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PDF SG1577A Data sheet ( Hoja de datos )
| Número de pieza | SG1577A | |
| Descripción | Dual Synchronous DC/DC Controller | |
| Fabricantes | Fairchild Semiconductor | |
| Logotipo |  |
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September 2009
SG1577A
Dual Synchronous DC/DC Controller
Features
Integrated Two Sets of MOSFET Drivers
Two Independent PWM Controllers
Constant Frequency Operation: Free-running Fixed
Frequency Oscillator Programmable: 61kHz to 340kHz
Maximum Input Supply Voltage: 15V
Programmable Output as Low as 0.7V
Internal Error Amplifier Reference Voltage:
0.7V±1.5%
Two Soft-Start / EN Functions
Programmable Over-Current Protection (OCP)
30V HIGH Voltage Pin for Bootstrap Voltage
Output Over-Voltage Protection (OVP)
20-Pin SOP
Description
The SG1577A is a high-efficiency, voltage-mode, dual-
channel, synchronous DC/DC PWM controller for two
independent outputs. The two channels are operated
out of phase. The internal reference voltage is trimmed
to 0.7V±1.5%. It is connected to the error amplifier’s
positive terminal for voltage feedback regulation.
The soft-start circuit ensures the output voltage can be
gradually and smoothly increased from zero to its final
regulated value. The soft-start pin can also be used for
chip-enable function. When two soft-start pins are
grounded, the chip is disabled and the total operation
current can be reduced to under 0.7mA.
The fixed-frequency is programmable from 60kHz to
340kHz. The Over-Current Protection (OCP) level can
be programmed by an external current sense resistor. It
has two integrated sets of internal MOSFET drivers.
SG1577A is available in a 20-pin SOP package.
Applications
CPU and GPU Vcore Power Supply
Power Supply Requiring Two Independent Outputs
Ordering Information
Part Number
SG1577ASY
Operating
Temperature Range
-40°C to +105°C
Eco Status
Green
Package
20-Lead, Small Outline
Package (SOP-20)
Packing
Method
Tape & Reel
For Fairchild’s definition of Eco Status, please visit: http://www.fairchildsemi.com/company/green/rohs_green.html.
www.DataSheet4U.com
© 2009 Fairchild Semiconductor Corporation
SG1577A • Rev. 1.0.0
www.fairchildsemi.com
1 page  
Absolute Maximum Ratings
Stresses exceeding the absolute maximum ratings may damage the device. The device may not function or be
operable above the recommended operating conditions and stressing the parts to these levels is not recommended.
In addition, extended exposure to stresses above the recommended operating conditions may affect device
reliability. The absolute maximum ratings are stress ratings only. All voltage values, except differential voltages, are
given with respect to the network ground terminal. Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device.
Symbol
VCC
BST1(or 2) –
CLN1(or 2)
CLN1(or 2) –
GND
BST1(or 2) –
GND
DH1(or 2) –
CLN1(or 2)
CLN1(or 2),
DL1(or 2)
PGND
ΘJA
TJ
TSTG
ESD
Parameter
Supply Voltage, VCC to GND
BST1(2) to CLN1(2)
CLN1(2) to GND for 100ns Transient
BST1(2) to GND for 100ns Transient
PGND to GND
Thermal Resistance, Junction-Air
Operating Junction Temperature
Storage Temperature Range
Electrostatic Discharge
Protection Level
Human Body Model (HBM)
Charged Device Model (CDM)
Min.
-4
-0.3
-40
-65
Max.
16
16
18
30
16
VCC+0.3
±1
90
+125
+150
2
1
Unit
V
V
V
V
V
V
V
°C/W
°C
°C
kV
Recommended Operating Conditions
The Recommended Operating Conditions table defines the conditions for actual device operation. Recommended
operating conditions are specified to ensure optimal performance to the datasheet specifications. Fairchild does not
recommend exceeding them or designing to absolute maximum ratings.
Symbol
VCC
TA
Parameter
Supply Voltage
Operating Ambient Temperature
Min.
-40
Max.
+15
+105
Unit
V
°C
www.DataSheet4U.com
© 2009 Fairchild Semiconductor Corporation
SG1577A • Rev. 1.0.0
5
www.fairchildsemi.com
5 Page 
Functional Description
The SG1577A is a dual-channel voltage-mode PWM
controller. It has two sets of synchronous MOSFET
driving circuits. The two channels are running 180-
degrees out of phase. The following descriptions
highlight the advantages of the SG1577A design.
