Transcript
Application Note AN-1046 Dual Synchronous PWM Controller and LDO Controller in TSSOP Package Eases Multi-Output and Two-Phase Power Supply Solutions By Parviz Parto, International Rectifier
Table of Contents Page DDR Memory Application .....................................................................1 Independent Mode ...............................................................................2 Dual-Phase Mode with Programmable Current Sensing......................3 Salient Features ...................................................................................5
Many applications like DDR memory, and set top boxes require at least two output voltages. And then there are some others such as graphics cards where the output power exceeds any single input power budget. Or, an application when the current required is too large and a twophase solution should be used. International Rectifier’s IRU3046, a monolithic dual synchronous PWM controller with a built-in linear regulator controller, offers unprecedented flexibility to configure these multiple types of power supplies.
www.irf.com
AN-1046
cover
APPLICATION NOTE
AN-1046
International Rectifier • 233 Kansas Street, El Segundo, CA 90245
USA
Dual Synchronous PWM Controller and LDO Controller In TSSOP Package Eases Multi-Output and Two-Phase Power Supply Solutions By Parviz Parto, International Rectifier Many applications like DDR memory, and set top boxes require at least two output voltages. And then there are some others such as graphics cards where the output power exceeds any single input power budget. Or, application when the current required is too large that two-phase solution should be used. International Rectifier’s IRU3046, a monolithic dual synchronous PWM controller with a built-in linear regulator controller, offers unprecedented flexibility to configure these multiple types of power supplies.
DDR Memory Application One such solution with two outputs for DDR memory is shown in figure 1. The channel 1 generates the Vcore (VDDQ) and the channel 2 generates the termination voltage (VTT=1/2 VDDQ) by tracking the Vcore, this is achieved by sensing the VDDQ and using the integrated uncommitted error amplifier (Vp2). The two external resistors (R5, R9) generate the reference voltage for channel 2 to track the VDDQ. The VTT tracking accuracy is about 1.5% for optimized data rate transfer accuracy. Figures 2 and 3 show how the VTT tracks the VDDQ both statically when the VDDQ changes from 2.5V to 2.87V and dynamically when the output current for VDDQ steps from 0-to 2A.
Until now, the traditional way to address these requirements has been to use separate controllers for each output with associated passive and discrete components. Now, with the introduction of IRU3046, that task is tremendously simplified. Housed in a low-cost 24-pin plastic TSSOP package, this single versatile bipolar device allows the user to configure two independent voltage outputs with either common or different inputs. Or, create a dual-phase design for single output with programmable current sharing when using two different input supplies. Or, two-phase application when high output current and high efficiency are required. In addition, it offers a separate linear controller for an additional independent adjustable voltage output. In short, the IRU3046 brings flexibility to the power supply Figure 1. IRU3046 configured for DDR Memory application designer that is unmatched.
www.irf.com
1
Application Note AN-1046
Independent Mode VDDQ
VTT
Figure 2. VDDQ changes from 2.5V to 2.87V and VTT tracks the half of VDDQ
In the independent mode, the output voltage of each independent channel is set and controlled by the output of the error amplifier. The output voltages can be set between 1.25 V and close to the input voltage. It is capable of supplying 10-15 A from single 5 V or 12 V. However, the input can be from the same supply or a separate operation for the two independent outputs. The output voltage of the each channel is set and controlled by the output of error amplifier and can be programmed by using two external resistors. This output voltage is defined by using the following equation: Vout1 = VREF x (1 + R7 /R8 ) Similarly, the output voltage of the linear regulator is programmed using the voltage reference and the external voltage divider (see figure 4).
VDDQ
VTT
2A 0A
Figure 3. Transient Response for VDDQ, VTT tracks VDDQ - Ch1: VDDQ, Ch2: VTT, Ch4: IDDQ, Step load 0-2A
2
Application Note AN-1046 D1
D2
12V C2 33uF
L1 5V C1 33uF
C3 1uF
C4 1uF
Q1 IRLR2703 R1 1K
C7 47uF
VcH1
VcH2
C11 0.1uF
C14 2x 47uF
1uF
HDrv1
Q2 IRF7460
L3
LDrv1
VOUT3
Q3 IRF7457
PGnd R7 442V
U1
R2 1K R3 C8 2200pF
22K
Fb3 IRU3046 VFb1 Rt REF Sync Vp2 HDrv2
C17 2x 150uF Q4 L4 IRF7457 3.9uH Q5 IRF7457
Comp1 LDrv2
R4 C9 25K 1500pF PGood C10 0.1uF
1.8V @ 8A C16 2x 150uF
4.7uH
VccLDO VSEN33
3.3V C6 47uF
C13 VCL Vcc
C5 1uF
2.5V @ 2A
L2 1uH
1uH
R8 1K 2.5V @ 8A C12 2x 150uF
Comp2 PGood SS
R5 1K
Fb2 Gnd
R9 1K
Figure 4. IRU3046 configured for two independent outputs
Dual-Phase Mode With Programmable Current Sharing
and Vin2=12V @ 2A, Pin2=24W. As you see each of the inputs cannot provide the total output power. But, if we can combine the two inputs we can get the total output power (Fig.5). By appropriately selecting the two current sense resistors, the IRU3046 can combine these two input supplies and generate one single output with the total output power.
