End of Life. Last Available Purchase Date is 31-Dec-2014
Si9121
Vishay Siliconix
High-Voltage, Non-Isolated Buck-Boost Converter
for ISDN Digital Phones
FEATURES
Fixed +5-V or +3.3-V Output
Integrated Floating Feedback Amplifier
On-Chip 70-V, 1.5- N-Channel
MOSFET Switch
Integrated High Voltage Start-Up Circuit,
with V
CC
Regulator
−10-V to −60-V Input Voltage Range
95-kHz PWM Operation
Integrated Soft-Start and Oscillator
High Efficiency Over Full Load Range
Under Voltage Lockout
Current Mode Control
Hiccup Mode Short Circuit
Protection
Thermal Shutdown
SOIC-8 Narrow-Body Package
DESCRIPTION
The Si9121 simplifies the −48-V to +5-V or +3.3-V converter
design for ISDN application by integrating the floating
feedback error amplifier providing direct output voltage
regulation. This approach eliminates the need for an external
shunt regulator. The Si9121 also integrates a high voltage
depletion mode MOSFET which allows the converter to be
powered directly from the high input bus voltage without
requiring an external start-up circuit. Combined with simple
magnetic design due to its non-isolated topology, the Si9121
provides a one-chip solution for complete ISDN power supply.
In order to reduce external component count, the Si9121 has
a fully integrated 95-kHz oscillator and soft-start circuit.
The Si9121 is available in both standard and lead (Pb)-free
SOIC-8 pin packages, and is offered in either +5-V or +3.3-V
fixed output options (Si9121DY-5 or Si9121DY-3,
respectively). In order to satisfy the stringent ambient
temperature requirements in many applications, the Si9121 is
rated to the industrial temperature range of −40 C to 85 C.
FUNCTIONAL BLOCK DIAGRAM
GND
V
CC
Regulator
V
CC
Reference Generator
V
OUT
BYPASS
L
X
Control
V
OUT
+5 V/400 mA
or
+3.3 V/400 mA
COMP
V
NEG
C
S
V
NEG
−48 V
Document Number: 71112
S-40708—Rev. C, 19-Apr-04
www.vishay.com
1
Si9121
Vishay Siliconix
ABSOLUTE MAXIMUM RATINGS (ALL VOLTAGES REFERENCED TO GND = 0 V)
V
NEG
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
−63
V
V
CS
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V
NEG
−0.3
V to V
CC
+ 0.3 V
V
CC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V
NEG
+ 13.2 V
I
LX
(peak current ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 A
V
OUT
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 V
Bypass, CS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V
NEG
−0.3
V to V
CC
+0.3 V
(V
LX
−
V
CS
) internal power MOSFET . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 V
Storage Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
−65
to 150_C
Operating Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150_C
Power Dissipation (Package)
a
8-Pin SOIC (Y Suffix)
b
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.25 W
Thermal Impedance (Q
JA
)
a
8-Pin SOIC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
_C/W
Notes
a. Device mounted with all leads soldered or welded to PC board.
b. Derate 10 mW/_C above 25_C.
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation
of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating
conditions for extended periods may affect device reliability.
RECOMMENDED OPERATING RANGE (ALL VOLTAGES REFERENCED TO GND = 0 V)
V
NEG
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
−10
V to
−60
V
V
CC
(internally regulated) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V
NEG
+ 8.5 V
V
CC
(externally supplied) . . . . . . . . . . . . . . . . V
NEG
+ 9.5 V to V
NEG
+ 12.0 V
Digital Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 V to V
CC
RECOMMENDED EXTERNAL COMPONENTS ( SEE TYPICAL APPLICATIONS CIRCUIT )
L = 68
mH,
C
OUT
= 220
mF
// 0.1
mF,
CIN = 33
mF,
C
BYPASS
= 0.1
mF,
C
VCC
= 1
mF,
R
SENSE
= 0.25
W,
0.5 W
SPECIFICATIONS
a
(All Voltages Are With Respect To V
NEG
Unless Otherwise Specified)
Test Conditions (Internally Regulated)
Unless Otherwise Specified
p
Parameter
+5-V Converter
+3.3-V Converter
Limits
−40
to 85_C
Symbol
V
NEG
=
−10
to
−60
V
Temp
b
Full
Full
Min
c
4.80
3.17
Typ
d
5.00
3.30
Max
c
5.20
3.43
Unit
Output Voltage (with respect to GND = 0 V)
V
OUT
10 mA <I
LOAD
< 250 mA
V
Line Regulation (with respect to GND = 0 V)
Line Regulation
−60
V
v
V
NEG
v
−40
V
Full
1
%
V
CC
(Internal Regulator)
V
CC
Bias Voltage
V
CC
Full
7.5
8.5
9.5
V
UVLO
Under Voltage Lockout
Hysteresis
V
CC
−
V
NEG
DV
Turn-On
Full
Room
6.6
7.6
0.6
8.7
V
Soft-Start
Error Amplifier Start-Up Current
I
SS
V
OUT
= 0 V
Room
10
mA
Oscillator
Switching Frequency
f
OSC
Room
80
95
110
kHz
Error Amplifier
Transconductance
Clamp Voltage
gm
V
CL
Internal Error Amplifier
Output Clamp Voltage
Room
Room
10
15
3.5
20
umho
V
Current Limit
Threshold Voltage
V
CS
Full
0.57
0.67
0.77
V
MOSFET Switch
N-Channel MOSFET
www.vishay.com
r
DS(on)
Room
1.5
2.5
W
2
Document Number: 71112
S-40708—Rev. C, 19-Apr-04
Si9121
Vishay Siliconix
SPECIFICATIONS
a
(All Voltages Are With Respect To V
NEG
Unless Otherwise Specified)
Test Conditions (Internally Regulated)
Unless Otherwise Specified
p
Parameter
Supply
Supply Current
(Internally Regulater)
Supply Current
(External V
CC
Applied)
V
OUT
supply Current
Start-Up Current
I
GND
I
CC
I
OUT
I
START
GND to V
NEG
V
CC
to V
NEG
+10 V; V
NEG
>−20 V
V
OUT
to V
NEG
V
CC
= 0 V
Full
Full
Full
Full
1.2
1.5
0.2
5
1.5
2.0
0.3
30
mA
Limits
−40
to 85_C
Symbol
V
NEG
=
−10
to
−60
V
Temp
b
Min
c
Typ
d
Max
c
Unit
Thermal Shutdown
Thermal Shutdown Temperature
Thermal Hysteresis
T
OTP
T
HYS
170
25
_C
Efficiency
Efficiency
400-mA Output,
400 mA Output V
NEG
=
−48
V
48
+5 V
+3.3 V
Room
Room
77
73
%
Notes
a. Refer to PROCESS OPTION FLOWCHART for additional information.
