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LTC1876EG#PBF

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LTC1876
1
1876fa
APPLICATIO S
U
FEATURES
DESCRIPTIO
U
TYPICAL APPLICATIO
U
High Efficiency, 2-Phase,
Dual Synchronous Step-Down Switching
Controller and Step-Up Regulator
The LTC
®
1876 is a high performance triple output switching
regulator. It incorporates a dual step-down switching con-
troller that drives all N-channel synchronous power MOSFET
stages. A step-up regulator with an internal 1A, 36V switch
provides the third output.
The step-down controllers minimize power loss and noise
by operating the output stage of each controller out of
phase. OPTI-LOOP compensation allows the transient
response to be optimized over a wide range of output
capacitance and ESR values. A RUN/SS pin for each
controller provides both soft-start and an optional timed,
short-circuit shutdown that can be configured to latch off
one or both controllers. Current foldback provides
additional short-circuit protection. In an overvoltage
condition, the bottom MOSFET is latched on until V
OUT
returns to normal. The FCB pin can be used to inhibit Burst
Mode operation or to enable regulation of a secondary
output voltage.
The step-up regulator operates at 1.2MHz, allowing the
use of tiny low cost capacitors and inductors. In addition,
its internal 1A switch allows high current outputs to be
generated. Its current mode control scheme provides
excellent line and load regulation.
Step-Down Controller
■
Out-of-Phase Controllers Reduce Required Input
Capacitance and Power Supply Induced Noise
■
Power Good Output Voltage Indicator
■
OPTI-LOOP
TM
Compensation Minimizes C
OUT
■
DC Programmed Fixed Frequency 150kHz to 300kHz
■
Wide V
IN
Range: 3.5V to 36V Operation
■
Very Low Dropout Operation: 99% Duty Cycle
■
Adjustable Soft-Start Current Ramping
■
Latched Short-Circuit Shutdown with Defeat Option
■
Remote Output Voltage Sense and OV Protection
■
5V and 3.3V Standby Regulators
■
Selectable Const. Freq. or Burst Mode
TM
Operation
Step-Up Regulator
■
High Operating Switching Frequency of 1.2MHz
■
Low Internal V
CESAT
Switch: 400mV @ 1A, V
IN
= 3V
■
Wide V
IN
Range: 2.6V to 16V Operation
■
High Output Voltage: Up to 34V
■
3.3V Input Step-Down Converter
■
Notebook and Palmtop Computers, PDAs
■
Battery-Operated Digital Devices
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode and OPTI-LOOP are trademarks of Linear Technology Corporation.
Figure 1. High Efficiency Triple 5V/3.3V/12V Power Supply
4.7µF
10V
M4
M3
0.1µF
63.4k
1%
1000pF
6.3µH
220pF
1µF
CER
33µF
35V
ALUM
10µF
35V
CER
+
56µF
4V
SP
0.01Ω
20k
1%
15k
V
OUT2
3.3V
5A
M2
M1
0.1µF
105k
1%
6.8µH
220pF
1000pF
+
+
+
+
47µF
6.3V
SP
0.01Ω
20k
1%
10.2k
1%
15k
V
OUT1
5V
4A
V
OUT3
12V
200mA
TG2 TG1
BOOST2 BOOST1
