參數(shù)資料
型號: TPS53851RHHT
廠商: TEXAS INSTRUMENTS INC
元件分類: 穩(wěn)壓器
英文描述: SWITCHING CONTROLLER, PQCC36
封裝: PLASTIC, VQFN-36
文件頁數(shù): 50/66頁
文件大?。?/td> 1264K
代理商: TPS53851RHHT
L
NPH
OUT
RIPPLE
sw
V
I
=
× 0.455 = 1.573A
L × f
SLUS985 – DECEMBER 2009
www.ti.com
6.3
Example 3: Four-Phase Single Output Configuration From 12 V to 1.8 V DC-to-DC
Converter Using Two TPS53851
The following example illustrates the design process and component selection for a four phase single
output synchronous buck converter using two TPS53851.
Here, two modules are designed. One is a master module. The other one is a slave module. Each module
contains two phases and each phase handle 5-A. The two modules are stacked together to form a
4-phase converter. More slave modules can be stacked to this converter to get the desired phases. The
modules are plugged into a mother board.
The design goal parameters are given in Table 6-3.
Table 6-3. Design Goal Parameters
PARAMETER
TEST CONDITION
MIN
TYP
MAX
UNIT
VIN
Input Voltage
10.8
12
13.2
V
VOUT
Output voltage
1.8
V
VRIPPLE
Output ripple
IO = 20 A
1%VO
V
IPH
Phase current
5
A
fsw
Switching frequency
650
kHz
NPH
Phase number
4
6.3.1
Step 1: Output Capacitor Selection
The output capacitor is typically selected by the output load transient response requirement. Equation 22
in the dual output design example is used. Also, as mentioned in the two phase design example, the
inductor is equivalent to
. Based on a 10A load transient with a maximum of 30 mV deviation, a
minimum 370
μF output capacitor is required. In the design, one 180μF, 6.3V, SP capacitor is placed on
the mother board. Four 22-
μF, 6,3V ceramic capacitors are placed on each module. The total output
capacitance is 356
μF.
The output ripple current cancellation factor is calculated to be 0.455 based on Equation 56.
So the maximum output ripple current is calculated by:
(60)
With 356
μF output capacitance, the ripple voltage at the capacitor is calculated to be 850 μV. In the
specification, the output ripple voltage should be less than 18 mV, so based on Equation 23, the required
maximum ESR is 11 m
. The selected capacitors can reach this requirement.
6.3.2
Step 2: Input Capacitor Selection
The input voltage ripple depends on the input capacitance and the ESR. The minimum capacitor and the
maximum ESR can be estimated by Equation 24 and Equation 25 in the dual output design example.
For this design, assume is 50mV and is 30mV, also each phase inductor ripple current is 50%, so the
calculated minimum capacitance is 93-
μF and the maximum ESR is 4.6 m. In this case, one 33-μF 6.3-V
SP-capacitor is placed on the mother board and each module has two 22-
μF, 6.3-V ceramic capacitors.
The maximum input ripple RMS current is calculated to be 2.57 A with the minimum input voltage based
on Equation 58. The selected capacitors are sufficient to meet this requirement.
54
DESIGN EXAMPLES
Copyright 2009, Texas Instruments Incorporated
Product Folder Link(s): TPS53851
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