Dual Synchronous Voltage Mode
Controller with Current Sharing Circuitry
POWER MANAGEMENT
Description
The SC2677 is a versatile 2 phase, synchronous, volt-
age mode PWM controller that may be used in two dis-
tinct ways. First, the SC2677 is ideal for applications
where point of use output power exceeds any single in-
put power budget. Alternatively, the SC2677 can be used
as a dual switcher. The SC2677 features a temperature
compensated voltage reference, an under voltage lock-
out over current protection and internal level-shifted, high-
side drive circuitry.
In current sharing configuration, the SC2677 can pro-
duce a single output voltage from two separate voltage
sources (which can be different voltage levels) while
maintaining current sharing between the channels. Cur-
rent sharing is programmable to allow loading each input
supply as required by the application.
In dual switcher configuration, two feedback paths are
provided for independent control of the separate outputs.
The device will provide a regulated output from flexibly
configured inputs (3.3V, 5V, 12V), provided 5V is present
for V
CC
. The phasing between the two switchers is ad-
justable to minimize the input and output ripple.
SC2677
Features
300kHz to 1MHz externally programmable
frequency operation
Soft Start and Enable function
Power Good output provided
Under voltage short circuit protection
Phase-shifted switchers minimize ripple
High efficiency operation, >90%
Programmable output(s) as low as 0.5V
Industrial temperature range
TSSOP-20 package
Bias voltage as low as 4.5V
Adjustable phase shift between channels
Tw o Phase, Current Sharing Controller
Flexible, same or separate V
IN
Programmable current sharing
Thermal distribution via multi-phase output
Applications
Graphics cards
Peripheral add-in card
Dual-Phase power supply
Power supplies requiring two outputs
Simplified Application Schematic
+5V
M1
C1
M2
C2
+12V
C3
L1
1
2
Vout1
PWRGD
ENABLE
R1
C5
R4
20
19
18
17
16
15
14
13
12
11
1uF
R2
R3
C4
P S
HA ING
S /E
S NA
-IN1
CO P
M 1
B T1
S
DH1
DL1
P RG
W D
B TC
S
G
ND
R5
R6
0R0
R7
U1
FRE
Q
V F
RE
+
IN2
V
CC
SC2677
CO P
M 2
P ND
G
B T2
S
DH2
-IN2
DL2
C6
10
R8
1
2
3
4
5
6
7
8
C7
R11
R10
+3.3V
C8
+12V
9
R9
L2
1
M3
C9
M4
C10
2
Vout2
Revision: NOV. 15, 2004
1
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SC2677
POWER MANAGEMENT
Absolute Maximum Rating
Exceeding the specifications below may result in permanent damage to the device, or device malfunction. Operation outside of the parameters specified
in the Electrical Characteristics section is not implied.
Parameter
V
CC
to GND
PGND to GND
BST1, BST2 to GND
BSTC to GND
-IN1, +/-IN2 to GND
COMP1, COMP2 to GND
DH1, DH2 to GND
DL1, DL2 to GND
Symbol
V
IN
Limits
-0.3 to 15
±1
-0.3 to 20
-0.3 to 20
7
7
-0.3 to 20
-0.3 to BSTC + 0.3
-3 peak (50nS)
(1)
Units
V
V
V
V
V
V
V
V
V
V
V
V
°C/W
°C/W
°C
°C
°C
°C
PWRGD to GND
PHASING
SS/ENA to GND
Thermal Resistance Junction to Case
Thermal Resistance Junction to Ambient
Operating Ambient Temperature Range
Operating Junction Temperature Range
Storage Temperature Range
Lead Temperature (Soldering) 10 sec
θ
JC
θ
JA
T
A
T
J
T
STG
T
LEAD
V
CC
+ 0.3
7
-0.3 to 7
17
90
0 to 70
0 to 125
-65 to +150
300
Electrical Characteristics
Unless Specified: V
CC
= 4.75 to 5.25V, GND = PGND = 0V, FB = V
O
, T
J
= 25°C, V
BSTC
= V
BST
= 12V
Parameter
Output Voltage
Supply Voltage
Supply C urrent
UVLO
UVLO Hysteresi s
Reference
Reference Load Regulati on
Reference Li ne Regulati on
Output Li ne Regulati on
Gai n (Gm) (Error Ampli fi er)
Bi as C urrent Offset (Slave Error Ampli fi er)
Max C urrent (Error Ampli fi er)
C onditions
V
OUT
= V
FB
V
CC
V
CC
= 5.0
V
CC
Ramp up Threshold
V
CC
Min
0.495
4.5
Typ
0.500
Max
0.505
15
U nits
V
V
mA
V
mV
V
10
2.84
100
0.5
V
REF
source 10uA ~ 100uA
5V < V
C C
< 15V
5V < V
IN
< 15V
C OMP pi n source 100uA
4
-2
Source
Si nk
200
400
5
-1
250
460
0.2
0.7
0.7
6
0
%
%
%
mA/V
mV
uA
uA
Input Bi as C urrent
Short C i rcui t Protecti on Threshold
Osci llator Frequency Range
-IN1, +IN2, -IN2
45
300
55
2
65
1000
µA
%
kHz
©
2004 Semtech Corp.
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SC2677
POWER MANAGEMENT
Electrical Characteristics (Cont.)