SW2 SW1
BG2 BG1
PGND
PGOOD
AUXSW
AUXV
FB
AUXSD
SENSE2
+
SENSE1
+
SENSE2
–
SENSE1
–
V
OSENSE2
V
OSENSE1
I
TH2
I
TH1
AUXV
IN
V
IN
INTV
CC
RUN/SS2 RUN/SS1
V
IN
5.2V
TO 28V
M1, M2, M3, M4: FDS6680A
1876 TA01
0.1µF
0.1µF
LTC1876
SGND
86.6k, 1%
10µH
10µF
20V
LTC1876
2
1876fa
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Main Control Loops
V
OSENSE1, 2
Regulated Feedback Voltage I
TH1, 2
Voltage = 1.2V (Note 4) ● 0.792 0.800 0.808 V
I
VOSENSE1, 2
Feedback Current (Note 4) –5 –50 nA
V
REFLNREG
Reference Voltage Line Regulation V
IN
= 3.6V to 30V (Note 4) 0.002 0.02 %/V
V
LOADREG
Output Voltage Load Regulation (Note 4)
Measured in Servo Loop; ∆I
TH
Voltage = 1.2V to 0.7V ● 0.1 0.5 %
Measured in Servo Loop; ∆I
TH
Voltage = 1.2V to 2V ● –0.1 –0.5 %
g
m1, 2
Transconductance Amplifier g
m
I
TH1, 2
= 1.2V; Sink/Source 5µA; (Note 4) 1.3 mmho
g
mOL1, 2
Transconductance Amplifier GBW I
TH1, 2
= 1.2V; (Note 4) 3 MHz
I
Q
Input DC Supply Current (Note 5)
Normal Mode V
IN
= 15V; EXTV
CC
Tied to V
OUT1
; V
OUT1
= 5V 350 µA
Standby V
RUN/SS1, 2
= 0V, V
STBYMD
> 2V 125 µA
Shutdown V
RUN/SS1, 2
= 0V, V
STBYMD
= Open 20 35 µA
V
FCB
Forced Continuous Threshold ● 0.76 0.800 0.84 V
I
FCB
Forced Continuous Current V
FCB
= 0.85V –0.3 –0.18 –0.1 µA
V
BINHIBIT
Burst Inhibit (Constant Frequency) Measured at FCB pin 4.3 4.8 V
Threshold
Input Supply Voltage (V
IN
).........................36V to –0.3V
Topside Driver Voltages
(BOOST1, BOOST2) ...................................42V to –0.3V
Switch Voltage (SW1, SW2) .........................36V to –5V
INTV
CC,
EXTV
CC
, RUN/SS1, RUN/SS2, PGOOD,
(BOOST1-SW1), (BOOST2-SW2), ...............7V to –0.3V
SENSE1
+
, SENSE2
+
, SENSE1
–
, SENSE2
–
Voltages ...................................(1.1)INTV
CC
to –0.3V
FREQSET, STBYMD, FCB, PGOOD
Voltages ..................................................7V to –0.3V
I
TH1,
I
TH2
, V
OSENSE1
, V
OSENSE2
Voltages ...2.7V to –0.3V
Peak Output Current <10µs (TG1, TG2, BG1, BG2) ... 3A
INTV
CC
Peak Output Current ................................ 50mA
AUXV
IN
..................................................................
16V to –0.3V
AUXSD..................................................................... 10V
AUXSW..................................................... 36V to –0.3V
AUXV
FB
Voltage ....................................... 2.5V to –0.3V
Current into AUXV
FB
.......................................................
±1mA
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
ORDER PART
NUMBER
T
JMAX
= 125°C, θ
JA
= 95°C/W
Consult factory for parts specified with wider operating temperature ranges.
LTC1876EG
ABSOLUTE AXI U RATI GS
W
WW
U
PACKAGE/ORDER I FOR ATIO
UUW
(Note 1)
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V, V
RUN/SS1, 2
= 5V, AUXV
IN
= 3V unless otherwise noted.
