LT1106 Datasheet, PDF (6/8 Pages) Linear Technology – Micropower Step-Up DC/DC Converter for PCMCIA Card Flash Memory

LT1106
W
BLOCK DIAGRA
12/5
SELECT
1
AVPP
19
VPP1
18
VPP2
17
ON/0FF
20
G1 G2
16 15
BIAS
565k
–
+
299k
4k
100k
V_REF 1.24V
–
+
V_REF
V_CC
C3
+
200k
C2
14 VPP VALID
–
–
C1
+
V_CC
+
–
3.7V
OFF
500kHz
OSCILLATOR
5 3/5
V_CC
3,4
36mV
–+
R2
R1
700Ω ^3Ω
Q3
BIAS
2
SOFT START
SW
9,10,11
Q2
1×
Q1
50×
13
GND
6,7
PGND
LT1106 • BD
APPLICATIONS INFORMATION
Functional Description
The LT1106 is a micropower, step-up DC/DC converter
specifically configured for PCMCIA flash memory card
VPP generation. The device generates a 5V or 12V output
selectable via the 12/5 Select pin. If 12V is present on
either the VPP1 or VPP2 pins, gate drive outputs G1 and
G2 are driven low, turning on external PMOS devices. The
switching regulator inside the LT1106 is idled when 12V
is present on VPP1 or VPP2.
The VPP VALID output goes low when the voltage at AVPP
exceeds 11.4V This signal can be used to indicate pres-
ence of a valid programming voltage. The 3/5 comparator
indicates whether the input voltage is 3.3V or 5V.
The Soft Start pin can be used to limit inrush current upon
start-up. A 0.1µF capacitor in parallel with a 1M resistor is
connected between this pin and ground to limit peak
inductor current at start-up.
Switching Regulator Operation
When 12V is not present on the VPP1 or VPP2 pins and the
device is enabled (ON/OFF = 1), the LT1106 generates a
regulated voltage at the AVPP pin. This voltage is pro-
grammable between 5V or 12V depending on the state of
the 12/5 Select pin. Referring to the block diagram, hyster-
etic comparator C1 monitors AVPP via the resistor divider.
When the negative input of C2 falls below 1.24V, C1’s
6