Unless Specified: V
CC
= 4.75 to 5.25V, GND = PGND = 0V, FB = V
O
, T
J
= 25°C, V
BSTC
= V
BST
= 12V
Parameter
Oscillator Frequency
Oscillator Max Duty Cycle
Phasing of DH2 and DL1
DH Sink Current
DH Sink Current
DH Source Current
DH Source Current
DL Sink Current
DL Sink Current
DL Source Current
DL Source Current
Dead Time
Soft Start Charge Current
(2)
Soft Start Enable
Soft Start End
Soft Start Transition Threshold
(2)
Power Good Threshold
Power Good Pull Down
Conditions
R
SET
= 2.5kohm
F
OSC
= 500kHz
V
PHASING
= 0.585V
DH - PGND = 3.5V
DH - PGND = 2.5V
BSTH - DH = 3.75V
BSTH - DH = 3V
DL - PGNG = 3.5V
DL - PGND = 2.5V
BSTL - DL = 3.75V
BSTL - DL = 3V
Note 5
Min
450
86
Typ
500
90
180
Max
550
Units
kHz
%
°C
A
A
A
A
A
A
A
A
1.7
0.85
1.7
0.85
1.7
0.85
1.7
0.85
50
85
50
120
ns
µA
mV
mV
V
0% duty cycle
100% duty cycle
Synchronous mode
V
OUT
ramping up
Sink Current = 2mA
83%
400
825
1.22
88%
93%
0.4
V
OUT
V
NOTES:
(1) Measured from 50% to 50% pulse amplitude.
(2) The soft start pin sources 50µA to an external capacitor. The converter operates in synchronous mode
above the soft start transition threshold and in asynchronous mode below it.
(3) Power good is an open collector output which is pulled low when the output voltage is under 75%.
(4) This device is ESD sensitive. Use of standard ESD handling precautions is required.
(5) 120ns maximum at 70
°C.
Marking Information
(TSSOP-20)
TOP
yyww = Datecode (Example: 9908)
xxxx = Semtech Lot # (Example: 90101
)
©
2004 Semtech Corp.
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SC2677
POWER MANAGEMENT
Pin Configuration
Top View
Ordering Information
D evice
(1)
SC 2677TSTR
SC 2677TSTRT
(2)
SC 2677EVB-1
SC 2677EVB-2
P ackag e
TSSOP-20
TSSOP-20
C urrent Share Evaluati on Board
D ual C hannel Evaluati on Board
Notes:
(1) Only available in tape and reel packaging. A reel con-
tains 2500 devices.
(2) Lead free package.
(TSSOP-20 Pin)
Pin Descriptions
EXPANDED PIN DESCRIPTION
Pin 1:
(VREF)
Internal 0.5V reference. Connected to the + input of
the master channel error amplifier.
Pin 2:
(FREQ)
External frequency adjustment. Connect a resistor to
AGND to set the switching frequency. Please see
more information in Application section.
Pin 3:
(VCC)
Bias pin for the controller. Connect a ceramic
decoupling capacitor from this pin to AGND with
minimum trace length.
Pin 4:
(+IN2)
“+” input of the slave error amplifier.
Pin 5, 16:
(-IN2, -IN1)
“-” inputs of the error amplifiers.
Pin 6, 15:
(COMP2, COMP1)
Compensation pins of the error amplifiers.
Pin 7, 14:
(BST2, BST1)
Supply pins for the high side drivers. Usually con-
nected to bootstrap circuit.
Pin 8, 13:
(DH2, DH1)
Gate drive pins for the top MOSFETs. Requires a
small series resistor.
Pin 9, 12:
(DL2, DL1)
Gate drive pins for the bottom MOSFETs. Requires a
small series resistor.
©
2004 Semtech Corp.
4
Pin 10:
(PGND)
Power GND. Return of the high side and low side gate
drivers.
Pin 11:
(BSTC)
Supply pin for bottom MOSFET gate drivers.
Pin 17:
(PHASING)
This pin controls the phase shift between master and
slave for optimum noise immunity. Use a resistive
divider from the FREQ pin (pin 2) to AGND, and
connect the tap of the resistive divider to pin 17.
Please see more information in Application section.
Pin 18:
(SS/ENA)
Soft start pin. Connect a ceramic capacitor from this
pin to AGND, and there is an internal current source
charging up this capacitor during soft start. The PWM
operation can be disabled if this pin is pulled low.
Pin 19:
(PWRGD)
Power good signal. This is an open collector output. It
is pulled low internally if output voltage is outside the
power good window.
Pin 20:
(GND)
Analog GND. Return of the analog signals and bias of
the chip.
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SC2677
POWER MANAGEMENT
Block Diagram
1.25V
50uA
NOTES
(1) Channel 1 is the Master and Channel 2 is the Slave in current sharing configuration.
(2) For dual output operation, tie +IN2 to VREF and the two PWM channels are independent.
©
2004 Semtech Corp.
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