Soft Start
An internal start-up current (35/15µA) flows out of
SS/EN pin to charge an external capacitor. During the
startup sequence, SG1577A isn’t enabled until the
SS/ENB pin is higher than 1.2V. From 1.2V to (1.2 + 1.6
x DON / DON_MAX) V, the PWM duty cycle gradually
increases following the SS/ENB pin voltage to bring
output rising. After (1.2 + 1.6 x DON / DON_MAX) V, the
soft-start period ends and SS/ENB pin continually rises
to 4.8V. When input power is abnormal, the external
capacitor on the SS pin is shorted to ground and the
chip is disabled.
5
CSS1 × (1.4V
- 1.2V) = 35uA × t1;
CSS1
× (1.2V
+ 1.6 ×
12
0.9
- 1.4V) = 15µA
× t2
; t1 + t2 = tSS1
3.3
CSS2
× (1.4V
- 1.2V) = 35µA × t1;
CSS2
× (1.2V + 1.6 ×
12
0.9
- 1.4V) = 15µA × t2
; t1 + t2 = tSS2
CSS1 ×1.2V = 35µA × t3;
CSS2 × 0.3V
15µA
+
CSS2
× (1.2V
35µA
-
0.3V)
=
t4
; t4 - t3 = ttime-shift
(1)
Over-Current Protection (OCP)
Over-current protection is implemented by sensing the
voltage drop across the drain and the source of external
high-side MOSFET. Over-current protection is triggered
when the voltage drop on external high-side MOSFET’s
RDS(ON) is greater than the programmable current limit
voltage threshold. 120µA flowing through an external
resistor between input voltage and the CLP pin sets the
threshold of current limit voltage. When over-current
condition is true, the system is protected against the
cycle-by-cycle current limit. A counter counts a series of
over-current peak values to eight cycles; the soft-start
capacitor is discharged by a 50µA current until the
voltage on SS pin reaches 1.2V. During the discharge
period, the high-side driver is turned off and the low-
side driver is turned on. Once the voltage on SS/ENB
pin is under 1.2V, the normal soft-start sequence is
initiated and the 35/15µA current charges the soft-start
capacitor again.
IL(OCP)= [(RSENSE x IOCSET + VOFFSET) / RDS(ON) -
(VIN - VOUT) x VOUT / (fOSC x LOUT x VIN x 2) ]
(2)
where VOFFSET ( ≒ 10mV) is the offset voltage
www.DatacSohneterti4bUut.ecdomby the internal OCP comparator.
Error Amplifier
The IN1 and IN2 pins are connected to the
corresponding internal error amplifier’s inverting input
and the outputs of the error amplifiers are connected to
the corresponding COMP1 and COMP2 pins. The
COMP1 and COMP2 pins are available for control-loop
compensation externally. Non-inverting inputs are
internally tied to a fixed 0.7V ± 1.5% reference voltage.
Oscillator Operation
The SG1577A has a frequency-programmable
oscillator. The oscillator is running at 61kHz when the
RT pin is floating. The oscillator frequency can be
adjusted from 61kHz up to 340kHz by an external
resistor RRT between RT pin and the ground. The
oscillator generates a sawtooth wave that has 90%
rising duty. Sawtooth wave voltage threshold is from
1.2V to 2.8V. The frequency of oscillator can be
programmed according to the following equation:
fOSC, RT(kHz) = 61kHz + 8522 / RRT(kΩ)
(3)
Output Driver
The high-side gate drivers need an external
bootstrapping circuit to provide the required boost
voltage. The highest gate driver’s output (15V is the
allowed) on high-side and low-side MOSFETs forces
external MOSFETs to have the lowest RDS(ON), which
results in higher efficiency.
Over-Temperature Protection (OTP)
The device is over-temperature protected. When chip
temperature is over 150oC, the chip enters tri-state
(high-side driver is turned off). The hysteresis is 20oC.
Type II Compensation Design
(for Output Capacitors with High ESR)
SG1577A is a voltage-mode controller; the control loop
is a single voltage feedback path, including an error
amplifier and PWM comparator, as shown in Figure 23.
To achieve fast transient response and accurate output
regulation, an adequate compensator design is
necessary. A stable control loop has a 0dB gain
crossing with -20dB/decade slope and a phase margin
greater than 45°.
Figure 23. Closed Loop
© 2009 Fairchild Semiconductor Corporation
SG1577A • Rev. 1.0.0
11
www.fairchildsemi.com
11 Page | ||
| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet SG1577A.PDF ] | |
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