IR3081A International Rectifier Corp., IR3081A Datasheet - Page 12

• Manufacturer Part Number: IR3081A
• Description: Xphasetm Vr 10 Control Ic
• Manufacturer: International Rectifier Corp.

IR3081A THEORY OF OPERATION
Block Diagram
The Block diagram of the IR3081A is shown in Fig. 6, and specific features are discussed in the following sections.
VID Control
A 6-bit VID voltage compatible with VR 10, as shown in Table 1, is available at the VDAC pin. A detailed block
diagram of the VID control circuitry can be found in Figure 7. The VID pins require an external bias voltage and
should not be floated. The VID input comparators, with 0.6V reference, monitor the VID pins and control the 6 bit
Digital-to-Analog Converter (DAC) whose output is sent to the VDAC buffer amplifier. The output of the buffer
amplifier is the VDAC pin. The VDAC voltage is post-package trimmed to compensate for the input offsets of the
Error Amplifier to provide a 0.5% system set-point accuracy. The actual VDAC voltage does not determine the
system accuracy and has a wider tolerance.
Page 12 of 39
ENABLE
VOSNS-
RMPOUT
SS/DEL
BBFB
VBIAS
ROSC
VCC
VID5
VID0
VID1
VID2
VID3
VID4
9.7V
8.9V
+
-
+
-
IDISCHG
50%
DUTY
CYCLE
0.6V
VCHG
3.8V
ENABLE
COMPARATOR
6uA
IROSC
IROSC
IROSC
IROSC
IROSC
IROSC
START
STOP
IROSC
VID
CONTROL
-
+
-
+
IROSC
+
-
IDISCHG
RAMP GENERATOR
VCC UVLO
COMPARATOR
ICHG
70uA
ON
VID DAC OUTPUT
VID = 11111X
VID STEP-DOWN
IROSC
ICHG
65mV
115mV
0.2V
OFF
DISCHARGE
COMPARATOR
5.0V
1.0V
+
-
OCICHG
DELAY
COMPARATOR
IDISCHG
40uA
Figure 6. IR3081A Block Diagram
VBIAS
IROSC
-
+
SS/DEL
DISCHARGE
OVER
CURRENT
CURRENT
SOURCE
GENERATOR
VBIAS
REGULATOR
SET THRESHOLD
0.7V (1.3-0.6V)
+
-
ROSC
BUFFER
AMPLIFIER
+
-
1.2V
PRECONDITION
RESET COMPARATOR
0.6V
PRECONDITION
SET COMPARATOR
+
-
FAULT
LATCH
SET
DOMINANT
6.8V
S
R
+
-
+
-
+
-
Q
SOFT START CLAMP
+
-
1.3V
OVER CURRENT
COMPARATOR
PRECONDITION
LATCH
RESET
DOMINANT
S
R
Q
IROSC
-
+
10k
IROSC
ERROR
AMPLIFIER
IFB
+
-
+
VDRP
AMPLIFIER
DISABLE
+
-
IR3081A
1/31
IOCSET
/05
PWRGD
OCSET
IIN
VDRP
EAOUT
VDAC
FB
LGND