b. Room = 25_C, Full = as determined by the operating temperature suffix.
c. The algebraic convention whereby the most negative value is a minimum and the most positive a maximum.
d. Typical values are for DESIGN AID ONLY, not guaranteed nor subject to production testing.
DETAILED BLOCK DIAGRAM
4
10
mA
V
CC
−
GM
+
R2*
+
−
V
REF
1.25 V
+
−
−
+
H
Soft Start
2
mA
V
NEG
V
OUT
5
R1*
COMP
3.5 V
GND
6
1.5 V
L
Hiccup Discharge Mode
OSC
V
CC
7
0.6 V
Low Side
Error Amp
−
−
+
R
S
3
Bias/
Reference
Circuit
OCL
+
0.67 V
−
Q
+
OTP
8
50% Max.
PWM Duty Cycle
L
X
−V
IN
BYPASS
1
−
+
2
V
NEG
Document Number: 71112
S-40708—Rev. C, 19-Apr-04
8.5 V
+
−
−
+
CS
0.6-V Hysteresis
*R1 and R2 are internal voltage setting resistors used to set
output voltage to fixed 3.3 V or 5 V.
www.vishay.com
3
Si9121
Vishay Siliconix
TYPICAL CHARACTERISTICS (INTERNALLY REGULATED, 25_C UNLESS NOTED)
5.15
5.10
5.05
V
OUT
(V)
5.00
4.95
4.90
4.85
−40
V
OUT
(V)
5-V V
OUT
vs. Temperature
3.45
3.40
3.35
3.30
3.25
3.20
3.15
−40
3.3-V V
OUT
vs. Temperature
−20
0
20
40
60
80
100
−20
0
20
40
60
80
100
Temperature (_C)
Temperature (_C)
2.5
r
DS(on)
vs. Temperature
Frequency vs. Temperature
105
r
DS(on)
−
On-Resistance (
W
)
2.0
Frequency (kHz)
−20
0
20
40
60
80
100
100
1.5
95
1.0
90
0.5
−40
85
−40
−20
0
20
40
60
80
100
Temperature (_C)
Temperature (_C)
1.4
Supply Current vs. V
NEG
Supply Current (I
GND
)
1.3
25_C
1.2
85_C
−40_C
1.1
1.0
−60
−50
−40
−30
−20
−10
V
NEG
−
(V)
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4
Document Number: 71112
S-40708—Rev. C, 19-Apr-04
Si9121
Vishay Siliconix
TYPICAL CHARACTERISTICS (INTERNALLY REGULATED, 25_C UNLESS NOTED)
90
80
70
Efficiency (%)
Output Load vs. Efficiency (Si9121DY-3)
No V
CC
Winding
V
IN
= 10 V
90
80
70
Efficiency (%)
60
50
40
30
20
10
0
Output Load vs. Efficiency (Si9121DY-5)
No V
CC
Winding
10 V
IN
60
50
40
30
20
10
0
10
100
I
OUT
(mA)
1000
V
IN
= 48 V
V
IN
= 60 V
48 V
IN
60 V
IN
10
100
I
OUT
(mA)
1000
90
80
70
Output Load vs. Efficiency (Si9121DY-3)
With V
CC
Winding
V
NEG
=
−10
V
90
80
70
Output Load vs. Efficiency (Si9121DY-5)
With V
CC
Winding
48 V
IN
10 V
IN
60 V
IN
Efficiency (%)
V
NEG
=
−48
V
Efficiency (%)
60
50
40
30
20
10
0
10
60
50
40
30
20
10
0
V
NEG
=
−60
V
100
I
OUT
(mA)
1000
10
100
I
OUT
(mA)
1000
Document Number: 71112
S-40708—Rev. C, 19-Apr-04
www.vishay.com
5
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