* SPICE netlist
R1 N003 N010 100K
R2 N003 N012 100K
V1 N003 0 3.3
R3 N009 N015 887K
R4 N015 0 412K
R5 N009 N011 16.5K
R6 N011 0 13K
R7 N001 N007 1
R8 N007 0 100K
MQ1 N001 N004 N002 N002 Si4420DY
V2 N001 0 PWL(0 0 1 3.3)
R9 N002 0 100
C1 0 N004 1
XU1 N001 N007 N011 N015 N009 0 N013 N005 N012 N010 N004 N002 LTC2923 ;pnba Vcc)ON)Track1)Track2)RampBuf)GND)FB2)FB1)_SDO)Status)Gate)Ramp
R10 N013 0 400K
R11 N014 N013 400K
G1 0 N014 N016 N013 1
V3 N016 0 1
R12 N005 0 15K
R13 N006 N005 15K
G2 0 N006 N008 N005 1
V4 N008 0 1
.tran 1 2 0 1m

* LTspice schematic (.asc)
Version 4
SHEET 1 1216 672
WIRE -384 -336 -608 -336
WIRE -80 -336 -384 -336
WIRE -48 -336 -80 -336
WIRE 144 -336 48 -336
WIRE 160 -336 144 -336
WIRE 256 -336 240 -336
WIRE 320 -336 304 -336
WIRE 416 -336 400 -336
WIRE -608 -320 -608 -336
WIRE -384 -288 -384 -336
WIRE 32 -272 32 -288
WIRE 112 -272 96 -272
WIRE -608 -224 -608 -240
WIRE -80 -224 -80 -336
WIRE 32 -224 32 -272
WIRE 144 -224 144 -336
WIRE 400 -208 384 -208
WIRE 496 -208 480 -208
WIRE 512 -208 496 -208
WIRE 608 -208 592 -208
WIRE 608 -176 608 -208
WIRE -384 -160 -384 -208
WIRE -128 -160 -384 -160
WIRE 496 -160 496 -208
WIRE 496 -160 192 -160
WIRE 560 -160 496 -160
WIRE -384 -144 -384 -160
WIRE 560 -112 528 -112
WIRE 528 -96 528 -112
WIRE 608 -80 608 -96
WIRE -384 -48 -384 -64
WIRE -224 -48 -336 -48
WIRE -128 -48 -224 -48
WIRE 208 -48 192 -48
WIRE 304 -48 304 -336
WIRE 304 -48 288 -48
WIRE -336 -32 -336 -48
WIRE 528 0 528 -16
WIRE -336 64 -336 48
WIRE -128 64 -336 64
WIRE 208 64 192 64
WIRE 304 64 304 -48
WIRE 304 64 288 64
WIRE -336 80 -336 64
WIRE -224 80 -224 -48
WIRE 304 128 288 128
WIRE 400 128 384 128
WIRE 416 128 400 128
WIRE 512 128 496 128
WIRE 512 160 512 128
WIRE -336 176 -336 160
WIRE -224 176 -224 160
WIRE -128 176 -224 176
WIRE 400 176 400 128
WIRE 400 176 192 176
WIRE 464 176 400 176
WIRE -224 192 -224 176
WIRE 464 224 432 224
WIRE 32 240 32 224
WIRE 432 240 432 224
WIRE 512 256 512 240
WIRE -224 288 -224 272
WIRE 432 336 432 320
FLAG 416 -336 0
FLAG -224 288 0
FLAG 32 240 0
FLAG -336 176 0
FLAG -384 -48 0
FLAG 256 -336 0
FLAG -608 -224 0
FLAG 112 -272 0
FLAG 288 128 0
FLAG 432 336 0
FLAG 512 256 0
FLAG 384 -208 0
FLAG 528 0 0
FLAG 608 -80 0
SYMBOL res 304 -64 R90
SYMATTR InstName R1
SYMATTR Value 100K
SYMBOL res 304 48 R90
SYMATTR InstName R2
SYMATTR Value 100K
SYMBOL voltage 304 -336 R270
SYMATTR InstName V1
SYMATTR Value 3.3
SYMBOL res -240 64 R0
SYMATTR InstName R3
SYMATTR Value 887K
SYMBOL res -240 176 R0
SYMATTR InstName R4
SYMATTR Value 412K
SYMBOL res -352 -48 R0
SYMATTR InstName R5
SYMATTR Value 16.5K
SYMBOL res -352 64 R0
SYMATTR InstName R6
SYMATTR Value 13K
SYMBOL res -400 -304 R0
SYMATTR InstName R7
SYMATTR Value 1
SYMBOL res -400 -160 R0
SYMATTR InstName R8
SYMATTR Value 100K
SYMBOL nmos -48 -288 R270
SYMATTR InstName Q1
SYMATTR Value Si4420DY
SYMBOL voltage -608 -336 R0
SYMATTR InstName V2
SYMATTR Value PWL(0 0 1 3.3)
SYMBOL res 144 -320 R270
SYMATTR InstName R9
SYMATTR Value 100
SYMBOL cap 96 -288 R90
SYMATTR InstName C1
SYMATTR Value 1
SYMBOL PowerProducts\\LTC2923 32 0 R0
SYMATTR InstName U1
SYMBOL res 400 112 R90
SYMATTR InstName R10
SYMATTR Value 400K
SYMBOL res 512 112 R90
SYMATTR InstName R11
SYMATTR Value 400K
SYMBOL g2 512 144 R0
SYMATTR InstName G1
SYMATTR Value 1
SYMBOL voltage 432 224 R0
SYMATTR InstName V3
SYMATTR Value 1
SYMBOL res 496 -224 R90
SYMATTR InstName R12
SYMATTR Value 15K
SYMBOL res 608 -224 R90
SYMATTR InstName R13
SYMATTR Value 15K
SYMBOL g2 608 -192 R0
SYMATTR InstName G2
SYMATTR Value 1
SYMBOL voltage 528 -112 R0
SYMATTR InstName V4
SYMATTR Value 1