ST L6935 User Manual
High performance 3 A ULDO linear regulator
Features
■ Up to 5 V input voltage range
■ 60 mΩ max R
■
35 µA shut-down current
■ 3 A maximum output current
■ Split bias and power supplies
■ Adjustable output voltage: 0.5 V to 3.0 V
■ Excellent load and line regulation: 1 %
accuracy (over temperature)
■ MLCC supported
■ Programmable soft-start
■ Short-circuit protection
■ 3.5 A overcurrent protection
■ Thermal shut-down
■ VFQFPN20 4 x 4 x 1.0 mm package
DS(on)
L6935
VFQFPN20
(4.0 x 4.0 x 1.0 mm)
Description
L6935 is an ultra low drop output linear regulator
operating up to 5 V input and is able to support
output current up to 3 A. Designed with an
internal low-R
be used for on-board DC-DC conversions saving
in real estate, list of components and power
dissipation.
Bias input and power input are split to allow linear
conversion from buses lower than 1.2 V
minimizing power losses.
N-channel MOSFET, it can
DS(on)
Applications
■ Motherboard
■ Mobile PC
■ Hand-held instruments
■ PCMCIA cards
■ Processors I/O
■ Chipset and RAM supply
voltage from 0.5 V to 3.0 V with a voltage
regulation accuracy of 1 %. soft-start is available
to program the output voltage rise-time according
to the external capacitor connected.
Enable and Power Good functions make L6935
suitable for complex systems and programmable
start-up sequencing.
The current limit at 3 A protects the system during
a short circuit. The current is sensed in the power
DMOS in order to limit the power dissipation.
Thermal shut down limits the internal temperature
at 150 °C with a hysteresis of 20 °C.
Table 1. Device summary
L6935 provides the application with an adjustable
Order codes Package Packing
L6935
VFQFPN20
Tu b e
L6935TR Tape and reel
May 2008 Rev 1 1/20
www.st.com
20
Contents L6935
Contents
1 Typical application circuit and block diagram . . . . . . . . . . . . . . . . . . . . 3
1.1 Application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2 Pins description and connection diagrams . . . . . . . . . . . . . . . . . . . . . . 5
2.1 Pin descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3 Electrical specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.1 Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2 Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.3 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4 Typical performances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5 Device description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5.1 Soft-start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5.2 Power Good . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.3 VIN vs VBIAS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.4 Protections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.4.1 Over-current protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.4.2 Thermal protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
6 Application information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
6.1 Components selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
6.1.1 Input capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
6.1.2 Output capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
6.2 VIN, VBIAS and sequencing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
7 Demonstration board description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
8 VFQFPN20 mechanical data and package dimensions . . . . . . . . . . . . 18
9 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2/20
Typical application circuit and block diagram L6935
1 Typical application circuit and block diagram
1.1 Application circuit
Figure 1. Typical application circuit - VIN = VBIAS
V
EN
IN
VIN
C
IN
EN
VBIAS
L6935
VOUT
ADJ
V
OUT
= 0.5V to 3.0V
R
1
C
OUT
SS GND PGOOD
C
SS
L6935 Reference Schematic
Figure 2. Typical application circuit - VIN
V
BIAS
VIN = 0.75V to V
EN
BIAS
VIN
EN
C
IN
SS GND PGOOD
C
SS
PAD
≠ VBIAS
VBIAS
L6935
PAD
VOUT
ADJ
R
2
PGOOD
V
OUT
> 0.5V (*)
R
1
R
2
C
OUT
PGOOD
L6935 Reference Schematic
(*) Vin may decrease until the minimum drop is reached. Conversely, Vout can rise untile the minimum drop is reached.
3/20
Typical application circuit and block diagram L6935
1.2 Block diagram
Figure 3. Block diagram
VIN
VBIAS
SS
GND
CHARGE
PUMP
VREF
0.9 VREF
+
-
ERROR
AMPLIFIER
+
-
REFERENCE
0.500V
ENABLEEN
THERMAL
SENSOR
CURRENT
DRIVER
LIMIT
VOUT
ADJ
PGOOD
4/20
Pins description and connection diagrams L6935
2 Pins description and connection diagrams
Figure 4. Pins connection (top view)
2.1 Pin descriptions
Table 2. Pins descriptions
Pin # Name Function
1 N.C. Not internally connected.
2 GND Ground connection. Connect to PCB ground plane.
3, 4 N.C. Not internally connected.
N.C.
N.C.
N.C.
N.C.
N.C.
VIN
VIN
VIN
10987
11
12
13
L6935
14
15
16 17 18 19
VOUT
VOUT
EN
VOUT
VBIAS
6
20
SS
ADJ
5
4
3
2
1
PGOOD
N.C.
N.C.
GND
N.C.
Power Good output flag: the pin is open drain and it is forced low if the
5 PGOOD
6 VBIAS
7EN
8 to 10 VIN
11 to15 N.C. Not internally connected.
16 to 18 VOUT
5/20
output voltage is lower than 90 % of the programmed voltage. If not used, it
can be left floating.
Input bias supply. This pin supplies the internal logic to drive the power
N-channel MOSFET that realize the voltage conversion. Connect directly to
or to a different supply ranging from VIN to 5 V.
V
IN
The voltage connected to this pin MUST always be higher or equal that V
Enables the device if a voltage higher than 1 V is applied.
When pulled low, the device is in low-power consumption: everything inside
the controller is kept OFF.
See Section 6.2 for details about EN signal and power sequencing.
Power supply voltage. This pin is connected to the drain of the internal
N-channel MOSFET.
Filter to GND with capacitor larger than the one used for V
Regulated output voltage. This pin is connected to the source of the
internal N-mos. MLCC capacitor are supported. Filter to GND with
capacitor smaller than the one used for V
.
IN
.
OUT
.
IN
Pins description and connection diagrams L6935
Table 2. Pins descriptions (continued)
Pin # Name Function
Feedback for the IC regulation.
19 ADJ
20 SS
PA D G ND
Connecting this pin through a voltage divider to V
, it is possible to
OUT
program the output voltage between 0.5 V and 3.0 V.
Soft-start pin. The soft-start time is programmed connecting an external
capacitor C
from this pin to GND.
SS
In steady state regulation, the voltage at this pin is 3.3 V.
Ground connection. Connect to PCB GND Plane with enough VIAs to
improve thermal conductivity.
6/20