SI9138 Datasheet, PDF (12/14 Pages) Vishay Siliconix – Multi-Output, Individual On/Off Control Power-Supply Controller

Si9138
Vishay Siliconix
New Product
DETAILED FUNCTIONAL BLOCK DIAGRAMS
5-V
V_IN
Linear
Regulator
V_L
ON3
ON5
4V
3.3-V
Reference
2.4 V
4.5 V
Reset
Handler
FIGURE 7. Complete Si9138 Block Diagram
Enable
3.3 V
Buck
Controller
Good 3
Enable
5V
Buck
Controller
Good 5
Enable
5- to 12-V
Adjustable
Buck-Boost
Controller
FB₃
CS₃
BST₃
DH₃
LX₃
DL₃
FB₅
CS₅
BST₅
DH₅
LX₅
DL₅
FBFY
CSP
CSN
BSTFY
DHFY
LXFY
DLFY
RESET
DESCRIPTION OF OPERATION
Shutdown Mode
The logic threshold for the ON3 and ON5 pins is 1.6 V. Input
voltage must be 0.8 V or less for logic low and 2.4 V or higher
for logic high.
Start-up Sequence
Start-up is controlled by individual ON/OFF control. The 3.3 V
output is controlled by ON 3 whilst the 5-V and the 5-12 V
adjustable outputs are both controlled by ON 5.
When both the 3.3-V and 5-V SMPS outputs are within
tolerance and 32,000 clock cycles (typically equal to 107 mm)
have elapsed since the second SMPS output went into
regulation, the RESET pin will go high, signifying that all
converters are operating correctly (see RESET Power Good
Voltage Monitor).
The Si9138 converts a 5.5-V to 30-V input voltage to five
different output voltages; two buck (step-down) high current,
PWM, switch-mode supplies of 3.3-V and 5-V, one
“Buck-Boost” PWM switch-mode supply adjustable from 5 V
to 12 V, one precision 3.3-V reference and one 5-V low drop
out (LDO) linear regulator output. Switch-mode supply output
current capabilities depend on external components (can be
selected to exceed 10 A). In the standard application circuit
illustrated in Figure 1, each buck converter is capable of
delivering 5 A, with the Buck-Boost converter delivering
250 mA. The recommended load current for the precision
3.3-V reference output is less than 1 mA, and for the 5-V LDO
output is less than 30 mA. In order to maximize power
efficiency of the converter, when the 5-V buck converter output
(FB5) voltage is above 4.5-V, the internal 5-V LDO is turned off
and V_L is supplied by the 5-V converter output.
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Document Number: 71446
S-20642—Rev. B, 13-May-02