal P-channel power
MOSFETs with a parallel combined resistance of 0.6Ω (at
a supply of 10V). The Adaptive Power output stage selec-
tively drives one or both of the switches at frequencies up
to 700kHz to reduce switching losses and maintain high
efficiencies at low output currents.
The LTC1433/LTC1434 are capable of supplying up to
450mA of output current and boasts a
±2.4%
output
voltage accuracy. An internal low-battery detector has the
same level of accuracy as the output voltage. A power-on
reset timer (POR) is included which generates a signal
delayed by 65536/f
CLK
(300ms typ) after the output is
within 5% of the regulated output voltage.
Ideal for current sensitive applications, the devices draw
only 470µA of quiescent current. In shutdown the devices
draw a mere 15µA. To further maximize the life of the
battery source, the internal P-channel MOSFET switch is
turned on continuously in dropout.
FEATURES
s
s
s
s
s
s
s
s
s
s
s
s
High Efficiency: Up to 93%
Constant Frequency Adaptive Power
TM
Operation
Input Voltage Range: 3V to 13.5V
Internal 0.6Ω Power Switch (V
IN
= 10V)
Low Dropout Operation: 100% Duty Cycle
Low-Battery Detector
Internal Power-On Reset Timer
Current Mode Operation for Excellent Line and Load
Transient Response
Low Quiescent Current: 470µA
Shutdown Mode Draws Only 15µA Supply Current
±1%
Reference Accuracy
Available in 16- and 20-Lead Narrow SSOP
APPLICATIONS
s
s
s
s
s
s
s
Cellular Telephones
Portable Instruments
Wireless Modems
RF Communications
Distributed Power Systems
Scanners
Battery-Powered Equipment
, LTC and LT are registered trademarks of Linear Technology Corporation.
Adaptive Power is a trademark of Linear Technology Corporation.
TYPICAL APPLICATION
0.1µF
D1
L1
100µH
1
2
3
4
5
6
0.1µF
7
8
SSW
NC
BSW
NC
LTC1433
68µF**
20V
100
16
PWRV
IN
PGND 15
SV
IN
C
OSC
POR
I
TH
V
OSENSE
V
PROG
14
13
12
11
10
9
6800pF
D1: MOTOROLA MBRS130LT3 *AVX TPSD107M010R0100
** AVX TPSE686M020R0150
L1: COILCRAFT D03316-104
1433/34 F01
V
IN
3.5V TO 12V
90
+
100µF*
10V
EFFICIENCY (%)
V
OUT
3.3V
10k
80
70
V
IN
= 9V
60
50
40
0.001
SGND
RUN/SS
LBO
LBI
POWER-ON
RESET
5.1k
680pF
47pF
Figure 1. High Efficiency Step-Down Converter
U
U
U
LTC1433 Efficiency for
V
OUT
= 3.3V
V
IN
= 5V
V
IN
= 12V
+
0.01
0.1
LOAD CURRENT (A)
1
1433/34 TA01
1
LTC1433/LTC1434
ABSOLUTE
AXI U
RATI GS
(Voltages Referred to PGND Pin)
Input Supply Voltage (PWRV
IN
, SV
IN
) ... 13.5V to – 0.3V
DC Small Switch Current (SSW) ......................... 100mA
Peak Small Switch Current (SSW) ..................... 300mA
Small Switch Voltage
(SSW) ................................(V
IN
+ 0.3V) to (V
IN
– 13.5V)
DC Large Switch Current (BSW) ....................... 600mA
Peak Large Switch Current (BSW) .......................... 1.2A
Large Switch Voltage
(BSW) ................................(V
IN
+ 0.3V) to (V
IN
– 13.5V)
PLLIN, PLL LPF, I
TH
, C
OSC
........................2.7V to – 0.3V
POR, LBO .................................................. 12V to – 0.3V
LBI, V
OSENSE
..............................................10V to – 0.3V
PACKAGE/ORDER I FOR ATIO
TOP VIEW
SSW
NC
BSW
NC
SGND
RUN/SS
LBO
LBI
1
2
3
4
5
6
7
8
16 PWRV
IN
15 PGND
14 SV
IN
13 C
OSC
12 POR
11 I
TH
10 V
OSENSE
9
V
PROG
ORDER PART
NUMBER
LTC1433CGN
LTC1433IGN
GN PACKAGE
16-LEAD PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 150°C/ W
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
T
A
= 25°C, V
IN
= 10V, V
RUN/SS
= 5V, unless otherwise noted. (Notes 2, 3)
