L5970AD STMicroelectronics, L5970AD Datasheet - Page 4

• Manufacturer Part Number: L5970AD
• Description: IC REG SW 1.5A STEP DOWN 8-SOIC
• Manufacturer: STMicroelectronics
• Type: Step-Down (Buck)r

Specifications of L5970AD

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 1.24 ~ 35 V
• Current - Output: 1.5A
• Frequency - Switching: 500kHz
• Voltage - Input: 4.4 ~ 36 V
• Operating Temperature: -40°C ~ 150°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Power - Output: 750mW
• Output Voltage: 35 V
• Operating Temperature Range: - 40 C to + 150 C
• Mounting Style: SMD/SMT
• Low Dropout Operation: 100% DUTY CYCLE
• For Use With: 497-8849 - BOARD DEMO STW9N150 100W 3PHASE
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

L5970AD
3
The main internal blocks are shown in Fig. 4, where is reported the device block diagram. They are:
Figure 4. Block Diagram
3.1 POWER SUPPLY & VOLTAGE REFERENCE
The internal regulator circuit (shown in Figure 2) consists of a start-up circuit, an internal voltage Prereg-
ulator, the Bandgap voltage reference and the Bias block that provides current to all the blocks.
The Starter gives the start-up currents to the whole device when the input voltage goes high and the de-
vice is enabled (inhibit pin connected to ground).
The Preregulator block supplies the Bandgap cell with a preregulated voltage V
supply voltage noise sensitivity.
3.2 VOLTAGES MONITOR
An internal block senses continuously the V
regulator starts to work. There is also an hysteresis on the V
4/11
Functional Description
COMP
SYNC
INH
FB
●
●
●
●
●
●
●
●
●
A voltage regulator that supplies the internal circuitry. From this regulator, a 3.3V reference
voltage is externally available.
A voltage monitor circuit that checks the input and internal voltages.
A fully integrated sawtooth oscillator whose frequency is500KHz
Two embedded current limitations circuitries which control the current that flows through the
power switch. The Pulse by Pulse Current Limit forces the power switch OFF cycle by cycle
if the current reaches an internal threshold, while the Frequency Shifter reduces the switch-
ing frequency in order to strongly reduce the duty cycle.
A transconductance error amplifier.
A pulse width modulator (PWM) comparator and the relative logic circuitry necessary to drive
the internal power.
An high side driver for the internal P-MOS switch.
An inhibit block for stand-by operation.
A circuit to realize the thermal protection function.
1.235V
TRIMMING
INHIBIT
+
-
OSCILLATOR
E/A
+
-
PWM
VOLTAGES
MONITOR
SHUTDOWN
THERMAL
cc
, V
ref
and V
bg
CURRENT LIMIT
GND
PEAK TO PEAK
. If the voltages go higher than their thresholds, the
1.235V 3.5V
D
CC
Ck
SUPPLY
Q
(UVLO).
FREQUENCY
SHIFTER
DRIVER
VCC
OUT
LPDMOS
POWER
REG
BUFFER
V
REF
D00IN1125
that has a very low
V REF