The same device can also be configured for the application when the output power exceeds any single input power budget. For example we have the following application: Vout=1.5V @ 17A, Ptotal=25.5W. And two input supplies are Vin1=5V @ 3A, Pin1=15W 5V 12V L2 1uH
D1 BAT54S C3 0.1uF C7 1uF
VCL
VcH1
Vcc
C8 1uF
VcH2
3.3V
C4 47uF
C5 330uF
C32 47uF
C31 330uF
C9 1uF
HDrv1 D2 BAT54A
VccLDO
C6 1uF Q1 IRF7460
2.5V @ 2A C30 1uF
Fb3 R7 1K C18 47uF
R13 15K
R16 29.4K R21 16.5K
R10 1K
U1 IRU3046
C34 6.8nF
PGnd
Sync
Fb1
Comp1
Fb2
Comp2
SS
C15 1uF
R5 4.7 V
1.5V @ 16A
R8 200
HDrv2
PGood C29 0.1uF
C10,C11,C12 3x 150uF
5mV
V REF
D4 BAT54A
PGood
C14 470pF
Vp2
Rt
C24 2200pF
Q2 IRF7457
LDrv1
VOUT3
L3 2.2uH R3
VSEN33 R6 10 V C13 47uF Q3 IRLR2703
C1 33uF
L1 1uH
C2 33uF
LDrv2 Gnd
Q4 IRF7460
Q5 IRF7457
R12 1K
C23 1uF L4 3.3uH C26 470pF
C19,C20,C21 3x 150uF
R17 5mV
R19 4.7 V
Figure 5. IRU3046 configured as 2-phase converter with current sharing. 5V input is the Master channel and set the output and 12V input is the slave channel that monitors the currents for achieving an accurate current sharing 3
Application Note AN-1046
In this Mode, the first error amplifier (E/A) acts as a master and sets the output voltage, while the second E/A acts as a slave and monitors the currents for current sharing. The slave’s error amplifier measures the voltage drop across the current sense resistors, and the differential of these signals is amplified and compared with the ramp signal to generate the fixed-frequency pulses of variable duty cycle to match the output currents. Two sense resistors (R3, R17 in figure 5) are used for current sharing. The relationship between the master and slave output current is expressed by: Rsen1*Imaster = Rsens2*Islave For equal current sharing Rsens1=Rsen2. To ensure accurate current sharing, proper attention must be paid to layout to create a symmetrical path. Because the two output stages are 180 degrees out of phase, the two inductor ripple currents cancel each other to result in a substantial reduction of output ripple current, thereby permitting a smaller output capacitor for the same ripple voltage requirement, Figure 6 shows the inductors ripple current and current matching.
Figure 6. Inductors current matching. Ch1: Gate signal for sync FET(master) (10V/div). Ch2: Gate signal for sync FET(slave) (10V/div). Ch3: Inductor current for master channel (5A/div). Ch4: Inductor current for slave channel (5A/div). VMASTER=5V, VSLAVE=12V, IOUT=10A
For fast load response and steady state output, the designer must pay careful attention to the feedback control loops. It must provide a loop gain function with a high bandwidth (high zero-crossover frequency) and adequate phase margin (for details see AN-1043). Figure 7 shows load transient response when the output current steps from 0 to 10A.
4
Application Note AN-1046 Salient Features VOUT
10A
0A
Figure 7. Load Transient Response, 0-10A Ch1:Vout, Ch4:Iout
However, if single supply powers both the phases, the 2-phase configuration reduces the input ripple current. This results in much smaller RMS current in the input capacitor and reduction of input capacitor. Figure 8 shows the estimate RMS current for 2-phase versus single-phase converters.
0.5
Single phase
0.4
IRMS(IN)
Other key features offered by this device include programmable soft-start, programmable switching frequency up to 400 kHz, under-voltage lockout (UVLO) function, power good signal, shutdown mode, shortcircuit protection and frequency synchronization. While soft-start controls the output voltage and limits the current surge at the start-up, the UVLO circuit assures that the MOSFET driver outputs and LDO controller remain in the off-state whenever the supply voltages drop below set parameters. Normal operation will resume once the supply voltages rise above the set values. Likewise, the IRU3046 provides a power good pin, which is an open collector output that switches low when any of the outputs are outside the specified under voltage trip point. By sensing the output voltage constantly, the unit shuts down the PWM signal and LDO controller when the output drops below the threshold, guaranteeing protection against short-circuit. The IRU3046 also allows frequency synchronization with an external clock signal using the Sync pin. More information for selecting of components and layout tips can be found on IRU3046 data sheet.
0.3
IOUT 0.2
Two phase
0.1 0
0
0.1
0.2
0.3
0.4
0.5
D
Figure 8. Normalized input RMS current vs. duty cycle
5