SYMBOL
I
IN
V
OSENSE
V
OSENSE
PARAMETER
Feedback Current
Regulated Output Voltage
1.19V (Adjustable) Selected
3.3V Selected
5V Selected
Output Overvoltage Lockout
Reference Voltage Line Regulation
Output Voltage Load Regulation
CONDITIONS
V
PROG
Pin Open (Note 5)
(Note 5)
V
PROG
Pin Open
V
PROG
= 0V
V
PROG
= V
IN
V
PROG
Pin Open
V
IN
= 3.6V to 13V (Note 5), V
PROG
Pin Open
I
TH
Sinking 5µA (Note 5)
I
TH
Sourcing 5µA (Note 5)
q
q
q
q
q
Main Control Loop
10
1.178
3.220
4.880
1.24
1.190
3.300
5.000
1.28
0.002
0.5
– 0.5
50
1.202
3.380
5.120
1.32
0.01
0.8
– 0.8
nA
V
V
V
V
%/V
%
%
V
OVL
∆V
OSENSE
V
LOADREG
2
U
U
W
W W
U
W
(Note 1)
RUN/SS, V
PROG
Voltages
V
IN
≥
11.7V ...........................................12V to – 0.3V
V
IN
< 11.7V ............................... (V
IN
+ 0.3V) to – 0.3V
Commercial Temperature Range
LTC1433C/LTC1434C .............................. 0°C to 70°C
Extended Commercial Operating Temperature
Range (Note 2) ....................................... – 40°C to 85°C
Industrial Temperature Range (Note 3)
LTC1433I/LTC1434I ........................... – 40°C to 85°C
Junction Temperature (Note 4)............................. 125°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
TOP VIEW
NC
SSW
NC
BSW
SGND
NC
RUN/SS
NC
LBO
1
2
3
4
5
6
7
8
9
20 PWRV
IN
19 PGND
18 SV
IN
17 PLLIN
16 PLL LPF
15 C
OSC
14 POR
13 I
TH
12 V
OSENSE
11 V
PROG
ORDER PART
NUMBER
LTC1434CGN
LTC1434IGN
LBI 10
GN PACKAGE
20-LEAD PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 150°C/ W
MIN
TYP
MAX
UNITS
LTC1433/LTC1434
ELECTRICAL CHARACTERISTICS
T
A
= 25°C, V
IN
= 10V, V
RUN/SS
= 5V, unless otherwise noted.
SYMBOL
I
PROG
PARAMETER
V
PROG
Input Current
CONDITIONS
0.5V > V
PROG
V
IN
– 0.5V < V
PROG
< V
IN
(Note 6)
3.6V < V
IN
< 13V
V
RUN/SS
= 0V, 3.6V < V
IN
< 13V, LBI > 0.9V
V
RUN/SS
= 0V, 3.6V < V
IN
< 13V, LBI
≤
0.48V
q
MIN
TYP
–4
4
MAX
– 10
10
UNITS
µA
µA
Main Control Loop
I
Q
Input DC Supply Current
Normal Mode
Shutdown, Reference Alive
Complete Shutdown
RUN/SS Threshold
Soft Start Current Source
Oscillator Frequency
V
CO
High
PLL Input Resistance
Phase Detector Output Current
Sinking Capability
Sourcing Capability
POR Saturation Voltage
POR Leakage
POR Trip Voltage from Regulated
Output
POR Delay
LBO Saturation Voltage
LBO Leakage
LBI Trip Voltage
Low-Battery Comparator Hysteresis
Low-Battery Shutdown Trip Point
LBI Input Current
R
DS(ON)
of Small FET
R
DS(ON)
of Big FET
Small FET Leakage
Big FET Leakage
V
LBI
= 1.19V
I
SSW
= 15mA
I
BSW
= 150mA
V
RUN/SS
= 0V
V
RUN/SS
= 0V
q
q
470
35
15
0.8
1.2
112
200
1.3
3
125
240
50
70
30
2
4.5
142
µA
µA
µA
V
µA
kHz
kHz
kΩ
V
RUN/SS
I
RUN/SS
f
OSC
R
PLLIN
I
PLL LPF
V
RUN/SS
= 0V
C
OSC
= 100pF (Note 7)
V
PLL LPF
= 2.4V
Oscillator and Phase-Locked Loop
f
PLLIN
< f
OSC
f
PLLIN
> f
OSC
I
POR
= 1.6mA, V
OSENSE
= 1V, V
PROG
Open
V
POR
= 10V, V
OSENSE
= 1.2V, V
PROG
Open
V
PROG
Pin Open, V
OSENSE
Ramping Negative
V
PROG
Pin Open
I
LBO
= 1.6mA, V
LBI
= 1.1V
V
LBO
= 10V, V
LBI
= 1.4V
High to Low Transition on LBO
10
10
15
15
0.6
0.2
20
20
1.0
1.0
–4
µA
µA
V
µA
%
Cycles
Power-On Reset
V
SATPOR
I
LPOR
V
TRPOR
t
DPOR
V
SATLBO
I
LLBO
V
TRLBI
V
HYSTLB
V
SDLB
I
INLBI
R
SMFET
R
BIGFET
I
LSSW
I
LBSW
– 11
– 7.5
65536
0.6
0.01
Low-Battery Comparator
1.0
1.0
1.22
V
µA
V
mV
V
50
4.1
1.2
1000
1000
nA
Ω
Ω
nA
nA
1.16
1.19
40
0.74
1
3.3
0.8
7
5
P-Channel Power FETs Characteristics
The
q
denotes specifications which apply over the specified temperature
range.
