SC2446A Semtech Corporation, SC2446A Datasheet

SC2446A

Manufacturer Part Number

SC2446A

Description

Dual-Phase Single or Two Output Synchronous Step-Down Controller

Manufacturer

Semtech Corporation

Datasheet

1.SC2446A.pdf (27 pages)

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Bonase Electronics (HK) Co., Limited

Part Number:

SC2446AITS

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SEMTECH

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3 800

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The SC2446A is a high-frequency dual synchronous step-

down switching power supply controller. It provides out-

of-phase output gate signals. The SC2446A operates in

synchronous continuous-conduction mode. Both phases

are capable of maintaining regulation with sourcing or

sinking load currents, making the SC2446A suitable for

generating both V

cations.

The SC2446A employs fixed frequency peak current-

mode control for the ease of frequency compensation

and fast transient response.

The dual-phase step-down controllers of the SC2446A

can be configured to provide two individually controlled

and regulated outputs or a single output with shared

current in each phase. The Step-down controllers oper-

ate from an input of at least 4.7V and are capable of

regulating outputs as low as 0.5V

The step-down controllers in the SC2446A have the pro-

vision to sense inductor R

control. This sensing scheme eliminates the need of the

current-sense resistor and is more noise-immune than

direct sensing of the high-side or the low-side MOSFET

voltage. Precise current-sensing with sense resistor is

optional.

Individual soft-start and overload shutdown timer is in-

cluded in each step-down controller. The SC2446A imple-

ments hiccup overload protection. In two-phase single-

output configuration, the master timer controls the soft-

start and overload shutdown functions of both control-

lers.

POWER MANAGEMENT

Revision: November 9, 2005

Typical Application Circuit

Description

Figure 1

VO1

VO1GND

C 74

DDQ

R 28

R 13

and the tracking V

C 62

R CS-6

voltage drop for current-mode

R 46

C 40

R 29

C 45

C 6

In te gra te d M O S F E T /D rive r

C 29

VDDO

VSSO

VIN

REF OUT (0. 5V)

for DDR appli-

U 10

VDDC

VSSC

R 47

C 72

R 53

C 68

C 73

R 55

R 45

REF OUT (0. 5V)

BST1

GDH 1

GD L1

PGND

VPN 1

CS1+

CS1-

IN1-

COMP1

REF

AGND

R osc

AVCC

R EFOU T

SC2446A

Synchronous Step-Down Controller

U 3

V IN (1 2 V )

Dual-Phase, Single or Dual Output

SS1/EN 1

SS2/EN 2

COMP2

REFIN

SYNC

Features

PVCC

GDH 2

Applications

GD L2

VPN 2

CS2+

BST2

CS2-

VIN 2

IN2-

2-Phase synchronous continuous conduction mode

for high efficiency step-down converters

Out of phase operation for low input current ripples

Output source and sink currents

Fixed frequency peak current-mode control

50mV/-75mV maximum current sense voltage

Inductive current-sensing for low-cost applications

Optional resistor current-sensing for precise cur-

rent-limit

Dual outputs or 2-phase single output operation

Excellent current sharing between individual phases

Wide input voltage range: 4.7V to 16V

Individual soft-start, overload shutdown and enable

Duty cycle up to 88%

0.5V feedback voltage for low-voltage outputs

External reference input for DDR applications

Programmable frequency up to 1MHz per phase

External synchronization

Industrial temperature range

28-lead TSSOP lead free package. This product is

fully WEEE and RoHS compliant

Telecommunication power supplies

DDR memory power supplies

Graphic power supplies

Servers and base stations

C 71

C 67

R 52

C 70

R 49

REF OUT (0. 5V)

In te gra te d M O S F E T /D rive r

TP11

VSSC

VDDC

U 9

VDDO

VSSO

C 63

C 65

C 64

R 48

C 7

R 14

C 23

R CS-5

V IN G N D

www.DataSheet4U.com

R 50

R 51

SC2446A

C 75

www.semtech.com

VO2GND

VO2

Related parts for SC2446A

SC2446A Summary of contents

Page 1

... The Step-down controllers oper- ate from an input of at least 4.7V and are capable of regulating outputs as low as 0.5V The step-down controllers in the SC2446A have the pro- vision to sense inductor R voltage drop for current-mode DC control ...

Page 2

... SC2446A www.DataSheet4U.com ...

Page 3

... SC2446A www.DataSheet4U.com ± ...

Page 4

... < I < < < SC2446A www.DataSheet4U.com ...

Page 5

... Only available in tape and reel packaging. A reel BST1 contains 2500 devices for TSSOP package. GDH1 (2) Lead free product. This product is fully WEEE and RoHS compliant. GDL1 PVCC PGND GDL2 GDH2 BST2 VPN2 VIN2 AVCC SS2/EN2 5 SC2446A www.DataSheet4U.com ...

Page 6

... SC2446A www.DataSheet4U.com ...

Page 7

... SC2446A www.DataSheet4U.com ...

Page 8

... DSBL1 Overload OCN1 Hiccup Control 1 0.5 (REFOUT) CLK2 SEL 0.5 (REFIN) ANALOG SWITCH PWM2 Soft-Start OL2 And DSBL2 Overload OCN2 Hiccup Control 2 0.5 (REFIN) Figure 3. SC2446A Block Diagram 8 SC2446A www.DataSheet4U.com REFERENCE 0.5V 0.5V UVLO 4.3/4. SEL Y www.semtech.com AVCC 16 BST1 26 GDH1 25 VPN1 27 GDL1 24 PGND 22 SS1/EN1 ...