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TOP VIEW
G PACKAGE
36-LEAD PLASTIC SSOP
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PGOOD
TG1
SW1
BOOST1
V
IN
BG1
EXTV
CC
INTV
CC
PGND
BG2
BOOST2
SW2
TG2
RUN/SS2
AUXSD
AUXV
IN
AUXPGND
AUXPGND
RUN/SS1
SENSE1
+
SENSE1
–
V
OSENSE1
FREQSET
STBYMD
FCB
I
TH1
SGND
3.3V
OUT
I
ITH2
V
OSENSE2
SENSE2
–
SENSE2
+
AUXSGND
AUXV
FB
AUXSW
AUXSW
LTC1876
3
1876fa
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
UVLO Undervoltage Lockout V
IN
Ramping Down ● 3.5 4 V
V
OVL
Overvoltage Feedback Threshold Measured at V
OSENSE1, 2
● 0.84 0.86 0.88 V
I
SENSE
Sense Pins Total Source Current (Each Channel); V
SENSE1
–
, 2
–
= V
SENSE1
+
, 2
+
= 0V –85 –60 µA
V
STBYMD
MS Master Shutdown Threshold V
STBYMD
Ramping Down 0.4 0.6 V
V
STBYMD
KA Keep-Alive Power On-Threshold V
STBYMD
Ramping Up, RUN
SS1, 2
= 0V 1.5 2 V
DF
MAX
Maximum Duty Factor In Dropout 98 99.4 %
I
RUN/SS1, 2
Soft-Start Charge Current V
RUN/SS1, 2
= 1.9V 0.5 1.2 µA
V
RUN/SS1, 2
ON RUN/SS Pin ON Threshold V
RUN/SS1,
V
RUN/SS2
Rising 1.0 1.5 1.9 V
V
RUN/SS1, 2
LT RUN/SS Pin Latchoff Arming Threshold V
RUN/SS1,
V
RUN/SS2
Rising from 3V 4.1 4.5 V
I
SCL1, 2
RUN/SS Discharge Current Soft Short Condition V
OSENSE1, 2
= 0.5V; 0.5 2 4 µA
V
RUN/SS1, 2
= 4.5V
I
SDLHO
Shutdown Latch Disable Current V
OSENSE1, 2
=0.5V 1.6 5 µA
V
SENSE(MAX)
Maximum Current Sense Threshold V
OSENSE1, 2
= 0.7V
,
V
SENSE1
–
, 2
–
= 5V ● 62 75 88 mV
TG Transition Time:
TG1, 2 t
r
Rise Time C
LOAD
= 3300pF 50 90 ns
TG1, 2 t
f
Fall Time C
LOAD
= 3300pF 50 90 ns
BG Transition Time:
BG1, 2 t
r
Rise Time C
LOAD
= 3300pF 40 90 ns
BG1, 2 t
f
Fall Time C
LOAD
= 3300pF 40 80 ns
TG/BG t
1D
Top Gate Off to Bottom Gate On Delay
Synchronous Switch-On Delay Time C
LOAD
= 3300pF Each Driver 90 ns
BG/TG t
2D
Bottom Gate Off to Top Gate On Delay
Top Switch-On Delay Time C
LOAD
= 3300pF Each Driver 90 ns
t
ON(MIN)
Minimum ON-Time Tested with a Square Wave (Note 7) 180 ns
INTV
CC
Linear Regulator
V
INTVCC
Internal V
CC
Voltage 6V < V
IN
< 30V, V
EXTVCC
= 4V 4.8 5.0 5.2 V
V
LDO
INT INTV
CC
Load Regulation I
CC
= 0 to 20mA, V
EXTVCC
= 4V 0.2 1.0 %
V
LDO
EXT EXTV
CC
Voltage Drop I
CC
= 20mA, V
EXTVCC
= 5V 80 160 mV
V
EXTVCC
EXTV
CC
Switchover Voltage I
CC
= 20mA, EXTV
CC
Ramping Positive ● 4.5 4.7 V
V
LDOHYS
EXTV
CC
Hysteresis 0.2 V
Oscillator
f
OSC
Oscillator frequency V
FREQSET
= Open (Note 8) 190 220 250 kHz
f
LOW
Lowest Frequency V
FREQSET
= 0V 120 140 160 kHz
f
HIGH
Highest Frequency V
FREQSET
= 2.4V 280 310 360 kHz
I
FREQSET
FREQSET
Input Current V
FREQSET
= 2.4V –2 –1 µA
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V, V
RUN/SS1, 2
= 5V, AUXV
IN
= 3V unless otherwise noted.
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LTC1876EG#PBF

Mfr. #:
Buy LTC1876EG#PBF
Manufacturer:
Analog Devices / Linear Technology
Description:
Switching Voltage Regulators 2-phase,Dual Step-dn + Boost Reg
Lifecycle:
New from this manufacturer.
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