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
C-grade device specifications are guaranteed over the 0°C to 70°C
temperature range. In addition, C-grade device specifications are assured
over the – 40°C to 85°C temperature range by design or correlation, but
are not production tested.
Note 3:
I-grade device specifications are guaranteed over the – 40°C to
85°C temperature range by design, testing or correlation.
Note 4:
T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formula:
LTC1433/LTC1434: T
J
= T
A
+ (P
D
)(150°C/W)
Note 5:
The LTC1433/LTC1434 are tested in a feedback loop which servos
V
OSENSE
to the feedback point for the error amplifier (V
ITH
= 1.19V).
Note 6:
Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency.
Note 7:
Oscillator frequency is tested by measuring the C
OSC
charge and
discharge currents and applying the formula:
8.4(10
8
)
1 + 1
–1
f
OSC
(kHz) = C
OSC
(pF) + 11 I
CHG
I
DIS
(
)(
)
3
LTC1433/LTC1434
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency of Figure 1 for L = 22µH
100
V
IN
= 3.6V
90
460
480
SUPPLY CURRENT (µA)
OUTPUT VOLTAGE (V)
EFFICIENCY (%)
80
70
V
IN
= 5V
V
IN
= 12V
60
50
40
0.001
V
OUT
= 3.3V
L = 22µH
C
SOC
= 47pF
0.01
0.1
LOAD CURRENT (A)
1
1433/34 G01
Dropout Characteristics at Different
Load Currents (V
OUT
= 5V)
5.1
800
MAXIMUM OUTPUT CURRENT (mA)
5.0
4.9
OUTPUT VOLTAGE (V)
REFERENCE VOLTAGE (V)
I
OUT
200mA
I
OUT
400mA
I
OUT
300mA
4.8
4.7
4.6
4.5
4.4
4.3
4.2
4.6
4.8
V
PROG
= V
IN
L = 20µH
C
OSC
= 50pF
5.0 5.2 5.4 5.6 5.8
SUPPLY VOLTAGE (V)
6.0
6.2
Switch Resistance of Small FET
8
7
R
DS(ON)
OF SMALL FET (Ω)
R
DS(ON)
OF BIG FET (Ω)
6
5
4
3
2
1
0
T
A
= 0°C
T
A
= 25°C
T
A
= 70°C
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
3
4
5
6 7 8 9 10 11 12 13
SUPPLY VOLTAGE (V)
1433/34 G07
SWITCH LEAKAGE AT SSW PIN (nA)
4
U W
1433/34 G04
Supply Current vs Supply Voltage
3.4
3.3
Dropout Characteristics at Different
Load Currents (V
OUT
= 3.3V)
I
OUT
3.2 300mA
3.1
3.0
2.9
2.8
2.7
2.6
2.5
I
OUT
400mA
I
OUT
500mA
V
PROG
= 0V
L = 20µH
C
OSC
= 50pF
440
420
400
380
360
3
4
8
9
6
5
7
SUPPLY VOLTAGE (V)
10
11
2.4
3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 5.2
SUPPLY VOLTAGE (V)
1433/34 G03
1433/34 G02
Maximum Output Current
vs Input Supply
1.202
L = 22µH
C
OSC
= 50pF
V
OUT
3.3V
1.198
1.194
1.190
1.186
1.182
1.178
1.174
3
5
9
11
7
SUPPLY VOLTAGE (V)
13
1433/34 G05
Reference Voltage
vs Temperature
700
600
500
400
300
200
V
OUT
5V
1.170
– 45 – 25
–5
15 35 55 75
TEMPERATURE (°C)
95
115
1433/34 G06
Switch Resistance of Big FET
70
60
50
40
30
20
10
0
Switch Leakage Current
vs Temperature
280
V
IN
= 13.5V
SWITCH LEAKAGE AT BSW PIN (nA)
240
200
160
120
80
SSW PIN
BSW PIN
40
0
140
T
A
= 25°C
T
A
= 70°C
T
A
= 0°C
0
3
4
5
6 7 8 9 10 11 12 13
SUPPLY VOLTAGE (V)
1433/34 G08
0
20
80
60
100
40
TEMPERATURE (°C)
120
1433/34 G09
LTC1433/LTC1434
PIN FUNCTIONS
SSW (Pin 1/Pin 2):
Drain of the Small P-Channel MOSFET
Switch.
