SI9113 Datasheet, PDF (7/10 Pages) Vishay Siliconix – High-Voltage Current Mode PWM Controller for ISDN Power Supplies

DETAILED BLOCK DIAGRAM
New Product
Si9113
Vishay Siliconix
13
COMP
4
PWR_GOOD
12
FB
11
V_REF
Ref
Gen
10
SS
V_CC
Error
Amplifier 3.6 V
–
+– –
+
+
+
–
0.6 V
OSC
PWM
Comparator
Clock (¹/₂ f_OSC)
R
Q
S
C/L
Comparator
7
V_CC
2
V_IN
STOP
1
Programmable
Enable
Start-Up
Pre-Regulator
14
Start/Stop
START
Circuit
8
OSCIN
9
OSCOUT
MOS Driver
6
5
DRIVER
–V_IN
3
SENSE
DETAILED DESCRIPTION
Start-Up
The Si9113 start-up circuit prevents the internal circuits from
turning on until the voltage on the +V_IN pin, via the resistor
divider R₃, R₄, R₅, is sufficiently positive such that the voltage
across R₃ (V_START) is >8.8 V (typical value for the internal
reference V_UVSTART [see Figure 2]). When this occurs, the
internal 1.3-V reference, soft-start and oscillator circuits are
enabled. A constant current source provides the current to the
external soft-start capacitor, which allows the output voltage to
rise gradually without overshoot. The output drive circuit is
disabled until the soft-start voltage reaches 3.3 V. The
controller is continuously powered in the state until the V_IN
voltage falls and V_STOP drops below 8.8 V (the typical value for
the internal reference V_UVSTOP). The user can program the
+V_IN START and +V_IN STOP voltage with the external resistor
divider R₃–R₅ (see Figure 2) as follows:
ǒ Ǔ V_IN(START) +
R₃ ) R₄ ) R₅
R₅
V_UVSTART
(1)
ǒ Ǔ V_IN(STOP) +
R₃ ) R₅
R₅
V_UVSTOP
(2)
Since V_UVSTART = V_UVSTOP = 8.8 V (typical) the hysteresis
voltage can be expressed as:
Document Number: 71093
S-99453—Rev. A . 29-Nov-99
www.siliconix.com S FaxBack 408-970-5600
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