Page 9

... POWER MANAGEMENT Block Diagram IN- 0.5(V ) REFOUT / 0.5(V ) REFIN SS/EN UVLO Figure 4. Soft-Start and Overload Hiccup Control Circuit 2005 Semtech Corp. OCN - + 0.5V/3.2V 0.8V/1.2V 9 SC2446A www.DataSheet4U.com DSBL www.semtech.com ...

Page 10

... EM interference. Minimum Switch On Time Consideration In the SC2446A the falling edge of the clock turns on the top MOSFET gate. The inductor current and the sensed voltage ramp up. After the sensed voltage crosses a threshold determined by the error amplifier output, the top MOSFET gate is turned off ...

Page 11

... Rosc (k Ohm) Figure 5. Free running frequency vs. R Inductor (L) and Ripple Current Both step-down controllers in the SC2446A operate in synchronous continuous-conduction mode (CCM) regardless of the output load. The output inductor selection/design is based on the output DC and transient requirements. Both output current and voltage ripples are reduced with larger inductors but it takes longer to change the inductor current during load transients ...

Page 12

... The total equivalent ESR is not simply the parallel combination of all the individual ESR’s either. Instead they should be calculated using the following formulae. 12 SC2446A www.DataSheet4U.com . The RMS current ripple rating should also ...

Page 13

... Capacitors with low ESL should be used also important to place the input capacitor close to the MOSFETs on the PC board to reduce trace inductances around the pulse current loop. The RMS value of the capacitor current is approximately 13 SC2446A www.DataSheet4U.com and the input capacitor C has an ESR ...

Page 14

... The two step-down channels of the SC2446A operate at 180 degrees from each other. If both step- down channels in the SC2446A are connected in parallel, both the input and the output RMS currents will be reduced. Ripple cancellation effect of interleaving allows the use of smaller input capacitors ...

Page 15

... In the current mode control as implemented in SC2446A, the voltage ripple critical for PWM operation fact, the AC voltage ripple peak-to-peak value of V ...

Page 16

... The voltage feedback gain h=0.5/V value as Once either R calculated for the desired output voltage V number of standard resistance values is limited, the calculated resistance may not be available as a standard value resistor result, there will be a set error in the 16 SC2446A www.DataSheet4U.com ...

Page 17

... Semtech Corp. The inner current-loop is unstable (sub-harmonic oscillation) unless the inductor current up-slope is steeper than the inductor current down-slope. For stable operation above 50% duty-cycle, a compensation ramp is added to the sensed-current. In the SC2446A the compensation ramp is made duty-ratio dependent. The compensation ramp is approximately ...

Page 18

... If the converter crossover frequency is set around 1/ the switching frequency parameters then can be calculated where, (260 µ use SC2446A www.DataSheet4U.com T(s)=G (s)C(s). vc << and specifies the loop crossover noted that the crossover frequency c g hkR ...

Page 19

... The load f 5 × transient response behavior is further tested and measured to meet the specification. 19 SC2446A www.DataSheet4U.com ...

Page 20

... The followings are suggested for proper layout. Power Stage 1) Separate the power ground from the signal ground. In SC2446A, the power ground PGND should be tied to the source terminal of lower MOSFETs. The signal ground AGND should be tied to the negative terminal of the output capacitor. ...

Page 21

... POWER MANAGEMENT Typical Application Schematic 2005 Semtech Corp. 21 SC2446A www.DataSheet4U.com www.semtech.com ...

Page 22

... SC2446A www.DataSheet4U.com Channel 1: Vo1 = 2.5V Channel 2: Vo2 = 1. fic fic erm als erm als erm als 1 ...

Page 23

... POWER MANAGEMENT Typical Characteristics (Cont.) Ch1 (2.5V) Output voltage ripple = 14.0mV p-p Ch2 (1.2V) Output voltage ripple = 15.6mV p-p 2005 Semtech Corp. 23 SC2446A www.DataSheet4U.com www.semtech.com ...

Page 24

... POWER MANAGEMENT Typical Characteristics (Cont.) Ch1 (2.5V) Full load start-up Ch1 (2.5V) Shutdown 2005 Semtech Corp. 24 SC2446A www.DataSheet4U.com Vin = 12V Io1 Vout1 = 2.5V Vin = 12V Vout1 = 2.5V www.semtech.com ...

Page 25

... POWER MANAGEMENT Typical Characteristics (Cont.) Ch2 (1.2V) Full load start-up Ch2 (1.2V) Shutdown 2005 Semtech Corp. 25 SC2446A www.DataSheet4U.com Vin = 12V Io2 Vout2 = 1.2V Vin = 12V Vout2 = 1.2V www.semtech.com ...

Page 26

... Typical Characteristics (Cont.) Vin = 12V, Dual output, Fsw = 500KHz, Tamb = Vin = 12V, Dual output, Fsw = 500KHz, Tamb = 2005 Semtech Corp. ° C, 0LFM 2.5V Output short and release. ° C, 0LFM 1.2V Output short and release. 26 SC2446A www.DataSheet4U.com www.semtech.com ...

Page 27

... AND - DETERMINED AT DATUM PLANE -H- DIMENSIONS DIM INCHES (.222 .161 .026 X .016 Y .061 Y Z .283 Semtech Corporation Power Management Products Division 200 Flynn Road, Camarillo, CA 93012 27 SC2446A www.DataSheet4U.com DIMENSIONS INCHES MILLIMETERS NOM MAX MIN NOM MAX - - - - .047 1. .006 0.05 0.15 - .042 0.80 - 1.05 ...

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