BSW (Pin 3/Pin 4):
Drain of the Large P-Channel MOSFET
Switch.
SGND (Pin 5):
Small-Signal Ground. Must be routed
separately from other grounds to the (–) terminal of C
OUT
.
RUN/SS (Pin 6/Pin 7):
Combination of Soft Start and Run
Control Inputs. A capacitor to ground at this pin sets the
ramp time to full current output. The time is approxi-
mately 0.5s/µF. Forcing this pin below 1.3V causes all
circuitry to be shut down except the low-battery com-
parator. For input voltages above 6V this pin is clamped by
a 6V Zener (see Functional Diagram). Applying voltages
greater than 6V to this pin will cause additional current to
flow into this pin.
LBO (Pin 7/Pin 9):
Open-Drain Output of an N-Channel
Pull-Down. This pin will sink current when LBI goes below
1.19V.
LBI (Pin 8/Pin 10):
The (+) Input of the Low-Battery
Voltage Comparator. The (–) input is connected to the
1.19V reference. When LBI is grounded along with RUN/
SS, this comparator will shut down along with the rest of
the control circuitry. LBO will go to high impedance.
V
PROG
(Pin 9/Pin 11):
The voltage at this pin selects the
output voltage. When V
PROG
= 0V or V
PROG
= V
IN
, the
output is set to 3.3V and 5V respectively, with V
OSENSE
connected to the output. Leaving V
PROG
open (DC) allows
the output voltage to be set by an external resistive divider.
V
OSENSE
is then connected to the common node of the
resistive divider.
V
OSENSE
(Pin 10/Pin 12):
This pin receives the feedback
voltage either from the output or from an external resistive
divider across the output. The V
PROG
pin determines at
which point V
OSENSE
must be connected.
V
PROG
= 0V
V
PROG =
V
IN
V
PROG
= Open (DC)
V
OUT
= 3.3V
V
OUT
= 5V
V
OUT
= Adjustable
U
U
U
(LTC1433/LTC1434)
I
TH
(Pin 11/Pin 13):
Error Amplifier Compensation Point.
The current comparator threshold increases with this
control voltage. Nominal voltage range for this pin is 0V
to 2.4V.
POR (Pin 12/Pin 14):
Open-Drain Output of an N-Chan-
nel Pull-Down. This pin sinks current when the output
voltage is 7.5% out of regulation. When the output rises
to – 5% of its regulated value, the pin goes into high
impedance after 2
16
(65536) oscillator cycles. The POR
output is asserted when the device is in shutdown,
independent of V
OUT
.
C
OSC
(Pin 13/Pin 15):
External capacitor connects be-
tween this pin and ground to set the operating frequency.
PLL LPF (Pin 16 LTC1434):
Output of the Phase Detector
and Control Input of the Oscillator. Normally a series RC
lowpass network is connected from this pin to ground. Tie
this pin to SGND in applications which do not use the
phase-locked loop. Can be driven by a 0V to 2.4V logic
signal for a frequency shifting option.
PLLIN (Pin 17 LTC1434):
External Synchronizing Input to
the Phase Detector. This pin is internally terminated to
SGND with 50kΩ. Tie this pin to SGND in applications
which do not use the phase-locked loop.
SV
IN
(Pin 14/Pin 18):
Main Supply for All the Control
Circuitry.
PGND (Pin 15/Pin 19):
Switch Driver Ground. Connects to
the (–) terminal of C
IN
. Anode of the Schottky diode must
be connected close to this pin.
PWRV
IN
(Pin 16/Pin 20):
Supply for the Internal Power
MOSFETs and Switch Drivers. Must decouple this pin
properly to ground.
NC (Pins 2, 4,/Pins 1, 3, 6, 8):
No Connection.
5
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