参数资料
型号: LTC3569EFE#TRPBF
厂商: Linear Technology
文件页数: 18/26页
文件大小: 0K
描述: IC REG BUCK SYNC ADJ 16TSSOP
标准包装: 2,500
类型: 降压(降压)
输出类型: 可调式
输出数: 3
输出电压: 0.43 V ~ 5.5 V
输入电压: 2.5 V ~ 5.5 V
PWM 型: 电流模式,混合
频率 - 开关: 2.25MHz,1MHz ~ 3MHz
电流 - 输出: 600mA,1.2A
同步整流器:
工作温度: -40°C ~ 125°C
安装类型: 表面贴装
封装/外壳: 16-TSSOP(0.173",4.40mm)裸露焊盘
包装: 带卷 (TR)
供应商设备封装: 16-TSSOP-EP
LTC3569
APPLICATIONS INFORMATION
Selecting The Inductors
Calculating the inductor values for 30% ripple current at
maximum SV IN :
L1 = 2.5V/(2.25MHz ?240mA)?(1–2.5V/4.2V)= 1.9μH
L2 = 1.8V/(2.25MHz ?120mA)?(1–1.8V/4.2V)= 3.8μH
L3 = 1.2V/(2.25MHz ?120mA)?(1–1.2V/4.2V)= 3.1μH
Choosing a vendor’s closest values gives L1 = 2.2μH, L2
= L3 = 3.3μH. These values result in the maximum ripple
currents of:
? I L1 = 2.5V/(2.25MHz ?2.2μH)?(1–2.5V/4.2V) = 204mA
? I L2 = 1.8V/(2.25MHz ?3.3μH)?(1–1.8V/4.2V) = 139mA
? I L3 = 1.2V/(2.25MHz ?3.3μH)?(1–1.2V/4.2V) = 115mA
Selecting The Output Capacitors
The value of the output capacitors are calculated based
on a 5% load droop for maximum load current step. The
output droop is usually about 2.5 times the linear drop
of the first cycle and is estimated based on the following
formula:
C OUT = 2.5 ?I OUT(MAX) /(f CLK ?V DROOP )
The output capacitor values are calculated as:
C OUT1 = 2.5 ?800mA/(2.25MHz ?125mV) = 7.1μF
C OUT2 = 2.5 ?400mA/(2.25MHz ?90mV) = 4.9μF
C OUT3 = 2.5 ?400mA/(2.25MHz ?60mV) = 7.4μF
Choosing the closest standard values gives, C OUT1 = 10μF,
C OUT2 = 4.7μF and C OUT3 = 10μF.
A 22μF input capacitor is selected since the Li-Ion battery
has sufficiently low output impedance.
Setting The Output Voltages
Without toggling the EN pins the LTC3569 develops a 0.8V
reference voltage for each of the feedback pins. The output
voltages are set by a resistive divider as follows:
V OUT = 0.8 ?(1 + R1/R2)
The resistors in Figure 5 are selected as the nearest 1%
standard resistor values. To improve frequency response
feedforward capacitors of 10pF and 20pF are used.
V IN 2.9V TO 4.2V
22μF SV IN
EN1
PV IN
SW1
FB1
L1
2.2μH*
243k
10pF
OUT1
2.5V AT 800mA
C OUT1
10μF
Design Example 1: Burst Mode Operation
100
V IN = 2.9V TO 4.2V
470k
EN2
LTC3569
EN3
R T
MODE
SW2
FB2
L2
3.3μH**
115k
187k
20pF
OUT2
1.8V AT 400mA
C OUT2
4.7μF
90
80
PGOOD
SGND
PGND
SW3
FB3
L3
3.3μH**
150k
187k
374k
20pF
OUT3
1.2V AT 400mA
C OUT3
10μF
70
60
50
0.1
1
10
100
BUCK1 = 2.5V
BUCK2 = 1.8V
BUCK3 = 1.2V
1000 10000
3569 F05a
I LOAD (mA)
3569 F05b
* WURTH 7447745022
** WURTH 7447745033
Figure 5. Triple Buck DC/DC Regulators: 800mA, 400mA, 400mA
3569fd
18
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